Knock-on effects…

TP 1st brood Phils Heath 2018_001During the course of ringing some of the first brood Stonechat chicks, we noticed that several broods were slow in development. Some chicks which were technically a week old hadn’t developed as much as expected given their age. So it seems that some pairs have had difficulty finding enough food for their young, even though these were only fairly small broods, some with only 2 or 3 chicks. We also had more than our usual share of unhatched eggs this time round – several broods have had between 1 to 3 unhatched eggs.

March 2018In theory, the adults should have had an easier time finding food to feed their young on Dersingham Bog so far. We have fewer pairs this year and some territories which were divided into as many as three new territories last year are now occupied by only one pair. So there should have been less pressure on the overall food supply, so we’ve assumed that the winter weather has also impacted our insect survival rates.

Without empirical data, we’re left with speculation,  but possible causes could be:

  • As the adults presumably approached the breeding season in poor condition after the late winter weather, this, in turn, may have affected their ability to provision their young. But this could also be more complex than the cold snap directly affecting the parents’ ability to put on weight. Poor body condition of any species tends to lead to other complications, such as a higher predisposition to pathogens or parasites.
  • Galloway cattleTaking a very different example, the Galloway cattle on the reserve suffered a higher incidence of mites this year than they have before (probably due to cold conditions forcing down body weight and confinement in close proximity – they didn’t wander too far from their food). This meant they started the season in poor body condition and have taken quite a while to regain it.
  • View from Phils HeathReduced prey abundance due to winter / spring conditions – there are always winners and losers as a result of adverse weather. This partly relates to phenology of the species in relation to prevailing weather at a particular point of their lifecycle. The cold snap occurring when it did may have impacted on the early season invertebrate prey of the Stonechats. Whilst species that emerged later may not have been affected, those coming out around the time of the cold snap may well be showing depressed numbers. It needs more time to confirm this but it appears that the cold weather has reduced the numbers of heather beetle and it’s conceivable that this may provide a significant part of the Stonechat’s diet in spring.
  • Or, there could be a myriad other causes. Recent vegetation quadrat surveys at Scolt, compared to photos of the plots from the previous year, showed a change in structure (almost certainly related to the weather). This could have massive implications for nest site selection and predation risk, thus increasing the need for more adult vigilance at the possible expense of time spent feeding.

SC-Happy Valley - Les BunyanAnother indication of the impact of the winter weather on our Stonechat population has been a comparison of the number of ringed birds from last year to this. So far we have only 4 ringed birds, with the remaining 8 Stonechats on territory being unringed. This compares with last year when we had 25 ringed adults holding territory during the breeding season. And of those 4 ringed Stonechats this season, only 2 are territory holders from last year. Both these ringed birds spent the winter off the reserve, so wherever they ended up, fortunately they somehow survived the bad weather to return to the same territories for SC juv Henry Pagethis season.

It’s only been a couple of years of monitoring winter occupation and site fidelity  so it’s too early to draw any firm conclusions but a rough pattern was emerging of considerable site faithfulness. So we can only assume that the rest of those 23 ringed birds from last year may not have survived the winter. Certainly, of the Stonechats which occupied the reserve during the winter, none remained through the bad weather and into the spring so the losses may have been considerable.

On a practical note, we’re experiencing the same survey difficulties we’ve had in the past when the majority of our birds were unringed. With some core territories being close together, it makes it trickier for our volunteers to be sure which Stonechats they’re seeing. We’ve certainly been spoiled in the past with so many ringed birds on the reserve making it easier to ID birds.

So far our core territories are the only ones which are occupied and large territories, which had divided into 3 territories last year with the arrival of new pairs, are now back to being one extensive territory. So, hopefully, that will help with food supply for the pairs and chicks. How and if the situation changes for second and third broods remains to be seen… but we’ll keep you posted!

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Off the starting blocks…

SC male Tranquil valley unringed2Round one of the Stonechat breeding season on Dersingham Bog for 2018 can probably be summed up as… less than we hoped but more than we feared.

After the late blast of winter weather, we headed into spring with just 5 pairs of Stonechats on territory but we’ve managed to boost that to 6, with one pair arriving nearly a month later than usual. This was way below last year’s total of 13 pairs but given that some areas of Norfolk have reported a complete wipeout of their Stonechat numbers, we’ve been very lucky.

Happy Valley SC 1st brood nest 2018_001

Stonechat 1st brood nest

All our pairs have been staggered in their breeding timings as well, with some still on eggs while others were already feeding chicks. This at least meant it was easier to plan our volunteer effort and any bad weather striking the reserve didn’t hit all the pairs at a vulnerable time and cause big losses, which happened last season with our first broods when May’s bad weather wiped out 50% of our first broods.

