Category: Blog

Blog by Malcolm Burgess

An open access scientific paper has just published in Ibis https://onlinelibrary.wiley.com/doi/10.1111/ibi.13017, led by PhD student Fraser Bell at the University of Exeter, with scientists from the RSPB Centre for Conservation Science and the Swiss Ornithological Institute, and fieldworkers from PiedFly.Net. The paper reveals the full annual migration of British breeding Pied flycatchers for the first time. The work identifies important stopover sites used on migration, some previously unknown, and refines previous work in identifying where they spend most of our winter. It also illustrates how flexible migration behaviour can be, which may help species like the pied flycatcher adapt to the changing conditions they encounter on migration in the face of a rapidly changing climate.

The Pied flycatcher is a songbird that can be found breeding in oak woodlands across western Britain, and readily breed in nestboxes. Because of this preference for nest boxes, they are one of the best studied songbirds in Europe and so we know a great deal about their breeding ecology. But like many migratory birds they are in decline. Despite our in-depth knowledge of their ecology in breeding areas, the causes of decline remain largely unknown. One of the difficulties in trying to understand declines of migratory songbirds is that we know little about their migrations and where they go during our northern winter. We need this knowledge to direct our conservation detective work at the right places. What route do they take? How often do they stop, where do they stop and how long for? Where is their ultimate winter destination? It is only in the last decade that we can really start to answer these questions, through miniaturised tracking technology. This study did just that, and reveals lots of new information about the migration of British breeding pied flycatchers.

Answers from the field

Thanks to funding from Devon Birds and Natural England, we tracked adult pied flycatchers from the East Dartmoor breeding population in Devon. This nestbox population grew from the 1950s and is now one of the longest monitored populations and nestbox schemes in Europe. Earlier pioneering tracking work published in 2016, tracked two male pied flycatchers from this same population to a rough area in West Africa around Liberia/Guinea. Technology and analytical techniques have since improved, now allowing us to examine this migration in more detail.

The team, including University of Exeter PhD student Fraser Bell who also led the tricky analysis of the data, put on tiny geolocator tracking devices to adult pied flycatchers. The tags weighed just 0.42 grams! These data loggers record light levels against a time, enabling us to estimate daily locations from the times of sunrise and sunset. While not as precise as GPS or satellite tracking, which is not (yet) possible for such small birds, these still enable us to determine when a bird moves between breeding and wintering sites and any stop-over sites used on migration, and estimate these locations. The small size of the tags meant we can’t download the data remotely, they required us to recapture the birds the following year to remove the tag and obtain the stored information. Breeding in nestboxes and individuals returning to the same woodland each year to breed made this possible.

Which route do they take, and where do they stop?

After breeding, pied flycatchers departed Dartmoor from mid July to mid August, first migrating along the west of France. All flycatchers first stopped in Iberia, mostly in Portugal, where they stopped for around 11 days. This must be a very important fuelling region for them. At the end of August or early September they then continued south, flying around the western edge of the Sahara, possibly including some flight over the sea. Most make the Sahara crossing in an incredible single non-stop flight which takes a minimum of 36 hours, flying continuously day and night!

But not all birds made it over the Sahara in a single flight. We discovered that 3 crossings in autumn and 2 in spring were paused for up to a day. Incredibly one flycatcher aborted a spring desert crossing part way across, returning south for a rest before making a complete crossing 14 days later. It is likely interrupting crossings results from meeting poor weather such as strong winds or sand storms, this is the focus of forthcoming research from the same team. Geolocators only provide data from birds that survive so we don't know how often birds die from weather conditions faced on migration, but we learnt that they can survive such interruptions.

Immediately after the autumn Sahara crossing most, but not all, flycatchers stopped at another stopover site, mostly in Senegal or Mauritania, for about a week. We had no idea they did this! Next they flew to final destinations arriving from mid September. This was a relatively small region of West Africa centred on Guinea but encompassing Sierra Leone, Liberia and Ivory Coast. Intriguingly males and females wintered in slightly different regions, with females west of males. Females stayed in these areas for 25 days longer than males, mainly because they departed later. Females commenced the spring Sahara crossing 11 days later than males, and arrived back to Dartmoor about 9 days later.

Departing wintering areas in late March, on spring migration most flycatchers stopped after crossing the Sahara for around a week, in similar areas of North Africa and Iberia to where they stopped in autumn, before then migrating directly back to Dartmoor.

