The New Neotropical Companion

relative abundances of various insect prey. One seasonal

and dramatic switch is seen with the Eastern Kingbird

(Tyrannus tyrannus; plate 8- 35). One of 32 tyrannid

species that migrate to breed in North America (returning

to winter in the Neotropics), the Eastern Kingbird feeds on

insects on its summer breeding grounds. However, when

on its wintering grounds in southwestern Amazonia it

feeds mostly on fruit, forming large flocks that wander

nomadically in search of fruiting trees.

Another flycatcher, one that resides year- round in

the Neotropics, has evolved a fully fruit- based diet.

The nondescript Ochre- bellied Flycatcher (Mionectes

oleagineus) is an abundant forest flycatcher, widespread

in the region. Its inordinate numerical abundance

compared with other tyrannids may be due to its diet

shift from arthropods to fruit, which is an abundant

and easily “captured” resource. This bird is described in

more detail in chapter 10.

Overall, the ability of varied tyrannids to find food

in virtually all habitats has likely been a major factor

promoting speciation within the group. Species have

specialized on certain types of arthropods and other

food, captured in distinct ways.

This tour of flycatcher diversity has only scratched the

surface. In plumage and habitat as well, some of these birds

show remarkable diversity. The widespread Cattle Tyrant

(Machetornis rixosa; plate 8- 36) inhabits open fields and

grassy areas as well as disturbed areas and pastures (hence

the common name). It typically forages on the ground. The

White- headed Marsh- Tyrant (Arundinicola leucocephala;

plate 8- 37) and the Pied Water- Tyrant (Fluvicola pica;

plate 8- 38) are two tyrannids that are common in marshes.

Plate 8- 36. The Cattle Tyrant is primarily a ground- dwelling

tyrannid flycatcher that inhabits open grassy areas such as

cattle pastures. Photo by John Kricher.

Plate 8- 37. The White- headed Marsh- Tyrant is a common

inhabitant of marshes throughout much of the Neotropics.

Photo by John Kricher.

Plate 8- 38. The Pied Water- Tyrant, like the White- headed

Marsh- Tyrant (plate 8- 37), specializes in foraging along the

edges of freshwater marshes. Photo by John Kricher.

Plate 8- 39. The spectacular Fork- tailed Flycatcher migrates

in sometimes immense flocks. It is fairly common in open

areas throughout Central and South America. Photo by John

Kricher.

chapter 8 evolutionary cornucopia 127