Estimating breeding success in Newfoundland Atlantic puffin colonies: A methodological comparison

Raul Zabala Belenguer, Katja Helgeson Kochvar , Antoine Morel , Amy C Wilson, Sabina I Wilhelm, Pierre-Paul Bitton

Atlantic puffin (Fratercula arctica) colonies in the Eastern Atlantic have been experiencing decades of declining numbers, trends revealed by the presence of breeding success monitoring programs. Collecting such data is challenging because puffins have their nest inside burrows, which are usually assessed by hand or burrowscopes. However, it is not clear how comparable the results from these two techniques are. Here, we created a field realistic double-blind experiment to compare the performance of these two assessment methods on Great Island, Newfoundland, Canada. We also surveyed the breeding success of five colonies across the province in 2021 and 2022 and compared them to historical data. Our experiment reveals that handgrubbing and the use of a burrowscope do not generate comparable results and that survey method and observer identity influence breeding success survey outcomes. Burrowscopes generate the most accurate assessments, but they are less consistent between observers than handgrubbing when detecting eggs and chicks. Nevertheless, our results together with the available historical data show successful breeding success across the province, higher than other large Atlantic puffin colonies in the East Atlantic. Our study provides evidence that Newfoundland hosts the largest stable/growing Atlantic puffin colonies in the world for this declining species.