 

Piezos SC 1st brood nest 2018_001Our total number of chicks from first broods this year was just 18. Our first chicks were ringed at the beginning of May and our 6th pair’s first brood ringed at the end of that month, with the chicks from the other pairs ringed at roughly weekly intervals in between.

Our first pair to nest produced only 2 chicks but laid 5 eggs, which seems to be a common occurrence on this particular territory. Given that this is the third pair to nest on this heath, it’s curious that each time the different females have laid 5 eggs but only 2 have hatched and subsequently fledged. Our next brood on another territory produced 3 chicks but only 2 fledged, with the runt dying in the nest.

SC Triangle 1st brood 20180 (2)

Stonechat brood near fledging

Fortunately, this was followed by a healthy brood of 5 chicks from a regularly occupied territory, and then 4 chicks from another core territory. Our first brood failure was of 4 chicks which were predated from the nest before they were ringed but the final pair which arrived late managed to produce 4 chicks.

 

Even with these reduced numbers, we’ve managed to use up almost all our dark green colour-ringed combinations and we’ve switched now to dark blue for the rest of this season.

Bryants TP 1st brood nest 20182_001We’ve also been quite lucky with the weather so far this spring. Whilst we’ve had spells of cold northerly winds and sometimes foggy conditions, we haven’t had prolonged or heavy spells of rain, and this has also been balanced with very warm settled spells of sunshine and light winds. Sometimes we seem to have experienced both winter and summer within the same week.

Piezos SC 1st brood 2018-Jason

Stonechat 1st brood nest deep in bracken

The nests have been in a mixture of habitats – 4 in heather, 1 in bracken and 1 in a mixture of sparse heather in a grass tussock, and the range of nest sites chosen has been equally varied. 4 have been right on the floor, 1 high and deep in a tunnel in dead bracken, and 1 well hidden in the middle of a substantial heather bush.

 

As our successful pairs start their second nests, the pair which experienced a first brood failure have already nested again, the female building another nest within a week. She laid 6 eggs and 5 healthy chicks were ringed this week.

 

 

Roger - Bryant's_001So over the next couple of weeks, we can hopefully see the remaining 5 pairs beginning to incubate their second broods and our volunteers will be busy nest finding, as well as keeping an eye on the currently empty territories to see if any new pairs sneak in.

Other areas of Norfolk seem equally affected by low Stonechat numbers. While there are 2 pairs in Snettisham Coastal Park and 1 pair on Scolt Head Island, our volunteers haven’t found Stonechat pairs in areas where they’ve bred regularly over the past few years, such as Brancaster, Thornham, the Drift, Dersingham, and Hunstanton Golf Course and we hear reports of other areas of the Norfolk coast being similarly affected.

TP - Phils Heath 1st brood 2018 0 (2)

Tree Pipit 1st brood nest

For our other Bog specialties the breeding picture is mixed. Our Tree Pipits only have 4 territories occupied this year, with 2 nests found so far. More worryingly, 4 other Tree Pipit territories which are nearly always occupied remain empty. Our Tree Pipits were also late arriving back and it seems to have been a similar picture with other summer migrants, both on the reserve and elsewhere either late arriving or not arriving at all. Other reserves and birders are reporting late arrivals or low numbers of summer migrants like Whinchat, Garden Warbler and Reed Warbler. Presumably the storms in Europe during migration have impacted how many have been able to return?

Nightjar survey work has only just begun so we should gain a clearer picture of their numbers soon but so far we have 4 nests with 3 other females found.

WL Sheperds 1st brood 2018_001

Woodlark 1st brood near fledging

With our Woodlarks, 1 pair produced 4 young and 2 other territories seemed occupied in early spring but although no first nests were found, those males are now singing again so we can assume second brood attempts are imminent. Interestingly, 2 territories which we thought were empty early in the season are now occupied. So whether this is a late occupation or they’ve managed to get first broods off under our noses isn’t clear.

The timing for our Stonechat breeding attempts has also been affected, with most of the first broods being several weeks later than usual compared to previous years. We can confidently expect each pair to attempt a second brood but how many go on to make a third breeding attempt remains to be seen.

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Double Blow

Throughout much of the 2017/2018 winter, events in the Stonechat world on Dersingham Bog (National Nature Reserve) continued in pretty much the same vein as in previous winters, with a combination of occupied and unoccupied territories. As before, we had a mix of new ringed birds taking over from the previous season’s breeding pairs and on some territories, the same breeding pair remained on their territory throughout the winter.

