Annual Dispersal of Endangered Burrowing Owls (Athene cunicularia): Implications for Estimating Survival
Creators: Wall, Morganne
Publisher: name: University of Alberta Library
Year: 2022

<p>The migratory population of Burrowing Owl (Athene cunicularia) in Canada has undergone significant declines over the past five decades. Monitoring of Burrowing Owl includes estimation of annual survival which is predominantly obtained using mark-recapture data. Survival is calculated based on individuals resighted each year. These survival estimates are very low and a fundamental question is why? Two methodological explanations exist to explain low survival estimates: 1) emigration outside the study area is not accounted for; and/or 2) individuals within study areas are not always detected. Both of these issues are likely to result in survival being underestimated. To accurately estimate survival, a better understanding of dispersal is required. I corrected survival estimates using three different methods that account for dispersal and detection error within finite study areas. I also evaluated whether mark-recapture estimates that integrated dispersal provides similar answers relative to using dispersal patterns from satellite-tracked individuals (tracked via platform transmitter terminals). First, I used dispersal simulations to determine what proportion of individuals was likely to move outside a fixed study area each year due to chance. This approach ignores detection error within a study area. Second, I used a standard Cormack-Jolly-Seber model (CJS) that adjusts for missed detections which could be caused by individuals moving in and out of study areas between years or being present within a study area but not detected. Finally, I used a spatial CJS model that accounts for missed detections in a spatial context by explicitly including dispersal patterns in survival estimates and actual nest locations within study areas. For juveniles, survival was estimated to be 0.060 with 95% CI [0.046, 0.077] from the dispersal simulations, 0.41 [0.33, 0.49] using CJS, and 0.036 [0.00, 0.17] from spatial CJS. For adult males, survival was estimated from the dispersal simulations to be 0.37 [0.28, 0.45], 0.32 [0.22, 0.45] using CJS, and 0.36 [0.30, 0.43] from spatial CJS. For adult females, survival was 0.17 [0.12, 0.21] using dispersal simulations based on banding, and increased to 0.29 [0.21, 0.37] using dispersal simulations based on tracking data. The standard CJS model estimated survival to be 0.26 [0.19, 0.34] which increased to 0.28 [0.19, 0.36] in the spatial CJS model. The detection probability parameters estimated from both the adult female CJS model (0.40 [0.25, 0.56] and spatial CJS model (0.42 [0.25, 0.59]) were used to correct the dispersal simulations for the platform transmitter terminal (PTT) tracked birds. The resulting survival estimates were much higher than the previous methods: CJS detection informed = 0.74 [0.44, 1.3], and spatial CJS detection informed = 0.69 [0.43, 1.2]. While each method increased the observed survival estimate compared to uncorrected methods, they all are limited by one or more factors that make it difficult to estimate true survival. Future studies must develop approaches that better incorporate detection and long-distance dispersal to correctly estimate survival for migratory species such as Burrowing Owls, especially when these numbers inform management strategies. In particular, more tracking of individual dispersal patterns using satellite tags is needed to better estimate survival rates for Burrowing Owl in Canada.</p>