Distribution, relative abundance and population size of Williamson’s Sapsucker in south-central British Columbia

Les W. Gyug1, John M. Cooper2, and Chris Steeger3

1Okanagan Wildlife Consulting, 3130 Ensign Way, West Kelowna, B.C. V4T 1T9 Canada e-mail: les_gyug@shaw.ca
2current address: Cooper Beauchesne and Associates Ltd, Box 646, Errington, BC V0R 1V0 e-mail: jcooper@cooperbeauchesne.com
3current address: ECL Environmental Solutions, 13 – 991 Hornby Street, Vancouver, B.C. V6Z 1V3 e-mail: csteeger@eclenvironmental.ca

Abstract: The Extent of Occurrence (EO) of Williamson’s Sapsucker in British Columbia has not changed since last spatially defined in 2007 despite intensive survey efforts including the B.C. Breeding Bird Atlas from 2008-2012. The Area of Occupancy (AO) has now been spatially defined for the Merritt-Princeton area in addition to that already defined in 2007 for the Okanagan-Boundary. Relative abundance in terms of numbers of detections per call- and drum-playback (CPB) declined significantly as the breeding season progressed, being highest in April as territories are established. Nest or breeding territory population size was estimated independently by three methods for the Merritt-Princeton and OkanaganBoundary AOs combined. In 2008, a nest population of 399 (SE 155) was estimated using a simple random sample of 174 225-m radius plots each searched intensively for nests. Only using data collected prior to 2008, breeding territory population size was estimated to be 381 (no SE available) by extrapolating from the sum of assumed areas sampled by CPB and follow-up nest searches over a number of years. In 2012, breeding territory population size of 526 (SE 107) was predicted from the linear regression of breeding territory density with average habitat suitability ratings in 30 census areas. In 2007 a nest population estimate was attempted in the remainder of the EO west of Okanagan Lake using 3038 variable-radius CPB plots but no reliable statistical estimate could be made as only one nest was discovered. Mean nest density was estimated to be 0.28/km within the combined Merritt-Princeton and Okanagan-Boundary AOs. Within the remainder of the EO west of Okanagan Lake, densities were too low to reliably estimate.

Keywords: Williamson’s Sapsucker, Sphyrapicus thyroideus, distribution, relative abundance, breeding population size, breeding density

PDFicon Gyug, L.W., J.M. Cooper, and C. Steeger. 2014. Distribution, Relative Abundance and Population Size of Williamson’s Sapsucker in Southcentral British Columbia. British Columbia Birds 24:9–19. First published on-line October 2013.


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