Thousands of birds are taken in by animal care centers each year for rehabilitation. Birds returned to health by some centers are banded for later identification, but very few are ever reencountered following their return to the wild. We report here, information on the post-release survival of Caspian Terns (Hydroprogne caspia) in southern California as well as on their recruitment into a local breeding population and colony site fidelity

Collins, Charles T

Duerr, Rebecca S

Skoglund, Julie M

English

Occidental College Scholar

Bulletin of the Southern California Academy of Sciences 
Volume 119 Issue 1 Article 1 
2020 
Survival and Recruitment of Rehabilitated Caspian Terns in 
Southern California 
Julie M. Skoglund 
International Bird Rescue, julie.skoglund@bird-rescue.org 
Rebecca S. Duerr 
International Bird Rescue, rebecca.duerr@bird-rescue.org 
Charles T. Collins 
Department of Biological Sciences, California State University, Long Beach, charles.collins@csulb.edu 
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Recommended Citation 
Skoglund, Julie M.; Duerr, Rebecca S.; and Collins, Charles T. () "Survival and Recruitment of Rehabilitated 
Caspian Terns in Southern California," Bulletin of the Southern California Academy of Sciences: Vol. 119: 
Iss. 1. 
Available at: https://scholar.oxy.edu/scas/vol119/iss1/1 
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Bull. Southern California Acad. Sci.
119(1), 2020, pp. 1–5
© Southern California Academy of Sciences, 2020
Survival and Recruitment of Rehabilitated Caspian Terns in
Southern California
Julie M. Skoglund,1∗ Rebecca S. Duerr,1 and Charles T. Collins2
1International Bird Rescue, Los Angeles Center, 3601 South Gaﬀey Street, San Pedro,
California 90751
2Department of Biological Sciences, California State University, Long Beach,
California 90840-3702
Every year thousands of birds are brought into care centers for rehabilitation in hopes
that they can be treated and returned to the wild (McRuer et al. 2017). Many are victims
of oil spills and other anthropogenic activities (Duerr et al. 2016; Henkel and Ziccardi
2018). In southern California, International Bird Rescue, Los Angeles (hereafter “IBR”)
rehabilitates and releases 300 to 500 aquatic birds annually. Caspian Terns (Hydroprogne
caspia) are among the many species of birds treated at IBR. Caspian Terns currently breed
at three colony sites in southern California (Cuthbert and Wires 1999; Suryan et al. 2004;
Collins 2006). Two of these sites—Pier 400 in the Port of Los Angeles, Los Angeles County
(“Pier 400”), and Bolsa Chica State Ecological Reserve in northern Orange County (“Bolsa
Chica”)—are approximately 18 km apart. The third is 180 km south on salt evaporation
pond levees in the South San Diego Bay Unit of the San Diego Bay National Wildlife
Refuge (“Salt-Works”) (Collins 2006). Since 2001, when IBR opened its Los Angeles facil-
ity, 69 Caspian Terns have been rehabilitated. Forty-four (63%) of these terns came from
two separate incidents on barges anchored in Long Beach Harbor; nine others (13%) had
injuries related to ﬁsh hooks and entanglement in ﬁshing line. These barges presented an
island-like habitat for nesting in an area that historically had islands available. Caspian
Terns are known to have a prolonged post-ﬂedging period during which young terns ac-
company their parents on foraging trips and migration (Cuthbert and Wires 1999), and
thus it was not certain whether chicks rescued from these events and raised in captivity
would survive and subsequently recruit into the breeding population.
The ﬁrst barge incident took place in 2006 when an estimated 360 pairs of Elegant Terns
(Sterna elegans) and 586 pairs of Caspian Terns nested on two barges anchored in the outer
Long Beach Harbor (California Department of Fish and Wildlife, 2007 unpublished data).
The barges’ owners directed their employees to wash the nests and small chicks overboard
prior to moving the barges out of the area. This was an illegal activity, since these species
are protected under the Migratory Bird Treaty Act of 1918 (the owners were successfully
prosecuted and damages were assessed). Most of the chicks died; 413 dead chicks were
recovered (California Department of Fish and Wildlife, 2007 unpublished data). Twenty-
