PRECEDENTIAL

        UNITED STATES COURT OF APPEALS
             FOR THE THIRD CIRCUIT
                 _______________

                      No. 16-3667
                    _______________

          CHARLES WESLEY BLACKLEDGE,
                              Appellant
                      v.

         OLGA GRIGORIEVNA BLACKLEDGE
                 _______________

      On Appeal from the United States District Court
         for the Western District of Pennsylvania
              (W.D. Pa. No. 2-16-cv-01004)
        Honorable Nora B. Fischer, District Judge
                   _______________

                  Argued: May 19, 2017

   Before: AMBRO, KRAUSE, and NYGAARD, Circuit
                     Judges

              (Opinion Filed: August 3, 2017)

James C. Martin, Esq.
Reed Smith
225 Fifth Avenue, Suite 1200
Pittsburgh, PA 15222
Michael P. Yingling, Esq. (Argued)
Reed Smith
10 South Wacker Drive, 40th Floor
Chicago, IL 60606

Attorneys for Petitioner-Appellant1

Barbara B. Ernsberger, Esq. (Argued)
Behrend & Ernsberger
355 Fifth Avenue
Suite 1200, Park Building
Pittsburgh, PA 15222

Attorney for Respondent-Appellee

                      _______________

                OPINION OF THE COURT
                    _______________

KRAUSE, Circuit Judge.

       Petitioner, a German resident, appeals the denial of his
petition alleging that his wife wrongfully retained their then-
eight-year-old son in the United States in violation of the
Hague Convention on the Civil Aspects of International Child


      1
         We express our gratitude to Appellant’s counsel for
accepting our appointment of this matter and for their
excellent briefing and argument in this case. Lawyers who
act pro bono fulfill the highest service that members of the
bar can offer to indigent parties and to the legal profession.




                              2
Abduction. Because we conclude that, to the extent an
agreement between the parties can be gleaned from the
record, the parents’ shared intent was that the child would
move to the United States not for a transient visit, but with a
settled purpose, and because the child had acclimatized to his
life in the United States at the time of the retention, the
United States was then his habitual residence and the
retention was not wrongful under the Convention.
Accordingly, we will affirm.

I.     Factual Background

       A.     J.B.’s Early Years and Initial Two-Year
              Residence in Pittsburgh

        J.B., a United States citizen, was born in the Ukraine
in 2008 to Petitioner Charles Blackledge, a United States
citizen who currently resides in Berlin, Germany, and
Respondent Olga Blackledge, a Ukrainian citizen and lawful
permanent resident of the United States who currently resides
in Pittsburgh, United States. For the first three years of J.B.’s
life, the family lived in Kharkiv, Ukraine, and Dublin,
Ireland, while also spending some weeks in Vilnius,
Lithuania. In the spring of 2011, when the family was staying
in Lithuania and then Ukraine, Petitioner secured a job as a
patent agent in Germany at about the same time Respondent
was accepted to a Ph.D. program at the University of
Pittsburgh. The family left Ukraine and, after a seven-week
summer holiday in Munich, Germany, Respondent and J.B.
moved to Pittsburgh and lived for the next two years
separately from Petitioner, who lived and worked in Berlin,
Germany, while regularly visiting and communicating with
J.B. According to Petitioner, the plan was for the family to
eventually reunite—either Respondent would finish her




                               3
coursework in Pittsburgh and go to Germany or Petitioner
would use his position in Germany “as a stepping stone to get
back to the [United States].” J.A. 240.

        In the summer of 2013, after Respondent and J.B. had
lived in Pittsburgh for two years, J.B. underwent cardiac
surgery at the Children’s Hospital in Pittsburgh. Petitioner
went to Pittsburgh to be with J.B. during his recuperation and
to seek jobs in the United States. When those efforts proved
fruitless, Petitioner decided to return to Germany and
Respondent agreed to join him, both because she had agreed,
before the initial move to Pittsburgh, to move to Germany for
two years and because she was financially unable to support
herself at that point. Respondent then arranged for storage of
toys, books, furniture, and other belongings with a friend in
Pittsburgh, and Petitioner, Respondent, and J.B. moved
together to Berlin, Germany, in August 2013. For J.B., this
was the first time he had ever been to Berlin or ever resided in
Germany.

       B.     J.B.’s Move to Germany

       After the move, Respondent continued to pursue her
Ph.D. studies at the University of Pittsburgh, remotely, and
J.B. was enrolled in the J.F.K. School, a public school
“founded in conjunction [with the] American Embassy and
German Government” with a “bilingual/bicultural” focus,
intending to provide American students with an “easier time
to adjust to the[ir] German” residency while still
“preserv[ing] their language and continu[ing] to work on their
language skills and all of the subjects in English.” J.A. 430-
31. J.B. also attended an afterschool program at J.F.K., where
students could play and do their homework, joined a soccer
team, and played chess at the Russian House.




                               4
        In August 2015, when J.B. was seven years old,
Respondent sought to return to Pittsburgh to complete the
final phase of her Ph.D. program. By this point, according to
both parties, the marriage had become acrimonious, and,
according to Respondent, they had “agreed that [they would]
divorce” and that it was only “a matter of time [as to] when.”
J.A. 421-22. While the nature of the parties’ disagreement
over J.B.’s continued residence underlies this appeal and will
be discussed in more detail below, Petitioner initially agreed
that Respondent and J.B. would return to Pittsburgh, and they
requested a one-year leave of absence for J.B. from the J.F.K.
School and secured German visas for themselves and J.B. that
were valid through 2018. Given the belongings they had
stored in Pittsburgh in August 2013, Respondent and J.B.
opted to leave in Germany items that were difficult to
transport, such as toys, Legos, and a bike, when they returned
to Pittsburgh in August 2015.

      C.      J.B.’s Return to Pittsburgh

        Back in Pittsburgh, J.B. attended second grade in the
2015-2016 school year and, according to his teacher,
“performed as a wonderful second grader,” earning,
cumulatively, at the end of the year As in spelling,
handwriting, math, and grammar, and a B in reading, and
finishing the year on “academic high honor roll.” J.A. 328-
30. J.B.’s teacher described him as a “well-behaved” child
who “followed rules and routines easily,” “made friends
easily,” J.A. 330, was “[k]ind, happy, loving, eager to learn,”
and was generally “well-adjusted,” J.A. 334. Despite an
initial deficiency in reading, J.B. finished the fourth quarter
with “an excellent grade,” showing what his teacher termed
“dramatic improvement” in his reading level throughout the
year. J.A. 333, 451. J.B.’s love of reading extended beyond




                              5
the school year, when J.B. joined a summer reading
challenge, completing the fifteen-book assignment by July 5,
two months ahead of the August 31 deadline.

