Details - Grassland bird surveys in north Valley County, Montana : 2001-2006

Grassland bird surveys in north Valley County, Montana

Title

Grassland bird surveys in north Valley County, Montana : 2001-2006

By

Hendricks, Paul, 1951-

Lenard, Susan.
Currier, Coburn, 1970-
Carlson, John C.
Montana Natural Heritage Program.

Type

Book

Material

Published material

Publication info

Helena, MT, Montana Natural Heritage Program, c2007

Notes

Prepared for: Bureau of Land Management Glasgow Field Office.

Populations of grassland-associated birds have exhibited the steepest declines of any suite of bird species in North America over the past several decades. Loss of habitat throughout North America, resulting from conversion of native prairie to agricultural production, has been identified as the primary cause of historic grassland bird declines. Large blocks of intact prairie lands remaining in Montana, therefore, provide critically important breeding habitat for many grassland bird species. Bureau of Land Management (BLM) lands, especially in the northeastern and north-central portions of the state, are important breeding habitats for many imperiled grassland species endemic to the Great Plains, as the primary land cover in this area is native mixed-grass prairie. Few areas in the state contain such extensive blocks of intact grasslands. Recognizing land management decisions can greatly influence native fauna by altering vegetation structure and plant composition, biologists in the Glasgow Field Office of the BLM initiated a grassland bird project to identify the diversity and abundance of prairie birds on BLM lands in north Valley County. The degree to which livestock grazing, the Bureaus primary land management activity in the county, can influence native bird species varies widely and is dependent upon many factors. To better understand the impact of different grazing histories on presence and relative abundance of native prairie bird species, fixed-radius point counts were randomly placed across BLM lands in north Valley County in areas with native grassland plant cover. Transects consisting of three point locations were surveyed using standard avian point-count protocols to document bird species abundance and diversity across pastures with differing grazing histories. The project, which began in 2001, evolved into a multi-year inventory, and has completed six consecutive years of point counts. No other project focused on grassland birds in Montana has gathered consistent data at the same locations for this length of time. The information gathered during this project will provide critical information on grassland bird/grazing dynamics and the current status of prairie birds in this increasingly rare ecosystem. This report summarizes bird species presence and relative abundance during the first six years of inventory, and examines some factors that may affect bird presence and abundance on the north Valley County grassland landscape. Seventy-five species of birds were recorded on 1203 avian point counts (63 - 69 transects run each year) in north Valley County during the early summer months of 2001 through 2006. Twenty-nine species (38.7% of the total) have been recorded on at least one point count every year, and two additional species were recorded on point counts in five of the six years of surveys. These 31 bird species represent nearly the full suite likely to regularly breed in grassland habitat in this region of Montana. Sixteen bird species recorded on north Valley County point counts are Montana Species of Concern, including seven which are endemic to the Northern Great Plains: Ferruginous Hawk (Buteo regalis), Long-billed Curlew (Numenius americanus), Spragues Pipit (Anthus spragueii), Lark Bunting (Calamospiza melanocorys), Bairds Sparrow (Ammodramus bairdii), McCowns Longspur (Calcarius mccownii), and Chestnut-collared Longspur (Calcarius ornatus). Other Species of Concern also recorded on point counts included American White Pelican (Pelecanus erythrorhynchos), Greater Sage-Grouse (Centrocercus urophasianus), Swainsons Hawk (Buteo swainsoni), Franklins Gull (Larus pipixcan), Common Tern (Sterna hirundo), Loggerhead Shrike (Lanius ludovicianus), Brewers Sparrow (Spizella breweri), Grasshopper Sparrow (Ammodramus savannarum), and Bobolink (Dolichonyx oryzivorous). Nine Species of Concern were recorded every year, of which three (Spragues Pipit, Bairds Sparrow, Chestnut-collared Longspur) occurred annually on 32% or more of all points. Among the six years of study, birds varied in both number of individuals counted and percentage of point counts on which they occurred. Preliminary analyses for seven Species of Concern indicate that the number of point counts on which they are detected may be strongly correlated with the mean number of individuals recorded per point count, and that both metrics provide a long-term means of tracking general trends across a large landscape, such as north Valley County. However, it seems probable that conditions at the local landscape scale that affect vegetation structure have a strong influence on the number of individuals that settle at any specific location. Identifying these conditions will aid managers in developing management activities that favor the conservation of grassland birds. Some conditions, however, may be beyond the ability of local land managers to control. Preliminary analyses also indicate that annual variation in abundance of some grassland bird Species of Concern is strongly related to total April - May precipitation. More than 85% of the total individuals recorded during the six-year inventory were represented by 12 species, seven of which are state Species of Concern. Six of these are species endemic to the Northern Great Plains. Their presence and relative abundance reflects the uniqueness and importance of north Valley County; few places remain in the Northern Great Plains that supports such a composition of species. Their abundance also reflects a landscape diverse in vegetation characteristics, as each species requires unique habitat elements for breeding and foraging. Chestnut-collared Longspurs and Spragues Pipits require areas with moderate levels of grass cover and litter, for example, while Bairds Sparrows require dense grass and litter, and McCowns Longspurs require sparse grass and bare ground. In addition to habitat availability, the condition is also critical. A heterogeneous prairie mosaic can support a greater number of grassland endemics. Although once plentiful across the Northern Great Plains, large blocks of intact native prairie habitat are now rare. Protecting these lands from conversion and other activities in conflict with historic disturbances (e.g. grazing and fire regimes that mimic the natural frequency and intensity) is critical to maintaining native prairie capable of supporting a diverse species assemblage. Without this protection, many of these endemics would likely disappear from the landscape.