Copyright © 2005 Ecostudies Institute
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| A nonprofit organization committed to ecological research and conservation |
| ECOSTUDIES INSTITUTE |
| ECOSTUDIES INSTITUTE |
| Contact Information: Ecostudies Institute P.O. Box 703 Mount Vernon, WA 98273 305-213-8829 ecostudies@ecoinst.org |
Often described through an analogy
to the monotony of the open ocean,
and for most people known only
from movies or a cross-country car
trip, the grasslands of North America
rarely elicit the enthusiasm exhibited
by William Clark as he wandered
through a Nebraska prairie in pursuit
of elk. Although only a shadow of
what they once were, when grizzly
bears, wolves, and endless herds of
bison roamed the prairies of the
United States and Canada, our
grasslands are still a biologically rich
region home to many species of
plants and animals that live nowhere
else.
to the monotony of the open ocean,
and for most people known only
from movies or a cross-country car
trip, the grasslands of North America
rarely elicit the enthusiasm exhibited
by William Clark as he wandered
through a Nebraska prairie in pursuit
of elk. Although only a shadow of
what they once were, when grizzly
bears, wolves, and endless herds of
bison roamed the prairies of the
United States and Canada, our
grasslands are still a biologically rich
region home to many species of
plants and animals that live nowhere
else.
| Native mixed-grass prairie on the Medicine Lake National Wildlife Refuge, located in eastern Montana. Dominant grass species include Stipa comata, S. viridula, Koeleria cristata, Agropyron smithii, and Bouteloua gracilis. Photo Copyright © 2006 John Lloyd. |
Historical estimates (Kuchler 1964, Barbour and Billings 1988)
suggest that grasslands occupied 50 million hectares in Canada
and 300 million hectares in the United States; that amounts to
nearly one-quarter of the land area of North America. By 1979,
Jeffrey Klopatek and his colleagues estimated that nearly half of
the North American grasslands
suggest that grasslands occupied 50 million hectares in Canada
and 300 million hectares in the United States; that amounts to
nearly one-quarter of the land area of North America. By 1979,
Jeffrey Klopatek and his colleagues estimated that nearly half of
the North American grasslands
"Came Suddenly into an open and bound less
Prarie, I Say bound less because I could not
See the extent of the plain in any Derection...this
prospect was So Sudden and entertaining that I
forgot the object of my prosute" - William Clark,
1804, describing the prairie he encountered
near present-day Nebraska City, Nebraska.
Prarie, I Say bound less because I could not
See the extent of the plain in any Derection...this
prospect was So Sudden and entertaining that I
forgot the object of my prosute" - William Clark,
1804, describing the prairie he encountered
near present-day Nebraska City, Nebraska.
| Generalized location of different prairie types in the United States. Map Courtesy of the Black-footed Ferret Recovery Program. |
| Summer thunderstorms roll across the mixed-grass prairie at Medicine Lake National Wildlife Refuge in Montana. Photo Copyright © 2006 John Lloyd. |
The North American grasslands actually consist of at least six
unique types. Tall-grass prairie, all but plowed under for
agriculture, once ranged from eastern Oklahoma and Texas to
Indiana to south-eastern Manitoba. Further west, mixed-grass
prairie includes elements of both tall-grass prairie and the
short-grass prairies that are found in the dry, high plains east
of the Rocky Mountains. The tall-, mixed-, and short-grass
prairies make up the core of the North American grasslands,
but other important types included the desert grasslands of
the southwestern United States, the cool-season bunchgrass
prairies of California, and Palouse Prairie, which is found in the
dry mountainous areas of the northwestern United States and
southwestern Canada.
unique types. Tall-grass prairie, all but plowed under for
agriculture, once ranged from eastern Oklahoma and Texas to
Indiana to south-eastern Manitoba. Further west, mixed-grass
prairie includes elements of both tall-grass prairie and the
short-grass prairies that are found in the dry, high plains east
of the Rocky Mountains. The tall-, mixed-, and short-grass
prairies make up the core of the North American grasslands,
but other important types included the desert grasslands of
the southwestern United States, the cool-season bunchgrass
prairies of California, and Palouse Prairie, which is found in the
dry mountainous areas of the northwestern United States and
southwestern Canada.
had been lost, most through
conversion to cropland. The
loss of so much habitat led,
predictably, to widespread
declines in species that relied
on the grasslands. Grassland
birds, particularly those
breeding in the prairie regions,
have been especially hard hit.
The most recent summary of
Breeding Bird Survey data
(including the years from
1966-2005) shows 18 species
with significant population
declines and only 2 with
significant population
increases. Another 7 species
show non-significant declines.