       J.B. was also a member of a four-student robotics club,
organized by a parent of one of his classmates. The team met
every Saturday or Sunday afternoon when the students would
design missions and submit the mission to a robotics
competition, winning first place in Pennsylvania and twenty-
ninth in the United States. J.B. was tentative at first, because
he didn’t know how to program the robot and thought the
tasks were “impossible,” but by the end “he was . . . so
excited” by the project, and he was able to explain his
favorite mission and how the students accomplished it. J.A.
355-56. J.B. and the classmate whose mother had organized
the robotics club “stayed friends after the robotic project”
ended, playing Legos and soccer together. J.A. 358.

       In addition, J.B. bonded with his teammates on his
swim team, which ran for three trimesters—from September
through December, January through April, and May through
July. The goal for students on the team was to master the
four competitive strokes so that they would be able to do
them “correctly if they decide[d] to compete.” J.A. 369-70.
At the start of the year, J.B. was “able to swim the length of
the pool free style” and had “a pretty good breast stroke kick,
but his endurance—swimming the length of the pool was
difficult.” J.A. 371. By spring, however, he was able to
compete in four meets, “better[ing] his times pretty much
every meet” and, by summer, “he was able to swim all four
strokes,” do “flip turns,” and “dive.” J.A. 371-72.

       J.B. made many friends in Pittsburgh and enjoyed play
dates, birthday parties, video-gaming, playing soccer, playing




                               6
card games, sleepovers, and other outings with various young
people. J.B.’s own birthday party, when he turned eight in
June 2016, was attended by many of those friends.
Respondent’s friends and colleagues also developed a bond
with J.B., enjoying dinners together, attending university
events and spending weekends and holidays together, going
to the park, attending theater festivals and puppet shows
together, and generally playing with and babysitting J.B.

        Respondent and J.B. also explored the broader
Pittsburgh environs, including trips to Erie, Pennsylvania,
Frank Lloyd Wright’s Fallingwater in Mill Run,
Pennsylvania, and Pittsburgh’s four Carnegie Museums.
They also became members of a local museum called the
Mattress Factory where J.B. enjoyed “showing off his
knowledge . . . to his friends,” whom he sometimes invited to
join him. J.A. 446-47. J.B.’s interests extended as well to
sports, and he became familiar with the local sports teams and
was a fan of the Pittsburgh Penguins hockey team and the
Riverhounds soccer team.

      D.     Parents’ Dispute Over J.B.’s Continued
             Residence

       Within the first month of J.B.’s stay in the United
States, Petitioner sent Respondent an email, referencing job
applications he had sent to the United States and elsewhere,
and indicating that he might be moving to another country so
that J.B. would not be returning to Germany at all.
Respondent assured Petitioner that J.B. “is pretty happy in
Pittsburgh, so by the end of the year, going back to Berlin
might not be exactly what he wants.” J.A. 199. Petitioner
replied to this email but did not comment on, or reject, the
possibility of J.B. remaining in Pittsburgh.




                              7
        However, five months later, in February 2016,
Petitioner initiated a series of emails with Respondent that
form the bulk of the record of the parties’ shared intent as to
J.B.’s habitual residence. These began with Petitioner’s
request that Respondent “confirm [her] commitment to our
agreement” that J.B. would return to Germany for the 2016-
17 academic year. J.A. 188-90. For her part, the Respondent
did not deny the existence of an agreement but asked the
Petitioner to “reconsider it,” J.A. 172, explaining, “I do not
think . . . it is a good idea for a child [J.B.’s] age to live with
one parent for a year, and with the other for a year,” J.A. 181.
That agreement, Respondent stated, “presupposes . . . yearly
adaptation to living with different parents [which] is
psychologically disadvantageous” to J.B., and urged
Petitioner to consider J.B.’s well-being, J.A. 177, suggesting
that Petitioner move “somewhere close” so that they could
both “take care of [J.B.] on a permanent basis” and not
“change [J.B.’s] permanent caregiver every year.” J.A. 181.

        In response, Petitioner observed that Respondent had
not expressed any concerns about J.B. “spend[ing] alternate
years with us when the agreement was made.” J.A. 178. And
while Petitioner acknowledged Respondent’s “concerns about
stability of dwelling,” he explained that he did not “think
there [we]re better options than maintaining [their] previous
agreement,” J.A. 179 (emphasis omitted), which he
characterized as: “[J.B.] would go with you to Pitt[sburgh]
and return to me for 2016-2017 academic year. Then back to
you . . . .” J.A. 176. In subsequent correspondence,
Petitioner advised Respondent to “prepare [herself] for
fulfillment of [the] agreement that [J.B.] returns to
[Respondent] for 2016-2017,” reassuring her, “You’ll have
him again in 2017,” J.A. 168. And in May, the parties again




                                8
discussed the prospect of J.B. alternating years between his
parents, with Petitioner documenting in his notes of their call
that Respondent continued to oppose “any plan for [J.B.] to
alternate between Germany and [the] USA,” because she
believed that it “put[] too much pressure on [J.B.] to go back
and forth” and “insist[ed] upon more consistency.” J.A. 156-
58.

        While the dispute between the parties over J.B.’s long-
term residency arrangements was ongoing, Respondent filed
petitions for divorce and custody and, at the end of May, the
Family Court in Allegheny County, Pennsylvania issued an
interim custody order that, in terms of physical custody,
allowed J.B. to continue to reside with the Respondent,
pending a final custody determination, and granted Petitioner
visitation over the summer and holidays.

       On June 9, Petitioner informed Respondent that he had
found a good rate for J.B. to return to Berlin on June 19 and
that he wanted J.B. to stay in Berlin and go to school there
“like we planned.” J.A. 144. Respondent objected on the
grounds that, under the interim custody order, any trip to
Berlin would only be for a visit, not for the school year, and
that J.B., in any event, was committed through August 3 to
attend robotics and other summer camps, which Petitioner
had not told her to cancel and for which the cancellation
deadline had then passed.

          Declaring that the interim custody order was “not
valid,” Petitioner “demand[ed] that [J.B.] return on 19 June,”
J.A. 143, and reiterated that he was looking at tickets for both
Respondent and J.B., even though Respondent objected that
“. . . it sounds like you are planning to abduct [J.B.],” and that
Petitioner should “contest the court’s decision . . . legal[l]y,”




                                9
J.A. 143. After a few additional exchanges in which
Respondent sought assurance from Petitioner about the length
of J.B.’s visit before she would consent to his return to
Germany, Petitioner stated that he was “still waiting to hear
anything more from the mediators.” J.A. 140. The record
reflects no additional email communications between the
parties.

      On July 6, 2016, Petitioner filed a petition in the
United States District Court for the Western District of
Pennsylvania, seeking J.B.’s return to Germany under the
Hague Convention.

