Resource matching or mismatching: Does food limit breeding success of a native urban songbird?

Background/Question/Methods

Urban areas often have reduced avian species richness, but greater biomass and abundance per species than non-urban habitats as communities become dominated by a few apparently successful urban species. We looked for indirect evidence of enhanced per capita food resources during the breeding season (the urban food enhancement hypothesis) or of reduced per capita food availability (the urban food over-match hypothesis) in the Northern Mockingbird (Mimus polyglottos), which is more abundant in urban than non-urban habitats. We monitored 970 mockingbird nests during 2005-2008 in northern Florida, USA and quantified reproductive parameters associated with food availability.

Results/Conclusions

We found no significant differences between urban and non-urban habitats in hatching success, nestling mass or condition, brood reduction, nestling survival, or number of fledglings produced per successful nest. Number of fledglings produced per unit area was significantly higher in urban habitats in all years. We found that in one year pastures had larger clutch sizes and cameras placed at nests showed that non-urban nestlings were fed larger prey items. These differences, however, had no significant effects on nestling mass or on fledging success. The higher abundances of mockingbirds and higher production of fledglings per unit area may reflect greater food abundance per unit area in urban areas, but individuals appear to be distributed among habitats such that per capita food was roughly equally available in all territories (an ideal free distribution). Therefore, mockingbirds appeared to closely match food availability; urban food mismatches may be rare in species that establish breeding territories each spring but may be more likely in species that feed on non-defendable resources.