Greater Yellowlegs opportunistically forage on vulnerable mating darners Alexandra Anderson and Gill Holmes Introduction The Greater Yellowlegs ( Tringa melan - and daily counts of Greater Yellowlegs oleuca ) is a medium-sized shorebird that can exceed one hundred individuals per breeds in muskeg swamps in the boreal day on these surveys (Friis 2018). This region of Canada and Alaska (Elphick congregation of Greater Yellowlegs pro - and Tibbitts 1998). In Ontario, these vides an opportunity to learn more birds are known to breed in the Hudson about the ecology of this under-studied Bay Lowlands (Harris 2007) and pass shorebird. through southern Ontario during migra - tion. Although they migrate to winter - Predation Behaviour ing areas in a broad front across North We noticed an unusual foraging behav - America, Greater Yellowlegs are rarely iour of Greater Yellowlegs during a high- observed in large numbers at a single tide shorebird survey at North Bluff location during their annual cycle (Elph - Point (51.4839°N, 80.4517°W) on 20 ick and Tibbitts 1998). This, combined August 2017. We walked 3.5 km of coast with the remote location of their breed - to record shorebird abundance, diversity ing sites, has resulted in a lack of knowl - and behaviour as part of the James Bay edge of the biology of Greater Yellowlegs Shorebird Project. On this day, many compared to other shorebird species. darner dragonflies ( Aeshna spp.) (Figure During southbound migration, Greater 1) were flying across exposed intertidal Yellowlegs are commonly observed along mud flats and mating. This may have the southwestern coast of James Bay, been triggered by warmer temperatures Ontario, an important stop over site for that day (20°C at 11:00 compared to many shorebird species. Shorebirds are temperatures less than 16°C on preced - surveyed and monitored there by the ing mornings). Mating darners were James Bay Shorebird Project ea ch fall, attached in tandem (Figure 2) , 16 Ontario Birds Apri l 2019 Figure 1. An up-close view of a Subarctic Darner. Photo: Alexandra Anderson Figure 2. Subarctic Darners in tandem mating. Photo: Gill Holmes canadensis ), Lake Darner ( Aeshna eremi - ta ), Variable Darner ( Aesh na interrupta ), Sedge Darner ( Aeshna juncea ), Zigzag Darner ( Aeshna sitchensis ), Subarctic Darner ( Aeshna subarctica ) and Shadow Darner ( Aeshna umbrosa ) have been observed in the Hudson Bay Lowlands (Sutherland et al. 2005). Greater Yellowlegs were foraging at flying together and landing on the mud - the waterline on the incoming tide dur - flats or small exposed rocks. We observed ing this survey (Figure 3). We observed mating darners 80 0m from shore over the 62 adult Greater Yellowlegs, six juveniles mudflats as the tide was rising. We did and an additional 12 un-aged Greater not identify all of the species of darners Yellowlegs. Most of the yellowlegs were mating on this day, but several species, loafing, but 13 adults and one juvenile including Canada Darner ( Aeshna were feeding. Of the 13 foraging adults, Volume 37 Number 1 17 Figure 3. Greater Yellowlegs on intertidal flats, southwest James Bay. Photo: Jean Iron we observed four birds preying upon mat - scope; however, it is easier to identify large ing darners. The yellowlegs grabbed vul - prey items, for example, we have observed nerable darners while pairs were attached Greater Yellowlegs eating stickleback fish in tandem. They then dunked the darner (Gasterosteus sp .) at this site. pairs under water repeatedly until the darners detached or appeared stunned. Importance The yellowlegs swallowed the darners one Knowledge of the diet of Greater Yel - at a time in only a few gulps and then lowlegs is limited to stomach contents continued foraging. The whole process, from fewer than 20 individuals (Elphick capture to consumption, occurred in and Tibbitts 1998) and personal observa - approximately 30 seconds. This was the tions. Greater Yellowlegs have been first and only instance that we noticed known to eat dragonfly naiads (Bent yellowlegs depredating darners during the 1927, Brooks 1967a, b) and occasionally daily shorebird surveys which occurred adult dragonflies (Elphick and Tibbitts over two months. We did not notice 1998). The predation by Greater Yellow - darners mating over the intertidal area in legs of darners in tandem is an observation large numbers any other day during the that, to our knowledge, has not been doc - season. Most prey items consumed by for - umented in the literature. The con sump - aging shorebirds in this area are not iden - tion of adult darners is not surprising tifiable by observation with a spotting given their shared habitat; however 18 Ontario Birds Apri l 2019 dragonflies are agile flyers (Bomphrey et Elphick, C.S. and T.L. Tibbitts . 1998. al. 2016, Paulson 2019) and may fre - Greater Yellowlegs ( Tringa melanoleuca ), quently escape predation by yellowlegs. version 2.0 In The Birds of North America Our observation indicates that Greater Online (A. F. Poole and F. B. Gill, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. Yellowlegs are opportunistic foragers and https://birdsna.org/Species_Account/bna/ can prey on vulnerable darners, such as species/greyel/introduction when they are flying in tandem and their Friis, C . 2018. James Bay Shorebird Project flight maneuverability is limited. 2017 Report. Environment and Climate Change Canada’s Canadian Wildlife Service, Acknowledgements Ontario Ministry of Natural Resources and We thank the James Bay Shorebird Project Forestry, Bird Studies Canada, Moose Cree partners including the Canadian Wild life First Nation and Trent University. Toronto, Service, Environment and Climate Ontario. 30 pp. Change Canada, the Ontario Ministry of Harris, R. 2007. Greater Yellowlegs. Natural Resources and Forestry, Moose Pp. 224-225 in Cadman, M.D., D.A. Cree First Nation and Trent University for Sutherland, G.G. Beck, D. Lepage and A.R. their efforts to monitor and conserve Couturier, eds. Atlas of the Breeding Birds shorebirds along James Bay. We thank of Ontario, 2001-2005. Bird Studies Canada, Environment Canada, Ontario Field Don Sutherland and Colin Jones for assis - Ornithologists, Ontario Ministry of Natural tance identifying darners in photos. Resources and Ontario Nature. Toronto, Ontario. Paulson, D . 2019. Dragonflies and dam - Literature Cited selflies — a natural history. Ivy Press, Brighton, Bent, A.C. 1927. Life histories of North UK. 224 pp. American shore birds, Part 1. Smithsonian Sutherland, D.A., M.J. Oldham, C.D. Jones Institution United States National Museum and P.D. Pratt . 2005. Odonata of Ontario’s Bulletin 142. Dover Publications, Inc., New Hudson Bay Lowland. Ontario Odonata York, NY, USA. 327 pp. Accessed online at: 6:1-11. https://www.gutenberg.org/files/47028/47028 -h/47028-h.htm#Page_327 Alexandra Anderson Bomphrey, R.J., T. Nakata, P. Henningsson Environmental and Life Sciences and H.T. Lin . 2016. Flight of the dragonflies Graduate Program and damselflies. Philosophical Transactions of 1600 West Bank Drive the Royal Society B 371(1704), p.20150389. Trent University Brooks, W.S. 1967a. Food and feeding habits Peterborough, Ontario K9J 0G2 of autumn migrant shorebirds at a small mid - E-mail: [email protected] western pond. Wilson Bulletin 79:307-315. Brooks, W.S. 1967b. Organisms consumed Gill Holmes by various migrating shorebirds. Auk 84: Environmental and Life Sciences 128-130. Graduate Program 1600 West Bank Drive Trent University Peterborough, Ontario K9J 0G2 Volume 37 Number 1 19.