EXPERIMENTAL FEEDING OF SUBURBAN EASTERN SCREECH-OWLS OTUS-ASIO HAS FEW EFFECTS ON REPRODUCTION APART FROM NONEXPERIMENTAL FACTORS

Experimental feeding regimes in the field with laboratory mice tested the null hypothesis that food does not influence the reproduction of E astern Screech-Owls. Dead mice were put in nest boxes. Only yearling f emales chose provisioned over unprovisioned boxes for nesting, but all owls took more mice from fed boxes in which they nested and increased consumption with the approach of egg laying. Experimental food did no t affect laying date, which was earlier in warmer springs and among ol der females; nor did it influence clutch size, which was increased by warmer temperatures, more natural food, and female age. However, exper imental food may have increased incubation attentiveness leading to mo re hatchlings and hence fledglings per egg in successful nests. Becaus e female age (breeding experience) and environmental factors were the strongest or only determinants of egg laying, the null hypothesis was supported with modifications about nest-site selection and hatching. F avorable natural factors offset most effects of experimental food, sug gesting that they should be measured and controlled statistically in o rder to place experimental food in its proper perspective in field sit uations. Also, the amount of experimental food relative to daily maint enance must be specified, because different amounts may alter natural provisioning and experimental results.