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9 April 2019 Effects of Great Horned Owls (Bubo virginianus) on a Leach'S Storm-Petrel (Oceanodroma leucorhoa) population
Ingrid L. Pollet, Dave Shutler
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Populations of Leach's Storm-Petrels (Oceanodroma leucorhoa) are in decline globally, but causes of these declines are unclear. One possibility is predation at breeding colonies. To estimate effects of one pair of Great Horned Owls (Bubo virginianus) on a Leach's Storm-Petrel colony, we analyzed owl pellets collected from Bon Portage Island, Nova Scotia, Canada, over 5 consecutive breeding seasons (2011–2015). Great Horned Owl diets were mainly Leach's Storm-Petrels by number (79%) and by mass (66%). Muskrats (Ondatra zibethicus), meadow voles (Microtus pennsylvanicus), and masked shrews (Sorex cinereus) completed the diet. This is, to our knowledge, one of the most specialized diets reported for this species of owl. We estimate that this specialized diet reduced by at most 1% annually the population of Leach's Storm-Petrels on this island.

Ingrid L. Pollet and Dave Shutler "Effects of Great Horned Owls (Bubo virginianus) on a Leach'S Storm-Petrel (Oceanodroma leucorhoa) population," The Wilson Journal of Ornithology 131(1), 152-155, (9 April 2019).
Received: 18 October 2017; Accepted: 14 September 2018; Published: 9 April 2019

Bon Portage Island
Bubo virginianus
great horned owl
Leach's Storm-Petrel
Oceanodroma leucorhoa
pellet analysis
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