Document Details

Determining thresholds of habitat quality for breeding birds in rangeland ecosystems in the Cariboo Region
Green, David
Maintaining the ecological resilience of BC?s rangelands is of vital importance to the ranching industry and to conserving rangeland biodiversity. BC?s rangelands are a dynamic ecosystem with change driven by grazing, fire and changing climatic conditions. The purpose of this project is to determine if there are thresholds of habitat quality for rangeland birds in the Southern Interior. We will do this by defining response curves for the relationship between habitat structure and composition across a gradient of rangeland (dry forest and grassland) vegetation communities associated with varying levels of livestock grazing and the diversity, abundance and productivity of rangeland birds. In this project we will address the following research questions: 1) What are the threshold levels of key structural and compositional habitat variables related to bird community indices in grassland and forest rangelands 2) What are the threshold levels of key structural and compositional habitat variables related to productivity of selected rangeland bird species? 3) At the micro-habitat scale, what habitat attributes are rangeland birds selecting for nesting habitat and is that selection related to nest success? Defining key habitat attributes for biodiversity indictors is a powerful approach allowing managers to tie indicator responses to anthropogenic habitat alteration. North American rangeland birds have shown more persistent and widespread declines than other avian groups, with almost all grassland species showing significant 30 year declines (Vickery et al. 1999, Sauer et al. 2005, Brennan and Kuvlesky 2005). Livestock grazing adversely affects some bird species but favour others, therefore, bird species assemblages have been used as indicators of rangeland quality (Bock et al. 1993, Saab et al. 1995, Bradford et al. 1998, Walk and Warner 2000). Horned Larks prefer reduced cover and thrive under moderate levels of grazing, while Western Meadowlarks require more cover and may be at risk under similar grazing regimes (Bock et al. 1984, Davis 2005). Grazing can have negative impacts by reducing of nesting cover, altering vegetation composition and therefore important food resources and by trampling of nests. The issue addressed by this project is the sustainable resource use of rangelands, an essential ecosystem for avian diversity in the southern interior. The results will be applied to the development of Best Management Practices for land managers from government, industry and NGOs. To support the widest range of bird species, a variety of grazing conditions and intensities is needed. Rangelands in the Southern Interior are composed of a mosaic of grasslands and forests, habitats that support a diverse suite of birds and are widely grazed by cattle. Cattle grazing can alter natural vegetation assemblages in forests and grasslands by reducing vegetative cover and changing plant communities. Grazing affects habitat attributes of the forest-grassland edge such as age class, stem density and ecotone breadth (Belsky and Blumenthal 1997). Grazing allows the invasion of non-native weeds and shifts the grass community from late seral stage dominated by decreasers, (plant species that decrease with grazing), to early seral stage dominated by increasers, (plant species that increase with grazing; Gayton 2003). Most North American literature on rangeland bird responses to grazing comes from the prairies. In BC, where vegetation composition and structure is different, Hooper and Pitt (1993) showed Vesper Sparrows need sites with complex vegetation structure and were common in the absence of spring or summer grazing and Savannah Sparrows were more common on wetter sites with less grass cover. However, no studies in the Cariboo region have assessed how productivity is related to habitat characteristics; information that is critical in managing for viable bird populations. There is an almost total lack of information on the responses of birds ...
Report Number
Executive Summary
Year-End Report

EIRS Search Options

Useful Contacts