Linking foraging decisions to residential yard bird composition

Urban bird communities have higher densities but lower diversity compared with wildlands. However, recent studies show that residential urban yards with native plantings have higher native bird diversity compared with yards with exotic vegetation. Here we tested whether landscape designs also affect bird foraging behavior. We measured the amount of resources remaining, or giving-up densities (GUD) for final foragers on artificial food patches in residential yards in Phoenix, AZ, USA. We assessed how two yard designs (mesic: lush, exotic vegetation; xeric: drought-tolerant and native vegetation) differed in foraging costs. Further, we developed a statistical model to calculate GUDs for every species visiting the patch. Birds foraging in mesic yards depleted patches to a lower level (i.e. had lower GUDs) than birds foraging in xeric yards. After accounting for bird densities, the lower GUDs in mesic yards appeared largely driven by invasive and synanthropic species. Furthermore, yard design affected individual species behavioral responses. Species visiting trays in both yard designs had lower GUDs in mesic yards. Differences in the missed opportunity (alternative resources more abundant in xeric yards) and the digestive cost (moist conditions in mesic yards) both contributed to our results while predation costs did not. Enhancing the GUD method with our statistical model provided insights into how individual species and bird densities influenced the GUD. If the described differences we found in foraging behavior are indicative of differences in habitat quality, then this would lend additional support for native landscapes to help reverse the loss of urban bird diversity.