Legacy or colonization? Posteruption establishment of peregrine falcons ( Falco peregrinus ) on a volcanically active subarctic island

Abstract

How populations and communities reassemble following disturbances are affected by a number of factors, with the arrival order of founding populations often having a profound influence on later populations and community structure. Kasatochi Island is a small volcano located in the central Aleutian archipelago that erupted violently August 8, 2008, sterilizing the island of avian biodiversity. Prior to the eruption, Kasatochi was the center of abundance for breeding seabirds in the central Aleutian Islands and supported several breeding pairs of peregrine falcons (Falco peregrinus). We examined the reestablishment of peregrine falcons on Kasatochi by evaluating the genetic relatedness among legacy samples collected in 2006 to those collected posteruption and to other falcons breeding along the archipelago. No genotypes found in posteruption samples were identical to genotypes collected from pre-eruption samples. However, genetic analyses suggest that individuals closely related to peregrine falcons occupying pre-eruption Kasatochi returned following the eruption and successfully fledged young; thus, a genetic legacy of pre-eruption falcons was present on posteruption Kasatochi Island. We hypothesize that the rapid reestablishment of peregrine falcons on Kasatochi was likely facilitated by behavioral characteristics of peregrine falcons breeding in the Aleutian Islands, such as year-round residency and breeding site fidelity, the presence of an abundant food source (seabirds), and limited vegetation requirements by seabirds and falcons.

Full text

Ecology and Evoluon 2016; 1–8
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1
www.ecolevol.org
Received: 27 June 2016
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Revised: 18 October 2016
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Accepted: 31 October 2016
DOI: 10.1002/ece3.2631
ORIGINAL RESEARCH
Legacy or colonizaon? Posterupon establishment of
peregrine falcons (Falco peregrinus) on a volcanically acve
subarcc island
Sarah A. Sonsthagen1 | Jerey C. Williams2 | Gary S. Drew1 | Clayton M. White3 |
George K. Sage1 | Sandra L. Talbot1
This is an open access arcle under the terms of the Creave Commons Aribuon License, which permits use, distribuon and reproducon in any medium,
provided the original work is properly cited.
© 2016 The Authors. Ecology and Evoluon published by John Wiley & Sons Ltd.
1US Geological Survey, Alaska Science Center,
Anchorage, AK, USA
2US Fish and Wildlife Service, Alaska Marime
Naonal Wildlife Refuge, Homer, AK, USA
3Department of Plant and Wildlife
Sciences and Monte L. Bean Life Science
Museum, Brigham Young University, Provo,
UT, USA
Correspondence
Sarah A. Sonsthagen, US Geological Survey,
Alaska Science Center, Anchorage, AK, USA.
Email: ssonsthagen@usgs.gov
Funding informaon
U.S. Geological Survey; U.S. Fish and Wildlife
Service; Brigham Young University.
Abstract
How populaons and communies reassemble following disturbances are aected by
a number of factors, with the arrival order of founding populaons oen having a
profound inuence on later populaons and community structure. Kasatochi Island is
a small volcano located in the central Aleuan archipelago that erupted violently
August 8, 2008, sterilizing the island of avian biodiversity. Prior to the erupon,
Kasatochi was the center of abundance for breeding seabirds in the central Aleuan
Islands and supported several breeding pairs of peregrine falcons (Falco peregrinus).
We examined the reestablishment of peregrine falcons on Kasatochi by evaluang the
genec relatedness among legacy samples collected in 2006 to those collected post
erupon and to other falcons breeding along the archipelago. No genotypes found in
posterupon samples were idencal to genotypes collected from pre erupon sam
ples. However, genec analyses suggest that individuals closely related to peregrine
falcons occupying pre erupon Kasatochi returned following the erupon and suc
cessfully edged young; thus, a genec legacy of pre erupon falcons was present on
posterupon Kasatochi Island. We hypothesize that the rapid reestablishment of per
egrine falcons on Kasatochi was likely facilitated by behavioral characteriscs of per
egrine falcons breeding in the Aleuan Islands, such as year round residency and
breeding site delity, the presence of an abundant food source (seabirds), and limited
vegetaon requirements by seabirds and falcons.
