Lawrence D. Igl

AREA REQUIREMENTS OF GRASSLAND BIRDS: A REGIONAL PERSPECTIVE

Abstract Area requirements of grassland birds have not been studied except in tallgrass prairie. We studied the relation between both species-occurrence and density and patch size by conducting 699 fixed-radius point counts of 15 bird species on 303 restored grassland areas in nine counties in four northern Great Plains states. Northern Harrier (Circus cyaneus), Sedge Wren (Cistothorus platensis), Clay-colored Sparrow (Spizella pallida), Grasshopper Sparrow (Ammodramus savannarum), Bairds Sparrow (Ammodramus bairdii), Le Contes Sparrow (Ammodramus leconteii), and Bobolink (Dolichonyx oryzivorus) were shown to favor larger grassland patches in one or more counties. Evidence of area sensitivity was weak or ambivalent for Eastern Kingbird (Tyrannus tyrannus), Common Yellowthroat (Geothlypis trichas), Savannah Sparrow (Passerculus sandwichensis), and Western Meadowlark (Sturnella neglecta). Red-winged Blackbirds (Agelaius phoeniceus) preferred larger patches in some counties, and smaller patches in others. Mourning Doves (Zenaida macroura) and Brown- headed Cowbirds (Molothrus ater) tended to favor smaller grassland patches. Three species showed greater area sensitivity in counties where each species was more common. Five species demonstrated some spatial pattern of area sensitivity, either north to south or east to west. This study demonstrates the importance of replication in space; results from one area may not apply to others because of differences in study design, analytical methods, location relative to range of the species, and surrounding landscapes.

CHANGES IN BREEDING BIRD POPULATIONS IN NORTH DAKOTA: 1967 TO 1992-93

We compared breeding bird populations in North Dakota using surveys con- ducted in 1967 and 1992-93. In decreasing order, the five most frequently occurring species were Horned Lark (Eremophila alpestris), Brown-headed Cowbird (Molothrus ater), Western Meadowlark (Sturnella neglecta), Red-winged Blackbird (Agelaius phoeniceus), and Eastern King- bird (Tyrannus tyrannus). The five most abundant species-Horned Lark, Chestnut-collared Longspur (Calcarius ornatus), Red-winged Blackbird, Western Meadowlark, and Brown-headed Cowbird-accounted for 31-41% of the estimated statewide breeding bird population in the three years. Although species composition remained relatively similar among years, between- year patterns in abundance and frequency varied considerably among species. Data from this survey and the North American Breeding Bird Survey indicated that species exhibiting significant declines were primarily grassland- and wetland-breeding birds, whereas species exhibiting significant increases primarily were those associated with human structures and woody vegetation. Population declines and increases for species with similar habitat asso- ciations paralleled breeding habitat changes, providing evidence that factors on the breeding grounds are having a detectable effect on breeding birds in the northern Great Plains. Received 30 January 1996, accepted 18 September 1996. THE DECLINE OF BREEDING BIRD POPULATIONS in forests of eastern North America has received considerable recent attention (Askins et al. 1990, Hagan and Johnston 1992, Finch and Stangel 1993). The status of bird populations in grass- lands and midcontinental areas, however, has received far less attention. Yet, analyses of North American Breeding Bird Survey (BBS) data in- dicate that more breeding species are declining than increasing in the prairie regions of North America (Droege and Sauer 1994). Also, grass- land species show greater and more consistent patterns of decline at the continental level than do other ecological guilds, including long-dis- tance migrants in eastern forests (Askins 1993, Droege and Sauer 1994). These declines have been most pronounced in areas of intensive ag- riculture, such as the Midwest (Herkert 1991, 1995; Warner 1994) and the northern Great Plains (Johnson and Schwartz 1993, Reynolds et al. 1994). Although the BBS is the best source of quan- titative data on trends of breeding bird popu- lations in the midcontinent, it has several lim- itations, including sparse coverage in central North America and biases associated with road-

Habitat Associations of Migrating and Overwintering Grassland Birds in Southern Texas

We report on the habitat associations of 21 species of grassland birds overwintering in or migrating through southern Texas, during 1991-1992 and 1992-1993. Ninety percent of our grassland bird observations were made during winter and spring, and only 10% occurred during fall. Grassland species made up a high proportion of the total bird densities in grassland and shrub-grassland habitats, but much lower proportions in the habitats with more woody vegetation. Fewer grassland species were observed in grassland and woodland than in brushland, parkland, and shrub-grassland habitats. Grassland birds generally were found in higher densities in habitats that had woody canopy coverage of < 30%; densities of grassland birds were highest in shrub-grassland habitat and lowest in woodland habitat. Species that are grassland specialists on their breeding grounds tended to be more habitat specific during the nonbreeding season compared to shrub-grassland specialists, which were more general in their nonbreeding-habitat usage. Nonetheless, our data demonstrate that grassland birds occur in a variety of habitats during the nonbreeding season and seem to occupy a broader range of habitats than previously described.

Influence of Climate Change on Productivity of American White Pelicans, Pelecanus erythrorhynchos

In the past decade, severe weather and West Nile virus were major causes of chick mortality at American white pelican (Pelecanus erythrorhynchos) colonies in the northern plains of North America. At one of these colonies, Chase Lake National Wildlife Refuge in North Dakota, spring arrival by pelicans has advanced approximately 16 days over a period of 44 years (1965–2008). We examined phenology patterns of pelicans and timing of inclement weather through the 44-year period, and evaluated the consequence of earlier breeding relative to weather-related chick mortality. We found severe weather patterns to be random through time, rather than concurrently shifting with the advanced arrival of pelicans. In recent years, if nest initiations had followed the phenology patterns of 1965 (i.e., nesting initiated 16 days later), fewer chicks likely would have died from weather-related causes. That is, there would be fewer chicks exposed to severe weather during a vulnerable transition period that occurs between the stage when chicks are being brooded by adults and the stage when chicks from multiple nests become part of a thermally protective crèche.

Common Snapping Turtle Preys on an Adult Western Grebe

Abstract. The identification of predators of aquatic birds can be difficult. The Common Snapping Turtle (Chelydra serpentine) is considered a major predator of waterfowl and other aquatic birds, but the evidence for this reputation is based largely on circumstantial or indirect evidence rather than direct observations. Herein, the first documented observations of a snapping turtle attacking and killing an adult Western Grebe (Aechmophorus occidentalis) are described.