What determines the distribution of red-naped sapsuckers in the East River Valley?

Abstract

The conservation of keystone species and their associates is of great importance due to the disproportionately large role they play in community and ecosystem structure. The Red-naped Sapsucker (Sphyrapicus nuchalis) is considered part of an intricate keystone species complex in the aspen forests of the Rocky Mountains, in which sapsuckers drill nest cavities in aspen infected with heartrot fungus (genus Phellinus) each year. Abandoned nests provide habitat for secondary nesters such as the violet-green swallow, tree swallow, and house wren. Furthermore, the sap wells they drill into aspen and willow trunks provide a high-carbohydrate meal for many species of mammal, bird, and insect. Because willow stands provide such a significant food resource to sapsuckers, previous studies have suggested that proximity to willow is correlated with sapsucker distribution, using sapsucker damage on aspen as a proxy for distribution. However, it is unknown whether other ecological variables within aspen groves shape or limit sapsucker distribution. In this study, randomly generated quarter-hectare plots within aspen groves were surveyed for a number of ecological variables (including distance to willow and extent of sapsucker damage), and multiple regression analysis was performed to determine which variables best explained variation in sapsucker damage across sites. My analysis tentatively suggests that, once differences in elevation, extent of infection by Phellinus, and distance to meadow edge are taken into account, proximity to willow does not explain variation in sapsucker damage. This study provides more information about the ecological requirements of this keystone species complex, which is integral to its preservation. Key Words: Sphyrapicus nuchalis, Phellinus tremulae, Populus tremuloides, red-naped sapsucker, trembling aspen, heartrot fungus, keystone species, community structure