KEYWORDS
colonizaon, dispersal, Falco peregrinus, genec legacy, Kasatochi Island, peregrine falcon
1 | INTRODUCTION
How populaons are founded and how communies reassemble
following disturbances, such as volcanic erupons, are aected by
a number of factors, including the severity of disturbance, priority
eects (dispersal and arrival order; Hoverman & Relyea, 2008), and
availability of propagules (Mazzola et al., 2011) either from survivors
(represenng legacy biodiversity, Walker et al., 2013), or from coloniz
ers (represenng founder biodiversity). Most studies have examined
these factors retrospecvely (Fleischer, McIntosh, & Tarr, 1998; Percy
et al., 2008; Ricklefs, 2010; Shaw, 1996; Yang, Bishop, & Webster,
2008), as opportunies to study community reassembly following

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SONSTHAGEN ET Al.
major disturbances are rare. As colonizaon of newly sterilized areas
can occur rapidly (e.g., plants on Krakatau, Thornton, 1984; birds on
Surtsey, Petersen, 2009; predaceous ies on Kasatochi, Walker et al.,
2013), catastrophic disturbance events that simplify community rela
onships via the eliminaon of most or all ora and fauna provide par
cularly useful opportunies to study determinisc versus stochasc
processes inuencing the reassembly of communies (Mazzola et al.,
2011; Walker et al., 2013).
Inial founding events and the expansion of founding individuals
across the landscape may profoundly inuence later populaons (Yang
et al., 2008) and community structure in newly created habitats. For
example, among closely related species in the Hawaiian Archipelago,
there is generally a linear relaonship between island age and genec
distance (sequenal radiaon), suggesve of rapid colonizaon follow
ing island genesis, yet evidence of subsequent colonizaon was not
observed (e.g., Fleischer et al., 1988; Percy et al., 2008; Shaw, 1996).
This paern of colonizaon illustrates the importance of inial found
ing events, as inial founders may impact the ability of subsequent
dispersers to successfully colonize (Waters, Fraser, & Hewi, 2012).
Therefore, species and/or individuals that survived the erupon may
play a pivotal role in the success of subsequent colonizaon aempts
by other species or individuals (Franklin, 2005), ulmately impacng
community assemblage posterupon (Walker et al., 2013).
Establishment, or reestablishment, of terrestrial fauna and asso
ciated food webs on islands following major disturbances (or new
geological formaon) can also depend upon the presence of plants
for nesng substrate (i.e., birds on Anak Krakatau; Thornton, Zann,
& Stephenson, 1990) and associated food base (i.e., prey for insec
vores/carnivores or vegetaon for herbivores, frugivores, and nec
tarivores; Walker et al., 2013). Thus, establishment of local breeding
populaons for certain species lags unl a sucient level of habitat
development has occurred. This limitaon, however, may favor rapid
colonizaon and establishment of species that are not dependent
upon terrestrial vegetaon, such as seabirds and marine mammals.
Highly mobile animal species that rely on the marine environment for
their food base should not be constrained in their ability to rapidly
colonize or recolonize disturbed islands. The limited habitat require
ments of seabirds are exemplied on Surtsey Island, which emerged
o the south coast of Iceland in an extended series of erupons. Only
2 weeks aer the erupon began, gulls (Larus sp.) were observed
landing on the island between erupon events (Gudmundsson, 1966;
Petersen, 2009). Within 7 years of emergence of the island, 3 years
aer the cessaon of volcanic acvity, marine birds started nesng on
the island (Fridriksson & Magnússon, 1992; Petersen, 2009). Similarly,
marine birds increased in abundance following the erupon on San
Benedicto Island, Islas Revillagigedo, Mexico, despite poor survival of
seeds and vegetaon (Ball and Gluscksman 1975). Therefore, highly
vagile species characterized by minimal terrestrial habitat require
ments should be early founders in newly sterilized areas and play a piv
otal role in how communies are reassembled, through, for example,
the facilitaon of subsequent colonizaon of other species via passive
dispersal, or provision of a food source.
