The predatory behaviour and impact of red foxes (Vulpes vulpes) on the seabird colonies of Baccalieu Island, Newfoundland

Sklepkovych, B.O. (1986) The predatory behaviour and impact of red foxes (Vulpes vulpes) on the seabird colonies of Baccalieu Island, Newfoundland. Masters thesis, Memorial University of Newfoundland.

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Abstract

The predatory behaviour of red foxes (Vulpes vulpes) in relation to a large multi-species seabird community was studied on Baccalieu Island, Newfoundland, from 1983-1986. Fox diet was assessed by examining faecal composition, avian prey remains and larder hoarded prey. Leach’s Storm-Petrels (Oceanodroma leucorhoa) made up of 75% of scat by wet weight, 89% of remains and 95% of prey items in and scattered about larders. Black-Legged Kittiwakes (Rissa tridactyla), Atlantic Puffins (Fratercula arctica), Common Murres (Uria aalge) Northern Gannets (Sula bassanus) and Herring Gulls (Larus argentatus) formed 19% of scat by wet weight and 11% of remains. Comparisons are drawn between seasons and different methods of analysis. -- The Leach’s Storm Petrel population was estimated at 3,360,000 ± 317,000 adult breeding pairs. Based on harvest levels and the estimated energy requirements of the resident fox population, 31,000 ± 3,000 adult storm-petrels would be taken annually. Factors which tend to keep predatory impact at low levels are (1) the massive size of the storm-petrel colony and (2) the scarcity on lack of winter food for the foxes. The high availability of Leach's Storm-Petrels also appears to hold impact on each of the other seabird species nesting on Baccalieu Island at < 1% of their adult breeding populations. The presence of foxes on Baccalieu Island may also deter ground-nesting avian predators (i.e. Herring Gulls and Great Black-Backed Gulls (Larus marinus)) from nesting and from preying extensively on the resident burrow-nesting seabirds on the island. -- Experiments on the scatter hoarding behaviour of red foxes were conducted in a semi-natural enclosure at Salmonier Nature Park. At low levels of food deprivation, increased levels of prey abundance were found to decrease the time spent in search of a cache site by foxes. Increased levels of food deprivation and prey abundance were also suggested to increase the motivation to hoard as evidenced in the decrease in mean time of prey pickup to cache initiation interval. The time spent caching and subsequent return to the prey patch were not significantly altered by the manipulations and possible reasons for the lack of experimental effect are discussed. Ninety-seven percent of all prey items set out were cached, of which, 75% were later recovered. On average, 54% of the available caches were recovered within 192 h of being set out, at a mean rate of 9.3% recovery/day. These present findings are considered in light of optimal foraging theory.

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