C-Ringed-Stonechat-femaleOf the new ringed birds on site, it was heartening to see 8 of the 2017 fledged youngsters pairing up with new partners and occupying existing territories. Two pairs also remained on the Bog from the 2017 breeding season. One pair near the Landfill end had originally bred in 2016 and remained on the same territory throughout that winter and then successfully bred there last year; so it was a continued occupation of one territory spanning more than 18 months. The male of the second pair was our oldest breeding male. Born in 2013, he would enter his fifth year in 2018 (affectionately known to volunteers as ‘white/orange’ for his colour ring combination). So, of the 15 existing territories, we had an encouraging 50% winter occupation.

As we entered our third winter of monitoring site fidelity by our Stonechats, it was following the same pattern as before, with some continued occupation by breeding territories holders but also typically, a new set of youngsters pairing up and taking over territories. And we fully expected it to be Groundhog Day again – that spring would see some of those winter pairs remaining, while others would be ousted by either the returning breeding pairs from the previous year, or by completely new pairings. We weren’t exactly blasé about it, but we were quietly confident we had a handle on what the pattern might be for the third winter on the trot.

DSCN0349However, the weather had other ideas. Since the Stonechat project began in 2012, we’ve been lucky. We’ve not experienced a really bad winter and any poor weather has been limited to short spells. We’ve certainly not had anything like the kind of weather that the two Beasts from the East delivered to not only Dersingham Bog but most of Norfolk and the rest of the UK. Unsurprisingly, it has had a significant effect on the numbers of Stonechat on the Bog and the occurrence of our ringed birds.

DSCF1031Fearing a complete wipeout, our volunteers have been monitoring the site and it has been disheartening to find very few or no Stonechats on the Bog on a number of visits. For a species relying on insects, any prolonged snow cover or ground frost can have a devastating impact on survival. We can only hope that some had found more sheltered habitat elsewhere, but given the extensive nature of the snow coverage and the length of time it lasted, there can’t have been many areas in East Anglia that Stonechats could have fled to in order to survive the harsh weather. In other parts of Norfolk, reserves were reporting similar reductions in numbers of other species such as Cetti’s Warblers and Little Egrets.

As we move from winter into early spring, fortunately the current picture is not as dire as we once feared it might be. We currently have 4 to 5 pairs of Stonechats on site occupying existing territories. Interestingly though, it has been all change in the composition of who remains. We have 4 ringed birds at the moment and none of them are the same as the ringed birds who wintered on site. We also currently have more unringed birds than ringed, so the recent ratio has been reversed. But given how precarious it could have been, we’ll take whatever Stonechats we can get at the moment!

male-stonechat-from-keithSadly, our oldest male, White/Orange, may have been a casualty of either his age (4 years and 7 months which is a fair age or a Stonechat) or the weather as he has not been seen since mid-February, just before the bad weather hit. Currently, an unringed male and a new female seem to be occupying his old territory – something he’d never have tolerated if he’d still been on site.

We can but hope that a few more migrant Stonechats will arrive to boost our numbers. Hopefully, we have ‘thrown out’ enough juvenile Stonechats into the surrounding countryside in the past few years (over 250 since the project began), that they will have boosted the Anglian population sufficiently that there is a good supply of replacement Stonechats out there to reinforce the birds on the Bog and plug a few gaps. Only time will tell.

So we now look forward to the approaching breeding season with cautious optimism. By this time last year, we had already confirmed 11 nests but at the moment, we have seen nest building by only 3 pairs. So whatever happens next with our weather, our first broods will already be much later than usual and our numbers much lower. We can but hope for some settled warmer weather into the spring to enable some initial success. We’ll keep you posted!

We’d like to thank one of our new volunteers, Allan Coleby for all his efforts. He helped keep track of territory occupation during the winter and, in particular, the depressing picture post-Beasts from the East. Hopefully, survey work will be more positive for all our volunteers as we move into the breeding season. We’d also like to welcome another new volunteer to the project, Jason Moss (https://twitter.com/mossjason85) of Oriole Birding(https://twitter.com/OrioleBirding) who joins us in time for the breeding season. We look forward to working with both of them and to the Stonechats recovering in numbers again and the project going from strength to strength.

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A Hat-trick & a Century

After the high failure rate of our first broods, a successful round two of nests, we were hopeful but unsure what any third breeding attempts would bring for our Stonechats. In previous years, we’ve had only a couple of pairs try for a third brood. This time, with so many failures on the first broods, we were more hopeful that more pairs would attempt another nest.

Once again the weather was kind to us for our third nesting attempts and with the timings of the pairs again spread out, any bad weather didn’t have a significant impact. So round three proved to be a mixture of pairs who attempted three nests and succeeded, while some pairs managed technically their second broods. In total, 9 pairs went for a third nesting attempt and we managed to ring 36 chicks. Once again, we missed one nest which fledged a minimum of 4 young, so we had a minimum of 40 young fledged from those 9 pairs.

