Red-Shouldered Hawk (Buteo Lineatus) Distribution, Productivity, Parasite Intensity, and Nesting Habitat on Marinette County Forest in Northeast Wisconsin

Abstract

Red-shouldered hawks have been listed as threatened in Wisconsin since 1979 and currently the effort to manage the birds and their habitat is reactive. Nest sites often are found during the cruising or marking stage of timber harvesting. If nest sites are known before initiation of timber harvest, foresters can employ a proactive approach to manage red-shouldered hawks. Marinette County Forest (MCF) encompasses approximately 94,000 ha in northeast Wisconsin and is the 2nd largest county forest in the state. Our objectives were to locate red-shouldered hawk nests on MCF, monitor nest productivity, evaluate blood parasites of nestlings, investigate nest site selection, and compile forest management recommendations for MCF because the state of Wisconsin has no published forest management guidelines for the species. During the spring of 2006 and 2007, we conducted call-broadcast surveys at 1,121 calling stations along forest roads and trails in MCF. One-hundred twenty one red-shouldered hawk responses were used to locate 41 occupied nesting territories. In 2006, 20 territories were active, 11 (55%) were successful and 28 nestlings successfully reached fledgling age. Productivity in 2006 was 1.4 young per breeding attempt and 2.6 young per successful nest. In 2007, 25 territories were active, 9 (36%) were successful and 20 nestlings successfully reached fledgling age. Productivity in 2007 was 0.8 young per breeding attempt and 2.2 young per successful nest. Research on red-shouldered hawks in Wisconsin has mainly focused on long-term monitoring of nest productivity and nest-site fidelity. Results suggest that productivity is low in this part of their range, but causes for low productivity have not been determined. Blood parasites can cause severe anemia or death in nestling raptors, but little is known about blood parasites in red-shouldered hawks and nestlings have not been evaluated for blood parasites. Blood samples were collected from 11 nests in both 2006 and 2007. Leucocytozoon toddi was present in 90.5% (38/42) of the nestlings sampled and 100% (n = 22) of the nests had one infected nestling. Intensity of L. toddi infection ranged from 2 to 213 infected cells per 2,000 erythrocytes (0.1%-10.7%) and averaged 48.6 ± 58.3 infected cells per 2,000 erythrocytes (2.4 ± 2.9%). Intensity was high when compared to other studies. Prevalence and intensity of L. toddi was difficult to relate to nestling mortality because most nestlings were infected, however, L. toddi could possibly contribute to low productivity. To determine nest site selection, we compared habitat variables between active nest sites (n = 34) and stratified random or non-use sites (n = 61). Logistic regression with information-theoretic model selection identified a model with number of tree species and distance to closed wetland as the best-approximating model. Red-shouldered hawk nest locations were negatively associated with distance to closed wetland and positively associated with number of tree species in the plot. Discriminant Function Analysis (DFA) showed similar results as red-shouldered hawk nest site selection was best explained by number of tree species in the plot, distance to closed wetlands, volume of downed woody debris, number of small sawlogs, and distance to streams. Univariate comparisons indicated four of the five aforementioned variables were similar to the DFA model, however, snag trees were considered significant instead of small sawlogs. As a result, forest management for red-shouldered hawk nest sites should focus on tree richness, closed wetlands, down woody debris, and streams. Forest management recommendations from this study will increase the capacity of managers to locate and plan for continued persistence of this species on MCF.