six chicks were rescued and taken to IBR for rehabilitation and release. One Caspian Tern
chick was euthanized after 44 d in care because of an elbow infection; one Elegant Tern
chick was euthanized on arrival because of a wing fracture. On average the chicks were in
care at IBR for 46 d (range was 43–52 d). Nine Elegant Tern and 15 Caspian Tern chicks
survived and were deemed strong enough to be safely released to the wild (Table 1). Since
∗ Corresponding author: Julie.Skoglund@bird-rescue.org
1
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Skoglund et al.: Survival/Recruitment of Rehabilitated Caspian Terns
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Table 1. Age, admission weight, and ﬁnal disposition of Caspian ad Elegant Tern chicks admitted for
rehabilitation after 2006 and 2007 barge incidents.
Admission weight (g) Days in care Disposition
Year, age Mean* Range Mean Range Euthanized Released N
Caspian Terns
2006
Downy 263.0 190-336 50.8 50-52 4 4
Pre-ﬂedge 460.5 344-566 50.5 44-52 1 10 11
2007
Downy 294.0 61 1 1
Pre-ﬂedge 517.0 397-684 8.3** 1-32 2 25 27
Elegant Terns
2006 178.4 74-216 41.5 1-57 1 9 10
*Adult body mass Caspian Tern: 538-782g (Cuthbert and Wires 1999).
**Mean shown includes birds kept longer due to injury.
adult Elegant Terns were still foraging in Los Angeles Harbor, the Elegant Tern chicks were
released locally to join them prior to leaving on migration. Since most of the adult Caspian
Terns had already departed, the Caspian Tern chicks were released at Salton Sea National
Wildlife Refuge. The Salton Sea is an important migratory stop-over and foraging location
for Paciﬁc Coast Caspian Terns (Craig and Larson 2017).
The second barge incident took place in 2007 when a group of Caspian Terns nested
on the ﬂat deck of the Arctic Challenger, a large sea-going barge anchored in Long Beach
Harbor (Ross 2008). The colony was estimated to be fewer than 100 pairs (Ross 2008),
but it was not possible to get a deﬁnite count given that human disturbance can cause
colony desertion (Cuthbert and Wires 1999). In late July 2007, several larger, nearly ﬂedged
chicks were found swimming near the barge. These had likely fallen oﬀ the ﬂat edge of the
deck, but numerous potential human disturbances that had taken place in the harbor near
the barge during the nesting period may have contributed to these chicks falling into the
water (Ross, 2008). Additionally, some chicks, having made a ﬁrst ﬂight oﬀ the barge, may
have lacked the strength to return to the elevated deck and instead landed in the water
nearby. Twenty-eight chicks were rescued and taken to IBR for rehabilitation. Chicks were
deemed to be in releasable condition if in good body condition with blood values within
normal limits and normal waterproof plumage, and if they were free from injuries or signs
of disease. One chick with respiratory problems was euthanized. Most chicks were held at
IBR for 2–5 d (Table 1), the intent being to reunite them with their colony at the barge and
ideally with their parents. Four chicks were held longer at IBR because of age or injury,
and were released at the Salton Sea in the same manner used in the 2006 release described
above.
Twenty-three chicks were returned via boat to the vicinity of the barge over the course of
several days while adults were still in the vicinity. All chicks being released were removed
from transport kennels and held in hand to encourage vocalization in order to draw the
attention of the adult terns on and near the barge. Once several adult terns were vocaliz-
ing and ﬂying overhead, the chicks were allowed to ﬂy away at will, and appeared to join
the adults. It is unknown, but possible, that individual chicks were reunited with their par-
ents or were adopted by other adults, a phenomenon reported for two other tern species
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SURVIVAL/RECRUITMENT OF REHABILITATED CASPIAN TERNS 3
Table 2. Sightings of rehabilitated Caspian Terns at nesting colonies at Bolsa Chica and Pier 400. Iden-
tiﬁcation of individual terns made by reading U.S. Fish and Wildlife Service numbered aluminum bands
with a 20x-60x zoom spotting scope. Search eﬀort varied by year.
Band number 2009 2010 2011-4 2015 2016 2017 2018 2019
925-76171 - BC - - - - - -