Little Nose 100th chick 2017

Our 100th Stonechat chick for 2017!

So the big news for the project is that we crossed the century mark for the first time which was an amazing achievement, both for the birds and the volunteers. Ringing the 100th chick felt like quite a landmark and a cause for celebration. We didn’t quite wet the baby’s head but it was a close run thing…

 

In total over the whole season, we had found 33 nests, missed 2 more nests and ringed 113 chicks, with a further 8 chicks to add to the total from nests we missed. Considering that it was as recently as 2013 that we only had 2 pairs of Stonechats on Dersingham Bog, producing 10 chicks over a whole season, the increase in the population has been nothing short of remarkable.

In trying to sum up the various territories, this is where it gets complicated… Overall, 8 of our Stonechat pairs made three nesting attempts, with 6 of those pairs being successful. One of those pairs was remarkably prolific in terms of numbers, with 5 chicks from the first nest, 6 from the second and 4 from the third.

4 of our pairs nested twice, with 3 of those pairs successfully raising two broods and one pair failed on both of their nesting attempts. 3 territories held 5 pairs of Stonechats in total, 2 of those territories changing occupants partway through the season. Those 5 pairs made a single nesting attempt each and 3 out of the 5 pairs were successful.

Roger 2The territories where the occupants changed was a result of territories being abandoned by their original pairs after the first breeding attempt and later being replaced by new pairs. Curiously, one of those abandoned territories had been successful with a first nesting attempt so it was puzzling why the successful pair left. Those supposedly empty territories took everyone by surprise when they were reoccupied, with one of our volunteers literally making a chance discovery of a pair carrying food, but it shows the value of checking all the territories regularly. It perhaps also reflects the increasing numbers of Stonechats in the area now that suitable territories don’t remain empty for long during a breeding season. It’s a comforting thought that Dersingham Bog may now be a Stonechat nursery for the repopulation of West Norfolk.

It’s been a fascinating season and our Stonechats continue to be an absorbing, yet at times frustrating, species to study and our volunteers have put in a huge amount of time and effort to ensure we found as many nests as possible. It remains to be seen if next season will be just as busy and even if any more territories can be squeezed onto the reserve or whether we’ve reached our carrying capacity. We’re conscious a lot could depend on whether we experience a bad weather winter, for the first time in several years, which could have a significant impact on the numbers which return to breed. Our luck can’t hold forever.

IMG_20170712_143152546_HDRWe’ll attempt to monitor what Stonechats remain on the reserve through the winter as we did last year, to continue to build up a clearer picture of winter territory occupation. We’d very much welcome any reports of our dispersing Stonechats, both adults and juveniles, through the winter around Norfolk and perhaps beyond, as well as those which continue to occupy territories on Dersingham Bog. Meanwhile our volunteers, Roger and Irene, can probably be found recovering in a home for the bewildered through the winter… (aka the pub).

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Round two…

After our mixed Stonechat fortunes for our first nests, with more than a 50% failure rate, we were hoping that our second broods would fare better… and so it proved.

SC chicks almost ready to fledge

We still have 13 occupied territories and found 12 nests, with 11 successful broods ringed. We missed 1 nest entirely and 1 nest failed at the egg stage. 45 young were ringed, with an additional 4 or 5 extra unringed juveniles to add to the total from the brood we missed.

We had a mixture of brood sizes, with some very small broods of only 2 or 3 but we also had 3 broods of 6 young, which is the first time we’ve had pairs produce 6 eggs, let along fledge 6 young. One of those pairs had failed on their first brood but the second pair with 6 chicks had already produced a successful first brood of 5 young, so it’ll be interesting to see if they try again. Our third pair with 6 youngsters is a new pair occupying one of the previously abandoned territories. We also had several females lay 6 eggs but only between 2-4 hatched.

Our first nest with 6 eggs

The weather was a lot more settled for round two and simply because it was later in the breeding season, the temperatures were a lot warmer anyway even on rainy days. The only spells of bad weather didn’t last for long this time and a spell of very hot weather will have helped the availability of food.

The first brood failures resulted in the timings for the second nesting attempts being more spread out and the pairs were not as synced this time, so any bad weather did not affect all our pairs at once, as it did so disastrously before. The second nesting attempts have been so spread out that we’ve been ringing second broods on the same day as early third broods.

This staggered nesting has also allowed us to spread out our volunteer efforts. With limited time available for our two volunteers, it meant we could target our efforts more effectively as we had a good idea of the status of each of the territories and weren’t wasting time on ones which weren’t ‘ready’ yet. All of that, of course, was made possible by finding every first brood nest and monitoring its progress, which then unlocked the timings for the rest of the season.

