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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 124. No. 1. March 2012 
TABLE 2. Frequency of occurrence (%) and size range (standard length in mm) of individual fish taxa ingested by 
three Sargassum specialists: Audubon’s Shearwater (/i = 48), Bridled Terns (n = 16), and Royal Terns (n = 8). 
Frequency of occurrence (%) and size range (mm) 
Audubon's Shearwalcr 
Bridled Tern 
Royal Tern 
Exocoetidae (flying fish) 
6.2 (40-60) 
6.2 (30) 
0 
Syngnathidae (pipefish) 
0 
6.2 (23) 
0 
Priaccmlhus sp. (bigeye) 
4.2 (15) 
12.5 (20) 
0 
Heteropriacamhus cruentatus (glasseye) 
2.1 (45) 
0 
0 
Caranx sp. (jack) 
14.6 (45-50) 
0 
12.5 (70) 
C. hippos (erevalle jack) 
2.1 (25) 
0 
0 
Decapterus sp. (scad) 
4.2 
6.2 
0 
Trachurus laihami (rough scad) 
2.1 (75) 
0 
0 
Stromatcidae (buiterfish) 
4.2 (15) 
12.5 (30-40) 
12.5 
Psenes sp. (driftfish) 
0 
0 
12.5 (70-105) 
Balistidae (triggerfish) 
8.3 (15-20) 
25.0 (20) 
0 
Aluterus sp. (filefish) 
12.5 (40) 
0 
12.5 (40) 
Monacanthus sp. (filefish) 
68.8 (15-50) 
31.2 (10-22) 
62.5 (40) 
Monacanthus ciliatus (fringed filefish) 
2.1 (25) 
0 
0 
Stephanolepis hispidus (planehead filefish) 
2.1 (30-52) 
0 
12.5 (45) 
Uictophrys sp. (trunkfish) 
0 
12.5 (6-10) 
0 
Chilomycterus sp. (biinfish) 
0 
0 
12.5 
Sphoeroides sp. (puffer) 
2.1 (7-12) 
18.7 (10-20) 
0 
S. maculatus (northern puffer) 
0 
6.2 (10-12) 
0 
dipping (following Ashmole 1971). We observed 
Audubon s Shearwater feeding near the surface, 
either by shallow diving (1-2 m), surface-seizing, 
or hydroplaning in and around Sargassum reefs. 
However, in the Bahamas, this shearwater feeds 
by pursuit diving during the nesting season with 
dives averaging 7.6 m (n = 136) to a maximum of 
29 m (Mackin 2004). Phalaropes. which prey on 
aquatic invertebrates in shallow pools in the 
tundra by surface feeding (Haney 1985), use the 
same behavior when seizing snails and crusta¬ 
ceans from Sargassum mats. The spinning beha\ 
ior associated with phalaropc feeding in freshw. 
ter habitats (Obst ct al. 1996) was not observed ; 
sea. Sargass um-associated prey taken by sma 
seabirds were rarely >50 mm. indicating thes 
birds picked prey from within the alga, as oppose 
to diving beneath it where larger fish are typical I 
found (Moser et al. 1998). An advantage c 
foraging in Sargassum reefs is that piscivorou 
predators drive prey up into the Sargassum mat? 
where it is more accessible to the smaller-bodie 
seabirds (Safina and Burger 1985, Haney 1986). 
Prey types in digestive tracts provided additions 
information about seabird feeding. Both frequenc 
,°n r C TT L ? Hnd numeric «' abundance offish pre : 
■n Bridled Terns indicated they select relative.; 
uncommon members of the Sargassum fish fauna 
tetradontids (puffers), ostraciids (trunkfishes), stro- 
mateids (driftfish), and priacanthids (bigeyes) 
(Dooley 1972, Settle 1993). However, these fishes 
may occur at the periphery of Sargassum patches, 
where they are less frequently collected during 
Sargassum sampling with nets (Casazza and Ross 
2008). In contrast. Royal Terns, Audubon’s Shear¬ 
waters. and Red Phalaropes fed on prey that are 
dominant members of the Sargassum community- 
filefishcs. jacks, and Sargassum shrimp (Fine 1970. 
Dooley 1972, Settle 1993 , Casazza and Ross 2008). 
Haney (1986) found a significant relationship 
between bird hotly size and Sargassum patch size 
We noted that large-bodied Royal Terns contained 
relatively large prey: but this was likely a function 
of their feeding mode (plunging) rather than 
Sargassum patch size. 
Sargassum foraging w as documented during all 
months of the year despite the Sargussuin mat 
structure and attendant fish community changing 
seasonally and in response to w eather I Moser 
et al. 1998, Casazza and Ross 2008. Gower and 
King 2011). Fine (1970) noted that faunal 
composition in Sargassum collected from tk 
Gulf Stream and Sargasso Sea was similar, bid 
that non-colonial macrofauna were more abundant 
in spring than in full. This may affect the way 
seabirds use Sargassum habitat. Royal Terns 
