Monday, 20 July 2015

Roding at Rotherfield

by Andrew Hoodless, Head of Wetland Research, GWCT

Owing to the presence of several large blocks of diverse woodland at Rotherfield Park and, probably also, the fact that minimum tillage is employed with most of the crops, the estate supports large numbers of woodcock in winter.

Last winter, we ringed 149 woodcock as part of an ongoing study to quantify rates of wintering site fidelity. However, not all the woodcock are migrants and each summer we conduct counts of displaying males to provide an index of population status.

From late February, the unique roding call can be heard over the woods at dawn and dusk. Once the hubbub of blackbirds, song thrushes and robins laying claim to breeding territories has dwindled in the evening, a shrill whistle announces the woodcock’s dark silhouette above the canopy and its peculiar frog-like croaks can be heard as it passes overhead.

The ‘roding’ or display flights made by male woodcock are quite different from the rapid flights to and from cover at dawn and dusk in winter. Their purpose is the location of a receptive female with whom to mate and they consist of slow patrolling at tree-top height, announced by the unmistakeable call.

The term ‘roding’ comes from the Anglo-Saxon word ‘rode’ for a woodland ride, because the birds often seek out and follow rides and the edges of clearings. These are where the females will be waiting to get the males’ attention.

In March and early April, roding may only last 20-30 minutes, or barely take place at all on cold evenings, but from mid-May to early July the evening roding period lasts for about an hour.

Woodcock nests are notoriously difficult to find
The conspicuous roding displays of male woodcock offer a unique opportunity to survey a species that is otherwise seldom seen in summer. However, early radio-tracking studies in the 1980s showed that woodcock males do not hold territories and do not pair for the breeding season in the way that most other waders and woodland birds do.

Instead, roding males patrol areas of suitable breeding habitat and older, more dominant birds obtain most matings with females. The male stays with a female only until she commences egg-laying and then resumes his crepuscular search for another female in his urge to pass on his genes. The female alone is responsible for incubating the eggs and rearing the young.

This potentially causes a problem with surveying woodcock because one or more woodcock may pass over the same point in a wood on a given evening. Our breakthrough came when we examined recordings of woodcock calls and found that each male has a slightly different, unique call.

This enabled us to demonstrate that the level of roding activity at a wood was related to the number of individual males and that counts of roding passes therefore provide an index for assessing trends in breeding numbers of this otherwise elusive and cryptic species.

Spectrographs of the roding calls of two woodcock. The first has four croak elements to the call and a low frequency whistle, the other three croaks and a higher frequency whistle
We have just finished our roding counts at Rotherfield and, as at other sites this year, the tally is down slightly on 2013 and 2014.

However, we still managed a count of 22 passes in one wood and breeding woodcock seem to be doing well at Rotherfield compared to many parts of southern England. The main change here in recent years has been in one wood where the birch has grown up and some thinning is probably required to improve the habitat for woodcock again.

Nationally, however, breeding woodcock are not faring well. Our 2013 survey with the British Trust for Ornithology suggested 22% occupancy of 1-km squares containing more than 10 ha of woodland, compared with 35% in 2003.

It is now particularly noticeable in southern England that sites occupied by breeding woodcock are clustered in areas with extensive blocks of woodland, such as the Forest of Dean, New Forest and Thetford Forest. We have started work to better understand the key habitat requirements of breeding woodcock and the factors driving the decline.

Please help us continue our work on this project

Monday, 6 July 2015

Grey partridge stepfather steps up

by Francis Buner, Senior Conservation Scientist, GWCT

Last Friday we were fortunate to stumble across our second Grey Partridge brood at Rotherfield this season.

The reason for our sighting was because we were looking at our re-established wildbird seed mixes, together with John Davy the contractor and Tim Furbank from Oakbank Game & Conservation Ltd, who provides us with both seeds and advice on these mixes, but finding the partridges was a real bonus.

A pair of Grey partridges with their three day old chicks, foraging on a re-drilled wildbird mix along a 3rd year mix
As luck would have it, this was the brood of the parent-reared pair that regularly visits my chicken feeder. Their leg ring combinations made any confusion impossible. We counted 10 three-day old chicks which seemed a bit odd, given that this was an early brood.

Grey partridges lay an average of 16 eggs here in the UK (no other bird in the world is known to have such big average clutch sizes) so there must have already been some losses during the first couple of days after hatching. Perhaps it was the Kestrel that also killed one of the lapwing chicks earlier this season? Talking of which, the Kestrel family is struggling themselves to get their brood through this year: out of four chicks, one died in the nest and one fell out before fledging, completely starved.

The area the partridges hatched off has plenty of excellent nesting cover but unfortunately no suitable brood rearing cover nearby (breeding partridges typically have territories that are only 2ha in size).

Partridges regularly  take their broods for foraging, dust bathing and sun bathing on farm tracks during
summer but unfortunately that exposes them to predators
This is probably why I later observed them foraging on a dusty track along conventionally grown winter wheat, which is too thick and without any suitable insect food for a partridge brood. They ran another 100m down the track to reach another block of wildbird mix, of which half we just re-established in early June. This is where I managed to photograph them.

Two days later our doorbell rings and a rather sad looking Peter Rose (the estate’s keeper) holds a dead partridge under my nose. Its rings clearly identify it as ‘my’ garden cock who became a father across the road just five days earlier. How annoying (my real reaction was rather less polite)!

Grey partridge killed by sparrowhawk
The signs of his injuries undoubtedly indicated a Sparrowhawk kill. Should I therefore direct all my anger at the hawk? Well, not really, no. I suspect it was just too easy for him.

First, male and female partridge were reared and released, so their anti-predator behaviour may not have been 100% correct even though they had been living in the wild for more than half a year. And second, the habitat was not 100% in their favour. We’ll have to get it right next year.

Today I saw the brood again. Sadly the number of chicks has now decreased to only four. Will any of them survive I ask myself?

Well maybe, as they just received some much-needed help: the hen is with what might look like her reincarnated partner if not for his different leg-rings, which identify him as a wild, translocated cock, now escorting her and her brood! Now that’s what I call real altruism (which is extremely rare in nature)!

How was that possible in such a short time and why would a partridge do such an incredible thing? Well, the first is easy to explain.

This lonely cock has been calling almost every evening around my house since spring, desperately trying to attract a female. Unluckily for him there were not enough females around to please all the males, which is normal in partridge populations.

Now his fortunes had finally changed, as the female must have been calling to find her dead mate. Partridges look for their partners for about two days, after which they give up. So the widowed hen attracted the single male and that’s that. And what is in store for the male?

Well, if he and his new partner make it all the way through to next spring he has a major advantage: he doesn’t have to look for a female, which is extremely dangerous (up to 50% of cocks are either predated during the pairing period, disperse, or never find a partner). It’s certainly a tough life if you’re a grey partridge – and being a partridge conservationist isn’t easy either!

Please help us continue our work on this project