First evidence of plastic ingestion by white-tailed tropicbirds from O'ahu, Hawai'i

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Hyrenbach et al.: Plastic ingestion by White-tailed Tropicbirds 167
Marine Ornithology 41: 167–169 (2013)
Ingested plastics have been reported in necropsies of marine birds,
turtles, mammals, fish, crustaceans and squid (Laist 1997, Ocean
Studies Board 2008). Herein, we report the first record of plastic
ingestion by a White-tailed Tropicbird Phaethon lepturus (hereafter
WTTR) sampled on O’ahu (Hawai’i). This observation adds a second
tropicbird species (order Phaethontiformes) to the one sampled thus
far and found to ingest plastic, and increases to 116 the number of
seabird species in which this phenomenon has been observed.
Previously, comprehensive reviews of the literature reported evidence
of plastic ingestion for at least 36.9% (115 of 311) of the seabird
species sampled to date (Laist 1997, Ocean Studies Board 2008).
Yet, there are significant differences in the incidence of ingestion
among different orders, with tubenose seabirds (Procellariiformes:
albatrosses, petrels, shearwaters, storm-petrels, diving petrels) most
susceptible (63.4%, 64 of 101), and penguins (Sphenisciformes)
the least (12.5%, 2 of 16). These disparities have been attributed
to the higher susceptibility of surface-foragers to scavenge and eat
floating plastic (e.g., Ryan 1987). Yet, despite the oceanic habits of
tropicbirds, plastic ingestion has been investigated in only one of
the three tropicbird species to date (Table 2).
As part of a collaborative research program in which specimens are
salvaged for investigation of heath, diet and plastic ingestion, we
investigated seabird specimens delivered to Sea Life Park, O’ahu
(Hawai’i), since 2009. Two of us (JAJ and KDH) necropsied three
WTTRs following standardized necropsy protocols (van Franeker
2004). The specimens belonged to the dorothea subspecies and were
juveniles (first- or second-year birds), on the basis of their plumage
(Pyle 2008). They were in poor body condition, as evidenced by
the low breast muscle (pectoralis) scores (value range: 0 to 3) and
subcutaneous / intestinal fat scores (value range: 0 to 3; Table 1).
The stomach of one of these specimens contained a large (14.5 cm
long, 3.25 cm wide) pale blue plastic fragment (Fig. 1). We contend
that this large floating item was mistaken for an epipelagic fish,
because of its size, shape and coloration.
WTTR is a widely distributed species, ranging throughout the
world’s tropical and subtropical oceans: the southern Indian, the
western and central Pacific, the south Atlantic, and the Caribbean
(Lee & Walsh-McGehee 1998). Approximately 1 800 pairs breed
in Hawai’i, mostly in the main Hawaiian Islands: Kauai, Moloka’i,
La
-na’i, Hawai’i, and the offshore islet of Mokoli’i. Although a
few pairs nest on some areas of O’ahu, their abundance is poorly
known (Harrison 1990, Lee & Walsh-McGehee 1998). WTTRs
forage in deep water, rarely in association with subsurface predators
(Harrison 1990), and feed on epipelagic prey, largely flying fish
(2–12 cm in length), supplemented with squid and crustaceans
(Harrison 1990, Lee & Walsh-McGehee 1998). WTTRs forage by
plunge diving from 15–20 m above the water, and can consume very
large fish, up to 18% of their body mass (Harrison 1990). While
WTTRs do not forage in multi-species flocks involving subsurface
FIRST EVIDENCE OF PLASTIC INGESTION BY WHITE-TAILED
TROPICBIRDS FROM O’AHU, HAWAI’I
K. DAVID HYRENBACH1, MICHELLE, M. HESTER2, JOHN A. JOHNSON1, SHANNON LYDAY1,
SANDRA BINGHAM3, JEFF PAWLOSKI3
1Hawai’i Pacific University, Oceanic Institute, 41-202 Kalaniana’ole Hwy, Waimanalo, HI 96795, USA (khyrenbach@hpu.edu)
2Oikonos Ecosystem Knowledge, P.O. Box 1918, Kailua, HI 96734, USA
3Sea Life Park, 41-202 Kalaniana’ole Hwy, Waimanalo, HI 96795, USA
Submitted 27 May 2013; accepted 17 June 2013
167
TABLE 1
Summary of necropsy results of three juvenile White-tailed Tropicbirds
Collection date Age Sex diagnostics Weight (g) Wing
(mm)
Tarsus
(mm)
Breast
scorea
Fat
scorea
Stomach
contents
weight (g)
Description
17 November 2012 FY–SY ♂
largest testis:
5 x 1 mm
252 255 20.2 0 1/0 7 No plastic.
7 squid beaks
31 December 2010 SY ♀
oviduct code 1
follicle < 1 mm
191 235 22.8 1 0/0 15 1 plastic
fragment.
No prey
17 January 2010 FY–SY ♂
largest testis:
4 × 2 mm
205 224 21.1 1 1/0 0 Empty
FY = first year; SY = second year
a Van Franeker (2004).

