PARENT SESSION
Contributed Oral Session 52: Avian Nesting and Breeding
Tuesday, August 9, 8:00 AM - 11:30 AM, Meeting Room 524 A, Level 5, Palais des congrès de Montréal
Food availability and thermal constraints on nestling provisioning rates in birds.
Bolger, Douglas*,1, Hellmuth, Sara1, Mahar, Emily1, Walters, Eric1, Morrison, Scott2, 1 Environmental Studies Program, Hanover, NH, USA2 The Nature Conservancy, San Diego, CA, USA
ABSTRACT- Adequately provisioning food to rapidly growing nestlings is known to pose a significant physiological challenge to parent birds. Nestling provisioning rates were examined in three bird species in the coastal sage scrub habitat in coastal southern California, USA in 1998 and 2004. Provisioning rates varied with species, brood size, time of day, date (early vs late breeding season), and arthropod food availability as assayed by pitfall traps. Total provisioning rate was higher in the ground foraging California towhee (Pipilo crissalis) than in the ground-foraging rufous-crowned sparrow (Aimophila ruficeps) and the foliage-gleaning wrentit (Chamaea fasciata). Provisioning rate in all three species declined as the breeding season progressed. This appeared to be related to both food availability and weather. Food availability declined as the season advanced. In addition, thermal constraints on parental foraging appeared to be more severe late in the season. Particularly in the rufous-crowned sparrow, parents spent more time shading and fanning nestlings later in the season, apparently at the expense of foraging and provisioning. For two of the three species, rates of provisioning also declined significantly during the hot mid-day period. Only the California towhee did not display this pattern; provisioning rates were constant during the day for this species. This independence of temperature is responsible for the overall higher provisioning rates in California towhees. Provisioning rates were also significantly correlated with our plot-level measures of food availability.
Key words: birds, food resources, nestling provisioning, coastal sage scrub