Les W. Gyug1 and Jason T. Weir2
1 Okanagan Wildlife Consulting, 3130 Ensign Way, West Kelowna, BC V4T 1T9 les_gyug@shaw.ca
2 Dept. of Biological Sciences and Dept. of Ecology and Evolution, University of Toronto, 1265 Military Trail, ON M1C 1A4 jason.weir@utoronto.ca
Abstract: The largest and most consistently used American Avocet (Recurvirostra americana) colony in British Columbia is located in the southern half of the former Alki Lake, Kelowna. This lake was a landfill active from the 1960’s to 1980’s, and is now slated to be filled in completely as the landfill re-expands into the remnants of the lake. Here, we report avocet behaviour, nest conditions and foraging habitat characteristics in 1999 at Alki Lake and five other wetlands in the Kelowna area to inform future mitigation strategies for this colony. Thirteen breeding pairs initiated 21 nests (including renesting after failed attempts) at Alki Lake in 1999, with no nests from other Kelowna area localities. Fifteen nests were on islands, five on 1.2-m square floating nest platforms, and one on a shoreline mudflat. Nesting on floating nest platforms had not been previously reported for American Avocets. Foraging areas regularly used by individual pairs were not necessarily adjacent to the nest, and increased from 0.32 ha during the incubation period to 0.53 ha after hatching. Avocets foraged primarily in soft silt substrates along non-vegetated shorelines and in shallow mudflats at a mean depth of 10 cm. Foraging accounted for 50.2% of all behaviours observed during repeated sweep scans of adults. Gulls, corvids, and various raptors were common potential predators. Of these, Golden Eagle was the most aggressively attacked by avocets. Alkalinity (pH) of Alki Lake was 9.2 and along with Robert Lake at 9.4 was higher than the wetlands not used by avocets in the Kelowna area. Potential invertebrate prey densities of chironomid (midge) larvae, ephydrid (brine fly) larvae and of corixids (water boatmen) were higher at Alki Lake than any other wetland examined in the Kelowna area. Cladocerans (water fleas) were also found at Alki and Robert lakes but not at other wetlands in the Kelowna area. Construction of a mitigation wetland should include low-relief nesting islands in a highly alkaline and saline shallow wetland dominated by unvegetated fine substrates. It should be greater than 10 ha in size to maintain sufficient space for 20 avocet breeding territories.
Key words: American Avocet, Recurvirostra americana, British Columbia, Alki Lake, Kelowna, nesting platform, foraging, habitat, behaviour, alkaline lake, invertebrate prey, mitigation wetland
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