Next steps

This work directed us to a fairly small region of West Africa where British breeding pied flycatchers spend half of the year. Fraser and a team from the RSPB Centre for Conservation Science and the BirdLife partner in Liberia (SCNL), have undertaken work in two areas of Liberia. Here they occupy a variety of forest habitat types, including open and dry Savannah forest, humid rainforest and farmed habitats containing trees. Work in Liberia has been to understand more about flycatchers ecological requirements, quite basic research but addressing fundamental knowledge gaps that is vitally important to know. We have been investigating how the different woodlands habitats they occupy influence fitness, for example infection levels by blood parasites that carry avian malaria may differ between these different habitats. Look out for the results of this work.

Continue reading

• Geolocators reveal variation and sex‐specific differences in the migratory strategies of a long‐distance migrant
• Light‐level geolocators reveal migratory connectivity in European populations of pied flycatchers
• No short or long term effects of geolocator attachment detected in Pied Flycatchers

Network member David Price gives the latest from Dunsford woods, from his visit on 13th May

As expected most of the birds in nest boxes were hard at it producing eggs on a daily basis, performing just like battery chickens.  The majority of the Pied Flys were in the midst of laying, some had started incubating and others were not far behind the rest with nest building.  In all there were 6 already incubating, 17 laying and 3 completed nests - a total of 26 active nests.  This is well up on last year's 22, and only two short of Dunsford's best ever total of 28 way back in 2007.  There were definitely some singing males that had as yet not got a nest site and perhaps not a partner, and there were one or two new nests at a very early stage which might develop – so there may be more breeding pairs to come.   After a protracted and slow start in April and early May, things are certainly looking a lot more encouraging.

However, it's not been all plain sailing for them.  Box 61 was an early nest where there had been one egg some 5 days earlier, so I approached quietly in the hope that the female may be sitting - (one of the advantages of the overnight rain was that the dead oak leaves underfoot were totally soggy and for a change didn't sound like walking on cream cracker biscuits!).  I managed to get to the box quietly and stuff my hand over the hole without that rather disappointing situation where the female flits out when you are literally only a metre away.  I looked inside hoping there may be an incubating bird present.  Instead I was surprised to see that the cup of the nest had been covered over with dry grass and leaves, rather like tits do when they leave their nests during laying.  Hmmm – interesting.  I teased the material aside to reveal how many eggs there might be, only to discover a totally empty cup.  What's happened here?  Did I make a mistake in recording one egg last time?  Then, looking closely, there in the bottom on an oak leaf was the evidence to exonerate my recording abilities - a small piece of blue broken shell.  I guess the egg or eggs had been predated and the birds had abandoned.  However, presumably not phased by this, the pair had picked themselves up from this set back and started again, as in the next but one box was a brand new nest compete with 2 eggs.  Let's hope they fare better with this attempt.  (The box in between was where the dormouse had been having a nap on last visit – but he was no longer using it for a bit of a siesta). ...continue reading "Dunsford wood update, 13th May"

Nest box monitor David Price gives an update from Dunsford Woods...

So another breeding season starts, but what sort of April have the Pied Flycatchers arrived and found?  Not great I'd suggest, particularly after such a mild winter.  I had one particular oak tree in leaf at the beginning of April, but then most of them seemed to go into some sort of torpid state and are only now really starting to do much.

First Pied Flycatcher arrivals at Dunsford were recorded on 11th (3-4 males).  They weren't there on 6th and in view of the gale force north westerlies from 7-9th, they probably didn't arrive until at least 10th.  Can't compete with Yarner's first arrivals on 6th.  No females recorded but the males were rather skulking and not singing much, so females could have been around.  All probably devoting most of their efforts to finding food I guess.

Since then not much demonstrative activity on show from most pairs, and as a result it's been difficult to assess actual numbers.  As of the last visit on 27 April, there were some 9 nests or what might be nests on the go, - though some of these may be abandoned.  Also at some nest box locations males were singing but there was no sign of nest building.  Taking these two factors together I optimistically reckon there may be 18 males/pairs present.  This is some way short of last year's 24 pairs, of which 22 were in boxes.  Are there still birds to arrive?  Wouldn't be surprised after the predominance of arctic northerly winds.  Doesn't look like the cold conditions will abate for at least another week.  I think I'd hang around in sunny Portugal for a bit longer if I was still on my way! ...continue reading "Latest news from Dunsford Wood"

The latest update from network member David Price who monitors at Dunsford Wood, Dartmoor.

With all the cold, wet weather and the gale force winds over the past two days, I set off this  morning with some trepidation as to how birds had fared trying to feed young.  It wasn't actually too bad - most of the tits were big enough to put up with a couple of days of cold weather and a "light" diet for a day or two.  The first brood of Pied Flys had one dead - but it was the runt of the brood, and the second was similar.  However all the rest had come through relatively unscathed.  Several Blue Tit broods had fledged - hopefully not in the middle of the worst of the weather on Monday afternoon.   One brood of 10 "exploded" on me - had hardly opened the lid and they were all out!  Pleased to see that they were all very competent fliers, and were straight into begging for food on various branches - the adults were a bit phased by this, but soon got stuck in. The remaining paltry survivors of Great Tit broods are close to fledging, not a great year for their productivity I'd guess.