925-76178 BC/P400 BC - - - - - -
1035-45297 - - - - - P400 P400 P400
1035-45303 - - - - - P400 - -
1035-45312 - - - P400 - - - -
1035-45318 - - - - - - P400 -
BC = Bolsa Chica.
P400 = Pier 400.
(Saino et al. 1994). One of these chicks was discovered several days later with an injured
carpal joint. An adult remained attentive by vocalizing and ﬂying overhead until IBR staﬀ
removed the chick from the area. That injured chick was later euthanized. The ability of
young Caspian Terns to dive and catch ﬁsh takes at least 60 d to develop (Cuthbert and
Wires 1999). Juveniles tend to stay with, and be fed by, parents for several months (Cuth-
bert and Wires 1999). Accordingly, releasing young birds in the company of adults was
thought to be important to their learning to forage for themselves and to follow on the
subsequent migration to wintering areas. The 2007 juveniles that were released locally may
have joined adults from the barge-nesting colony, and possibly their parents, before leaving
on migration.
Although IBR bands most birds at release and has banded more than 24,000 rehabil-
itated birds since 2002, band recoveries are not common. An important question is how
many rehabilitated birds survive and ultimately rejoin the breeding population. Several
Caspian Tern chicks rehabilitated in 2006 and 2007 not only survived and rejoined a lo-
cal breeding population, but also demonstrated subsequent nest-site ﬁdelity (Table 2). Of
the 15 chicks rehabilitated and released at the Salton Sea in 2006, two were seen breeding
in 2009 and 2010 in the colony at Bolsa Chica (Table 2). One of these two was then ob-
served at Bolsa Chica on 16 May 2009 and identiﬁed at Pier 400 on 25 June 2009. Such
inter-colony movement of breeding adults between Bolsa Chica and Pier 400 was noted
previously (Collins 2006). Of the 23 terns released in Long Beach Harbor in 2007, four
have been sighted as adults breeding in the Pier 400 colony (Table 2).
Caspian Terns typically start breeding when three years old (Cuthbert and Wires 1999),
but none of the 2007 chicks were observed until they were eight to ten years old. No
searches for banded Caspian Terns have been made at Salt-Works since 2007. One addi-
tional encounter with a banded tern was discovered in an examination of North American
encounter data for Caspian Terns provided by the USGS Bird Banding Laboratory. In this
encounter (1035-45301), the bird was recovered on 23 May 2011 near Laguna Beach in
southern Orange County after becoming entangled in ﬁshing line. Unfortunately, the band
was removed before the bird’s release, so any aﬃnity to one of the breeding colonies could
not be determined. Annual survival of adult Caspian Terns is high, with some individuals
reaching an age of >26 yr (Ludwig 1965). An adult originally banded as a chick at Bolsa
Chica was observed at Pier 400 in 2017 at 23 years of age. However, the period of greatest
mortality for Caspian Terns is the ﬁrst six months of life (Ludwig 1942; Ludwig 1965), and
only 57% of ﬂedglings reach adulthood on the Paciﬁc Coast (Gill and Mewaldt 1983).
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We do not know which colonies were used by the unbanded barge-nesting adult terns in
the years subsequent to 2006 and 2007. The ﬁdelity of ﬁrst-time breeding Caspian Terns to
their natal colony is low (10%) (Cuthbert and Wires 1999). However, older adult Caspian
Terns show substantial colony-site ﬁdelity, with 69% being recorded at the same colony
two years in a row, particularly if they bred successfully in the ﬁrst year (Cuthbert 1988;
Cuthbert and Wires 1999), and 29% breeding at nearby colonies. One of the 2006 chicks in
this study bred in two successive years at Bolsa Chica, and one of the 2007 chicks bred in
three successive years at Pier 400 (Table 2). The future survival and degree of colony-site
ﬁdelity of other 2007 individuals remain to be determined.
The observations reported here provide information on the survival of some of the
Caspian Terns rehabilitated in southern California and their subsequent recruitment into
a local breeding population. These observations also support high nest-site ﬁdelity in this
species. The rehabilitative eﬀorts described were aided by several factors: the chicks entered
