tremendously among species. Many species feed on fruit
as well as insects, and a few have diverged entirely from
capturing insects and become primarily fruit eaters.
As the name suggests, tyrant flycatchers catch flies. Their
basic behavior is to sit still on a perch and sally forth in
pursuit when a potential prey insect flies sufficiently close
to capture. The flycatcher snaps up the prey in its beak
and returns to the perch to consume it. The widespread
and easily observed Tropical Kingbird (Tyrannus
melancholicus; plate 8- 27) provides an example of this
classic flycatcher behavior, which is termed sally gleaning.
Many flycatcher species are typical sally gleaners, flying
from a perch to capture an insect, either in the air, on the
ground, or on a leaf surface. Because flycatchers often sit
on exposed perches, they are well suited to invade open
habitats such as forest edges, riverbanks, and savannas.
From the fundamental sally- gleaning technique,
tyrannids have evolved many specializations. There are
hawkers, ground feeders, runners, hoverers, water’s- edge
specialists, perch gleaners, and fruit eaters. The ecological
diversification among the hundreds of tyrannid species is
really quite amazing.
Body size and bill characteristics vary considerably
among the tyrannid species, representing anatomical
forms of specialization within the group. Generally
speaking, tyrannid bills are dark above and may be
lighter on the lower mandible, an adaptation to foraging
in areas of high light intensity, where a dark upper
mandible serves well to lessen glare. Bills are usually
wide and somewhat flattened. Some flycatchers make an
audible bill snap when they capture prey. Bills are usually
bordered by hairlike feathers called rictal bristles (plate
8- 28). These feathers, which are found on many bird
species that capture insects on the wing, help the bird
home in on its flying prey. Other birds that specialize
in sallying for prey also have prominent rictal bristles,
including the large nocturnal nightjars.
Large- billed tyrannid species are common in the
Neotropics, the bill size likely an evolutionary result
of the greater availability of large arthropod prey.
Interspecific competition within the group may
also have provided selection pressures resulting in
divergence of body size, bill, and feeding characteristics.
A number of Neotropical flycatcher species that have
yellow bellies and striped heads may present identification
problems for birders, but body size and bill variation is
strikingly evident among them. These differences in body
size and bill shape not only help with species identification,
they illustrate clearly what adaptive radiation really is. InPlate 8- 29. The Great Kiskadee is a widespread species that is
found from southern Texas to southern Amazonia. It is one
of the largest of the tyrant flycatchers. Note the formidable
bill, with a hook at the tip of the upper mandible. Kiskadees
frequent many habitats and are known to eat diverse kinds of
insects, as well as small vertebrates such as lizards and frogs.
Photo by John Kricher.Plate 8- 31. No, not a Great Kiskadee. This is a Boat- billed
Flycatcher. It is the size of a Great Kiskadee but has a much
wider, thicker bill. Photo by John Kricher.Plate 8- 30. The Lesser Kiskadee occupies much of the same
range as the Great Kiskadee but is smaller and more slender
and has a thinner bill. Photo by John Kricher.chapter 8 evolutionary cornucopia 125