Abstract. Coloration of exposed eggs of ground-nesting birds is thought to reduce predation, with camouflaged eggs that more closely match the area around the nest having greater survival. We tested this hypothesis using digital photographs of 374 Mountain Plover (Charadrius montanus) nests and the substrate surrounding each nest to produce covariates in nest survival models. Covariates included values representing the difference between the color of the eggs and that of the substrate, the average egg and substrate colors, and variation in both egg and substrate color. Nest survival decreased as the difference between the color of the eggs and substrate increased (accounted for by two different methods of quantifying color: b DE ¼À0.021, SE ¼ 0.024, 95% CI ¼À0.069, 0.026 and b DRGB ¼À0.004, SE ¼ 0.005, 95% CI ¼ À0.013, 0.005) and increased with increasing variability in substrate color (b DSDsub ¼ 2.624, SE ¼ 2.846, 95% CI ¼À2. 954, 8.202), although after model-averaging these effects were not well-supported. Model-averaged estimates of daily nest survival ranged from 0.90 to 0.98 (unconditional SEs from 0.004 to 0.129). Our results support the egg crypsis hypothesis because eggs that closely match their surroundings have greater survival.

Communal roosts are an important aspect of Turkey Vulture (Cathartes aura) biology, but remain inadequately studied. We observed the use patterns of Turkey Vultures at a communal roost in northeastern Iowa from their arrival on 17 March 2005 to their departure on 19 October 2005. The roost was on a forested hillside and vultures roosted below the forest canopy in 10 live deciduous trees, spending an estimated 10–16 h per day in the roost. The birds also used nearby pre‐ and postroost perch sites, and formed pre‐ and postroost kettles near the roost site. The number of vultures using the roost ranged from about 20 early in the season to a peak of 281 on 4 October. The apparent pattern was one of moderate and fluctuating numbers early in the 7‐month season, increasing numbers in the middle of the season, and high and fluctuating numbers late in the season. Hatching‐year vultures began to appear at the roost during the last week of August. The mean monthly time of departure from the roost ranged from 3 min before sunrise to 131 min after sunrise. Vultures departed the roost significantly later in the morning during the summer (June, July, and August) than during other months (April, May, September, and October), probably due to differences in soaring conditions (longer thermal generation times during the summer) and available foraging time (longer days in the summer).