Modelling variability and estimating power to detect change in Adélie penguin fledgling weights
Statistical models of variation in Adélie penguin fledgling weight data were used to examine the power to detect a change in fledgling weights after an impact. The statistical models were developed from first principles and incorporated both within- and between-year variability of fledgling weights. These models assume that data are collected during a fixed CEMP five-day period corresponding to the average peak fledging period. Modelling assumes that fledgling weights are likely to respond to resource availability as a step change represented as either a percentage increase or decrease after an impact. Fledgling weight was found to decline through the fledging period each year, but there was no evidence that the rate of decline differed between years. A consequence of this finding is that it may be possible to simplify future monitoring, such that fledgling weight is measured at a single time each year, without substantial loss of power to detect change. Further modelling work is identified to investigate this possibility. Modelling also indicated the potential for reducing the number of birds weighed in each five-day period from 50 to 30 without substantial loss of power. If practical, these findings could have substantial benefits by simplifying data collection.