Information from Bird Nests Monitored on the Colville River Delta, Alaska, 2011–2018

We used a variety of methods to determine the date on which a nest was initiated. The most accurate information on nest initiation is derived when a nest is found during the lay period. With such nests, we applied an egg-laying rate of 1 egg/day to determine the day on which the first egg was laid. If an egg was found during the incubation period, we used an egg floatation technique (Liebezeit et al. 2007) to estimate the age of the nest and used an Excel-based calculator from Brown et al. (2014) to estimate the date on which a nest was initiated. Such estimates are typically accurate to within ~3 days, and are useful for determining subsequent nest visits to ensure that the fate of the nest is documented accurately. If a nest whose eggs were floated was subsequently depredated or abandoned, the estimate of initiation date based on the floatation technique served as our best estimate for initiation. If, however, a nest whose eggs were floated was subsequently observed to hatch, we refined the initiation date estimate based by back-dating from the date of hatch by substracting the species-specific estimates of incubation duration (Brown et al. 2014) and the relevant clutch size (again assuming an egg-laying rate of 1 egg/day) for each such nest.