29 May 2012

Cuckoo patience rewarded

Given the appalling weather conditions in April, it’s no surprise that the Reed Warbler breeding season got off to a really slow start in 2012. A team of BTO staff monitor two populations near Thetford, one on the Nunnery Reserve and one at a site near Mundford, collecting data for the Nest Record Scheme and the Constant Effort Sites ringing scheme.

The first egg recorded in 2011 was laid on the 1st May, with many birds incubating by mid-May. The strong headwinds experienced during migration and the reduction in reed growth under low spring temperatures have conspired to delay the 2012 season, however; while the first female started to lay on 7th May, many birds have yet to complete their clutches.

All this must have been very frustrating for the Cuckoos, which have been back and bubbling away at both sites since the middle of April (click here for the latest developments in the BTO Cuckoo project). Their desperation to lay may explain the relatively high parasitism rates of the early clutches, with Cuckoo eggs appearing in four of the nests at Mundford thus far, the first of which hatched on 23rd May.

Before and after – the first Cuckoo egg of the year and the chick shortly after hatching on 23rd May, taking a breather between removing the first and second Reed Warbler eggs from the nest.

The first Cuckoo egg in a Reed Warbler nest at The Nunnery was recorded on the 28th May, a welcome return after a complete absence of parasitism in 2011 (although the warblers may beg to differ) save for a single egg in a Dunnock nest. Cuckoos continue to be very active at both sites so it will be interesting to see whether we can top the total of 12 parasitised nests monitored in 2011.

Thanks to Dave Leech for the pictures and writing the blog post.

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