The one failure was from a pair which failed first time round, also on eggs. This time it could have been to do with the location chosen for the nest – in low sparse heather with lots of bare ground around it. This pair may also have had an unfound failure as there was a very long gap between the first nest and the finding of their latest attempt, so it remains to be seen if they will try again. It’s a shame in a way as the male for this pair is our oldest  and previously most prolific male (white/orange), so maybe he’s chosen unwisely in his partner this year or maybe he’s firing blanks…

Our new pair’s chosen nest area

Two of the territories we thought were empty after first nest failures… weren’t! The original pair in one territory managed to raise a brood unnoticed right under our noses. The other empty territory has been re-occupied by a new pair; the male is one ousted from a neighbouring territory but the female is a completely new bird, not reported since she fledged last year. She was born in a second brood to our most prolific female so hopefully she has good genes!

We have no way of knowing where she’s been or whether she’s attempted to breed before, so this could be her first breeding attempt. Or perhaps she attempted elsewhere and failed? It’s perhaps unlikely she would have left a territory elsewhere if she’d been successful unless it was the loss of partner which triggered her move. Either way, she could try again.

As we gear up to monitor which of our territories will attempt third broods, our totals of fledged Stonechat young are looking a lot healthier, with 94 young ringed. So the question is, will we reach 100 chicks ringed for the first time in the project’s history? We missed it by a whisker last year, ending the year on 95 ringed young so we’re tantalisingly close already.

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ABANDON SHIP…

After the poor weather which had such an impact on our pairs during their first nesting attempts, it’s looking increasingly likely a handful of our Stonechats are missing. Four of our occupied territories on Dersingham Bog are now a Stonechat free zone.

After the mixed fortunes of the first broods, with 8 failures and 7 successes, we’ve been monitoring all 15 occupied territories to try and establish when each pair might attempt a second brood, or a relay in the case of the failures. So far, three of the territories which failed may have been abandoned entirely by the pairs and another territory, which successfully fledged five juveniles, is also now empty.

It’s too soon to be absolutely sure as it can take quite a while to confirm a territory is definitely empty and it’s not just that the female is being typically elusive while she’s sitting, but in three of the territories, the males appear to have gone AWOL too. And if they are now empty territories, we’ll never know what happened… whether the pair just abandoned the territory after their failure and moved elsewhere to try again, or if they’ve ceased breeding altogether for this season, or whether one or both of the adults has been lost, either through the bad weather or predation or illness.

But we can be fairly sure that one male has lost his female. One of the Bryant’s Heath males has been singing and displaying to the two females on neighbouring territories, much to the annoyance of their current partners. This is also having a knock-on effect on one of the neighbouring territories where second brood young have just hatched. The distraction means that the territory male is not pulling his weight by taking in the usual share of the food to the chicks as he’s spending too much time chasing off the intruding male.

It’s a shame to see these empty territories after such a consistent occupation over several years and it’s particularly poignant that our longest occupied territory at the Piezos now appears empty. We can only hope that some of them may be reoccupied again at some point, perhaps during the autumn and winter with the dispersal of this year’s young. Or perhaps we have now reached carrying capacity for the reserve and what’s happened shows that 15 occupied territories may be too many for the available food on the Bog, particularly when bad weather strikes early in the season?

However, it’s not all doom and gloom. The other pairs, both the initial failures and our successful first broods, have been getting on with their second nests as expected. So we now have a satisfying mixture of incubating females and newly hatched young, including some where the fledged first brood juveniles are still hanging around while the female sits on a new clutch.

In fact, several females which failed first time round during the appalling weather were incubating barely 2-3 weeks after the initial failure, which just goes to show how quickly Stonechats can go down on eggs again. Even knowing how quick this species can be with second broods, it’s still remarkable when you consider the weather conditions at the time and the strain on the females. In one territory, a pair had been feeding young for a week before they were predated and yet the female then got back into condition, built another nest and laid six eggs, all within 2 weeks of the first failure.

So, as we move into the time for starting to ring the second broods and the weather has become more settled (until today!), it’s looking good for a more productive round two. Although as the rain lashes against the window, let’s hope that’s not tempting fate again…

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Round one to the weather…

After the spell of bad weather which scuppered five of our Stonechat nests, we had hoped that the conditions would relent enough to allow the rest of the first brood attempts to succeed. But once again, the weather had other ideas. The spell of bad weather at the end of April (covered in a previous blog) continued, with prolonged northerlies which resulted in more Stonechat broods going down like ninepins.