Kasatochi Island, part of the U. S. Fish and Wildlife Service Alaska
Marime Naonal Wildlife Refuge (AMNWR), is a small volcano
(7.5 km2) located in the Andreanof island group in the central Aleuan
archipelago, 19 km from the nearest land mass (Figure 1). The violent
erupon of the Kasatochi volcano on August 8, 2008 completely cov
ered the island, as well as near shore interdal and shallow subdal
areas, with thick volcanic deposits that devastated wildlife nesng
and foraging habitat (Figure 2; DeGange, Byrd, Walker, & Waythomas,
2010). Biological resources on Kasatochi Island had been monitored
annually by AMNWR sta from 1996 to 2008, given the island’s im
portance as a center of abundance for breeding seabirds in the cen
tral Aleuan Islands (Drummond & Larned, 2007). In parcular, least
auklets (Aethia pusilla) and crested auklets (A. cristatella) nested in
immense numbers (>200,000 individuals; Williams, Drummond, &
Buxton, 2010). By the date of the erupon in 2008, many seabirds
had nished breeding for the year, and most adults had le the island;
it was assumed they survived to return the following year (Williams
et al., 2010). Several other seabird species were sll breeding and
along with nonedged young were entombed or perished otherwise
in the erupon.
FIGURE1 Localities of peregrine falcon populations sampled in the Aleutian archipelago with sample sizes in parentheses
50 km
50 mi
550 km0km
50 mi
Commander Islands (7)
Attu (5)
Buldir (5)
Amchitka (13)
Amatignak (1)
Kasatochi (21)
300 miles
Inset
Alaska

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SONSTHAGEN ET Al.
Similar to other islands along the Aleuan chain that host large
seabird colonies, a relavely large number of peregrine falcons (Falco
peregrinus) nested on Kasatochi (e.g., 9 eyries total, 2–6 acve eyries
in a given year pre erupon, along ca. 10 km of coastline [Figure 3]
versus an average density of one pair every 10–16 km of coastline
in the Aleuan Island Rat Island Group; White, 1976). Unlike sea
birds, peregrine falcons and the other primary avian predator in the
Aleuan Islands, bald eagles (Haliaeetus leucocephalus), are nonmigra
tory and remain close to their breeding islands throughout the year
(White, 1975; White, Emison, & Williamson, 1971). Given this general
breeding site delity, it was unclear whether avian predators and their
edglings survived the erupon. However, the presence of peregrine
falcons (almost exclusively predatory) and bald eagles (paral scaven
gers) within the rst year or two, respecvely, following the erupon
suggested that these species quickly recolonized, or at least ulized re
sources on, posterupon Kasatochi. It is not known, however, whether
individual birds that occupied pre erupon Kasatochi returned post
erupon (e.g., represented legacy biodiversity), or whether they were
new colonizers. Prior invesgaon of populaon and regional level
genec structuring suggests peregrine falcons occupying the Aleuan
Islands show signicant regional level structuring and are genecally
disnguishable from peregrine falcons occupying habitats elsewhere
in Alaska, but show lower levels of structuring across island groups
(S. L. Talbot, unpublished data). Thus, levels of natal site delity (philo
patry) are apparently not suciently high to isolate specic island
populaons, suggesng that individual peregrines occupying post
erupon Kasatochi cannot necessarily be assumed to represent legacy
biodiversity.
