- There are numerous potential prey items in addition
to small prey. In a now classic 1971 study Thomas
Schoener showed that insectivorous birds in the tropics
have a much wider range of bill length (among all
species) than those of the temperate zone. He attributed
this variety to the wider resource base available in the
tropics, especially of large insect prey items. Peruse any
field guide to Neotropical birds and you will marvel at
the range of bill sizes and body sizes among families
of birds such as tyrant flycatchers, ovenbirds and
woodcreepers (plate 9- 14), and many others. These
anatomical distinctions are evolutionary results, at least
in part, of each species being adapted to focus its energy
on capturing prey within a certain size range.- There is also year- round availability of nectar and
fruit. Nectar specialists include all the multiple
hummingbird species (see chapters 10 and 15) as well
as various flowerpiercers and some others (chapter 10).
Fruit- eating specialists include cotingas (plate 9- 15),
many tanagers, guans, curassows, and parrots. Add to
those iguanas and other reptiles, scores of monkeys,
and rodents such as agoutis and pacas, and you have
Plate 9- 14. The unique and well- named Long- billed
Woodcreeper (Nasica longirostris) is one of the largest of the
woodcreepers (36 cm/14 in). Its long bill probes for large
arthropods. There is no equivalent species outside of the
tropics. Photo by Andrew Whittaker.
Plate 9- 15. This Lovely Cotinga (Cotinga amabilis) approaches
a fruiting tree. A species such as this, with its dependency on
fruit, could not exist in the temperate zone. Photo by James
Adams.Plate 9- 16. The Spotted Antbird (Hylophylax naevioides) is
usually found in the company of army ant swarms. This bird is
a male. Photo by Kevin Zimmer.144 chapter 9 why are there so many species?