To sum up our 1st brood totals, we have 15 active territories and 33 chicks were ringed from 7 successful nests. By comparison, 44 chicks were produced from 12 nests for our 1st broods last year. We had 8 failures – 2 from predation, 3 failing on eggs and 3 at the chick stage, so more than a 50% failure rate, which is high for the Bog. While losses to predators are to be expected, the remainder of the failures were most likely down to the bad weather at the wrong time.

Most of our reserve is sheltered from the prevailing south westerly weather, which works in our favour most of the time. However, the entire length of the plateau is exposed to the north, so while we can usually ride out the odd spell of wind and rain from that direction, the fact that the northerlies lasted for a fortnight or more spelled disaster.

The high pressure system might have brought dry, warm weather to most of the country, but here in Norfolk it resulted in strong winds channelling down the North Sea, bringing bitterly cold conditions across the reserve. Inevitably, this suppressed the availability of insect food for both adults and their newly hatched young so the adults must have struggled to find enough food, not only themselves but their chicks. Some nests faced north and were in exposed spots on the plateaux, which can’t have helped.

As the male doesn’t incubate the eggs when the female comes off on a feeding circuit, the eggs are left uncovered. In inclement weather, the female must spend longer and longer off the eggs so eventually they chill too much and become unviable. Or her survival instinct kicks in and she has to abandon the nest in order to find enough food for her own survival.

Unsurprisingly, the pairs which succeeded have all nested in sheltered spots, although one pair was a surprise success. They nested on the ground in an exposed spot in a fairly obvious nest on a north facing slope – we’d have placed bets that it wouldn’t stand a chance but it produced 4 healthy young.

Until we start checking the territories for the second nesting attempts, we also won’t know if we’ve lost any of our females. We did last year during a similar bad weather event when we had a change of several partners, with ‘divorce, remarriage and house moves’ on some territories between the first and second broods.

We also can’t be sure how many of the fledged juveniles have survived the poor weather. Unusually, we’ve not seen many juveniles post-fledging so far. Hopefully, the parents have just taken their youngsters to more sheltered parts of their territories but it’s entirely possible that there have been other casualties, as the first few weeks out of the nest are a very vulnerable time for a small passerine reliant on insect food.

The timing of the bad weather and the length of time it lasted could not have come at a worse time, which is why small passerines play a numbers game and have at least two and sometimes three broods. The warmer weather of the last week or so will hopefully help not only the juveniles survive the first few weeks of life but allow the females to get back into condition again for another nesting attempt.

We’ve also been lucky that all our first brood nesting attempts were early this year. This time last year, we were still finding first brood nests in early to mid-May but all ours had gone down on eggs by mid-April, no doubt helped by the mild weather during March and April. So hopefully there is enough time now for those that failed to try again, hopefully twice. Certainly in previous years, those pairs which failed early went on to nest twice more in a season and mostly successfully.

So fingers crossed that the weather now settles into a warm spring… ready for round two!

 

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Does size really matter?

An interesting email exchange with John Furse prompted this blog post about the size of our Stonechat territories. As the Stonechat population at Dersingham Bog has increased, we’ve often speculated as to what seems to dictate the size of the territories themselves and the choice of boundaries.

With only a handful of Stonechat pairs until a couple of years ago, the territories were either very large or widely dispersed but as the reserve has hosted ever more Stonechats, the territory boundaries seem very much defined by the topography of the Bog rather than just the pure size of each territory. We’ve never been able to predict how big a Stonechat territory will be just by looking at acreage occupied – it’s always been defined by the layout of the habitat.

It’s a feature of Dersingham Bog that the habitat and topography can change in a relatively small area. Essentially, the reserve is almost on two levels, with the plateau extending the full length of the reserve and

Plateau, main track and mire

bordered on its northern side by the wetter mire, with the main footpath running through the middle. Dividing all that are various ridges or ‘noses’ – headlands extending out onto the mire which result in some valleys being closely bordered, giving a very sheltered and enclosed feel to some relatively small areas.

Two of those territories are long and narrow as a result of the topography rather than being squeezed in between other pairs. They are bounded on three sides by the plateau, so the territory has stretched out in a long rectangle onto the mire rather than spreading sideways as the plateau pairs do.

Three other territories have always been the largest, spanning areas which start up on the plateau and extend down the slopes and out onto the mire. But these territories have gradually been nibbled away this year with new pairs encroaching on the edges as it’s presumably harder to defend territories on separate levels.

Our oldest and most territorial male has always defended a very large territory. He has previously occupied an entire heath on the plateau, the slopes leading down to the area around the dragonfly pond, as well as a prominent ridge extending out into the mire and a large chunk of the mire itself. In the last year, two younger males have established territories on his boundaries, with one taking over the heath on the plateau and the other taking half of the mire area.

