Changes in technology and imperfect detection of nest contents impedes reliable estimates of population trends in burrowing seabirds

Abstract

One of the most fundamental aspects of conservation biology is understanding trends in the abundance \nof species and populations. This influences conservation interventions, threat abatement, and \nmanagement by implicitly or explicitly setting targets for favourable conservation states, such as an \nincreasing or stable population. Burrow-nesting seabirds present many challenges for determining \nabundance reliably, which is further hampered by variability in the quality of previous surveys. We used \nburrow scopes to determine the population status of Flesh-footed Shearwaters (Ardenna carneipes) at \ntheir largest colony on Lord Howe Island, Australia, in 2018. We estimated a breeding population of \n22,654 breeding pairs (95% CI: 8159-37,909). Comparing burrow scope models used in 2018 found more \nthan half of burrow contents (20/36 burrows examined) were classified differently. If this detection \nprobability is applied retroactively to surveys in 2002 and 2009, we estimate that the Flesh-footed \nShearwater population on Lord Howe has decreased by up to 50% in the last decade, but uncertainty \naround previous surveys’ ability to reliably determine burrow contents means a direct comparison is not \npossible. The decline in burrow density between 2018 and previous years adds further evidence that the \npopulation may not be stable. Our results highlight a need for regular surveys to quantify detection \nprobability so that as video technology advances, previous population estimates remain comparable. \nWe urge caution when comparing population counts of burrowing seabirds using different technologies, \nto ensure comparisons are meaningful.