Nest-site characteristics, nest distribution, and home range of urban merlins (Falco columbarius) in Winnipeg, Manitoba
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Date
2021-03-31
Authors
Josephson-Laidlaw, Justine
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Abstract
The development of urban forestry has created environments that have become ideal habitats for wildlife that exhibit generalist behaviours. Understanding the habitat features that urban wildlife rely upon is essential to protect species and to encourage successful human and wildlife cohabitation. Although not previously researched, Merlins (Falco columbarius) are commonly observed in the urban area of Winnipeg, Manitoba, Canada. Nests were documented throughout the city between 2017 and 2019. This research was conducted to understand how Merlins utilize this urban environment by developing baseline data on the nest site characteristics, nest density, nest site distribution, and breeding home range. To examine this, micro and macro-scale habitat features were measured using a subset of the total recorded nests (n=81). This subset included 30 occupied and 30 unoccupied nest sites that were surveyed and analyzed using generalized linear model (GLM) methods to determine nest site and habitat selection. Adult individuals (n=4) were tracked during the nesting period using high-precision GPS tags, and spatial movement patterns were analyzed using continuous movement methods (ctmm) to determine home range sizes. I found that all Merlin nests documented through the study were in unused American Crow (Corvus brachyrhynchos) nests located in mature spruce trees. The habitat selection analysis revealed nest trees were taller and fewer coniferous trees were found within 25 m of occupied nests as compared to unoccupied sites. Nest density of Merlins within Winnipeg was 6.73 nests/100 km2 and the spatial distribution of nests was non-random, with significant clustering patterns. Mean nearest neighbour distances between nests was 1.67 km. The mean home range size of four breeding male Merlins was 1.79 km2. During the 2018 field season, an apparent West Nile virus (WNV) outbreak occurred, and the impacts of this outbreak were documented within this study. Juvenile mortalities occurred at 71% of nests. A sample of 32 Merlins from the Winnipeg area presumably deceased due to WNV were necropsied at the Canadian Cooperative Wildlife Health Centre in Saskatoon, Saskatchewan, resulting in WNV positive results in 75% of the Winnipeg sample. Based on nest site selection results in this study, management for Merlins within Winnipeg should include the maintenance of mature spruce trees by both city planners and private property owners. Continued monitoring through community citizen science could provide important data to offer further insight into limiting factors and the ecology of Merlins in the urban environment of Winnipeg.
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Keywords
Urban raptors, Home range, Nest-site selection, West Nile virus, Falco columbarius, Merlins, Avian ecology, Nest density, Winnipeg, Telemetry, Urban, Falcon