Alderney’s gannet nesting sites could be close to capacity
GANNET numbers in Alderney continue to increase, according to newly-published research, but their nesting sites could be close to capacity.
A paper published in Seabird journal reported continual increases in the populations of gannets on the island, with over 8,700 pairs split between Ortac and Les Etacs as of 2015, when they were last counted.
The first recorded sighting of gannets in Alderney was one pair spotted on Ortac in 1940.
The paper was written by ex-Ramsar officer Joshua Copping, Alderney Wildlife Trust chief executive officer Roland Gauvain, British Trust for Ornithology senior ecologist Dr Phil Atkinson and previous AWT staff member Jennifer Godber.
Ramsar officer for AWT Daniele Clifford said the trust was pleased. ‘The gannet colony population counts are carried out every five years, with the next count planned for 2020, when we will be interested to see if the trend continues,’ she said.
To count the gannets, aerial images of the Ortac and Les Etacs colonies were taken and four people counted the number of apparently occupied sites, AOS.
An AOS is defined as when one or two gannets are present on a site regardless of whether nests or nest material can be seen.
Sites with unattended chicks are included in the count but sites with non-breeding, immature adults are excluded.
To count breeding adults only is the standard method used by the Joint Nature Conservation Committee for species population counts.
An average of 5,960 gannet pairs were found at Les Etacs and 2,777 at Ortac.
This gives a total of 8,737 gannet pairs, which is 3% of the British population, 1.3% of the European population and between 0.9 and 1.2% of the world population of northern gannets.
Since 2005, the population on Les Etacs has grown by 2.3% each year but only 0.9% on Ortac and the growth rate of both colonies has slowed in the past decade.
Ortac may be at its carrying capacity – the total number of animals an area can support – and Les Etacs could also be nearing its capacity.
It is unclear what will happen when both sites reach carrying capacity.
Coque Lihou is another islet the gannets may start using as a new nest site.
However, like other islets, it becomes connected to Alderney at low tide, which may expose nesting birds to rats.
AWT is working with the States of Alderney to monitor and assess that.
Despite the good news on gannet populations, this seabird experiences many threats. AWT recently reported that 100% of Alderney gannet nests contain plastic.
Growing volumes of marine litter, proposed wind farms in main gannet foraging areas, increasing sea temperatures and overfishing of oceans are all problems faced by seabirds.