Tesng for relave importance of in situ and ex situ survival vs. col
onizaon following disturbances, such as volcanic erupons, is oen
limited due to lack of historical informaon about predisturbance res
idents (Walker et al., 2013). This limitaon can be overcome if histor
ical data are sucient to disnguish colonizers from survivors (Yang
et al., 2008). Here, we examine the reestablishment of the peregrine
falcon on Kasatochi Island following the 2008 erupon, using genec
data obtained from feather samples collected pre and posterupon
and eggshell membranes collected posterupon. Prior to the erupon,
the nine eyries used by peregrine falcons were known to be acve
for three to 11 years from 1996 to 2008 (Figure 3; J. C. Williams,
unpublished data). In the rst year following the erupon, peregrine
falcons were present on the island, although no breeding aempts
were observed. In 2010, 2 years posterupon, one eyrie located on
the east side of the island at Rye Point (Figure 3) was conrmed as
acve. Peregrines nesng at this eyrie edged two young, in the rst
known successful avian breeding aempt on posterupon Kasatochi
(Figure 4). It is possible that at least one other eyrie was established
FIGURE2 Photographs of Kasatochi Island (a) pre eruption, July 2008, and (b) posteruption, October 2008. Photographic credit: Jerry
Morris (pilot), Security Aviation
(a) (b)
FIGURE3 Localities of historical (1996–2008) and current (2010)
eyries for peregrine falcons on Kasatochi Island (52.17°N, 175.51°W)
Rye Pt
2010
Crater Rim
2001
2007–2008
Northeast
1998–2002
2004–2005
Turre Fjord
2001
2003–2008
2010
Whiskey Dale
1999–2000
2003
Tundrin Talus
2003–2008
(2x in 2005)
2010
Mt Kasatochi
1996–2005
2002, 2005
Peregrine Ravine
1996–2008
Southwest
1999–2000
2003–2008
2010
01
Kilometer
N

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SONSTHAGEN ET Al.
in 2010, but visual conrmaon was not possible (J. C. Williams, un
published data). Our study addressed two quesons: (1) Are the pere
grines nesng on Kasatochi Island posterupon the same individuals
that nested pre erupon; and (2) If not, what is the genec relaon
ship among peregrines pre and posterupon?
2 | METHODS
2.1 | Samples
Molted feathers (total n = 12; four adults and eight juveniles) found on
beaches or near eyries and eggshell membranes (n = 2; 2010) were col
lected at peregrine falcon eyries posterupon (2009–2011) of Kasatochi
Island. It should be noted that juvenile feathers were molted from
adult (aer hatch year) birds. Posterupon feather samples were col
lected during the 1 to 3 day eld acvies on the island (June 13–17,
2009, August 10–12, 2009, June 18–19, 2010, August 30, 2010, June
17–18, 2011, and August 15–17, 2011). Legacy samples (total n = 7;
three adults and four juveniles) consisted of feathers collected from two
of the four acve eyries or within the territories of known pairs from
perches and plucking staons in 2006. Therefore, our legacy sample size
represents between 25% (n = 2/8) and 87.5% (n = 7/8) of the peregrine
falcons breeding in 2006. We assumed that molted feathers came from
individuals that were residents of Kasatochi and not peregrines from
nearby islands or nonbreeders, given their breeding site delity and ter
ritorial behavior (White, Clum, Cade, & Hunt, 2002). In addion, feather
and egg shell membranes (n = 31), collected as part of a larger regional
study from peregrine falcons breeding throughout the Aleuan Islands,
were included to derive insight into the contribuons of islands in the
reestablishment of falcons on Kasatochi Island (Figure 1).
2.2 | Laboratory techniques
DNA was extracted using a salt extracon following Talbot et al.
(2011). Genotype data were collected from 11 microsatellite loci
(NVHfp5, 13 1, 31, 46 1, 54, 79 4, 82 2, 86 2, 89 2, 92, and 107;
Nesje & Røed, 2000). This suite of microsatellite loci are suciently
variable to have high condence in our ability to idenfy unique in
dividuals based on genotype data; probability of identy (PID) was
1.084e−6, and PID among rst order relaves was 2.223e−3 within
the Aleuan Islands (Talbot et al., 2011). Polymerase chain reacon
(PCR) amplicaons and thermocycler condions followed Talbot
et al. (2011). Samples were assayed soon aer the compleon of eld
acvies each year. Feather samples were extracted separately from
eggshell membrane samples. In addion, 35% of the samples were
extracted, amplied and genotyped in duplicate for quality control.
No inconsistencies in genotype scores were observed. Microsatellite
genotype data are accessioned at the USGS Alaska Science Center
data repository (hp://dx.doi.org/10.5066/F7F18WV0).