II.    District Court Proceedings

       The District Court held a two-day bench trial in mid-
August.2 In addition to the above-referenced emails and the
testimony of Petitioner and Respondent, the trial record
included testimony and documentation offered by J.B.’s
teacher, swim coach, parents of J.B.’s school friends, and
Respondent’s friends, related to J.B.’s acclimatization to
Pittsburgh, as well as written statements from Petitioner’s
brother and friends and acquaintances in Germany, indicating
they understood that J.B. was to return to Germany for the

       2
          Prior to the hearing, the parties were referred to
mediation.     Unfortunately, mediation was unsuccessful.
While mediation enables parents, who are well-positioned to
know the needs of their child, to forge a resolution that best
serves the child’s interests, a court reviewing a Hague
Convention petition has the more limited mandate of
“restor[ing] the status quo that existed prior to the wrongful . .
. retention.” Didon v. Dominguez Castillo, 

, 320
(3d Cir. 2016) (internal quotation marks omitted).




                               10
2016-2017 school year. With regard to the testimony of
Petitioner and Respondent, the District Court found
Respondent generally to be more credible. Of the written
statements offered by Petitioner, only one was based on a
conversation in which Respondent was present, and the rest
were based on Petitioner’s representations to the declarants.
The District Court accorded these statements “diminished
weight” and “minimal significance,” on the grounds that they
were “the product of a concerted effort by Petitioner” and that
“several” of the letters “merely . . . parrot[ed] language
directly suggested by Petitioner.” Blackledge v. Blackledge,
No. 16-1004, 

, at *22 (W.D.
Pa. Aug. 26, 2016). The District Court also conducted an in
camera interview of J.B.

       On August 19, 2016, the District Court entered an
order denying the petition, and on August 26, 2016, it issued
a Memorandum Opinion in support of its order.3 See 

Its first order of business was to determine the retention
date so that it could then consider which forum was J.B.’s
habitual residence immediately prior to that date. Reasoning


      3
         Because the District Court concluded Petitioner did
not meet his burden to prove he was entitled to relief, it did
not address any of the affirmative defenses raised by
Respondent, which included that J.B. had attained the age and
maturity at which it was appropriate to take account of his
preferences, that J.B. preferred to remain in Pittsburgh, and
that returning to Germany would expose J.B. to a grave risk
of harm. See Hague Convention on the Civil Aspects of
International Child Abduction art. 13, Oct. 25, 1980, T.I.A.S.
No. 11,670; Blackledge, No. 16-1004, 

, at *7-15.




                              11
that Petitioner himself testified he originally agreed to permit
J.B. to live in Pittsburgh for one year, starting in August
2015, and that Petitioner had acquiesced to J.B. participating
in camps through the summer, the District Court calculated
the retention date as August 2016. 

& n.5.

        Turning to the question of habitual residence, the
District Court correctly recognized that it was required to
consider both the parents’ shared intent and the child’s
acclimatization. 

see Karkkainen v. Kovalchuk,

, 291-92 (3d Cir. 2006). As to shared parental
intent, it concluded there was “no credible evidence” that the
parties agreed that J.B.’s stay would be for a “specific
duration.” Blackledge, No. 16-1004, 

, at *24. And, considering evidence of J.B.’s activities
and expectations up until the August retention date, the Court
concluded that J.B. was acclimatized to Pittsburgh. 

*24. In so finding, it accorded “significant weight”
to J.B.’s in camera interview, including his stated preference
for Pittsburgh, because it found J.B. “to exhibit an unusual
degree of maturity and situational awareness.” 

n.6,
*15. As it concluded Pittsburgh was J.B.’s habitual residence
immediately prior to the August retention date, the District
Court held that the retention was not wrongful under the
Hague Convention. 

The consequence of this
holding was that J.B. could continue to reside in Pittsburgh
pending the resolution of his parents’ custody proceedings
before the Allegheny County Family Court. See generally

.

       Petitioner now appeals, seeking to reverse the District
Court’s denial of his petition, with the understanding that a
reversal would allow the Allegheny County interim custody
order to be vacated, custody proceedings to be initiated in




                              12
Germany, and J.B. to reside with Petitioner in Germany
pending the resolution of those proceedings.

III.   Jurisdiction and Standard of Review

       The District Court properly exercised jurisdiction
under 22 U.S.C. § 9003(a), which grants district courts
original jurisdiction over claims arising under the
Convention. We exercise jurisdiction under 28 U.S.C.
§ 1291.

       We review the District Court’s factual findings for
clear error and review legal conclusions and the application of
the law to the facts de novo. Didon v. Dominguez Castillo,

, 319-20 & n.13 (3d Cir. 2016). In the context
of Hague Convention cases, certain determinations involve
mixed questions of law and fact. We have held, for example,
that habitual residence is a mixed question of law and fact.
Feder v. Evans-Feder, 

, 222 n.9 (3d Cir. 1995).
And although our past cases have not addressed the issue in
explicit terms, we recognize today that the two factors
informing habitual residence, i.e., the parents’ shared
intentions regarding the child’s move and the child’s
acclimatization, themselves involve mixed questions, because
those factors depend both on case-specific fact-findings and
whether those findings meet the specified legal threshold.
See Ornelas v. United States, 

, 696-97 (1996)
(explaining that the “issue [of] whether the facts satisfy the
[relevant legal] standard” is a mixed question of law and
fact). For mixed questions of law and fact, we must “separate
the issue into its respective parts, applying the clearly
erroneous test to the factual component, [and] the plenary
standard to the legal.” N. River Ins. Co. v. CIGNA
Reinsurance Co., 

, 1218 (3d Cir. 1995).




                              13
IV.   Analysis

       The purposes of the Hague Convention are “to secure
the prompt return of children wrongfully removed to or
retained in any Contracting State” and “to ensure the rights of
custody and of access under the law of one Contracting State
are effectively respected in the other Contracting States.”
Hague Convention on the Civil Aspects of International Child
Abduction art. 1, Oct. 25, 1980, T.I.A.S. No. 11,670
[hereinafter Hague Convention]. The Convention was “not
designed to resolve international custody disputes.”

. Rather, in addressing Hague
Convention petitions, courts are limited “to restor[ing] the
status quo prior to any wrongful removal or retention, and to
deter[ring] parents from engaging in international forum
shopping in custody cases.” Id; see also 

(explaining that any return remedy merely “seeks to
restore the status quo that existed prior to the wrongful . . .
retention” (internal quotation marks omitted)).

