Abstract: Mate and nest-site fidelity are vital population parameters that affect population dynamics and breeding success. Research is needed to understand how these parameters perform when populations are declining. In a study addressing these issues, we characterized mate fidelity, nest-site fidelity and breeding dispersal in a declining population of urban burrowing owls (Athene cunicularia hypugaea) in northern California over a 17-year period from 1999-2016. Then, we examined factors that could affect those parameters including study year, age, breeding success the previous year, and years with a mate. Finally, we tested whether reproductive success--as measured by the number of emergent chicks--was affected by mate or nest-site fidelity, age, years with a mate or study year.
We used data from 65 banded burrowing owls for which we had three consecutive years of data, evaluating males and females separately. Mate and nest-site fidelity were strongly associated. Breeding success the previous year was an important factor in mate and nest-site fidelity for males while age was associated with mate and nest-site fidelity for females. However, for both males and females, the strongest relationship was between years with a mate and nest-site fidelity; the likelihood of nest-site fidelity increased the longer mates stayed together. No factors we tested were associated with breeding dispersal propensity or dispersal distance. When examining reproductive success, years with a mate was strongly associated with the number of chicks produced for both sexes; the longer pairs stayed together, the greater the number of chicks produced. Study year was not a factor in any of the analyses we conducted.
These results showed that, while the burrowing owl population declined precipitously during the study period, mate fidelity, nest-site fidelity and breeding dispersal parameters did not change. Thus, the population decline was not a result of a disruption of mate or nest-site fidelity behaviors. Rather, the decline was most likely due to a range of urban pressures such as increased predation, inadequate prey, habitat fragmentation and human disturbance. For burrowing owls to have the greatest reproductive success, they must be provided conditions that allow pairs to remain together. To achieve this, historic breeding sites must be protected over many years allowing mates to stay together in the same nest-site territory.