2.3 | Stascal analysis
Queller and Goodnight’s (1989) index of relatedness (rxy) was cal
culated among pairs of peregrine falcons on Kasatochi Island within
and across years and among individuals sampled throughout the ar
chipelago, as well as averaged across all individuals within an island
in a given year, using Idenx 1.1 (Belkhir, Castric, & Bonhomme,
2002). Relatedness values range from −1 to 1, where rxy equals 0.5
for rst order (i.e. full sibling, parent–ospring) relaonships, 0.25 for
second order (e.g., half sibling, grandparent) relaonships, 0 for unre
lated individuals, and −1 for outbred individuals. Isolaon by distance
(IBD) analyses were conducted to determine whether islands in closer
geographic proximity were also more genecally similar (FST) using
Isolaon by Distance web service version 3.23 (Bohonak, 2002) to
further invesgate the posterupon colonizaon of peregrine falcons
to Kasatochi Island. Two IBD analyses were conducted: (1) among
peregrine falcons sampled throughout the Aleuan Islands and the
2006 Kasatochi samples; and (2) among peregrine falcons sampled
throughout the Aleuan Islands and the 2009–2011 Kasatochi sam
ples. Geographic distances were calculated as straight line distance.
3 | RESULTS
3.1 | Genec relaonship across years
Genotypes from peregrine falcons breeding on Kasatochi prior to
the 2008 erupon did not share idencal genotypes with any falcons
sampled posterupon (2009–2011) and the proporon of familial
relaonships decreased each subsequent year (Table 1). However,
DNA from a feather (Kas09 003) collected in 2009 had high similar
ity with peregrine falcons sampled in 2006 (two comparisons with
rxy > 0.5, a value expected between rst order relaves, and four
comparisons with rxy = 0.24–0.34, values expected between second
order relaves). Among the posterupon samples, the genotype
obtained from this same sample (Kas09 003) was idencal at all 11
loci to the genotype obtained from an eggshell membrane collected
in 2010 (Kas10E02E). It is not possible that the feather and the egg
shell membrane represent the same individual; rather this match likely
FIGURE4 Two peregrine falcon young that were the first known
successful avian breeding attempt on posteruption Kasatochi Island
(June 2010; photograph by Jeffrey Williams)

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SONSTHAGEN ET Al.
represents a parent and its ospring, suggesng that at least one in
dividual present on posterupon Kasatochi during 2009 returned the
following year to Kasatochi Island to breed. Few rst order familial
relaonships were observed between the remaining two comparisons
(2009 & 2011, 2010 & 2011) with a greater proporon of second
order relaonships observed (Table 1).
3.2 | Genec relaonship within years
Overall rxy values esmated for Kasatochi peregrines within years were
negave (Table 1). In general, rxy values were more negave than val
ues esmated from other islands in the Aleuan archipelago (Table 2)
and the Aleuan Island peregrine falcons as a whole (rxy = −0.010,
variance = 0.066). Despite negave rxy values, greater than 66% of
the comparisons indicated either a rst or second order familial rela
onship in 2006 and 2011 (Table 1). Fewer familial relaonships were
observed among 2009 and 2010 falcons.
3.3 | Genec relaonship throughout the
Archipelago
Increasing genec dierenaon with increasing geographic dis
tance was not observed within the Aleuan Archipelago pre erupon
(r = .187, p = .28) or posterupon (r = .473, p = .14). However, the
percentage of rst and second order familial relaonships among
Kasatochi Island and Amagnak Island (about 275 km west of
Kasatochi; Figure 1) was higher in the posterupon samples than in
the 2006 samples, although Amagnak was represented by a sin
gle feather sampled from an adult found dead in 2009 (Table 2). In
contrast, the percentage of familial relaonships between Kasatochi
Island and the other sampled Aleuan Islands remained approximately
similar, or lower, posterupon (Table 2).
