How does shifting capelin biomass affect gull predation on seabird offspring? Gibson Rieger & Dr. Gail Davoren [email protected] Department of Biological Sciences, University of Manitoba, Winnipeg, MB, Canada Background Objective, Hypothesis & Prediction Expected Results Animal foraging behavior has a major impact on population Determine how gull predation of murre offspring and kleptoparasitism of adult Inshore arrival of capelin results in: dynamics murres changes before and after capelin arrival – Decreased predation on murre offspring and increased Optimal foragers maximize net energy gain (energy expenditure Hypothesis: Capelin inshore arrival influences rates of gull predation and kleptoparasitism by herring gulls 1,2 minus energy gained from prey) while foraging kleptoparasitism on common murres – Continued predation of murre offspring and low rates of – Ability to respond to changes kleptoparasitism by black-backed gulls Prediction: Capelin arrival will cause a shift from high gull predation of murre in prey population dynamics is – Both species maintain a similar proportion of time spent in eggs to high kleptoparasitism and lower predation of murre chicks important to fitness aggressive behaviours Migratory prey species drive Predation of offspring by Herring Gulls Study Site & Methods 5 changes in the diet niche of 4 Predators3,4,5 Study site: – Northeast Newfoundland 3 2 Capelin (Mallotus villosus) https://news.umanitoba.ca/gail-davorens-research-sheds-light-on-the-role-of- capelin-in-the-north-marine-food-web/ coast – Keystone forage fish species on 1 Fig. 1 On-shore capelin spawning site. – South Cabot Island of Number events/day Northeast Newfoundland coast 0 murre colony (10,000 Before After – Acts as pulsed resource when migrates inshore to spawn breeding pairs) Predation of offspring by Black-Backed Gulls – Decreased biomass since significant population collapse6 5 – Observations from North 4 Cabot Island gull colony Study Species 3 Study period: 2 https://www.lighthousefriends.com/light.asp?ID=1289, map modified from Irvine et al. (in revision) Great black-backed gull 1 – Before and after inshore Fig. 4 Aerial shot of North (bottom) and South Cabot Island (top) with Number of of Number events/day (Larus Marinus) and European 0 arrival of capelin (Fig. 5) a map of Northeast coast of Newfoundland. Murre breeding colonies Before After (red stars) and annually persistent capelin spawning sites (blue circles). herring gull (Larus argentatus) – Annually persistent capelin Fig. 7 Mean daily successful (green) and attempted (blue) kleptoparasitism and predation are colonial central place spawning sites monitored for inshore arrival events by herring and great black-backed gulls before and after inshore capelin arrival on the Newfoundland coast. foragers – Capelin spawning begins before murre hatching – Surface-feeders https://www.reddit.com/r/natureismetal/comments/iwgwlv/bunny_going_down_ Survey methods: Conclusion & Relevance the_hole_one_last_time_i_never/ – Dietary generalists: https://www.oiseaux.net/photos/arnaud.delberghe/european.herring.gull.2.html Scans: count all gulls on South Cabot by spotting scope • Spawning capelin Fig. 2 Great black-backed gull (left) and European – Focus on single field of view for 60s, record number Changing abundance of keystone prey species puts strain on herring gull (right). • Seabird eggs and chicks7 and species of gulls present, ecosystems Black-backed gulls larger, more intimidating than herring gulls June Gull eggs hatch, chick rearing begins proximity to murres, and – Shifting gull predation in response to capelin population – Less risk of injury during predation of seabird offspring behaviours collapse is potentially damaging to murre populations Results of our study can be used to inform gull management Common murre – Shift field of view until entire July programs (e.g. culling of adults, eggs and/or nest removal) on the (Uria aalge): Capelin migrate inshore to spawn island scanned Focal observations: pick one © Laurie Maynard Newfoundland coast – Dive up to 200m Fig. 6 Observations from N. – Lay one egg per gull, record behaviours for 10min Cabot Island. July Behaviours recorded: References year Murre eggs hatch, chick rearing begins – Abundant near – Non-aggressive: flying, walking, on water, preening, 1. Charnov E, 1976. Theor Popul Biol. 9:129-136. foraging, or social behavior 2. Tome M, 1988. Oecologia. 76:27-36. Newfoundland August 3. Araújo M et al., 2011. Ecol Lett. 14:948-958. – Aggressive: attempted or successful predation of 4. Walton Z et al., 2017. Oikos. 126:642-650. gull breeding Capelin migrate offshore to overwinter 5. Hansen J et al., 2020. Ecosystems. 23:292–306. https://upload.wikimedia.org/wikipedia/commons/a/a1/Common_Murre_Colony_(7172186722).jpg colonies egg/chick, attempted or successful kleptoparasitism, https://www.pinterest.ca/pin/12244230212559475/ Fig. 5 Timeline of seabird 6. Buren A et al., 2019. Mar Ecol Prog Ser. 616:155-170. Fig. 3 Common murre breeding colony and close-up. hatching and capelin migration. hovering over or walking in murre colony 7. Maynard L & Davoren G, 2020. 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