       A petitioner who initiates judicial proceedings for the
return of a child under the Hague Convention has the burden
to prove, by a preponderance of the evidence, that the child
has been wrongfully removed or retained. 22 U.S.C. §
9003(b), (e)(1)(A). The removal or retention of a child is
wrongful if:

      a       it is in breach of rights of custody attributed to a
              person . . . under the law of the State in which
              the child is habitually resident immediately
              before the removal or retention; and




                               14
       b      at the time of removal or retention those rights
              were actually exercised . . . or would have been
              so exercised but for the removal or retention.

Hague Convention, supra, art. 3. As we have explained in
interpreting these provisions, to determine if a petitioner is
entitled to relief, the court must answer four questions: “(1)
when the removal or retention took place; (2) the child’s
habitual residence immediately prior to such removal or
retention; (3) whether the removal or retention breached the
petitioner’s custody rights under the law of the child’s
habitual residence; and (4) whether the petitioner was
exercising his or her custody rights at the time of removal or
retention.” Yang v. Tsui, 

, 271 (3d Cir. 2007)
(citing 

).

        Here, as the District Court observed, there was no
dispute as to the fourth factor, i.e., that Petitioner had custody
rights under German law and that he was exercising those
rights. But, having determined that the retention date was
August 2016 and that J.B.’s habitual residence immediately
prior to that date was Pittsburgh, the District Court concluded,
on the basis of the first two factors, that Petitioner had not
met his burden of proving a wrongful retention.4 Blackledge,
No. 16-1004, 

, at *10, *25.

       Below we address, first, Petitioner’s argument that the
District Court erred in fixing the retention date, and, second,

       4
         As to the third factor, Petitioner made no argument
that the retention breached his custody rights under United
States or German law. Instead, his argument focused on
whether Germany still remained J.B.’s habitual residence at
the time of the retention.




                               15
Petitioner’s contention that it erred in determining J.B.’s
habitual residence immediately prior to that date.

      A.     Retention Date

       According to Petitioner, the District Court erred in
adopting August 2016 as the retention date because Petitioner
had withdrawn his consent to J.B. remaining in the United
States prior to August, when he had “clearly communicate[d]
[his] desire to regain custody” of J.B. in the June 9 email
demanding J.B.’s return by June 19. Appellant’s Br. 21-22
(second alteration in original) (quoting 

). Respondent, for her part, urges us to adopt the
District Court’s August date. We conclude neither June nor
August reflects the proper date under our case law.

        In Karkkainen we confronted a situation where the
noncustodial parent initially agreed to the child remaining in
the United States indefinitely, but then, in mid-July, emailed
the custodial parent demanding that the child return home on
August 10, the date for which she had purchased a return
flight for the child, insisting that retention beyond that date
would “constitute 

. In
determining the retention date, we recited, without adopting,
another court’s definition of “retention date” as the date the
noncustodial parent “clearly communicates her desire to
regain custody and asserts her parental right to have [her
child] live with her.” 

original) (emphasis
omitted) (quoting Slagenweit v. Slagenweit, 

,
270 (N.D. Iowa 1993)). Assuming this definition applied, we
held that by mid-July the noncustodial parent had clearly
communicated the withdrawal of consent for the child to
remain in the United States beyond August 10 and that
nothing in the record “suggest[ed] there was confusion about




                              16
[the noncustodial parent’s] opposition after mid-July.” 

While we acknowledged that the noncustodial parent
had originally agreed to let the child remain in the United
States indefinitely, 

and had communicated in mid-
July her withdrawal of that consent beyond August 10, we did
not adopt the mid-July notice date as the retention date, 

Nor did we accept the notion that the original agreement
for a longer period vitiated the noncustodial parent’s ability to
clearly communicate her desire to regain custody of the child.

recognized that a party may accelerate a
retention date by “withdraw[ing] her consent to have [the
child] remain” with the custodial parent, and we then settled
on August 10—i.e., the date on which consent actually
expired—as the retention date. 

       Building on Karkkainen, we hold that the retention
date is the date beyond which the noncustodial parent no
longer consents to the child’s continued habitation with the
custodial parent and instead seeks to reassert custody rights,
as clearly and unequivocally communicated through words,
actions, or some combination thereof. That determination is,
by necessity, fact-intensive and will vary with the
circumstances of each case. And while in some cases the
notice date and actual expiration date will coincide, in other
cases the notice will indicate a future date as the date consent
will be withdrawn, in which case that latter date, depending
on the facts of the case, will constitute the expiration date
and, hence, the retention date.

       In determining the retention date here, we conclude
that the District Court erred by looking solely to Petitioner’s
original consent for J.B. to reside in Pittsburgh through
August 2016 and failing to assess whether Petitioner’s
subsequent communications, up to and including the filing of




                               17
his Hague Convention petition, effected a withdrawal of that
consent.5 But, consistent with Karkkainen, we also reject
Petitioner’s argument in favor of a June 9, 2016 retention
date, as that date reflects merely Petitioner’s notice of a
possible expiration of consent on June 19, 2016.

       While in Karkkainen we rested on the prospective date
of expiration identified in that petitioner’s notice, 

significant differences between the facts of that case and this
one lead us to conclude that June 19 also does not reflect the
proper retention date here. In Karkkainen the noncustodial
parent took the affirmative step of purchasing a ticket,
asserted that any retention beyond the scheduled return date
would constitute “kidnapping,” and did not equivocate as to
that retention date. 

Here, in contrast, Petitioner
only researched the possibility of purchasing a ticket;
Respondent, not Petitioner, flagged a concern about
“abduct[ion],” J.A. 143; and Petitioner left open the
possibility of further negotiations, stating after his demand
email that he was “still waiting to hear anything more from
the mediators,” J.A. 140. Under these circumstances, we
conclude neither June 9 nor June 19 was the retention date,
and in the absence of any earlier communication in which
Petitioner clearly and unequivocally withdrew his prior
consent and sought to reassert his custody rights, we hold that


       5
          Indeed, given that the District Court purported to
exercise jurisdiction over this case since the filing of the
petition on July 6, 2016, an August 2016 retention date would
raise concerns about the ripeness of Petitioner’s claim and the
jurisdiction of the federal courts to adjudicate it. See
generally Thomas v. Union Carbide Agric. Prods. Co., 

, 579-80 (1985).




                               18
consent expired and J.B. was therefore “retained” on the date
Petitioner filed his Hague Convention petition, i.e., July 6.

       Below we consider the evidence concerning J.B.’s
habitual residence immediately prior to that retention date and
whether the District Court erred in its conclusions as to the
parents’ shared intent or J.B.’s acclimatization.

