The response of the avian community to 40 years of land cover change within the Aspen Parkland and Moist-mixed Grassland ecoregions of the Canadian prairies

Date
2015-03
Authors
Kovatch, Leah Catherine
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Faculty of Graduate Studies and Research, University of Regina
Abstract

Since European settlement, over 80% of grassland habitat has been lost in the Canadian prairies, primarily in the Moist-mixed Grassland and Aspen Parkland ecoregions. Native grassland continues to be lost and degraded. Reduction of fire and overgrazing by livestock has allowed woody vegetation to encroach on grasslands. Grassland bird populations in the northern extent of their range have undergone steep declines whereas woodland bird populations have increased. It is unknown whether population fluctuations over the past 40 years are a result of land cover changes during this period. The goal of my research was to address this knowledge gap with the use of long-term datasets from the Breeding Bird Survey (BBS) and remote sensing. My objectives were to: (1) assess changes in bird population trends over the past 40 years along a sub-set of representative BBS routes; (2) determine land cover change along these BBS routes from 1970 to 2012; and (3) determine if there is a relationship between land cover change and bird population trends over the past 40 years. I classified 1970 and 2012 land cover (cultivated, native grassland, and woodland) within an 800 m radius of point-count locations along nine BBS routes located in the Moist-mixed Grassland and Aspen Parkland ecoregions of Saskatchewan and Manitoba. Bird population trend estimates from 1970 to 2011 were compiled for each BBS route and I grouped species based on breeding habitat guild (grassland, scrubland, and woodland). On average, grassland and scrubland bird populations decreased by 1.5 %/yr and 0.7 %/yr, respectively, and woodland birds increased by 1.4 %/yr along routes. The amount of land cover change from 1970 to 2012 was small along routes, indicating the majority of landscape change occurred prior to 1970. Cultivated land and woodland increased on average by 2.2% and 0.1% respectively, and native grassland decreased by 2.1%. Although absolute native grassland loss was small overall, proportion of loss relative to what was present in 1970 was large. The relatively small change in woodland cover was likely a result of land being cleared for cultivation but at the same time encroaching on native grassland. Overall, I found no statistically significant relationship between land cover change and bird trend estimates. Possible explanations for a lack of a relationship include: (1) land cover change was too small to affect bird populations; (2) common and generalist species included in community analyses are less affected by the documented habitat changes; (3) factors other than recent land cover change are affecting bird populations (i.e., fragmentation, patch size, local vegetation); and (4) habitat loss is occurring on migration and winter areas. Additional research is needed to address shrub encroachment rates in my study area, as well as to investigate the effects of habitat changes on grassland specialists.

Description
A Thesis Submitted to the Faculty of Graduate Studies and Research In Partial Fulfillment of the Requirements for the Degree of Master of Science in Biology, University of Regina. ix, 74 p.
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