An inexpensive method for quantifying incubation patterns of open-cup nesting birds, with data for black-throated Blue warblers

Quantifying incubation patterns has often involved long observation periods in the field, video cameras, or the use of other electronic devices that sometimes require the partial destruction of clutches and insertion of artificial eggs. In this study, we used an inexpensive, nondestructive method involving temperature probes combined with data loggers to examine the incubation rhythm of female Black-throated Blue Warblers (Dendroica caerulescens). The method provided detailed records of on–off patterns for females for selected 24-h periods during incubation. Female warblers spent an average (±SE) of 64.0% of daylight hours incubating in bouts lasting 20.5 ± 1.5 min and made 2.4 ± 0.1 departures from the nest/h on trips that lasted 10.6 ± 0.7 min. Incubation bouts were longer and females spent more time incubating per hour in the mornings and late afternoons than at mid-day. Older females had longer incubation bouts and tended to have shorter incubation periods than did yearling females, suggesting that experienced individuals were more effective incubators. Because of its ease of use and because nests with probes were not depredated at a higher rate than controls, we suggest that the temperature probe/data logger method is an efficient and effective way to quantify incubation rhythms for open-cup nesting birds.