       B.     Habitual Residence

        To determine where a child is habitually resident we
“employ a mixed standard of review, accepting [a] district
court’s historical or narrative facts unless they are clearly
erroneous, but exercising plenary review of the court’s choice
of and interpretation of legal precepts and its application of
those precepts to the facts.” 

n.13
(alteration in original) (quoting 

n.9).
The Hague Convention does not define habitual residence,
and we have held that it “is a fact-intensive determination that
cannot be reduced to a predetermined formula and necessarily
varies with the circumstances of each case.” 

. That inquiry becomes all the more difficult
where “the petitioning parent initially agreed to allow the
child to stay abroad for an indefinite duration, but
subsequently had second thoughts about that decision.” 

difficult inquiry, it is not without guideposts and
our precedent assists us in navigating our path. Below we
discuss (1) guiding principles from our case law relevant to
habitual residence; (2) the record in this case concerning
shared parental intent; and (3) the evidence of J.B.’s
acclimatization.

              1.     Principles of Habitual Residence




                              19
       A child’s habitual residence is “the place where [the
child] has been physically present for an amount of time
sufficient for acclimatization and which has a degree of
settled purpose from the child’s perspective.” Baxter v.
Baxter, 

, 368 (3d Cir. 2005) (internal quotation
marks omitted) (quoting 

). To assess
whether a child’s habitual residence meets this threshold we
analyze both the child’s acclimatization and the “shared
parental intent”—a factor that is relevant because “the child’s
knowledge of [his parents’] intentions is likely to color [his]
attitude to the contacts [he] is making” and “affect the length
of time necessary for a child to become habitually resident or
otherwise influence a child’s ability to acclimatize,” and, in
addition, because it bears on the parents’ own intentions
“regarding their child’s presence in a particular place.”6

, 296 (internal quotation marks
omitted).

       As a general matter “courts will find no change in
habitual residence” where the evidence of shared parental
intent reflects that the “child’s initial move from an
established habitual residence was clearly intended to be for a
specific, limited duration.” Whiting v. Krassner, 

, 549 (3d Cir. 2004). However, we have recognized an
exception to this general rule where a move, though
temporary, carries “a degree of settled purpose . . . , even if


      6
         We give some “independent weight to the parents’
present, shared intentions” to “ensure that neither parent is
acting unilaterally to alter a joint understanding reached by
the parents.” 

(internal quotation
marks omitted).




                              20
such purpose is only for a limited period.” 

of “settled purpose,” then, does not require an intention “to
stay . . . indefinitely,” and may in fact be for a “limited
period,” precipitated by various motivations, including
“[e]ducation, business or profession, employment, health,
family or merely love of the place.” 

-
24. Regardless of the motivation for the location selected, or
whether the stay was meant to be permanent or temporary,
“[a]ll that is necessary is that the purpose of living where one
does has a sufficient degree of continuity to be properly
described as settled.” 

the relative weight given the parents’ shared
intent and the child’s acclimatization, we have held that when
a child is very young, he “cannot possibly decide the issue of
residency,” 

, and the parents’ shared
intent is, thus, “of paramount importance,” while
acclimatization is secondary, 

.
However, once a child is old enough “to develop a certain
routine and acquire a sense of environmental normalcy,”
acclimatization becomes the central inquiry. 

. Although we have not fixed the age when
acclimatization takes on this greater significance, and it
necessarily will vary depending on the maturity and cognitive
and social abilities of the child in question, we have
recognized that a typical four-year-old child “certainly has
this ability” because he is “able to develop a certain routine
and acquire a sense of environmental normalcy” and is “not
only aware of those around him, but is able to form
meaningful connections with the people and places he
encounters each day.” 

point, because the child has
“reached an age where [he is] capable of becoming firmly
rooted in a new country,” we attach greater significance to




                              21
acclimatization and give “less weight to shared parental
intent.” 

(internal quotation
marks omitted) (quoting Holder v. Holder, 

,
1119 (9th Cir. 2004)).




                          22
              2.     The Parents’ Shared Intent In This
                     Case

       Here, the District Court declined to apply the
presumption that there is, ordinarily, no change in habitual
residence when the child’s move is for a “specific, limited
duration” because it found that there was “no credible
evidence” that the parties had an agreement that J.B.’s stay in
Pittsburgh would be for a “specific duration.” Blackledge,
No. 16-1004, 

, at *23-25
(quoting 

n.3). We agree with
Petitioner that this finding was clearly erroneous, given the
evidence on this record that there was such an agreement.
But because that evidence overwhelmingly demonstrates the
parties intended J.B.’s residence in Pittsburgh, albeit of
specific, limited duration, to carry “a degree of settled
purpose,” 

, we nonetheless conclude
that the “shared parental intent” factor favors the United
States as J.B.’s habitual residence.

        At the outset, we cannot agree with the District Court
that there was no credible evidence that the parties had agreed
J.B.’s stay in Pittsburgh was intended to be for a specific
duration. While the Court acknowledged that the record
demonstrated the “existence of an agreement,” it nonetheless
found that it “does not speak to the specific terms of the
agreement,” Blackledge, No. 16-1004, 

, at *19, and therefore rejected the notion the stay
could be categorized as of specific, limited duration. But we
have not required great precision in the terms of the
agreement, nor even a specific return date, in order to
conclude a case involved an agreed-upon move of “specific,
limited duration.” 

. Instead, we




                              23
have considered cases to fall in that category where the move
was bounded by even a general time frame. See 

(describing the child’s residence with the
father, intended to be for the length of the mother’s
recuperation, as “a limited period of time”); 

, 549 & n.6 (discussing the child’s stay with her
mother for two years but “no later than October 19, 2003” as
“intended to be for a specific, limited duration”); see also

-24 (citing with approval In re Bates,
No. CA 122-89, High Court of Justice, Family Div’l Ct.
Royal Courts of Justice, U.K. (1989) (framing an
approximately three-month stay with mother, while father
was on a concert tour, as “for a limited period”)).

       Here, although the District Court was correct that the
parties’ emails stop short of identifying a date certain that was
originally agreed for J.B.’s return, or similarly “specific terms
of the agreement,” Blackledge, No. 16-1004, 2016 U.S. Dist.
LEXIS 114543, at *19, they make clear that the parties
intended J.B.’s stay in Pittsburgh to be of a “specific, limited
duration,” 

. For example, in
response to Petitioner’s references to the alleged “agreement”
in his emails in February 2016, and his requests that
Respondent “keep[] with [their] agreement that [J.B.] will
return to [Petitioner] for the academic year 2016-2017,” J.A.
190, Respondent did not reject the notion that there was an
agreement or that J.B.’s stay with her in Pittsburgh was
intended to be for a limited duration. Rather, she asked
Petitioner to “reconsider” the agreement, J.A. 172, so that J.B.
could stay with her “as a primary caregiver,” J.A. 171, rather
than requiring him to “yearly adapt[] to living” with a
different parent in alternating years, which she believed
would be “psychologically disadvantageous” for him, J.A.




