Graduate Thesis Or Dissertation
 

Habitat selection, reproductive success, and site fidelity of burrowing owls in a grassland ecosystem

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  • I used a comparative and experimental approach to examine nest habitat selection, reproductive success, and nest site fidelity of burrowing owls (Athene cunicularia) in a large, non-fragmented grassland in southwest California. In 1999, I compared habitat characteristics between nest sites (n = 31) and randomly selected, unoccupied burrows (n = 31) in the local vicinity of the nest (paired burrows). In 2000, I compared habitat characteristics between nest sites (n = 33) and randomly selected, unoccupied burrows (n 32) within the study area (unpaired burrows). I examined reproductive success and variation in nest habitat characteristics, diet quality, and intraspecific competition using data from 1998, 1999, and 2000. I experimentally (n = 11 control and 11 treatment nests) assessed the effect of satellite burrow (multiple auxiliary burrows near the nest) use on productivity and behavior. I found little variation in habitat between nest sites and unoccupied burrows. Habitat selection was not strong when nests and unoccupied burrows were spatially correlated (paired burrows). However, nest sites had a larger number of large diameter burrows, satellite burrows, and perches than the unpaired burrows. Nest success ( I young fledged) and productivity (the number of young alive at 14 -21 days) varied substantially among some years, though the habitat variables I tested did not explain reproductive success when both failed and successful nests were evaluated. When nests were successful, productivity was influenced by rodent consumption. Nest fidelity within the breeding season was highly correlated with nest success. Nest abandonment occurred at 83% (n = 15 of 18), 92% (n = 12 of 13), and 83% (n = 20 of 24) of the failed nests in 1998, 1999, and 2000, respectively. Results of the experimental manipulation of satellite burrow access showed that productivity did not differ between groups but demonstrated that burrowing owls will adjust their behavior to use satellites. Owls in the treatment group (71%; n = 5 of 7) responded by moving their families to areas with access to satellite burrows but none of the control group owl families moved. This study illustrates the importance of identifying critical factors affecting reproductive success of burrowing owls in large grasslands. Maintenance of burrowing mammal populations to provide nest and satellite burrows will be important for protecting burrowing owls. Also, temporal dynamics influenced reproductive success. Habitat characteristics that enhance foraging ability may benefit productivity, especially in years of low rodent numbers. Furthermore, temporal variation in nest success may lead to low nest site fidelity.
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