By contrast to other areas, this last part of the territory has very little in the way of defined features dividing it and the boundary line seems to be a cleared area halfway along the ridge. Both males have taken to patrolling back and forth either side of the clearing, displaying and posturing at one another like a couple of gunslingers!

Another male has also lost two portions of his territory this year. He once defended an extensive heather plateau, a gully, an area of mire and a low heather valley. It was always a difficult one to monitor to find nests as there are very few spots where you can see all of the territory from one place, so his territory defence must have been doubly difficult to maintain. This year, two new pairs have moved into the edges – one pair taking over the higher plateau, with another pair carving out part of the mire, leaving the original pair with roughly a third of the area they once occupied.

In another part of the reserve, what was one territory now holds three pairs and that area is unusual in that it’s large and flat, with no topographical features dividing up the ground. Feeding areas overlap but by and large, the birds stick to their boundaries.

The topography also defines how close territories may be to one another. Territories may be back to back either side of a ridge and technically within 50 metres of each other, but to all intents and purposes, they are hidden from neighbouring pairs so presumably the males don’t have to spend all their time on territory defence.

Some feeding areas on the boundaries do overlap, with pairs using the dividing ridges themselves, which the males tend to patrol as their boundary lines. As more pairs squeeze onto the reserve and existing territories are carved up into smaller chunks, presumably these shared feeding areas will increase as pairs seek enough food for themselves and their young.

So lots of food for thought, not least about how much of an impact does this territory carve up have on food availability for the pairs? Will we see an impact on productivity if it continues, especially if we get too bad weather events like last week during a breeding season?

It’s tempting to think that the overall boundaries of the Stonechat territories can’t be pushed out any further as the habitat shouldn’t be suitable. Currently, the only places on the reserve which are empty of Stonechait pairs are relatively small gaps right out on the mire, or up on one plateau which has very sparse heather cover at the moment as it was the last part of the reserve to be cleared of pines. However, the Stonechats have surprised us before with adopting areas we would have thought unsuitable so we’ve stopped making predictions!

Dersingham Bog has perhaps an unusual layout, the plateau being the line of an old sea cliff, with the mire occupying what was once the seashore. It can’t be a unique layout for a heathland reserve but it’s certainly unusual. So has the topography contributed towards helping the establishment of such a density of Stonechat territories? It would be interesting to discover how territories are divided up in reserves which share a similar topography to Dersingham Bog.

And our original and frequently asked question remains. Just what is the carrying capacity of Dersingham Bog? How many Stonechat territories can the reserve sustainably support?

Posted in Colour-ringing project, Dersingham Bog, Stonechats

Trials & Tribulations of Dersingham Bog

The weather this spring has been pretty kind to our Stonechats, with a high pressure system sitting on or close by for most of late March and April. This has allowed our birds to find suitable partners and territories, get down to nest making and start laying eggs. This also allowed us similar time to locate said territories and when we believed it safe to do so, to find the nests. Indeed, the weather was so benign that one pair was so far in advance of the norm that we nearly missed the young and the brood may have fledged before we had found it. Luckily, we got there in time.

So by 21st April, 14 nests had been located and the advanced nest youngsters rung. Of the 14 nests, two pairs were due to be rung, two had three-day old chicks and the rest were sitting tight on full clutches. All was looking good.

By our calculations, another visit on 25th April should have given us an opportunity to ring two pairs and check how the eggs were advancing for the other pairs. Wrong! Mother Nature decided to throw a spanner in the works and as strong winds with sleet, hail or even snow was forecast and unfortunately, duly arrived, we did not manage to visit until this morning, the 27th.

Although our two nests which we felt were ready for ringing had survived, the young were not as large as expected. Presumably the adults’ ability to find food must have inhibited their growth. Nevertheless, they were big enough and were suitably rung.

Another two nests had recently hatched and miraculously, the young were all alive, but of the remaining nests, four had failed at the egg stage. As we approached the nests, there was no alarming from the adults. Indeed, no adults were seen at all and it looked ominous. We presume that the female must have eventually been forced to think of her own survival and had abandoned the clutch.

Two of these nests were built on a plateau and would have been in direct line of a northerly blast and with no shelter from the rain. The other two are more mysterious, as the nest on ‘Piezos’, built by an experienced female, had been placed in a grass and bracken tussock facing away from the prevailing winds, although again with not much shelter from the rain. The other pair, again an experienced pair, had a full clutch of eggs on 8th April, so should have had young by now. So perhaps there’s another reason for the failure, which we can only speculate about.