4 | DISCUSSION
We found no genec evidence to indicate that individual peregrine
falcons known to have been present on Kasatochi Island pre
erupon returned posterupon. However, we cannot rule out that
pre erupon individuals returned; the absence of matching geno
types between pre erupon and posterupon individuals may be at
tributable to sampling bias. Although the number of occupied eyries
on pre erupon Kasatochi is greater than found on average in the
Aleuan Island archipelago (Ambrose et al., 1988), the four eyries oc
cupied on Kasatochi in 2006 likely represented approximately eight
adults, and the majority of the posterupon data for this study de
rived from feathers found during two 1 to 3 day eld acvies on a
small part of the island from 2009 to 2011. As well, peregrine falcons
may demonstrate high territory turnover rates; peregrine falcons
breeding on Haida Gwaii, Brish Columbia, another nonmigratory
TABLE1 Percent pairwise relatedness (rxy) values within and
among peregrine falcons sampled in 2006, and 2009–2011 on
Kasatochi Island along with mean relatedness within years. Here, we
dene a rst order familial relaonship as having a rxy value greater
than 0.40 (sharing at least one allele per locus) and second order
relaonship as having a rxy value between 0.20 and 0.39
Familial relaonship
rxy (variance)First order % Second order %
Kasatochi 2006
(n = 7)
38.1 (n = 8/21) 33.3 (n = 7/21) −0.240 (0.199)
& 2009 17.9 (n = 5/28) 32.1 (n = 9/28)
& 2010 9.5 (n = 4/42) 21.4 (n = 9/42)
& 2011 3.6 (n = 1/28) 17.9 (n = 5/28)
Kasatochi 2009
(n = 4)
16.7 (n = 1/6) 0.0 (n = 0/6) −0.341 (0.102)
& 2010 20.8a (n = 5/24) 12.5 (n = 3/24)
& 2011 0.0 (n = 0/16) 31.2 (n = 5/16)
Kasatochi 2010
(n = 6)
6.7b (n = 1/15) 6.7 (n = 1/15) −0.179 (0.089)
& 2011 4.2 (n = 1/24) 29.2 (n = 7/24)
Kasatochi 2011
(n = 4)
33.3 (n = 2/6) 33.3 (n = 2/6) −0.373 (0.259)
aDenotes a matching sample.
bDenotes egg shell membranes sampled from the same eyrie.
TABLE2 Percent pairwise relatedness (rxy) values among Kasatochi peregrine falcons sampled in 2006 and 2009–2011 with those
peregrines sampled throughout the Aleuan chain. Here, we dene a rst order familial relaonship as having a rxy value >0.40 (sharing at least
one allele per locus) and second order relaonship as having a rxy value between 0.20 and 0.39
rxy (variance)
Familial relaonships
Kasatochi 2006 Kasatochi 2009–2011
First order (%) Second order (%) Total (%) First order (%) Second order (%) Total (%)
Amagnak –0.0 (n = 0/7) 0.0 (n = 0/7) 0.0 7.1 (n = 1/14) 21.4 (n = 3/14) 28.6
Amchitka −0.068 (0.065) 8.8 (n = 8/91) 14.3 (n = 13/91) 23.1 7.1 (n = 13/182) 13.2 (n = 24/182) 20.3
Buldir −0.271 (0.080) 0.0 (n = 0/35) 25.7 (n = 9/35) 25.7 10.0 (n = 7/70) 4.3 (n = 3/70) 14.3
Au −0.192 (0.393) 5.7 (n = 2/35) 20.0 (n = 7/35) 25.7 11.4 (n = 8/70) 10.0 (n = 7/70) 21.4
Commander
Islands
−0.161 (0.064) 8.2 (n = 4/49) 24.5 (n = 11/49) 22.4 0.0 (n = 0/98) 11.2 (n = 11/98) 11.2

6
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SONSTHAGEN ET Al.
peregrine falcon populaon, have an adult median life expectancy of
2.8 years aer their second year of life (Nelson, 1990). Nevertheless,
our results did indicate that individuals closely related to peregrine
falcons occupying pre erupon Kasatochi returned following the
erupon. Fiy percent of comparisons indicated a familial relaon
ship among peregrine falcons breeding in 2006 and those who le
feathers in 2009 (Table 1). DNA from a feather collected in 2009 had
high genec aliaon with peregrine falcons sampled in 2006 and
this sample matched at all 11 microsatellite loci with a sample col
lected in 2010. Although this match is between a feather (2009) and
an egg shell membrane (2010) and, again, cannot represent the same
individual, it does indicate a rst order familial relaonship (parent–
ospring). Therefore, at least one peregrine, likely from a lineage that
occupied Kasatochi prior to the erupon, was “observed” in 2009
and, in 2010, edged the rst documented avian young on Kasatochi
Island posterupon. Thus, a genec legacy of pre erupon falcons
was present on posterupon Kasatochi Island via the presence of
close relaves in 2009 and subsequent producon of ospring in
2010.
