Sea Bird Food and Ocean Surface Fauna — Ashmole and Ashmole 
5 
Anous stolidus (Brown Noddy) 
Anous stolidus breeds on many of the tropical 
islands where Sterna fuscata is found, but gen- 
erally is less numerous. The birds are fairly 
easy to catch with a hand net at night, especially 
when there is no moon ; mist nets could doubt- 
less also be used, and unfledged young can be 
caught by hand. No general account of the 
breeding seasons of this species is available, but 
in many colonies breeding is probably less 
tightly synchronized than that of S. fuscata, 
while in some areas (including Christmas Is- 
land) individuals roost on the breeding islands 
even when they are not breeding. 
A. stolidus uses feeding methods similar to 
those of S. fuscata, but sometimes also feeds 
while swimming on the surface; there is no 
evidence that it feeds at night. In contrast to 
S. fuscata, A. stolidus apparently does not nor- 
mally feed more than about 50 miles from the 
colony, although the size of the zone utilized 
may be different in different areas. 
Nearly all our 38 samples from A. stolidus 
were obtained from roosting adults early in the 
night, soon after they had returned from feed- 
ing. They contained, on the average, 5.1 items 
each, 71% of these items being fish, the re- 
mainder squid. Over half of the fish were 
identified to the family level, so that about 243 
identifiable fish could be expected per 100 
samples. The identified fish belonged to nine 
families, of which Exocoetidae, Scombridae, 
Holocentridae, and Gempylidae occurred most 
regularly. All the identified squid were Om- 
mastrephidae. Of the fish, 94% were between 2 
and 12 cm in length, while all but 1 of the 50 
measurable squid had mantle lengths between 2 
and 8 cm. 
The advantages of A. stolidus as a sampler 
of the surface fauna of tropical seas are that the 
species is widely distributed, is available on 
some islands even outside the breeding season, 
and will often provide regurgitations when 
caught early in the night; its relatively limited 
feeding range means that animals obtained from 
it could normally be assumed to come from 
within 50 miles of the island. However, it is 
less abundant than S. fuscata and rather more 
difficult to catch. 
Anous tenuirostris (Black Noddy) 
This species (in which we include Anous 
minutus ), although it breeds only on islands 
where bushes, trees, or cliffs are available to 
provide nest sites, often occurs in large colonies. 
Young birds often regurgitate when handled, 
but more consistent sampling can be carried 
out by catching roosting birds with a hand net 
early in the night, since on Christmas Island and 
many other islands some birds are present at 
all times of year. 
A. tenuirostris feeds by the same methods as 
A. stolidus and S. fuscata; there is no conclusive 
evidence that it feeds at night. This species 
seems usually to feed even closer to its shore 
base than does A. stolidus: the Christmas Island 
birds fish very largely within 5 miles of the 
shore, but in some other areas (for instance 
Ascension Island, Atlantic Ocean) they go 
farther out to sea. 
Our 110 samples, which were mostly regurgi- 
tations from roosting adults, contained on the 
average 18.3 items each. Of these items, 95% 
were fish, nearly all the remainder being squid. 
The regurgitations were often in the form of 
tightly-packed masses, many of the items being 
in a rather advanced state of digestion. We 
identified only 27% of the fish to the family 
level, partly because a large number of the fish 
were fry that we could not identify. Neverthe- 
less, some 470 fish were identified per 100 
samples. The identified fish belonged to 17 
families, among which the most regularly rep- 
resented were Exocoetidae, Gempylidae, Scom- 
bridae, Blenniidae, Holocentridae, and Ernrnel- 
ichthyidae. The few identified squid were all 
Ommastrephidae. Of the fish, 98% were less 
than 6 cm long, and 77% between 1 and 4 cm. 
Of the few squid, 83% were between 2 and 6 cm 
in mantle length. 
A. tenuirostris was the only species which 
showed any dramatic differences in the diet at 
different seasons. In May 1963 and June 1964 we 
found in the diet a far higher proportion of fish 
less than 2 cm long than were present in our 
other sampling periods. 
This species has the advantages that it is 
abundant, easily caught while roosting, and on 
some islands is available all the year round ; the 
samples provide large numbers of fish, and these 
