Guilds
are groups of species in a community that exploit the same
set of resources in a similar manner, but are not
necessarily closely related taxonomically. Birds that hunt
for insects on the floor of a deciduous forest constitute a
guild; tropical American hummingbirds and butterflies
jointly form a guild of daytime nectar feeders; desert
sparrows, ants, and rodents constitute a seed-eating guild.
Members of guilds often differ in their precise food
requirements, thus reducing the potential for competition
among them when resources are limited. In a given locality,
the membership of a guild can change through the year as
migrants are added or subtracted. For example, in the oak
woodland on Stanford University's jasper Ridge Biological
Preserve, Chestnut-backed Chickadees, Hutton's Vireos, and
Plain Titmice are resident species that form the core of a
foliage- and bark-gleaning guild of insectivores. These are
joined as core species by Ruby-crowned Kinglets and
Yellow-rumped Warblers fall and winter, and by Blue-gray
Gnatcatchers in the spring. Other guild members include
Downy Woodpeckers, Bushtits, White-breasted Nuthatches,
Brown Creepers, Wrentits, Bewick's Wrens, Warbling Vireos,
and Townsend's Warblers. The arrival and departure of the
migrants do not seem to influence the foraging of the
resident guild members. In general, guild members with
similar foraging sites differ in bill size, suggesting they
eat prey of different sizes. Although the bill sizes of
the closely related kinglet and gnatcatcher are similar, the
species forage in different sites and are present in
different seasons. Only the chickadee and Hutton's Vireo are
potentially close competitors. If they actually are in
competition, experimental removal of either species should
lead to an increase in the other, although capturing enough
of either to sufficiently decrease its population would be
very difficult. One major problem in understanding guilds,
and the communities to which they belong, is the great
practical difficulty in doing such critical experiments.
Scientists must also always consider the ethical question of
how much disturbance is justified to gain knowledge about
the birds. SEE: Bird
Communities and Competition;
Bills;
How
Do We Find Out About Bird Biology? Copyright
® 1988 by Paul R. Ehrlich, David S. Dobkin, and Darryl
Wheye.