Wind-induced collision mortality in Grey-headed Albatrosses breeding on Marion Island

• Main Authors: 3rd World Seabird Conference 2021, Schoombie, Janine
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Underline Science Inc. 2021
• Subjects: Climate Change; Ecosystem; Antarctic; Kyle; Antarc*; Marion Island
• Online Access: https://dx.doi.org/10.48448/npkr-zs26; https://underline.io/lecture/34555-wind-induced-collision-mortality-in-grey-headed-albatrosses-breeding-on-marion-island

Abstract: A significant portion of the global population of Grey-headed Albatrosses (Thalassarche chrysostoma; Endangered) breed on sub-Antarctic Marion Island (46°53′ S 37°44′ E). Although most pairs breed on coastal cliffs, ca 4000 pairs breed on an inland ridge. These birds occasionally crash into the valley below the ridge, with birds either dying on impact or as a result of starvation if they are unable to take off again due to injury or absence of suitable wind conditions. We determined the number of birds affected and their distribution within the valley by counting carcasses and stranded birds in the valley on a regular basis between 2017 and 2019. Of the carcasses recovered, almost half are juveniles presumably killed during their first flight, with 41±23 killed per year (2.4% of chicks fledged each year). On average 45±21 adult carcasses were recovered each year, which represents 0.6% of the annual breeding population along the ridge, making wind-induced collision mortality a significant cause of death for a species that has a natural mortality rate of only ca 4% per year. Wind measurements taken in the area show this region is associated with high turbulence and gustiness. Simulations of wind around the ridge, using computational fluid dynamics (CFD), show that the flow over the area with the highest crash density is characterised by a concentrated down-draft under specific wind conditions. Although albatrosses are efficient at detecting and exploiting wind gradients at sea, operating near ground can be extremely risky, as these birds lack the power needed to respond to strong turbulence and downdrafts that are commonly associated with steep terrain. Crashes represent a source of mortality that is rarely considered. Further studies are needed to ascertain which wind conditions are most risky, whether they reduce the risk of crashing by avoiding taking off or landing under these conditions, and how the birds might be impacted by changing wind regimes. Simulating changes in wind speed and direction would aid in understanding the potential effects of wind as a factor of climate change on the local wind patterns and, subsequently, the population dynamics of Grey-headed Albatrosses breeding on Marion Island. Authors: Janine Schoombie¹, Stefan Schoombie², Kyle Goddard¹, Emily Shepard³, Peter Ryan⁴, Lelanie Smith¹, Ken Craig¹ ¹University of Pretoria, ²Nelson Mandela Metropolitan University, ³Swansea University, ⁴FitzPatric Institute of African Ornithology, University of Cape Town