Abstract
ABSTRACT
Fledglings of burrow-nesting seabirds are vulnerable to disorientation by artificial light at night (ALAN) and grounding in coastal human settlements, where most individuals presumably perish if not rescued. Accurate estimates of the effects of stranding on seabird populations remain elusive due to several levels of uncertainty, such as the number of stranded seabirds estimated to remain undiscovered by rescuers. One species subjected to stranding is the Atlantic puffin (
Fratercula arctica
). We hypothesized that the detection probability of puffin fledglings by the Puffin Patrol rescue program, operating in Newfoundland, Canada, is affected by light level, concealment level, and search effort. We deployed realistic puffin decoys in locations of varying light and concealment levels throughout two sites that are searched nightly by rescuers and measured the amount of time and search effort required until each decoy was found.
Approximately 78% more search effort was required to find a decoy in darkness (32.0 min) compared with illuminated conditions (18.0 min), and up to 100% more search effort was required to find a decoy placed in concealed conditions (35.5 min) than one in the open (17.5 min). After two hours of searching, on average over 10% of decoys were still not found, although each additional minute of search effort increased detection rate of an individual decoy by 0.6%. In combination with recent advances in our knowledge of seabird post-stranding behaviour, our study offers a first step in the development of correction factors which can be adapted to site-and species-specific requirements of other rescue programs around the world that rely on volunteers to search for stranded birds. Application of such correction factors will hopefully result in better estimation of mortality rates and their resultant effects on populations.
LAY SUMMARY
Each year when they leave their nests, young puffins and certain other seabirds become stranded in coastal towns, cannot re-orient to the sea, and are rescued by volunteers
It is unknown how many birds remain unfound each year, but this information is critical to estimate effects of stranding on populations
We deployed 3D-printed Atlantic Puffin decoys at real stranding locations in Newfoundland to determine if light levels, concealment levels, and/or search effort affect decoy detection by volunteers
In general, volunteers found decoys more easily in locations of brighter light and lower concealment, but still missed on average ≥10% of decoys after two hours regardless of search effort
Our results offer a first glimpse into the proportions of stranded seabirds potentially never found by rescue programs and thereby provide a starting point for estimating the true magnitude of stranding and its effects on populations