11 September 2012

What happened to the Pied Flies?

Many nest recorders (www.bto.org/nrs) and ringers (www.bto.org/ringing) have reported low breeding success among the populations of Blue and Great Tits that they have been monitoring during the 'summer' of 2012, with bad weather and a related lack of invertebrate food taking their toll at a number of sites. Migrant Pied Flycatchers have similar habitat preferences and diets, but breed slightly later - Peter Coffey from Merseyside Ringing Group summarises the season as experienced by his study population.

Upper Valley

"What a strange year for my Pied Flycatchers in Denbighshire! It started so well with the earliest record of a female nest-building on 14th April, followed by the first egg on 25th April (site record – 24th April). Four more clutches were started on 28th/29th April but then almost nothing until a late rush between 9th-13th May. Numbers of nesting pairs were slightly below average but nothing to worry about.

Then all hell broke loose! 36% of Pied Flycatcher nests were predated at the egg stage, compared to the norm of 5%. Chief suspects were Weasel and Wood Mouse; smears of blood on the inside of two boxes suggest the females were taken.

The surviving nests achieved remarkably good success considering the weather with 85.7% of chicks fledging. As the size and frequency of caterpillars in the food diminished towards the end of the season it was not surprising that weaker chicks in later broods perished.

Four very late nests were probably re-lays by females that had lost their first clutch (one female had been ringed earlier at a nest that was subsequently predated). By any standards their fate this year was abysmal – 19 eggs converted into 9 chicks of which only one fledged! It was a combination of egg predation (again), addled eggs and chick death. It reduced the overall chick/fledging success rate to 81.2% and the egg/fledging success rate to 49.2%.

Pied Flycatcher male

My RAS work also suffered. Early predation occurred before I’d had a chance to trap sitting females and it’s often a struggle to trap males at late nests – they’ve started their moult and can be disinterested! So imagine my joy when I trapped the only male seen at any of the late nests – and it was a control (not ringed locally), my only one of the season!"

Thanks for Peter for letting us know and for the photos.

1 comment:

  1. Will nest boxes be left for future predation?