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Avocet breeding habitat, behaviour, and nesting platform use ­ Gyug and Weir 13 American Avocet breeding habitat, behaviour and use of nesting platforms at Kelowna, British Columbia Les W. Gyug1 and Jason T. Weir2 1 Okanagan Wildlife Consulting, 3130 Ensign Way, West Kelowna, BC V4T 1T9 [email protected] 2 Dept. of Biological Sciences and Dept. of Ecology and Evolution, University of Toronto, 1265 Military Trail, Toronto, ON M1C 1A4 [email protected] 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 re­expands 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 in 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 non­vegetated 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 Gyug, L.W. and J.T. Weir. 2017. American Avocet breeding habitat, behaviour and use of nesting platforms at Kelowna, British Columbia. British Columbia Birds 27:13–29. First published on­line May 2016. American Avocets are a habitat specialist of the eph­ Introduction emeral wetlands of the arid regions of western North America, typically breeding in “salt ponds, potholes, and The American Avocet (Recurvirostra americana) is con­ shallow alkaline wetlands, as well as mudflats of inland sidered a rare summer visitor and localized breeder in British lakes, impoundments, and evaporation ponds” (Ackerman Columbia (Burger 2015). It was first recorded as a breeding et al. 2013). In the 1960’s, Alki Lake became the City of bird in B. C. in 1968 at Duck Lake, Creston (Campbell et al. Kelowna’s sanitary landfill. The lake was partially drained, 1990). Further breeding was not reported again until 1987 trenches were dug in the lake bottom, filled with garbage when three pairs nested in the province; two at Alki Lake, and then covered, forming a series of ridges. In the mid­ Kelowna, and one at Beresford Lake, southeast of Kamloops 1980’s, control of the southern half of Alki Lake reverted (Cannings et al. 1987; Campbell et al. 1990). In 1997, 19 to its original owners and was allowed to revert to a shal­ nests were found at Alki Lake (Weir 1997) representing the low alkaline lake. Conditions after the mid­1980’s ap­ largest known concentration of avocets in the province. As of peared to be suitable for avocets, i.e. a shallow alkaline 1998, Alki Lake was the only site with documented nesting in lake with nesting islands created by raised ridges of B.C. for more than two years (Gebauer 2000). covered refuse, resulting in the colony found by Weir Volume 27, 2017 British Columbia Birds 14 Avocet breeding habitat, behaviour, and nesting platform use ­ Gyug and Weir from 1997 to 2015 are described in a companion paper (Gyug and Weir 2017). Methods Study area Southern British Columbia is at the northern end of the breeding range of the American Avocet west of the Great Plains (Ackerman et al. 2013). The main breeding site in B.C. was previously identified as Alki Lake, Kelowna (Weir 1997; Gebauer 2000), which was the main study site for this project (Figure 1). As of 1999, no water remained in the north half of what was previously Alki Lake but the south half had reverted from landfill to alkaline wetland as described in the Introduction. Additional lakes and wet­ lands were visited in the Kelowna area to check for avocet occurrence, for possible breeding, and to record habitat parameters at wetlands where there were some areas of rel­ atively barren shallow water that might potentially be suit­ able for avocet foraging. These included those four other sites where avocets had been previously recorded: Robert Lake, Chichester Pond, Okanagan Lake and Simpson’s Figure 1. Locations of wetlands examined for avocet (Acland Rd.) Pond. Two other wetlands on Glenmore Rd. habitat characteristics in Kelowna area, 1999. (an unnamed wetland referred to as Slough No.2, 4.4 km north of Alki Lake, and Bubna Slough, 2.5 km north of Al­ (1997). In 1998, high water levels flooded all the raised ki Lake) were also included. ridges, reducing avocet nesting opportunities on islands so that only three avocet nests were found (Gyug and Weir Nest locations and characteristics 2017) compared to the 19 in 1997. In 1999, we discovered most nesting sites through ob­ Re­expansion of the landfill into the southern half of servation (using binoculars and a spotting scope) of avocets Alki Lake was proposed in the mid­1990’s, threatening this sitting regularly in the same spot. At Alki Lake the main ob­ avocet colony with extirpation. As avocets have been servation site was located atop a 70­m tall cliff which known to use constructed wetlands (e.g. Burgess and Hiron provided visual access to the entire lake. A number of nest­ 1992, Davis et al. 2008) the goal of this study was to de­ ing sites were discovered by observing nest building activit­ termine the local ecological requirements of breeding avo­ ies, and a few nests were discovered only after thorough cets so that effective mitigation habitat could be designed. searches from a canoe. All suspected nesting sites were con­ The Pied Avocet (R. avocetta) of Eurasia has successfully firmed while searching from a canoe. Evidence of nest de­ nested on floating nest platforms (Burgess and Hirons predation, i.e. broken eggs or spilled yolk, was recorded 1992). Such platforms could help mitigate the effect of wa­ while conducting nest searches. Factors resulting in nest dis­ ter level changes on the availability of suitable nesting is­ turbances, including possible research impacts caused by us, lands, either in a mitigation wetland, or in Alki Lake, but were recorded during all observational time periods. their use by American Avocets had not been tested. On initial discovery of a nest, measurements included Using local data, we describe structure, material and nest height above water (the vertical distance in cm micro­location of avocet nests; describe habitat charac­ between the water level at nest completion and the base of teristics of nest locations; identify foraging and rearing the nest), nest distance to water (the horizontal distance in habitat locations and characteristics including substrate, m between the rim of the nest and water), and nesting ma­ vegetation, water depths, and water chemistry; quantify terial composition. To avoid further disturbance to nests, potential avocet invertebrate prey density; describe nearest­neighbour conspecific nest distance (the horizontal predator risks to breeding and foraging avocets; and de­ distances in m to the next nearest avocet nest that was oc­ termine if floating platforms would be used by avocets cupied at the time of nest building) was measured only to nest to compensate for flooding of nesting islands. after nesting was completed. Avocet reproductive chronology and success, population Nest composition was recorded for each nest. Nests numbers and shifts in local nest locations at Kelowna were defined as either: a) unlined nest scrape (i.e. a shal­ British Columbia Birds Volume 27, 2017 Avocet breeding habitat, behaviour, and nesting platform use ­ Gyug and Weir 15 low, unlined depression in the ground); b) lined nest scrape (i.e. a shallow, sparsely lined depression in the ground); c) rimmed nest (i.e. a mere rim of nesting material with no bottom); d) sparse nest (i.e. nest with minimal amount of nesting material and poorly formed cup); or e) complete nest (nest with well­formed cup and considerable amounts of nesting material). We noted the substrates on which nests were established and the amount of vegetation cover immediately surrounding each nest in a 1­m radius. Floating nest platforms We designed and built eight square floating nesting platforms, 1.2­m on each side (Figure 2).

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