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

Breeding success data in burrowing birds can be obtained using several techniques, but hand search (or handgrubbing) and burrowscopes are two of the most widespread. Breeding success performance can be important in detecting positive or negative population trends; however, it is not clear how accurate, consistent, and 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 in Atlantic puffin (Fratercula arctica Linaeus, 1758) burrows on Great Island, Newfoundland, Canada and produced correction factors to ensure the comparability between the data obtained from the two different methods. We complement these results by surveying the breeding success status of five colonies across the province in 2021 and 2022 and comparing them to historical data. Our results suggest that burrowscopes generate the most accurate assessments, but they might be less consistent between observers than handgrubbing when detecting eggs and chicks. Furthermore, our combination of surveys and historical data, corrected for comparability, show high breeding success across the province, better 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.