Peregrine falcons rapidly recolonized Kasatochi Island, with simi
lar pre erupon numbers (feathers from four peregrine falcons were
collected on Kasatochi in 2009, six in 2010, and four in 2011; Table 1;
Figure 3). Behavioral characteriscs of peregrine falcons breeding in
the Aleuan Islands likely contributed to the rapid reestablishment
as displaced falcons would have a propensity to return to Kasatochi
(i.e., breeding site delity or philopatry) and displaced/neighboring
falcons could easily return as they occupy nearby islands year round
(White et al., 2002). This rapid reestablishment is parcularly note
worthy when compared to other islands that either experienced a vol
canic sterilizaon event or recently emerged. Peregrine falcons took
more than 93 years (rst record 1976; Rawlinson, Zann, van Balen, &
Thornton, 1992) to successfully colonize Krakatau Islands aer the
erupon in 1883. On Anak Krakatau, a volcanic island that emerged
from the sea in 1930, and later erupted in 1951–1952, peregrine
falcons were not observed unl almost 60 years later (1989; Zann &
Darjono, 1992). Furthermore, peregrine falcons are only visitors to the
volcanic islands of Motmot (emerged in 1968, Ball & Glucksman, 1975;
Schipper, Shanahan, Cook, & Thornton, 2001) and Islas Revillagigedo
(erupted in 1952; Hahn, Hogeback, Römer, & Vergara, 2012) and con
nue to be absent from Surtsey Island (emerged in 1963; Petersen,
2009). Although other volcanic islands have source populaons in rel
avely close geographic proximity, peregrine falcons breeding in the
Aleuan Islands are primarily nonmigratory with only some mid winter
interisland movement and juvenile dispersal (White, 1975; White
et al., 2002). The nearest nesng falcons are located on adjacent is
lands year round (ca. 19 km away), thereby increasing the opportu
nity for recolonizaon either via breeding or natal dispersal events.
Colonizaon on other volcanic islands, notably Islas Revillagigedo and
Surtsey, is restricted to migratory individuals, which may only pass by
the islands infrequently, thereby reducing the likelihood of peregrine
falcons becoming established on these islands. The paern of pos
terupon succession of avian taxa observed on Kasatochi has been
unique when compared to colonizaon paerns in the Krakataus, Islas
Revillagigedo, and Surtsey. On volcanic islands for which peregrine
falcons are not established, only larger bodied seabirds (Phoebastria
immutabilis, Phaethon aethereus; Pitman & Balance, 2002) have colo
nized the islands in large numbers on San Benedicto, Islas Revillagigedo
(where, historically, marine birds were abundant; Ball & Glucksman,
1975), and Surtsey (Larus sp.; Petersen, 2009). Only a few (<50) breed
ing birds (Anas superciliosa and Hirundo tahica) are present on Motmot
(Schipper et al., 2001). Among the Krakataus, community assembly
was needed to facilitate the reintroducon of avian predators, such as
the peregrine falcon. Zann and Darjono (1992) hypothesized that the
abundance of small passerines enabled the oriental hobby (F. severus)
to become established in 1985 on Anak Krakatau; the hobby was later
displaced by peregrine falcon. Presumably on the Krakataus, the ar
rival of passerines was dependent on the presence of suitable vege
taon and accompanying food source. In contrast, common avian
prey species are ubiquitous (e.g., 5,000,000 least auklets, 1,000,000
crested auklets) throughout the Aleuan Islands (see Gibson & Byrd,
2007 for addional esmates). Extensive peregrine prey analyses from
Amchitka Island, about 390 km west of Kasatochi (Figure 1), found six
species, none of which breed on that island but occupy the surrounding
FIGURE5 Auklets (Aethia sp.) on the colony surface at Kasatochi
Island (a) before (June 2004; photograph by Brie Dummond) and (b) after
the 2008 eruption (June 2009; photograph by Gary Drew). Photographs
were taken from approximately the same location and scale
(a)
(b)

|
7
SONSTHAGEN ET Al.