                               24
177. Indeed, the record is replete with references to the
parties’ agreement that “[J.B.] would go with [Respondent] to
Pitt[sburgh] and return to [Petitioner] for [the] 2016-2017
academic year. Then back to [Respondent].” J.A. 176; see
also J.A. 168 (warning Respondent to “prepare [herself] for
fulfillment of [their] agreement that [J.B.] returns to
[Petitioner] for 2016-2017” and reassuring her, “You’ll have
him again in 2017”); J.A. 178 (noting that Respondent had
not previously expressed concerns for J.B. to “spend alternate
years with us when the agreement was made”).

       Notwithstanding such error, “we may affirm on any
grounds supported by the record,” Maher Terminals, LLC v.
Port Auth. of N.Y. & N.J., 

, 105 n.4 (3d Cir.
2015), and “[w]hen the outcome is clear as a matter of law . .
. remand is not necessary,” Mahmood v. Gonzales, 

, 253 (3d Cir. 2005). Here, we conclude such an outcome
is clear as a matter of law because this case is on all fours
with our decision in Whiting v. Krassner, 

(3d
Cir. 2004).

       In Whiting, the parents had agreed in writing, after the
attack on the World Trade Center in New York City on
September 11, 2001, that the mother and child would leave
the United States and live in Canada for two years—i.e., for a
limited 

. Two months into the
move, however, the father changed his mind and removed the
child to the United States. 

As the child there was
only sixteen months old, see 

we focused on
shared parental intent, and not acclimatization, and we
concluded that the child’s habitual residence was Canada, 

After observing the parties intended for the mother
and child, albeit for that specified period, to put down roots
and take on the normal pattern of residential life in Canada,




                              25
including renting an apartment near the mother’s family
members, looking into childcare programs, and applying for
necessary documentation, such as a medical card, 

we concluded the move was accompanied by a “degree of
settled purpose,” 

Given that purpose, we observed,
the fact that the mother and child’s Canadian residence was
planned for two years “d[id] not in any way diminish the
parties’ settled intention that the two were to remain in
Canada for at least two years” and “in no way hinder[ed] the
finding of a change in habitual residence.” 

In
reaching our holding, we also rejected the father’s argument
that Canada could not have become the child’s habitual
residence because there was no shared intent to abandon the
United States, and we recognized that “abandonment,” as the
flipside of “habitual residence,” could also be for “a definite
and extended period,” i.e., until the child resumed her
habitual residence in the abandoned country, as scheduled.7

we also relied heavily upon and cited
approvingly to a British case that is even more analogous to
J.B.’s case. 

(citing In re Bates, No. CA 122-89,
High Court of Justice, Family Div’l Ct. Royal Courts of
Justice, U.K. (1989)); see also 

-24
(quoting In re Bates). There, the father was a musician who


      7
         In Whiting, we held that Canada had become the
child’s habitual residence based only on the parties’ shared

. Here, in contrast, not only the
shared parental intent, but also acclimatization, favor the
country of the custodial parent, see infra Part IV.B.3, making
this an even stronger case for the United States as J.B.’s
habitual residence.




                              26
travelled extensively, and the mother and child “had toured
with father for the majority of the girl’s life to that point.”

n.5. Though London “was the
family’s home base,” the parents decided that the mother and
daughter would live in New York while the father toured the
Far East, but after only two days, the father directed the
nanny to bring the girl back to London. 

reasoned that the accommodations made in New York to
which father had agreed, “however acrimoniously,” for the
three months before father “return[ed] to London amounted to
a purpose with a sufficient degree of continuity to enable it
properly to be described as settled.” 

(quoting In re Bates). The child’s habitual residence,
therefore, was New York. 

(citing In re Bates).

       Likewise, here, it is evident that J.B.’s move to the
United States, although of limited duration, was intended by
both Petitioner and Respondent to be accompanied by a
degree of “settled purpose.” 

. The
record reflects that J.B. moved to Pittsburgh in August 2015
for the purpose of assuming a full and normal life of an eight-
year-old boy during the intended period of his stay, making
long-term friends and plans, developing routines and a sense
of environmental normalcy, exploring his city and other parts
of the Commonwealth, and putting down roots, not only for
the 2015-2016 school year, but also, per the parents’ express
agreement, for future alternating years, interspersed with the
years he would be living with Petitioner in Germany. Under
these circumstances, as in Whiting, the fact that the parties
understood that J.B. would return to Germany “d[id] not in
any way diminish . . . the parties’ settled intention” that he
was to remain in the United States for at least a year, settling
into a normal routine, and the fact that J.B.’s stay was




                              27
intended to be of a limited duration “in no way hinder[ed]” a
finding that the United States was his habitual residence
during that time. 

this interpretation of the record,
arguing that this case more closely resembles that addressed
by the Ninth Circuit in Mozes v. Mozes, 

(9th
Cir. 2001). There the children, Israeli residents, traveled with
their mother to the United States for a fifteen-month visit to
“partake of American culture,” 

in what the court
analogized to a “study[] abroad” program, 

A year
into that visit, however, the mother filed for divorce and
retained the children in the United States. 

In
rejecting the mother’s argument that the United States had
become the children’s then-habitual residence, the Ninth
Circuit concluded that, when the children moved to the
United States, the “normal expectation,” shared by both the
parents and the children, was that the family would reunite in
their home in Israel and that Israel would, therefore, remain
their habitual residence. 

As the court explained,
the parents and the children were Israeli citizens; they had
lived all their lives in Israel and entered the United States on a
temporary visa; and neither parent had a prior connection to
the United States. 

1082.

       The record in J.B.’s case paints a very different
picture. Petitioner and Respondent did not intend J.B.’s stay
in Pittsburgh as a “study[] abroad” program or a transient
“American cultur[al]” visit. 

1083. On the
contrary, when Respondent and J.B. moved to the United
States, J.B. was returning to a country and culture with which
he was already familiar and a city in which he had previously
lived for two years—a city that, by the time of the retention
date, was the longest and most stable residence he had known




                               28
in his fairly nomadic early years; in addition to having
extended family in the United States, J.B. was a United States
citizen, as was his father, and his mother was a lawful
permanent resident; Respondent and J.B. had resided in
Germany for only two years between their two residences in
Pittsburgh; within the first month of J.B.’s residence in
Pittsburgh, his father made efforts to secure a job in the
United States and elsewhere, indicating at one point that he
felt “dirty” that J.B. might not have a home to return to in
Germany at the end of that year, J.A. 200; at the time of the
move, both Petitioner and Respondent recognized their
marriage had become acrimonious, and according to
Respondent, whom the District Court generally found more
credible, the parties had agreed to divorce and it was only “a
matter of time [as to] when,” J.A. 421-22; and the parents’
emails are explicit that they intended to continue living
separately in future years and for J.B. to alternate between
them, spending the 2015-2016 academic year in Pittsburgh,
the 2016-2017 academic year in Germany, and the 2017-2018
academic year back in Pittsburgh. Thus, this is not a case, as
in Mozes, where the noncustodial parent’s country had served
to that point as their “home countr[y]” or where it can be said
the “normal expectation” of the parties was that they would
return to that country to live as a family unit. See 

.

