Summary of the 2010 seabird breeding season on the Isle of May

After a series of very poor breeding seasons for seabirds on the Isle of May NNR, the 2010 season continued the marked improvement shown in 2009 for most species. Overall the season was one of the most successful in recent years.

Of the six species studied intensively, European shag had its highest productivity on record with only black-legged kittiwake and fulmar having productivity below average. All other species studied had their most productive season for at least seven years.  European shags had the highest return rate on record, while return rates for all other species were the highest since at least 2003. 

Although lesser sandeels remained the main food of young Atlantic puffins, razorbills and common guillemots fed their young mainly on clupeids, while European shags brought in mainly sandeels aged one year or older. For the first year since this study began clupeids formed a larger biomass than sandeels in the diet of black-legged kittiwakes.

Highlights

• Northern fulmar breeding success (0.34 chicks per incubating pair) was lower than 2009 and below the long term average.
• European shags had the most successful season on record (2.04 chicks per pair), eclipsing the previous record set last year. Return rate was the highest on record at 95%. Unlike the previous four years, the food was very consistent, with sandeels making up 91.5% by mass of the diet. Examination of sandeel otoliths indicated that all were from the adult age classes.

• Black-legged kittiwakes had a poor season with productivity (0.29 chicks per incubated nest) well below the long-term average. However, some plots suffered unusually high predation by a pair of carrion crows during incubation and from gulls during chick-rearing. Adult return rate (89%) was the highest since 1988. The proportion of sandeel in the diet (44% by biomass) was the lowest on record, while the proportion of clupeid (55% by biomass) was the highest.  
• Guillemots had a successful breeding season (0.80 chicks leaving per pair), which continued the improvement recorded in 2009 after a series of poor breeding seasons. Similarly, return rate of adults (92.4%) was similar to 2009 and close to the long-term average, following low levels the two previous winters. Adults fed their chicks mainly on medium-sized sprats (84% by number).
• Razorbill breeding success (0.68 chicks leaving per pair) was above the long-term average. Adult return rate (95.2%) was the second highest ever recorded on the Isle of May. Chick diet was mainly medium-sized sprats that were present in 67% of the loads.
• Atlantic puffins had a successful season with 0.74 chicks fledging per pair laying. The return rate for adults (90.9%) was high and continued the improvement noted in 2009 following the poor showing over the two previous winters. Chicks were mainly fed 0 group sandeels (68% by number, 54% by biomass). Although sprats made up only 3% by number, their large size resulted in their contributing 40% of the diet by weight.