Leaping Red Foxes Cause Chronic Mortality of Adult Leach’s Storm-Petrels Transiting Over Land

Sabina I. Wilhelm^1,*, Darren Sheppard², Kaylene Stagg², Christopher R.E. Ward¹, Laura E. King¹, and Jake L. Russell-Mercier³

¹Biology Department, University of Wisconsin-Whitewater, Whitewater, WI 53190.²Indian Bay Ecosystem Corporation, Indian Bay, NL A0G 2V0, Canada. ³Canadian Wildlife Service, Environment and Climate Change Canada, Gatineau, QC K1A 0H3, Canada. *Corresponding author.

Northeastern Naturalist, Volume 32, Issue 1 (2025): 66–79

First published early online: 8 February 2025

Abstract
Hydrobates leucorhous (Leach's Storm-Petrel) is a small seabird that has undergone significant population declines across its North Atlantic breeding range. Threat assessments have identified predation as an important contributing factor, with most predation studies describing significant mortalities at colonies or when recently fledged Leach’s Storm-Petrels strand on land during their maiden voyage in the fall. Through a combination of nighttime observations and weekly systematic searches for wings from June to October in 2022 and 2023, we documented chronic mortality of Leach’s Storm-Petrels transiting over Southern Bill, the most eastern point of land at Cape Freels, in northeastern Newfoundland and Labrador (NL), Canada. We observed Vulpes vulpes (Red Fox) leaping into the air to predate on flying birds and estimated this predatory behavior to kill a minimum of 320–850 individuals each year, with nightly mortality rates highest in June and lowest in September and October and impacting only adult birds. Long-lived species with a delayed breeding strategy, such as Leach’s Storm-Petrels, are inherently resilient to juvenile mortality, but are sensitive to small increases in adult mortality leading to population declines. Considering recent population declines, regular monitoring of major Leach’s Storm-Petrel colonies on NL’s northeast coast should be prioritized, as should surveying islands that are known to host Leach’s Storm-Petrels but have not been formally censused.

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