So of our 14 nests, four pairs have been rung. Five are still with full clutches and we have five failures so far. But at least now we will have staggered nesting attempts with not all our eggs, literally, reliant on one weather window. So, barring any further weather problems, hopefully the second broods may not be so catastrophic.

Roger Q Skeen

Posted in Colour-ringing project, Dersingham Bog, Stonechats | 1 Comment

Shuffling the pack…

Having built up a fairly clear picture during the winter of which pairs were occupying which territories, including any new colour-ringed Stonechats arrivals, there were still some surprises as we moved into the start of the 2017 breeding season.

We’ve been lucky with another mostly mild winter this year and while the numbers of Stonechats on the reserve have fluctuated, there have been regular sightings throughout the autumn and winter periods on most of the territories. Our only spell of bad weather was in February, when there was a brief spell of around a fortnight where Dersingham Bog appeared virtually devoid of any Stonechats.

When birds started to return to the site during March, that’s when the main changes took place and the situation is still fluid as we move into April, with several new colour-ringed arrivals only this week.

CxFbofLWgAE3IK1Several territories which had been occupied during the winter by the same pair that bred successfully in 2016 now have completely new pairs, colour-ringed birds which hadn’t been reported elsewhere or on Dersingham Bog since they fledged last year.

Other territories have given a convincing rendition of musical chairs. Two females have moved to other territories on the reserve, ousting the existing pair or becoming the new partner to an existing territory holder. One female (from Ugly Dale) has taken over another territory, right at the other end of the Bog, far from where she nested last year. And the female from that territory (Tranquil Valley) can now be found just around the corner in her neighbouring territory (Piezos), which was previously held by our most prolific female. Confused yet?!

As mentioned in our most recent blog, 2 other territories which were empty throughout the winter are suddenly re-occupied, one being again held by the 2016 breeding pair. Where had they been through the winter? Had they wintered together somewhere or were now returning separately to the site?

Either way, it’s interesting that they returned to exactly the same territory. As that has been empty throughout the winter, maybe they didn’t have the territory battles when they arrived that might have occurring in other parts of the reserve?sc-fem-ltbw-landfill-w-20163

Interestingly, a new colour-ringed pair which occupied a new territory on Phil’s Heath through the winter have remained into this breeding season, and on the same spot so far. Another of the new territories established during the winter, which had a new 2016 colour-ringed male present, now has another new, previously unreported colour-ringed male, also from last year’s crop.

As we’ve said many times before, without colour-ringing, we wouldn’t have noticed these changes at all. So far, all 3 new territories established through the winter are still occupied, though not necessarily with the same ringed pair that set them up in the first place.

Our oldest male has remained on his territory all winter and is now preparing for a new breeding season with a new female, also from the 2016 crop. He has a particularly large territory, spanning an area up on plateau and extending down onto the mire, although corners are being nibbled away by new pairs. Last year, the northern boundary of his territory on the mire was occupied by a successful pair (the male of which has just returned to the same territory again after being absent all winter).

The other large corner of our oldest male’s territory now has at least one, possibly two pairs, carving out a chunk of ground for themselves. One pair established a territory on the periphery during the winter and seem to be still there, and another is a new colour-ringed male.
Unfortunately, our oldest female may have disappeared, as there is a new female from the neighbouring territory now occupying her territory, and with a new ringed male. If she isn’t re-found, it’ll be a sad loss but she has contributed significantly to subsequent generations since she started breeding in 2014. Her progeny have been scattered through the reserve over the last few years forming new successful pairs and establishing new territories.

One of the most interesting aspects of this shuffling of the pack has been how late it occurred. We hadn’t exactly become complacent by the end of the winter but we were confident we had a handle on who was where as we entered the new breeding season. So in the space of a few weeks, after our only spell of bad weather cleared the site, findimale-stonechat-from-keithng that many of the territories had changed was a bit of a surprise for the volunteers as yet another new colour-ringed Stonechat popped up somewhere new!

Is this typical? A late winter shuffle around occupying pairs? Or was it governed by the weather and the empty site, allowing early new arrivals to take over empty territories? So if we’d had the bad weather earlier in the winter, would the shake-up also have occurred earlier, but with another potential late winter / early spring change as birds wintering offsite returned to the Bog? As always, lots of fascinating and unanswerable questions keep arising with these charismatic birds.

It remains to be seen how many more new territories can be squeezed onto the reserve, or if the current state of play remains the same, or whether further changes will happen before they begin nesting. We’ve already had nest building taking place and given how synched many of our Stonechat pairs have been over the past few years, it won’t be long before most of our females are incubating their first broods, weather permitting.

 

Posted in Colour-ringing project, Dersingham Bog, Stonechats