Additional methods for Ardia et al.
Nests were checked daily during egg laying to determine clutch initiation date and clutch size. Nests were visited daily near the end of the incubation period to determine actual hatching dates, hatching success, and the number of eggs that hatched each day. Four days after clutch completion, each breeding female was captured, weighed, and measured. Body mass was measured with a digital scale to the nearest 0.1 g. Head-bill length and the longest primary wing feather length were also recorded. Plumage was used to distinguish between yearling and older females.
When possible, broods of similar size were matched, otherwise only broods differing in one nestling were matched. If a brood of five was swapped with a brood of six, three nestlings were swapped. Only two nestlings were swapped between a brood of five and a brood of four. To swap nestling, we reweighed nestlings on day 3 and stratified nestlings by mass for swapping. For example, in a brood of six, we randomly chose one of the rank 1-2 nestlings, one of the rank 3-4 nestlings, and one of the rank 5-6 nestlings. In a brood of five, if three nestlings were swapped, a rank 1-2, a rank 3, and a rank 4-5 nestling was swapped. This method allowed for similar average body mass and coefficient of variation in broods on day 4 (average brood mass t31 = 0.9, P = 0..37; CV t31 = 0.6, P = 0.55), as well as similar brood size (t31 = 0.03, P = 0.97.
Insect sampling began prior to egg-laying and continued until the end of the nestling period. The sampler was located in the same open field in which nests were located; habitat was homogenous throughout and females were observed traveling across the entire study area to forage. After removing seeds and other debris, insect samples were dried in a drying oven for 48 hrs. We weighed the resulting samples to the nearest 0.1 mg on an analytical balance. For each female, insect availability and average temperature were averaged over the length of the incubation period. Insect biomass showed no trend over the breeding season (P = 0.6, R2 = 0.002).
Fifty-minute visual feeding observations were conducted on nestling days 8 and 13 for each nest, an age where feeding visits accurately reflect food delivered to the nest (McCarty, 2002). Nests were paired such that cross-fostered nests were observed simultaneously to control for the effects of weather, time of day, and insect availability. A feeding visit was recorded when 50% of the adult’s body entered the nest box. Provisioning males and females were differentiated by marking females with a patch of typewriter correction fluid between the wings.
iButton dataloggers do not affect female behavior, as there were no qualitative differences in behavior between control nests with dataloggers and nests without (Hartman and Oring, 2006; Weidinger, 2008)Ardia, D. R. unpubl. data). Onset of incubation from temperature profiles was determined using previously established criteria (Ardia et al., 2006a). To record internal nest-box temperature, an additional datalogger was attached to the nest-box wall 6-8 cm above the top of the nest, and at least 4 cm from the sides and top of the box. Ambient temperature was recorded via a datalogger in the shade under a centrally-located nest-box.Prior to placement in the field, each iButton datalogger was compared against two independent instruments: a HOBO U12 Thermocouple thermometer (Onset Corporation, Bourne, MA) and a Roetemp TM99-A Thermometer (Roetemp, San Diego, CA). Dataloggers that deviated by more than 0.5°C from these thermometers were not used in the study. We validated the effectiveness of iButtons for measuring incubation behavior using visual observations and video cameras.