       Petitioner, argues, however, that we should disregard
those portions of the parents’ communications reflecting that
they had agreed that J.B. would “spend alternate years with
[them] when the agreement was made,” J.A. 178, or that J.B.
would be returning to Pittsburgh for the 2017-2018 school
year, and that we should limit our consideration of the
parents’ agreement to those excerpts in which they discuss




                              29
J.B.’s return to Germany for the 2016-2017 school year. This
we decline to do. For as we have repeatedly recognized, the
parents’ agreement as to the allocation of custody between
them is highly relevant to the determination of “shared
parental intent.” See, e.g., 

-93,
296-97; 

-51. After all, the main
reason we look to “shared parental intent” as part of our
inquiry is its likelihood “to color [the child’s] attitude to the
contacts [he] is making” and to “affect the length of time
necessary for a child to become habitually resident or
otherwise influence a child’s ability to acclimatize”—factors
relevant to the determination whether the move carried a
“settled purpose ‘from the child’s perspective.’” 

, 296. For those reasons, where the parents
have agreed, in connection with a child’s move to a given
residence, that the child will henceforth split time between
them, and, thus, is expected to return to that residence at
regular intervals going forward, that shared parental intent
will undoubtedly affect the child’s attitude, expectations,
plans, and sense of purpose in undertaking the move to that
residence.8


       8
          The significance of the parents’ forward-looking
intent in this circumstance is different than in those cases
where courts have observed that the formation of an intention
to move does not convert the intended future residence into a
“habitual residence.” See, e.g., 

(citing
Friedrich v. Friedrich, 

(6th Cir. 1993)
(holding that a mother’s intention to move the child to the
United States did not make the United States the child’s
habitual residence prior to the move)). Where a child is
actually living in a given residence, and we are tasked with




                               30
        Indeed, Mozes, by its terms, distinguished the “rare
situation[s] where someone consistently splits time more or
less evenly between two locations, so as to retain alternating
habitual residences in 

n.17 (citing
Johnson v. Johnson, 

(Va. Ct. App. 1997)); see
also 

n.50 (explaining that where a child “spent
regularly alternating periods with each parent . . . , [he] might
thus have acquired dual habitual residence”). And more
recently the Ninth Circuit again observed in dictum that,
where the child splits time between his parents’ countries of
residence, he may be deemed to have “consecutive,
alternative habitual residences” where supported by the facts.
Valenzuela v. Michel, 

, 1178-79 (9th Cir. 2013)
(noting that the father also could have prevailed by showing
that the father and the mother “shared a settled intention to
abandon Mexico as the [children’s] sole habitual residence”).

        Likewise, the courts of other Hague Convention
member states have consistently recognized that the existence
of a so-called “shuttle custody” arrangement, in which a child
splits time between his parents’ countries of residence, bears
on the determination of habitual residence. See, e.g., Wilson
v. Huntley, 2005 Carswell Ont. 1606, at ¶¶ 8, 32, 50 (Can.
Ont. Sup. Ct. J.) (WL) (holding that, where the child split her
time in three-to-six month intervals between the mother and
the father’s homes, developing “similar social and family
bonds in each State,” and where the “parents clearly intended


determining whether the move to it was accompanied by a
settled purpose, the parents’ and child’s expectations that the
child will return to that residence on a regular basis in the
future is necessarily relevant to the child’s attitude regarding
the move itself.




                               31
to share custody of [the child], in the legal sense and in the
sense of physical, residential custody,” the child “could have
consecutive alternative habitual residences in two different
States at separate times”); J. v. J. [HFD] [Supreme
Administrative Decision] 1995 case no. 7505-1995 (Swed.),
translated at https://assets.hcch.net/incadat/fullcase/0080.htm
(holding that, where the parents agreed to be responsible for
the child “on an alternate basis” and to “share [the child’s] de
facto care,” the child was habitually resident in her mother’s
home country, where she was residing immediately prior to
the retention, because the child had spent the last two years
there and “ha[d] adjusted to circumstances in the place where
she [wa]s living”).

         While we have observed in dictum that the concept of
“alternating habitual residence” would appear to comport
with the Hague Convention so long as “a child has only one
habitual residence country at any given time,” 

n.20, we have not had prior occasion to address
the relevance or weight of an agreement that a child split time
between two parents. In doing so now, we emphasize that the
parents’ shared intent as to the custody arrangement between
them is probative—but not dispositive—in the determination
of habitual residence. That is, we agree with the observation
that “where residence with two parents is divided equally,
it . . . [is] unreal, in the absence of other differentiating
factors, to see the residence with one parent as primary and
stays with the other parent as interruptions.” Watson v.
Jamieson, 1997 Fam. L.R. 11, 14 (Scot.). At the same time,
we eschew any suggestion that an agreement to alternate
habitation between parents automatically equates to
“alternating habitual residences.”        Indeed, any such
categorical approach to shared custody or one-size-fits-all




                              32
framework for habitual residence would be inconsistent with
our case law, which rejects the application of a
“predetermined formula” to Hague Convention cases,

, and with the Convention, which
contemplates a fact-specific approach and encourages a
“flexible interpretation” of its terms, Eliza Perez-Vera,
Explanatory Report, in 3 Hague Conference on Private
International Law, Acts and Documents of the Fourteenth
Session, Child Abduction 426, 446 (1982).9

        Instead, we view a parental agreement that a child will
split time between the parents’ countries of residence as a
significant consideration, but as one among others, informing
the “necessarily fact-intensive and circumstantially based”
inquiry a court must undertake to determine whether a child’s
move was accompanied by a “degree of settled purpose.”

-48. Approaching the inquiry in this
way, we respect both our precedent and Congress’s
instruction that we pay heed to “the need for uniform
international interpretation of the Convention.” 22 U.S.C. §
9001(b)(3)(B).

       Undertaking that inquiry here, we consider, in addition
to the other record evidence discussed above concerning the
parents’ shared expectations for J.B.’s move to Pittsburgh in
2015, the parents’ agreement that J.B. would “alternate
between Germany and [the] USA” going forward, J.A. 157,

       9
         As we previously recognized, “Elisa Perez-Vera was
the official Hague Conference Reporter, and her report is
generally recognized as the official history and commentary
on the Convention.” 

n.3 (internal
quotation marks omitted).




