Life on the edge: The Eastern Screech-Owl in Winnipeg

Cavity-nesting birds may be sensitive to urbanization due to changes in the availability of breeding resources. Nonetheless, the Eastern Screech-Owl has higher productivity and survival in suburbs than rural areas in the southern portion of its range (Texas). Densities and life-history traits of birds may differ in range peripheral areas, rendering generalization about the effect of urbanization difficult. I examined the population density, reproduction, habitat selection, and diet of Eastern Screech-Owls in Manitoba to test whether the patterns observed in Texas held at the northern periphery of the range, and whether such patterns would be more or less pronounced. I conducted a random-stratified survey across a rural to urban gradient and monitored nests in natural cavities and nest boxes. I collected data on diet and measured variables related to the cavity tree and at the habitat level at nests and unused cavities.;The differences in density, reproductivity, and breeding phenology between suburban and rural areas, as well as the mechanisms involved, are similar to those found in Texas, suggesting that, at least in this case, the influence of urbanization is not strongly mitigated by latitude.;Eastern Screech-Owl density was positively correlated with human density, peaking in medium to high-density suburbs. Screech-owls preferred riparian habitat but densities and breeding in residential areas versus greenspace did not differ. Brood sizes peaked in suburban areas, where fledging averaged five days in advance of rural areas. Owls selected habitat where canopy cover was relatively high, and with sufficient potential nest-sites close to some coniferous trees. They selected nest sites in taller trees, closer to water and with lower shrub density below the nest than unused cavities. They avoided potential nest sites with more buildings and higher domestic cat activity. Screech-owls had a more diverse diet with more vertebrate prey in low-density suburban areas as opposed to rural and high-density suburban areas. The mechanisms behind this pattern appear to be the urban heat island, reduced predation, greater diversity of prey, and favorable habitat alteration including planted conifers and buildings for roosting and more open vegetation. The percentage of rufous morph screech-owls in Manitoba has fallen from 6--11% in the 1920s to <1% today, whereas no decline has occurred in Minnesota or North Dakota. I argue that, based on differences in survival rates between color morphs in extreme cold, this is evidence of a northward range expansion facilitated by the anthropogenic influences noted above.