Indeed, the prairies of North
America are almost perfectly
outlined by mapping the
average vulnerability to
extinction of bird species
across the continent; the area
of highest threat follows the
prairies from Texas to
Canada.
conversion to cropland. The
loss of so much habitat led,
predictably, to widespread
declines in species that relied
on the grasslands. Grassland
birds, particularly those
breeding in the prairie regions,
have been especially hard hit.
The most recent summary of
Breeding Bird Survey data
(including the years from
1966-2005) shows 18 species
with significant population
declines and only 2 with
significant population
increases. Another 7 species
show non-significant declines.
Indeed, the prairies of North
America are almost perfectly
outlined by mapping the
average vulnerability to
extinction of bird species
across the continent; the area
of highest threat follows the
prairies from Texas to
Canada.
| This map shows the average vulnerability to extinction of bird species breeding in different regions of the continent. Note how the area of highest average vulnerability corresponds with the distribution of the prairies as seen in the preceding map. Source: Rich et al. 2004, Partners in Flight North American Landbird Conservation Plan. Cornell Lab of Ornithology, Ithaca, NY. |
Habitat loss alone cannot explain all of the observed declines, however. Although nearly all of the tall-grass
prairie has been destroyed, large blocks of mixed- and short-grass prairie persist in Montana, Colorado, and
parts of North and South Dakota, yet birds breeding in these areas have experienced declines that parallel
those of species breeding in tall-grass prairie. Habitat degradation, most likely driven by changes in
disturbance regimes and the spread of invasive plants, may explain this apparent paradox. The plant
assemblages that make up the mixed- and short-grass prairie evolved in the presence of frequent
disturbance, be it grazing by bison or fire (in addition to lightning-started fires, Native Americans apparently
made frequent use of fire as a tool for habitat management; Merriweather Lewis made frequent
observations of this phenomenon during his westward voyage). In the absence of grazing or fire,
vegetation grows thick and rank, and many of the characteristic prairie plants decline in abundance.
Grassland birds gradually abandon these areas in search of suitable habitat elsewhere, and fields that are
left idle for long periods of time become nearly devoid of breeding birds. However, birds will rapidly
recolonize these fields following disturbance. For example, the photo below shows a well-camoflauged
Chestnut-collared Longspur nestling from a nest located in a field burned only two months earlier.
Grassland birds challenge the widely held notion that the best form of wildlife management is to simply leave
well alone.
prairie has been destroyed, large blocks of mixed- and short-grass prairie persist in Montana, Colorado, and
parts of North and South Dakota, yet birds breeding in these areas have experienced declines that parallel
those of species breeding in tall-grass prairie. Habitat degradation, most likely driven by changes in
disturbance regimes and the spread of invasive plants, may explain this apparent paradox. The plant
assemblages that make up the mixed- and short-grass prairie evolved in the presence of frequent
disturbance, be it grazing by bison or fire (in addition to lightning-started fires, Native Americans apparently
made frequent use of fire as a tool for habitat management; Merriweather Lewis made frequent
observations of this phenomenon during his westward voyage). In the absence of grazing or fire,
vegetation grows thick and rank, and many of the characteristic prairie plants decline in abundance.
Grassland birds gradually abandon these areas in search of suitable habitat elsewhere, and fields that are
left idle for long periods of time become nearly devoid of breeding birds. However, birds will rapidly
recolonize these fields following disturbance. For example, the photo below shows a well-camoflauged
Chestnut-collared Longspur nestling from a nest located in a field burned only two months earlier.
Grassland birds challenge the widely held notion that the best form of wildlife management is to simply leave
well alone.
| A nine-day old Chesnut-collared Longspur sits in a nest at Medicine Lake National Wildlife Refuge, Montana. The field in which this nest was placed was burned approximately two months prior to the taking of this picture. Photo Copyright © 2006 John Lloyd. |
John Lloyd, senior research ecologist
at Ecostudies Institute, investigated
another possible factor in the decline
of grassland birds: the spread of
exotic plants. In particular, he
compared the breeding ecology of
Chestnut-collared Longspurs in two
different habitats: native
mixed-grass prairie and fields of
crested wheatgrass, a grass
introduced from the steppes of
Eurasia. This species, originally
introduced to reduce soil erosion on
overgrazed rangeland and reclaimed
farm fields, has now spread to
occupy upwards of 10 million
hectares in the short- and
mixed-grass prairie regions. When it
invades native prairie, it often
eliminates it native competitors and
can form vast monocultures.
