Sprawl May Threaten Wildlife in Reserves

                      BOZEMAN, Montana, July 23, 2002 (ENS) - The subdivision of

                      land around wildlife preserves could degrade the best habitat for

                      birds and cut their population growth below sustainable levels,

                      concludes a new report.

                      "Our findings suggest that alteration and destruction of the remaining

                      productive habitats outside nature reserves will pose dire threats to

                      many wildlife populations," wrote Andrew Hansen and Jay Rotella of

                      Montana State University in the August issue of the journal

                      "Conservation Biology."

                      Much of the world's development is concentrated near biodiversity

                      hotspots. This is partly because private lands are more likely to have

                      productive habitats such as lowlands and coastal and riparian areas,

                      which have moderate climates, ample water and fertile soil.

                      In contrast, reserves are often at higher elevations and have poor soil,

                      which makes them less productive. This disparity means that species

                      in a reserve may depend on the more productive habitat on nearby

                      private lands, making the species vulnerable to development outside

                      the reserves.

                      Hansen and Rotella studied the effects of land use and habitat type

                      on bird populations in the Greater Yellowstone Ecosystem (GYE),

                      where rural residential development is on the rise. Development has

                      increased more than four times since 1970 in the Montana and

                      Wyoming parts of the GYE.

                      The 3,600 square mile study area ranged from a high elevation

                      plateau in Yellowstone National Park to privately owned lowlands.

                      The researchers assessed bird abundance and diversity at 100 sites

                      that represented the study area's range of topography, climate and

                      soils.

                      The team found 135 bird species in the study area, and sites

                      estimated to have 60 percent or more of the maximum bird

                      abundance and diversity were designated as bird hotspots. The

                      researchers also assessed the reproduction and population growth of

                      American robins and yellow warblers at two types of sites: low

                      elevation cottonwood stands and high elevation aspen stands.

                      Hansen and Rotella found that most of the bird hotspots were on or

                      near private lands at low elevations. Only about seven percent of the

                      bird hotspots were in reserves, concentrated at higher elevations.

                      Rural residential development was concentrated near the bird

                      hotspots on private lands. Home densities were almost 70 percent

                      higher within about a mile of hotspots than elsewhere on private

                      lands.

                      Hansen and Rotella found that robins may depend on the low

                      elevation hotspots. Their results suggest that robin populations are

                      increasing in the cottonwood but not in the aspen sites. The

                      researchers attribute this to the fact that the robin nesting season is

                      two weeks longer in the low elevation cottonwoods than in the high

                      elevation aspen, giving females more opportunity to make another

                      nesting attempt if their first attempt fails.

                      The researchers also found that yellow warblers may already be

                      threatened by development. Many of the cottonwood stands where

                      the birds tend to concentrate are surrounded by rural residential

                      development.

                      Areas with denser development have more nest predators, such as

                      magpies and crows, and parasitic cowbirds, which lay their eggs in

                      other birds' nests. The researchers found that cowbird parasitism of

                      warbler nests was five times higher in cottonwoods than in aspens.

                      "These trends cast doubt on the viability of current strategies that rely

                      on nature reserves for wildlife conservation and ignore intervening

                      lands. Conservation strategies to protect population source areas

                      outside reserves are likely necessary to reduce rates of future

                      extinction in nature reserves," wrote Hansen and Rotella.