Tuesday, 5 May 2015

Nest moving Terns dodge high tides

They’re back! The first Little Terns returned to Ireland last month and the first Little Tern was seen back in Kilcoole on the 19th of April. It won’t be long before the wardens are back on site, the fences are up and the beautiful Little Terns start nesting again. Let’s hope that we have another bumper year in Kilcoole after last year’s record breaking season.

They're back! © Andrew Power and Peter Cutler (Picture taken under NPWS  licence) 

The return of the Little Terns has also been marked by the publication of a paper by the 2014 Kilcoole team in the latest issue of IrishBirds based on observations we took of a unique response by the Kilcoole Little Terns to a dangerous high tide. While we do everything in our power to protect the Little Terns in Kilcoole, some things are out of our control. A high spring tide allied with a strong easterly wind has the power to wash out an entire colony. This happened in 2012 at Kilcoole, destroying every nest. The terns that year didn't stand a chance as the tides were just too strong. The bad weather meant that 2012 was a particularly bad season for terns in Britain and Ireland but, luckily, terns can bounce back quickly when conditions are suitable (just look at the success of last year). Although high tides are an ever present danger to Little Tern colonies, last season the Little Terns showed us they are not completely helpless to the forces of nature.

Spring tides last year © Andrew Power

Last year high tides hit the colony during the peak of the breeding season. When the tide receded and we wardens could survey the damage, we feared the worst, with the seaweed line having been thrown over a large section of nests. Confirming these fears 12 nests had been completely washed away. However, to our surprise, 13 pairs of terns had managed to re-gather and move their clutches into new nest scrapes further up the beach after inundation by the tide. Though the movement of eggs into new nests has been observed in waders and waterfowl, most notably in the Piping Plover, this behaviour has never previously been recorded in a tern species.
We closely observed the outcome in these nests and unsurprisingly found that a significantly higher proportion of eggs from tide affected nests failed to hatch than from nests that were unaffected by the tide. The chill of the Irish Sea coupled with the mechanical damage caused by tide inundation were likely to have been (literally) a killer combination for the developing embryos within the eggs. However the 13 Little Tern pairs which had nests inundated by the tide still managed to produce 20 fledglings (out of 32 eggs in these nests). This was a remarkable achievement given the circumstances, attesting to the robustness of the tern eggs and adaptability of the parent birds, key attributes when living in an unpredictable environment.
We also observed this behavior from a pair of Ringed Plover earlier in the year. Unfortunately the eggs did not hatch but they gave themselves a fighting chance. That combined with the hard work of the wardens and volunteers will hopefully ensure a bright future for the birds in Kilcoole.

The original nest scrape is on the left and the 4 eggs moved by the parents can be seen on the right © Andrew Power

Blog post by
Andrew Power and Darren O'Connell

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