168 Hyrenbach et al.: Plastic ingestion by White-tailed Tropicbirds
Marine Ornithology 41: 167–169 (2013)
predators around the Main Hawaiian Islands (Hebshi et al. 2008),
they frequently (45%, or 5 of 11 foraging birds) associate with
small multi-species seabird flocks over small (< 0.6 m) yellowfin
tuna Thunnus albacares and skipjack tuna Katsuwonus pelamis in
the Eastern Tropical Pacific (Spear & Ainley 2005).
Although the diet of WTTR in Hawai’i is poorly known, it is likely
similar to that of the Red-tailed Tropicbird (P. rubricauda, RTTR;
Schreiber & Schreiber 1993, Lee & Walsh-McGehee 1998; Spear
& Ainley 2007). Colony sampling and at-sea collections have
documented plastic ingestion by RTTR in the North Pacific (Table
2). Yet, because RTTRs ingest fragments considered too small for
direct ingestion, plastic pollution in this species has been attributed
to secondary ingestion via their prey (Harrison 1990), an indication
of potential emerging pathways of pollution transfer in epipelagic
food-webs. RTTRs do not forage in multi-species flocks involving
subsurface predators around the Main Hawaiian Islands (Hebshi et
al. 2008). However, they occasionally (28%, or 7 of 25 foraging
birds) feed in association with surface-feeding tuna and dolphinfish
Coryphaena hippurus in the Eastern Tropical Pacific (Spear &
Ainley 2005, 2007).
This new record highlights the susceptibility of tropicbirds to plastic
ingestion and underscores the need for additional information on the
other RTTR (4 subspecies) and WTTR (6 subspecies) populations (ITIS
2013). Additionally, three disjunct Red-billed Tropicbird Phaethon
aethereus (RBTR) subspecies, which inhabit tropical waters of the
Atlantic Ocean, the northwest Indian Ocean and the eastern Pacific,
have never been assessed for plastic ingestion. In the Eastern Tropical
Pacific, RBTR breed on the Galapagos Islands, Ecuador, and off the
coast of Mexico (del Hoyo et al. 1992). RBTR frequently (46%, or 5
of 13 foraging birds) feed over dolphins and small scombrids in the
Eastern Tropical Pacific (Spear & Ainley 2005).
Together, these observations of plastic ingestion reinforce the value
of marine birds as bio-indicators of ocean plastic pollution (Ryan
1987, Ryan et al. 2009). Thus, we advocate the establishment
of longitudinal sampling programs to quantify plastic ingestion
incidence and loads in epipelagic tropical ecosystems, targeting
seabirds and associated predatory fishes. Such monitoring could
rely on opportunistic sampling by long-term monitoring programs
(e.g., Robards et al. 1993, Nevins et al. 2005), augmented by
periodic multi-species studies (e.g., Sileo et al. 1990, Spear et
Fig. 1. Left panel: White-tailed Tropicbird specimen, with ingested plastic fragment still inside of the stomach lining. Right panel: close-up
of the ingested plastic fragment (14.5 cm long, 3.25 cm wide).
TABLE 2
Summary of tropicbird plastic ingestion records by species
Species Study type (site) Age Source Method Sample size
(incidence, %) Reference
RTTR At sea (E.T.P.) After hatch-year Collection Necropsy 6 (0) Spear et al. 1995
RTTR At sea (N.P.T.Z.) After hatch-year Bycatch Necropsy 1 (100) Robards et al. 1993
RTTR Colony (Midway) After hatch-year aSampling Lavage 47 (4) Sileo et al. 1990
RTTR Colony (Johnston) Hatch-year bSampling Lavage 50 (4) Sileo et al. 1990
RTTR Colony (Midway) Hatch-year bSampling Lavage 64 (12) Sileo et al. 1990
RTTR Colony (Tern Island) Hatch-year bSampling Lavage 50 (14) Sileo et al. 1990
WTTR Beach-cast (O’ahu) FY–SY Salvage Necropsy 3 (33) This study
Species: RTTR = red-tailed tropicbird; WTTR = white-tailed tropicbird;
Study sites: E.T.P. = Eastern Tropical Pacific. N.P.T.Z. = North Pacific Transition Zone;
Age classes: FY = first year; SY = second year.
a Breeding birds
b Chicks sampled on a nesting colony

Hyrenbach et al.: Plastic ingestion by White-tailed Tropicbirds 169
Marine Ornithology 41: 167–169 (2013)
al. 1995). Together, this monitoring could provide the time series
required for tracking emerging pollution trends in new locations and
species (e.g., Auman 2004, Ryan et al. 2009).
ACKNOWLEDGEMENTS
The National Fish and Wildlife Foundation provided funding for
supplies and salaries (grant 35765 to KDH). HPU supported JAJ
through a work-study position and provided the laboratory facilities
for performing necropsies and quantifying stomach contents. We
also thank Jan van Franeker, Peter Ryan and David Ainley, whose
suggestions greatly improved this manuscript.
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