habitat types. They can be found, often abundantly, in
dry forest, mangrove forest, montane forest, and rain
forest. Brushy successional areas are habitat for many
species, such as Gray Catbird (Dumetella carolinensis),
Common Yellowthroat (Geothlypis trichas), and Yellow-
breasted Chat (Icteria virens). Rain forests provide habitat
for Wood Thrushes (Hylocichla mustelina), Kentucky
Warblers (Geothlypis formosa; plate 15- 159), American
Redstarts (Setophaga ruticilla), and other wood warblers.
Many of these species also utilize successional areas.
Some Neotropical migrants— the Black- and- white
Warbler (Mniotilta varia; plate 15- 160), for example—
range widely in the Neotropics, occupying many kinds
of wintering habitat. Black- and- white Warblers, unique
among wood warblers for their habit of foraging for
arthropods on bark, somewhat like nuthatches, are
extraordinary in their inclination to range widely and
frequent virtually any terrestrial habitat. They can be
found in oak- pine forests, in mangroves, in plantations,
along any kind of forest edge and successional scrub, in
dry forests, and in interior rain forests anywhere from
western Mexico, the Antilles and West Indies, and
all parts of Central America through northern South
America.
In general, other migrants are more restricted (some
much more so), which puts them at risk should they
suffer from habitat loss. An example is the Cerulean
Warbler (Setophaga cerulea), which winters along a
narrow elevational belt at between 620 and 1300 m
(2,030– 4,265 ft) in the eastern Andean foothills of
Colombia, Ecuador, and Peru. Unfortunately, this
area has been and continues to be heavily deforested
and converted to agriculture, including cocaine fields,
putting the future of this species at some risk.
Many North American migrants eat a diet high
in fruit while in the tropics. Baltimore and Orchard
Orioles (Icterus galbula and I. spurius) and Scarlet
and Summer Tanagers (Piranga olivacea and P. r u b r a)
feed in cecropia and fig trees among mixed flocks of
euphonias, Neotropical tanagers, and honeycreepers.
Many researchers have noted that abundance of
migrants is high in successional areas and young
forests. Fruit availability may be one reason migrants
favor such areas. North American migrants are believed
to be important fruit consumers and seed dispersers,
especially for plants that typically grow in disturbed
areas. Some Neotropical migrant species, such as the
Orchard Oriole and Tennessee Warbler (Oreothlypis
peregrina), feed on nectar and are recognized as
potential pollinators while on their wintering grounds.
Given that North American migrants spend perhaps
the majority of their year in the Neotropics, it is not
surprising to learn that some are relatively specialized
when on their wintering grounds.
The degree to which North American migrants
interact with Neotropical resident birds is a subject
of ongoing research. Neotropical migrants are often
observed accompanying mixed flocks of resident birds
and have also been documented to attend army ant
swarms. This is hardly surprising given the advantages
that could be gained from watching experienced
resident birds as they forage.
Many if not most Neotropical migrant species are
territorial on their wintering ground and have a strong
tendency to return to the same wintering site annually.
Species as the Wood Thrush, Ovenbird (Seiurus
aurocapilla), Kentucky Warbler, and Gray Catbird
usually occupy exactly the same locations from one
winter to the next. Although these birds migrate north
to nest, they return in the fall to precisely the same
local wintering area used the previous year, a behavior
called winter site fidelity.
As one might expect, winter site fidelity often means
that the birds are territorial, defending those winter
sites. Wood Thrushes for example, establish and defend
winter territories, using subtle vocalizations and body
posturing. Each Wood Thrush has its own turf within
the rain forest. Survivorship among “floater” Wood
Thrushes, birds that have not succeeding in acquiring
and holding a winter territory, is very likely diminished.
In another example, male Hooded Warblers (Setophaga
citrina) obtain territories inside interior forest, while
females are territorial in disturbed, successional habitats.
Through a combination of techniques ranging from
banding to analysis of stable isotopes (such as carbon- 13)
contained in the feathers and blood of birds, it has been
learned that habitats vary in value to birds, and this
results in differences in overall robustness of the birds
and the timing of their return migration northward.
American Redstarts and Black- throated Blue Warblers
(Setophaga caerulescens; plate 15- 161) wintering in
marginal scrubby habitats where food is less abundant
than in interior forests do not tend to gain weight in
winter and do not reach nesting sites nearly as early as
healthier birds that winter in richer forest.
A relatively new research technique uses geolocating
devices, which are attached to the backs of birds and
measure daily day length as the bird moves through316 chapter 15 neotropical birds: the bustling crowd