Loss of Bird Abundance
In addition to
species of high tri-national concern due to high or severe threats, the
PIF assessment identified 42 other common bird species whose
populations have declined by 50% or more in the past 40 years (Appendix C). These species are
found in nearly every habitat type, breeding primarily in Canada and
the United States. It is likely that many common Mexican birds are
steeply declining as well, but we lack long-term monitoring data for
most Mexican species. Population declines of common species are an
important indicator of deteriorating environmental health.
Common Birds in Steep Decline
The combined loss of 42 steeply declining species is conservatively
estimated at a staggering 800 million breeding birds, about two-thirds
of those present 40 years ago. In total, more than half of the 882
landbird species show evidence of declines of at least 15%. This loss
of bird abundance is especially troubling in light of the vital
ecosystem services that these birds provide. To reverse population
declines, we need to address the underlying causes of declines in every
habitat, rather than manage for each species.
Declining species are found in every terrestrial habitat. Many of
these species are migrants and depend on a variety of habitats
throughout their lives. For example, tropical evergreen forests are
important for residents as well as wintering populations of
migrants.
Common birds are declining by 50% or more over much of the North
American continent, with the largest number of species breeding in the
northern United States and southern Canada (top). In winter, these
species are concentrated in the southern United States and Mexico
(bottom).
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Tropical evergreen forests
Several widespread speciesof tropical evergreen forest, including
Blackfaced Antthrush (left), Gray-headed Kite, and Plain Xenops, are
estimated to have declined by more than 50% in Mexico, based on the
reduction of their primary habitat over the last halfcentury. Tropical
habitats are also probably home to other common species in steep
decline, but we lack long-term monitoring data to identify these
species in Mexico. |
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Temperate forests
Among the most steeply declining species in temperate forests
are birds dependent on disturbed and early successional habitat,
including Ruffed Grouse (left), Whip-poorwill, Rufous Hummingbird,and
Prairie Warbler. Managing a mosaic of age classes of forests, as well
as maintaining natural disturbance regimes such as fire, will be
necessary to reverse declines of many forest birds.
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Aridlands
Many common aridland birds, such as Loggerhead Shrike (left),
Verdin, Rock Wren, and Brewer’s Sparrow, have lost more than half of
their breeding populations over the past 40 years. Sagebrush,
chaparral, and desert shrublands have been severely degraded and are
threatened by the spread of exotic plants, energy development, and
urban sprawl.
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Temperate grasslands
Grassland birds in this habitat have suffered among the steepest
declines of any North American landbirds. These include many familiar
birds of rural landscapes including Grasshopper Sparrow (left), Eastern
Meadowlark, Bobolink, Lark Bunting, and Horned Lark. Incentives for
bird-friendly agricultural practices and protection of native prairie
are essential for reversing declines of grassland birds.
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Boreal forests
Steep declines are occurring in permanent residents such as
Boreal Chickadee, temperate migrants such as Rusty Blackbird (left),
and long distance migrants such as Wilson's Warbler. The current rate
and extent of industrial resource extraction threatens the integrity of
our continent’s boreal nursery. Yet vast areas of remaining boreal
forest present large-scale opportunities for conservation.
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Urban areas
Among the common species in steep decline are several
urban-adapted generalists, such as Common Nighthawk (left), Chimney
Swift, and Northern Flicker. Providing urban greenspace
and reducing bird mortality from manmade structures and pesticides will
benefit generalist breeders and migrants.
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Photos, top to bottom: Manuel Grosselet, James
Livaudais (2), Greg Lavaty, Danny Bales, Greg Lavaty |
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