Crested wheatgrass is clearly a
threat to native plants - but how do
at Ecostudies Institute, investigated
another possible factor in the decline
of grassland birds: the spread of
exotic plants. In particular, he
compared the breeding ecology of
Chestnut-collared Longspurs in two
different habitats: native
mixed-grass prairie and fields of
crested wheatgrass, a grass
introduced from the steppes of
Eurasia. This species, originally
introduced to reduce soil erosion on
overgrazed rangeland and reclaimed
farm fields, has now spread to
occupy upwards of 10 million
hectares in the short- and
mixed-grass prairie regions. When it
invades native prairie, it often
eliminates it native competitors and
can form vast monocultures.
Crested wheatgrass is clearly a
threat to native plants - but how do
birds respond?
Dr. Lloyd began to answer this question with two important discoveries. First,
Chestnut-collared Longspurs do not appear to prefer native prairie to monocultures of
crested wheatgrass. This was most apparent when examining settlement patterns: males
settled in both habitats at about the same time, and in equal densities. Second, pairs that
nested in the exotic habitat suffered reduced reproductive success. The odds that a nest in
the native prairie was depredated were 17% lower than for a nest in a field of crested
wheatgrass; simply put, predators destroyed more nests in the exotic habitat. Because of
the increased rate of nest predation, the average number of young produced per nest in the
exotic habitat was only 1.0, contrasted with 1.6 young per nest in the native prairie.
Furthermore, nestlings in the exotic habitat grew more slowly and were of lower mass when
they left the nest. Many other studies have shown that future survival often depends
strongly on size at fledgling, and thus fledglings from the exotic habitat may experience
lower adult survival - potentially a significant additional cost.
Dr. Lloyd began to answer this question with two important discoveries. First,
Chestnut-collared Longspurs do not appear to prefer native prairie to monocultures of
crested wheatgrass. This was most apparent when examining settlement patterns: males
settled in both habitats at about the same time, and in equal densities. Second, pairs that
nested in the exotic habitat suffered reduced reproductive success. The odds that a nest in
the native prairie was depredated were 17% lower than for a nest in a field of crested
wheatgrass; simply put, predators destroyed more nests in the exotic habitat. Because of
the increased rate of nest predation, the average number of young produced per nest in the
exotic habitat was only 1.0, contrasted with 1.6 young per nest in the native prairie.
Furthermore, nestlings in the exotic habitat grew more slowly and were of lower mass when
they left the nest. Many other studies have shown that future survival often depends
strongly on size at fledgling, and thus fledglings from the exotic habitat may experience
lower adult survival - potentially a significant additional cost.
Based on this study, it appears that grasslands dominated by the exotic crested wheatgrass
may be ecological traps - that is, areas that appear to be suitable habitat but that in fact are
of very poor quality. It is unclear exactly what causes the observed patterns; perhaps less
food is available in fields of crested wheatgrass, and perhaps the structure of the vegetation
offers less concealment from predators. We hope to conduct additional work in this system
to clarify some of these intriguing and disturbing patterns.
may be ecological traps - that is, areas that appear to be suitable habitat but that in fact are
of very poor quality. It is unclear exactly what causes the observed patterns; perhaps less
food is available in fields of crested wheatgrass, and perhaps the structure of the vegetation
offers less concealment from predators. We hope to conduct additional work in this system
to clarify some of these intriguing and disturbing patterns.
What does this all mean for the conservation of grassland birds? First and foremost, it
indicates the importance of maintaining native plant communities. Restoring grassland bird
populations will take more than simply setting aside large pieces of prairie; in many cases it
will also require intensive management to maintain populations of native plants and to
discourage the spread of exotic species. For more information, please contact Dr. Lloyd.
You may also find the following papers useful:
Lloyd, J. D. and T.E. Martin. 2005. Reproductive success of Chestnut-collared Longspurs in native and
exotic grassland. Condor 107:363-374. PDF
Lloyd, J. D., and T. E. Martin. 2004. Nest-site preference and maternal effects on offspring growth.
Behavioral Ecology 15:816-823. PDF
indicates the importance of maintaining native plant communities. Restoring grassland bird
populations will take more than simply setting aside large pieces of prairie; in many cases it
will also require intensive management to maintain populations of native plants and to
discourage the spread of exotic species. For more information, please contact Dr. Lloyd.
You may also find the following papers useful:
Lloyd, J. D. and T.E. Martin. 2005. Reproductive success of Chestnut-collared Longspurs in native and
exotic grassland. Condor 107:363-374. PDF
Lloyd, J. D., and T. E. Martin. 2004. Nest-site preference and maternal effects on offspring growth.
Behavioral Ecology 15:816-823. PDF