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1 March 2013 Least Bittern Occupancy Dynamics and Detectability in Manitoba, Ontario, and Québec
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Abstract

We conducted 3,050 point counts from 2005–2009 (May–Jul) in 82 wetlands in three Canadian provinces (Ontario, Québec, and Manitoba) to quantify colonization and extinction dynamics of Least Bittern (Ixobrychus exilis) populations to detect geographic variations across provinces and to analyze effects of weather conditions, date, and survey methodology that may affect detection probability of Least Bitterns. Least Bitterns were detected at 773 (25%) of the 3,050 point counts with birds detected in 25, 26, and 28% of all point counts in Ontario, Québec, and Manitoba, respectively. Occupancy probability in the first year of the study was lower in Québec sites (0.26) compared to Manitoba sites (0.53). However, Québec sites had higher probabilities of colonization (0.67) than Ontario (0.32) and Manitoba (0.27). Probabilities of extinction did not differ across provinces but varied across years. Detection probability did not vary with weather variables (cloud cover, wind speed, air temperature – linear or quadratic effect) but decreased from mid-May (0.19) to mid-July (0.09). Detection probability was lower (0.13) for the first passive listening period than the call-broadcast period (0.28) and the second passive listening period (0.33). Observed differences in extinction and colonization probability between provinces and years show that occupancy dynamics vary both temporally and geographically, stressing the need to continue long-term monitoring of Least Bittern populations across the breeding range to detect geographic variation and changes in occupancy. We recommend Least Bittern surveys begin in mid-May at higher latitudes and use a second passive listening period following the call-broadcast period to increase detection of the species.

2013 by the Wilson Ornithological Society
Benoît Jobin, Marc J. Mazerolle, Nickolas D. Bartok, and Ron Bazin "Least Bittern Occupancy Dynamics and Detectability in Manitoba, Ontario, and Québec," The Wilson Journal of Ornithology 125(1), 62-69, (1 March 2013). https://doi.org/10.1676/12-046.1
Received: 20 March 2012; Accepted: 1 June 2012; Published: 1 March 2013
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