Sule Skerry – an overspill gannetry from Sule Stack

Abstract

Northern Gannets Morus bassanus first bred on Sule Skerry, Orkney, Scotland in 2003. A count made from photographs taken using a drone in July 2018 showed that the population had increased to 4,515 apparently occupied sites with a mean annual rate of increase of 19% between 2009 and 2018. As Gannet numbers increased, they displaced several hundred pairs of Common Guillemots Uria aalge and about 500 pairs of Atlantic Puffin Fratercula arctica. Ringing of Gannet chicks showed that some of the increase on Sule Skerry was due to immigration from Sule Stack 8 km away. Northern Gannets on Sule Stack appear to occupy all suitable nesting habitat, and the breeding population has been relatively stable at around 4,500 pairs for the last 100 years. The colony on Sule Skerry is now as large as that on Sule Stack. Given that there appears to be plenty of suitable nesting habitat for more Gannets on Sule Skerry, it seems likely that the colony will continue to increase to the detriment of the nationally important population of Atlantic Puffins.