Spatiotemporal Patterns of White-Tailed Deer Habitat Use on Hill Island in Thousand Islands National Park of Canada

Abstract

White-tailed deer (Odocoileus virginianus) are hyperabundant in parts of Thousand Islands National Park because of their ecological impact on its forests. To manage the high number of deer on Hill Island, an annual population reduction occurs in the park. This study is intended to inform managers on the seasonal habitat use of the island by deer, so they are better able to evaluate impacts on affected forests. Winter aerial surveys (10 historical surveys from 1992-2006, supplemented by surveys in 2018 and 2019) and seasonal deer pellet counts (winter 2018, summer 2018, winter 2019) were conducted to estimate resource selection and habitat use on Hill Island in Thousand Islands National Park. Recent aerial surveys were also used to test locational accuracy and detectability of observations during flights. Relative predictive surfaces were generated in a geographic information system where they could be compared to seek patterns of deer use contingent on method or season. Winter aerial surveys did not corroborate winter pellet surveys well. Detectability of deer during aerial surveys varied by cover type, and biased model results towards less important habitats. Model validation indicated that the selected aerial model had modest predictive capability at the scale used. Conversely, hilltops and areas with a high probability of hemlock occurrence, concentrated on the centre of the island, were judged to be high relative use areas by deer in winter when using pellet counting. Summer use was not well-predicted by any of the habitat variables tested, and spatial patterns were different than winter estimates. The results suggest that forest restoration and monitoring efforts in the park might be best focussed on upper elevation, high hemlock content areas in the centre of Hill Island to account for concentrated winter use there. Results also point to the need for an assessment of habitat use at a broader spatial extent to examine seasonal deer movement within the entire Thousand Islands region.