Managed to ring some more Pied Flycatcher broods, and catch a few more males birds. One bird at Box 21 foiled me at my second attempt - he obviously wasn't much into child care.  Was flitting about a fair bit, calling and occasionally singing, but wasn't going to bother providing food for his offspring.  As a result of capturing the male at Box 32 have detected yet another potentially unattached male - singing away whilst the breeding bird was safely ensconced in a bag. ...continue reading "June 3rd update from Dunsford Wood"

The latest update from Dunsford Woods from David Price...

Having provided an update for previous visits, I'm now in the situation of "I've started so I'll finish", so with apologies for the fact that this is becoming something of a rather rambling blog I'll carry on inflicting my home-spun observations on you.

Well, in Box 20, (where the "first Dunsford egg" was laid), three young had hatched yesterday with 4 eggs, still to do so.  In their monograph on the Pied Flycatcher, Lundberg and Alatalo give a range of 13-16 days for incubation so this was just about on cue after 13 days.  On the subject of incubation, I have noticed that in several cases on my previous visit (on 12^th May) I recorded typically 6 or 7 eggs that were warm (or perhaps "warmish") so on the basis that incubation had started and I assumed the clutch was complete, only to find yesterday that the clutch size had increased by one or two eggs or in one case from 6 to 9.  I started to doubt my ability to asses warm and cold.  However looking at the chapter in the book on incubation more closely, they mention that the female "actually starts incubation by gradually spending more time on eggs during the laying period" and by the time they get to laying the 5^th egg 82% of females will spend the night on the nest, though "full incubation normally begins when the last egg is laid".  It would seem that these "warmish" eggs that caused me confusion are a result of this increasing occupancy of the nest towards the end of laying.  There are several other pairs that are not far behind, and so should be hatching over the next few days - and as I sit here with the fire lit, and the wind and rain beating against the window, (and a rather unsettled weather forecast for the next few days) it's slightly worrying that this is perhaps not going to be great for feeding small young and trying to keep them warm. ...continue reading "Update from Dunsford Woods 18th May"

Measuring insect poo to help investigate the impacts of climate change on woodland birds.

As I mentioned in my last blog, the breeding success of hole-nesting woodland birds such as Blue Tits and Pied Flycatchers is thought to be dependent on the short seasonal spike in availability of caterpillar prey. These bird species usually have one nest attempt each year and so need to correctly time breeding to ensure that when their young are hungriest (when they are about 10 days old) enough food is available for them. Heavier fledglings are more likely to survive to become breeding birds themselves. Although these birds are able to adjust slightly, by delaying incubation after clutch completion for example, just a few days too late, or too early, can make the difference between brood death and survival.

Monitoring birds' timing of breeding and nest outcome is relatively easy, especially in nest box populations like I am involved with. Regular box inspections enable accurate calculation of when first eggs are laid, clutch size, the condition of nestlings at fledging and the number that fledge. Across the UK many thousands of nests in boxes are monitored annually. Monitoring invertebrates is less easy and relatively few people do this, and fewer still do so alongside detailed studies of breeding birds. But it is possible to estimate how invertebrate abundance changes during the breeding season using pretty simple techniques. The project I am involved in, with Ken Smith (now retired form the RSPB) and the universities of Edinburgh and Exeter, is interested in invertebrate abundance and how this changes during the course of spring, and how availability and timing varies spatially across the UK and between years. To achieve this we are encouraging citizen scientists who already monitor woodland breeding birds to additionally monitor invertebrates. Linking bird and invertebrate data gets 'bird people' thinking beyond just birds and participating and contributing to very worthwhile and important research. ...continue reading "Woodland birds response to climatic change: part 2"

The RSPB is investigating the impacts of climate change on the breeding success of woodland birds including the declining Pied Flycatcher.

The onset of spring is getting earlier. Understanding the effects of this on woodland phenology and on the breeding success of woodland birds is being investigated across northern Europe, including in the UK.

We know that our climate is rapidly changing, whatever its cause might be. One consequence of a changing climate, throughout northern Europe, is that the onset of spring has advanced - spring conditions occur earlier now than it did only a few decades ago. Spring is a very important time for many birds, plants and animals. Deciduous trees and many annual plants need to make the most of the short growing season and a huge variety of insects emerges that eats this new growth. Most birds breed in spring to take advantage of the super abundance of insect food available at this time. So how are they adapting to a changing spring? ...continue reading "Woodland birds’ response to climatic change"