Breeding Success!

Thursday 7th September comments: The numbers are crunched and the figures are in. Our friends at the Centre for Ecology & Hydrology (CEH) monitor several key seabird species on the island during the summer months, involving long hours and sleepless nights (some of the work involves 03:00 am starts!). Mark Newell leads the research team and the results of this season are extremely encouraging (in times of doom and gloom for seabirds nationally as CEH have concluded:

Results:

  • Guillemot breeding success at 0.74 chicks per pair laying was average.
  • Razorbill breeding success at 0.62 chicks per pair laying was average but the highest since 2010.
  • Puffin breeding success at 0.87 chicks per pair laying was well above average and the highest since 1989. Proving to be largely unaffected by the heavy rains.
  • Kittiwake breeding success at 0.94 chicks per completed nest was well above average for the fourth consecutive year.
  • Shag breeding success at 1.67 chicks per incubating nest was well above average for the 10th consecutive year.
  • Fulmar breeding success at 0.40 chicks per incubating nest was average although down on the previous four years.

In addition to recording the breeding success of the seabirds CEH mark a sample of birds with a unique combination of colour rings and by spending hours and hours searching for them each season we are able to ascertain the proportion of the population that return each year. This complements the all-isle counts carried out by SNH and goes some way to explaining the varying population changes.

Results:

  • Guillemot return rate at 84.2% was the only species below average and the lowest since 2007. A surprising result given the high attendance at the colonies during the preceding winter.
  • Razorbill return rate at 94.7% was above average and the highest since 2010.
  • Puffin return rate at 89.3% was above average.
  • Kittiwake return rate at 88.5% was the fourth highest on record.
  • Shag return rate at 93.9% was the highest on record.

The high return rate of kittiwakes helps explain the increased 2017 population count carried out by SNH. The 2016 return rate was also very high suggesting that the lower population count that year was due to a proportion of the birds being present but choosing not to breed.  Coupled with the high breeding success of the last few years there maybe signs that kittiwake numbers on the Isle of May could increase again in the next few years as those young are recruited into the population.

Why was 2017 such a productive season? Food supply is a likely cause and analysing samples obtained this year is currently ongoing.  For those results watch this space.

For more information check out: http://www.ceh.ac.uk/our-science/projects/isle-may-long-term-study

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