                              33
and, hence, that J.B. would be returning to Germany for only
a single academic year before resuming his residence in
Pittsburgh for the 2017-2018 year. In view of that agreement
and the totality of the record in this case, it is apparent that
J.B.’s 2015 move to Pittsburgh was accompanied, through at
least the July 6, 2016 retention date, by the requisite “degree
of settled purpose” and that the element of shared parental
intent thus supports the United States as J.B.’s then-habitual
residence.10 

.

              3.     The Record          Concerning      J.B.’s
                     Acclimatization

       Petitioner asserts two points of error on
acclimatization, arguing that the District Court applied the
wrong retention date and, therefore, improperly considered
irrelevant evidence of acclimatization, and that, when the
record is limited to the proper time frame, it does not support
a finding of acclimatization. While we agree that the District
Court mistakenly considered post-retention-date evidence, we

       10
           Petitioner’s argument that J.B. was expected to
return to Germany after the year in Pittsburgh is thus beside
the point. Although Petitioner accurately catalogues the
evidence supporting that expectation—e.g., the letter to J.B.’s
school requesting a one-year leave of absence and stating that
J.B. would return for the 2016-2017 academic year; the three-
year German visas the parties and J.B. obtained before the
Respondent and J.B. left the country; and that J.B. left some
of his belongings behind in Germany—that evidence is
entirely consistent with the parties’ agreement that J.B. was to
spend alternating years with each parent and that, during his
year in Pittsburgh, the United States was J.B.’s habitual
residence.




                              34
have no trouble concluding that error was harmless given the
substantial record concerning acclimatization as of the correct
retention date. See generally Winston ex rel. Winston v.
Children & Youth Servs. of Del. Cty., 

, 1391
n.7 (3d Cir. 1991) (holding that the court’s consideration of
inadmissible hearsay was harmless error where there was
“sufficient evidence without [the improperly admitted
evidence] to support the district court’s conclusion”).

       The evidence of J.B.’s acclimatization to Pittsburgh as
of July 6, 2016 is overwhelming. He had a tremendously
successful academic year, earning nearly all As and
overcoming an initial reading deficiency while demonstrating
“dramatic improvement” over the year. J.A. 329, 333, 451.
In addition, J.B. made friends “easily” and was, according to
his teacher, “well-adjusted” overall. J.A. 330, 334. J.B. also
enjoyed numerous activities outside of school, including
soccer, swim team, and a robotics club, which he was
handpicked to join by a fellow classmate. Over the course of
the year, J.B. learned how to successfully program a robot to
complete missions, despite feeling as though the task was
impossible when he first started. And on his swim team J.B.
mastered each of the competitive strokes, and was competing
by the end of the year, looking forward to stepping up into the
next group the following year.

       The record, likewise, reflects that J.B. was sufficiently
mature to form “meaningful connections with the people and
places he encounter[ed]” in Pittsburgh. 

. In a credibility determination, to which we defer
absent clear error, Cooper v. Harris, 

, 1468
(2017), the District Court found that J.B. “exhibit[ed] an
unusual degree of maturity and situational awareness,” and
therefore accorded “significant weight” to J.B.’s statements




                              35
that he was looking forward long-term to moving into a house
and getting a dog in Pittsburgh, that he understood “his place
in Pittsburgh,” that he preferred living in Pittsburgh over
Berlin because of his quality of life in the United States and
because he had “more and better friends in Pittsburgh.”11
Blackledge, No. 16-1004, 

, at
*12 n.6, 14-15. The in camera interview thus further
supports the District Court’s conclusion, based on the record
as a whole, that J.B. had “formed meaningful connections
with the people and places he encountered,” 

(quoting 

(brackets omitted)), and
“ha[d] attained a sufficient degree of continuity to be properly
described as settled,” 

marks omitted)
(quoting 

).

       While Petitioner argues the District Court relied
heavily on evidence of activities post-dating the July 6
retention date, that evidence, on inspection, reduces to three
minor points of testimony: J.B.’s swim team that ran from
September 2015 through the end of July 2016, a summer
reading challenge that ran from May 24 through August 31,
and J.B.’s summer camps. Petitioner argues that any
consideration of these activities constituted reversible error,


       11
          We consider J.B.’s preference for Pittsburgh here
because a child’s expressed preference for a country may,
considering his age and maturity, be a further indication that
the child has acclimatized to that country, see 

-95, regardless of whether that preference as
stated would satisfy the “wishes of the child” defense or
exception outlined in the Hague Convention, see 

(citing Hague Convention, supra, art. 13).




                              36
but we are not persuaded that the District Court erred, much
less that such error was prejudicial.12 For example, while the
reading challenge extended through August 31, J.B.
completed it on July 5, prior to the retention date. And while
J.B.’s participation on the swim team carried over through the
end of July, the testimony related to J.B.’s involvement dating
back to September 2015, with no mention of specific events
between July 6 and July 31. Even the evidence regarding
summer camps is relevant to the extent it informed J.B.’s
expectations and aspirations before July 6. Moreover, any
error in the District Court’s consideration of this evidence
was harmless because the post-retention-date activities were
merely duplicative and cumulative of other evidence in the
record concerning those same activities. See Howmet
Aluminum Corp. v. Hartford Accident and Indem. Co., 

, 478 (3d Cir. 1981) (citing Fed. R. Evid. 61)
(holding that consideration of inadmissible evidence that is
merely cumulative of properly admitted evidence is not
grounds for remand or reversal).

       In sum, given the extensive record evidence of J.B.’s
success in school, his participation in various activities and
sports, his many friendships, his experiences at cultural,
entertainment, and sporting events, and his own stated
preference for the United States, to which the District Court
afforded “significant weight” because of “the degree of


      12
          Because we conclude that any error in considering
evidence beyond July 6 was harmless, we need not address
the Respondent’s argument that the Petitioner waived his
objections to the District Court’s consideration of it because
he failed to preserve such objections at various points in the
proceedings.




                              37
maturity and situational awareness” J.B. exhibited,
Blackledge, No. 16-1004, 

, at
*12 n.6, the District Court did not clearly err in its fact-
finding related to J.B.’s acclimatization, nor did it commit
legal error in its determination that J.B. was acclimatized to
the United States at the time of retention.

V.    Conclusion

        Because the parents’ shared intent was for J.B. to
move to the United States with a “degree of settled purpose,”

, and because J.B. had acclimatized
to the United States by the date of retention, we agree with
the District Court’s holding that the United States was J.B.’s
habitual residence immediately prior to the retention date and
that the retention therefore was not wrongful under the Hague
Convention. Accordingly, we will affirm the order of the
District Court.




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