Nest-Site Selection And Renesting In The Blue-Gray Gnatcatcher (Polioptila Caerulea)

We monitored 93 nests of blue-gray gnatcatchers (Palioptila caerulea) from 1995-1997 in cast-central Illinois. Habitat selection was assessed at three spatial scales (I m sphere around nest, 0.005 ha plot and 0.04 ha plot). Leaf density at the 1 m scale was greater at nest sites than non-nest sites. This was the only variable differing between nest sites and paired random sites. Thus, habitat selection was not detected at the larger scales. Overall nest success was 11% (CI 95%: 6-18%); successful nests were significantly higher and farther from habitat edges than unsuccessful nests. Of 36 nests whose contents we could directly observe, 20 (56%) were parasitized by brown-headed cowbirds (Molothrus ater). Gnatcatchers abandoned 16 (80%) parasitized nests during egg-laying or the first 3 d of incubation, whereas only 1 (6%) unparasitized nests were abandoned during these stages. Daily nest success of renests was significantly lower (0.89 +/- 0.017) than that of first nests (0.94 +/- 0.009). The percentage of successful pairs was 36%. Habitat characteristics at a pair's second nest site were not different from its initial nesting attempt. Lack of specific habitat requirements and persistent renesting may be necessary for this species to achieve reproductive success in this study area.