care in sizable groups rather than as single chicks, many of the chicks were pre-ﬂedglings
so had spent several weeks with their parents, and the release locations and circumstances
were very carefully chosen. Barges are not thought to be preferable to natural locations as
nesting sites for Caspian terns, except possibly as a temporary option when new natural
sites are being developed. The limited success in rearing young tern chicks in captivity, as
documented here, does not suggest this is a viable alternative for augmenting populations
of critically endangered species such as the Chinese crested tern (Sterna bernsteini). How-
ever, our results do suggest that, when properly conducted, ex situ conservation methods
may prove successful in salvaging individuals that might otherwise perish because of an
acute calamity at a critically endangered breeding colony. It remains possible that Caspian
Terns may be more behaviorally ﬂexible than previously thought with regard to acquiring
adult life skills, but this may or may not be the case for other tern species.
Acknowledgments
Banding of the released terns was conducted under U.S. Fish and Wildlife Service Bird
Banding Permit No. 21214 issued to Jay Holcomb of IBR and No. 22804 issued to Kathy
Molina. Spencer Langdon, Kathy Keane, and the Port of Los Angeles made possible the
observations of banded Caspian Terns at Pier 400. Peter Knapp contributed his observa-
tions of the Caspian Terns nesting at Bolsa Chica in 2009 and 2010 to this study. Kathy
Molina banded chicks ready for release in 2006 and transported them from IBR to a re-
lease point at the Salton Sea. We are indebted to them both. Additional gratitude to the
staﬀ and volunteers at IBR, especially Jeri O’Donnell and Lauren Stoneburner.
Literature Cited
Collins, C.T. 2006. Banding studies of Caspian Terns in southern California. N. Amer. Bird Bander, 31:
10–17.
Craig, D.P. and K. Larson. 2017. Migratory connectivity of North American Caspian Tern (Hydroprogne
caspia) populations. Waterbirds 40:58–62.
Cuthbert, F.J. 1988. Reproductive success and colony-site tenacity in Caspian Terns. Auk, 105:334–344.
Cuthbert, F.J. and L.R Wires. 1999. Caspian Tern (Sterna caspia). In The Birds of North America, No. 403
(A. Poole and F. Gill, eds.). The Birds of North America, Inc., Philadelphia, PA.
Duerr, R.S., Ziccardi, M.H. and J.G.Massey. 2016. Investigations into mortalities during treatment: factors
aﬀecting oiled Common Murre (Uria aalge) survival to release through rehabilitation. J. Wildl. Dis.
52:495–505.
Gill, R., Jr., and R.M. Mewaldt. 1983. Paciﬁc coast Caspian Terns: dynamics of an expanding population.
Auk, 100:369–381.
4
Bulletin of the Southern California Academy of Sciences, Vol. 119, Iss. 1 [], Art. 1
https://scholar.oxy.edu/scas/vol119/iss1/1
SURVIVAL/RECRUITMENT OF REHABILITATED CASPIAN TERNS 5
Henkel, L.A. and M.H. Ziccardi. 2018. Life and death: how should we respond to oiled wildlife? J. Fish
Wildl. Manag., 9:296–301.
Ludwig, F.E. 1942. Migration of Caspian Terns banded in the Great Lakes area. Bird-Banding, 13:1–9.
Ludwig, J.P. 1965. Biology and structure of the Caspian Tern (Hydroprogne caspia) population of the Great
Lakes from 1896–1964. Bird-Banding, 36:217–233.
McRuer, D.L., Gray, L.C., Horne, L., and E.E. Clark. 2017. Free roaming cat interactions with wildlife
admitted to a wildlife hospital. J. Wildl. Manage., 81:163–173.
Ross, W. 2008. Caspian Tern nesting on a barge in the Long Beach harbor, 2007 season. California
Department of Fish and Wildlife, Wildlife Branch, Nongame Wildlife Program Report 2008-05.
Sacramento, CA. 5 pp.
Saino, N., Fasola, M. and E. Crocicchia. 1994. Adoption behaviour in Little and Common Terns (Aves;
Sternidae): Chick beneﬁts and parents’ ﬁtness costs. Ethology, 97:294–309.
Suryan, R.M., D.P. Craig, D.D. Roby, N.D. Chelgren, K. Collis, W.D. Shuford and D. E. Lyons. 2004.
Redistribution and growth of the Caspian Tern population in the Paciﬁc Coast region of North
America, 1981–2000. Condor, 106:777–790.
5
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Survival and Recruitment of Rehabilitated Caspian Terns in Southern California

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Survival and Recruitment of Rehabilitated Caspian Terns in Southern California

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