One common strategy to mitigate the loss of natural nest burrows for Burrowing Owls (Athene cunicularia) from ground-disturbing activities has been the installation of artificial burrows outside the disturbance area. I assessed the effectiveness of artificial burrows as a mitigation tool at two study sites in northern California. Parameters included nesting success at natural and artificial burrows; long-term occupancy rates of maintained and unmaintained artificial burrows; choice of burrow type (natural vs. artificial burrows) by owls raised in artificial burrows; and site fidelity and natal philopatry of Burrowing Owls raised in artificial burrows. I analyzed long-term datasets biologists collected from 1990 through 2012, including demographic data, band resightings, and burrow maintenance records. Nesting success at artificial burrows was significantly higher than at natural burrows at both study sites. At one site, nesting success at artificial burrows was 83% compared to 76% at natural burrows (P = 0.035); at the other site, nesting success at artificial burrows was 96% compared to 75% at natural burrows (P = 0.036). Artificial burrows that received annual surface maintenance were occupied for a significantly longer time (2.1 ± 1.9 yr; n = 57) than unmaintained artificial burrows (0.5 ±1.0 yr, n = 51; U = 561, P < 0.001) during the first 8 yr post-installation. Even with surface maintenance, occupancy rates declined from 44% (n = 25) of burrows occupied during the first year post-installation, to 28% (n = 15) of burrows occupied during the fourth year post-installation. Based on this decline, regular maintenance of the entire artificial burrow, including tunnel and nest chamber, may be crucial for longer-term use. Of 120 Burrowing Owls raised in maintained artificial burrows and resighted during subsequent breeding seasons, 70% occupied artificial burrows and 30% natural burrows. Only 3% of these owls occupied their natal burrow during the first nesting season post-fledging. Of those owls that were resighted during two or more nesting seasons, almost half (48%) occupied different artificial burrows from one year to the next; therefore, the number of artificial burrows at a management site should be sufficient to provide opportunities for Burrowing Owls to move between nest burrows from year to year.
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Vol. 52 • No. 2