Processes underlying nest predation by introduced red squirrels (Tamiasciurus hudsonicus) in the boreal forest of Newfoundland

Lewis, Keith P. (2004) Processes underlying nest predation by introduced red squirrels (Tamiasciurus hudsonicus) in the boreal forest of Newfoundland. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Predator-prey relationships are an important element of population and ecosystem dynamics, and influence the evolution of phenotypic traits, life-history strategies, and behaviour. Predation of songbird nests has been intensively studied from these perspectives, and implicated in declining songbird populations, although results vary among studies. However, few studies have explored ecological mechanisms that could influence nest predators. Red squirrels (Tamiasciurus hudsonicus) are an important nest predator throughout their range, and have been introduced to the boreal forest of Newfoundland. Newfoundland is an ideal system for studying nest predation due to the low habitat and nest predator diversity relative to the rest of the boreal forest. Furthermore, Newfoundland presents an opportunity to test the influence of introduced species on a boreal ecosystem. -- Within a predator assemblage, some predators have stronger interactions with their prey than others. I showed that exclusion of red squirrels caused a significant decline in nest predation, especially on ground nests. Unlike other regions of North America, there is no compensatory predation by other predators, i.e. red squirrels are the dominant nest predator. At a landscape level, red squirrel abundance and habitat use are influenced by gaps in the forest canopy created by the processes of disturbance and succession. Herbivory by introduced moose (Alces alces) and snowshoe hare (Lagopus americana), alters the vegetation in these gaps, indirectly influencing red squirrel predator avoidance behaviour. The result is substantially lower nest predation in gaps than in adjacent forest as reflected by patterns of red squirrel abundance. Finally, in an experiment testing multiple hypotheses, I found that nest predation was modestly influenced by red squirrel density but not nest concealment. I also tested a foraging theory based model of nest predation. This model predicts that variations in predator type, nest defense, alternate food for nest predators, and nest location influence nest predation, but I found that only supplemental food influenced nest predation. -- This work demonstrates that understanding nest predation requires a knowledge of the nest predator assemblage and interactions therein, the mechanisms by which large scale ecological processes and interactions indirectly influence nest predator behaviour, and nest predator density and foraging ecology.

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