Non-breeding season ecology of the Cape Sable seaside sparrow (Ammodramus maritimus mirabilis) 1997-1998 field season final report

Dean, Tylan; Morrison, Joan; Eagle Environmental, Inc.

Executive Summary: To date, the majority of the research on the endangered Cape Sable seaside sparrow has been conducted during the breeding season, when sparrows are visible, vocal, and easy to locate. However, to effectively manage for this sparrow, it is essential to understand the sparrow's habitat needs and behaviors throughout all aspects of its life history. To document the movements and habitat use of sparrows during the non-breeding season when sparrows are secretive and difficult to consistently locate, we attached radio transmitters to 21 Cape Sable seaside sparrows between July and February. We evaluated the effects of transmitters on sparrows to ensure that there were no severe detrimental effects to the birds. None of the four condition indicators we employed suggested that sparrows with transmitters declined in condition. We radio-tracked 18 individuals for extended periods (1-7 months). These data suggest that sparrows are relatively sedentary, and maintain a non-breeding season home range that is larger than average breeding season territories. Individual sparrows were generally consistent in their scope and frequency of movements, and most birds moved approx. 160 meters between consecutive locations. Though many sparrows made longer movements away from home ranges at some point, most returned to their previous home ranges. However, three individuals did not return to previous home ranges, and settled 450, 6000, and 7000 meters from previous home ranges. These data indicate that sparrows are capable of moving long distances within the muhly prairies. No sparrows used habitats other than the open muhly- and sawgrass-dominated prairies. At the landscape scale, sparrows generally occurred in the open prairies. They perched in sawgrass sways and small tree islands, but appeared to avoid large tree islands and tree-lines. Additionally, sparrows regularly occurred within old agricultural areas, but avoided old-grove agriculture areas that contain clumps of tall sawgrass and small trees or shrubs. Micro-scale habitat selection models were not consistently able to distinguish between habitat characteristics at random points and at points used by sparrows. However, when we compared the use of micro-habitats by sparrows under different hydrologic conditions, we found that selection of most habitat characteristics changed relative to the water depth at the site. Sparrows used muhly-dominated sites less frequently as water depths increased, and used sawgrass-dominated sites and sawgrass clumps more frequently as water depth increased. Use of other habitat characteristics also changed relative to water depth. Hydrologic condition of the prairies is one of the most variable environmental characteristics. Interpolated topographies of our two study sites indicated that there is as much as 20- 30 em of topographic variation within areas as small as 1 km^2. Water levels remained hi$h throughout the non-breeding season, and one of our sites was still completely inundated in February. Sparrow surveys in the muhly prairies provided supplementary evidence that sparrows do not drastically change distribution or habitat use between the seasons. Comparisons of point counts and rope-dragging transects also showed that transects were more effective for determining whether sparrows were present at a site. We used a Kaplan-Meier survival estimator with a staggered entry design to determine survival probabilities for radio-marked sparrows. We documented 4 sparrow mortalities during our study period, and 5 radio-marked sparrows disappeared. The survival rate from these data for the 7- month monitoring period was 0.63. Other estimates of survival rates for Cape Sable seaside sparrows vary substantially, but there is no evidence to suggest that radio-marked sparrows suffer higher mortality rates than unmarked sparrows.