waters, made up 69% of the prey (n = 548 total prey items; White,
Emison, & Williamson, 1973). Pre erupon densies of crested and
least auklets in waters surrounding Kasatochi Island did not change
posterupon (Drew, Dragoo, Renner, & Pia, 2010), and lack of crev
ices and vegetaon likely increased their suscepbility to predaon by
peregrine falcons (Figure 5; see gure 1 in Williams et al., 2010). Thus,
the circumstances on Kasatochi with regard to this top avian predator
support the heterotrophs rst (Hodkinson, Webb, & Coulson, 2002;
König, Kaufman, & Scheu, 2011) marine based model proposed for
predaceous ies that rapidly colonized Kasatochi following the erup
on (Sikes, O’Brien, and Baltesperger unpublished data, cited in Walker
et al., 2013). We contend, therefore, that crical factors in the rapid
reestablishment of Kasatochi Island, regardless of the genec anity
of the recolonizing falcons, include the abundance of near shore and
pelagic food sources through the Aleuans as well as on posterup
on Kasatochi, coupled with high vagility of peregrine falcons. These
characteriscs would enhance rapid recolonizaon, bolstering contri
buons due to delity to site, whether natal or simply breeding site
delity, and the species’ lack of dependence on vegetaon for nesng.
Given our sample size, it is dicult to determine the specic orig
in(s) of all the falcons that colonized Kasatochi Island following the
2008 erupon, aside from the lineage considered to have derived
from temporarily displaced Kasatochi peregrines. The correlaon
between genec and geographic distance increased from the pre
erupon to the posterupon me periods, albeit not signicantly,
is likely due to sample size limitaons. These trends suggest early
posterupon recruitment from displaced prior residents occupying
nearby islands, augmented in subsequent years by immigrants from
other islands. Dispersal propensity would likely be a benecial evolu
onary strategy for species occupying this highly dynamic landscape.
Therefore, species, such as peregrine falcons, that have rapidly col
onized (or recolonized) novel habitats in this region may be predis
posed to exhibit a metapopulaon dynamic and possess (or evolved)
characteriscs that exploit this interplay of source and sink dynamics
among neighboring islands. Indeed, source sink dynamics have also
been characterized for mainland peregrine falcons (e.g., Kauman,
Pollock, & Walton, 2004; Wooon & Bell, 2014). The Aleuan Island
archipelago is a geologically dynamic region and geologic and modern
records indicate high levels of volcanic acvity (Jicha, Scholl, Singer,
Yogodzinski, & Kay, 2006; Miller et al., 1998). Erupons occur approx
imately every 21–80 years among volcanically acve islands within
the Andreanof Island group (Alaska Volcano Observatory 2013;
Coats, 1950) and within the Archipelago, 14 of 52 historically acve
volcanoes have had a major erupon since 1990 (DeGange, 2010).
The relavely frequent paral or full sterilizaon of islands along the
Aleuan chain likely drives community dynamics within the archipel
ago, favoring species with high dispersal capability and colonizaon
propensity, such as the peregrine falcon, and ulmately inuencing
species composion of re assembled communies. Given the inu
ence of inial founder events on the success of subsequent coloni
zaon aempts by other species, this evoluonary strategy is likely
reinforced through me via posive selecon on characteriscs that
can exploit this ephemeral landscape.
ACKNOWLEDGMENTS
Funding was provided by the U.S. Geological Survey, U.S. Fish and
Wildlife Service, and Brigham Young University. We thank Brie
Drummond for collecon of the 2006 Kasatochi samples and the crew
of the Research Vessel Tiglax for safe transportaon to Kasatochi Island.
The manuscript was improved by comments from R. Wilson, University
of Alaska Fairbanks, J. Pearce, U.S. Geological Survey, R. Roseneld,
University of Wisconsin Stevens Point, and three anonymous review
ers. Any use of trade, product, or rm names is for descripve purposes
only and does not imply endorsement by the U.S. Government.
CONFLICT OF INTEREST
The authors have no conict of interest to declare.
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