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Author: Malcolm Burgess

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Partners: Devon Wildlife Trust, in a partnership with Dartmoor National Park Authority, Exmoor National Park Authority, Forestry England, National Trust, Somerset Wildlife Trust and Woodland Trust.

Funding: The National Lottery Heritage Fund

Summary: The Two Moors Pine Marten Project sought advice from PiedFly.Net to investigate the mitigation of potential negative impact of Pine martens on Pied flycatchers. Although nestbox modifications, well used across continental Europe, reduce predation by Pine martens, there is concern that modified nestbox designs may reduce occupancy by Pied flycatchers. Before advocating change across a large area for an important regional population PiedFly.Net:

-estimated the importance of nestboxes for the Southwest England Pied flycatcher population.

-experimentally tested nestbox design influence on hole-nesting bird occupancy.

For more information on the Two Moors Pine Marten Project see here.

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2024 Annual Meeting
!! 2024 Annual Meeting Saturday 9 March 2024 !!
Teign Valley Community Hall, Christow
10-3
This is our Annual Meeting where monitors come together for talks and a home-cooked lunch. This year Malcolm Burgess will summarise the 2023 monitoring results from the 45+ network sites and how network data has been used in scientific and monitoring projects. Guest speaker is Ilaria Lonero, PhD student at the University of Edinburgh. Ilaria is studying UK Redstart phenology and will present some of her results to date. Finally Malcolm Burgess will present some new results from tracking Pied flycatchers over the annual cycle from tags that record air pressure - enabling us to follow flight and location altitude over the year.

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by Malcolm Burgess

2022 was the 68th year of monitoring nestboxes at Yarner Wood, and the tally of monitored Pied flycatcher nests has now surpassed 3000! Nestboxes were originally provided in 1955 to research nest height choice by blue and great tits. The boxes attracted pied flycatchers to breed at the reserve and have been maintained and monitored ever since. Today, weekly nest monitoring is carried out by a group of Natural England staff and volunteers. These visits are supplemented by extra visits to collect more detailed data for the various science projects I lead.

Changes in populations

In 2022 52 pairs of Pied flycatchers bred in nestboxes at Yarner Wood, as well as 36 pairs of Blue tit, 11 Great tit, 4 Coal tit, 3 Common redstart and 1 Nuthatch.

The long-term monitoring enables us to see how populations have changed over the 68 years -Figure 1 shows this for the four most common nestbox using species since 1955. All these species breed in greater numbers now compared to the 1950s. The Pied flycatcher population increased rapidly through the late 1980s, before declining through the 1990s. Over the past twenty years the proportion of the nest boxes occupied by Pied flycatchers has been stable at around 20-30%, but because the number of boxes provided increased in 2011 the number of pairs at Yarner has actually increased from around 40 pairs in the 1990s to a little over 50 pairs on average over the past decade. 2022 was an average year for Pied flycatcher numbers. Common redstarts were more common in the 1980s, due to rainfall patterns in the Sahel where they spend our winter being favourable for them at that time. Blue tits have become more common at Yarner, probably from supplementary food provided at the bird feeders year-round since the 1980s, and warmer winters, meaning more survive the winter. Blue tit numbers have been lower in recent years however, and 2022 had the fewest number of pairs using the boxes since 1999, and the lowest nestbox occupation rate since 1988. Blue tits have experienced a run of six years prior to 2022 with low breeding success which has probably contributed to this.

Figure 1 - The proportion of nestboxes occupied at Yarner Wood annually since 1955.

Changes in timing

Monitoring nests over decades enables us to see changes in the timing of breeding. For me, the season starts in late March, when I start searching for the first arriving male Pied flycatchers. We have records of the first male seen at Yarner each year since the 1960s. In 2022, despite fine conditions for finding them, none arrived during the sunny mild period in late March (we have had arrivals in March before). We later could see from tracking devises that some were fitted with that they were further south on their migrations in March, not starting to cross the Sahara until the first week in April. Weather systems remained less favourable for northward migration, and it wasn't until April 13 that they started arriving. 2022 was the latest first arrival date since 2013. But despite this, the timing of egg laying closely followed the long-term trend, which is for earlier laying since the 1950s due to climatic change advancing the onset of spring. Egg laying dates of Blue and Great tits also track this change in the timing of spring.

Changes in nest success

The success of nests varies considerably year to year which is why we need long term monitoring to detect change. The most common cause of nest failure in the nestboxes is wet weather at the chick stage. On wet (and cold) days food takes longer to find, and so adults are away from the chicks for longer periods of time and spend less time brooding them (sitting over them to warm them up), and as young chicks cannot thermoregulate they chill and eventually stop begging for food and perish. In 2022, while we had some wet days during the chick stage, it was mostly dry and there was good nest success for Blue tit (6 chicks per nest - the highest rate since 2011) and Great tit (3 chicks per nest), with average success for Pied flycatchers (4 chicks per nest). Pied flycatchers were knocked back a little by nest predation which isn't common in our largely predator resilient oak boxes. This year the most significant predator was actually a mammal species we like to see doing well - Common dormouse! Dormice predate nests when they are laying eggs, the birds lay one egg per day and don't use the box during the day until they start incubating once the entire clutch is laid. This gives dormice an opportunity to use the largely undefended nestbox as a day roost, and if the nest happens to contain eggs, well that is a handy meal. We record this annually, and it happens most often in years when the egg laying period coincides with when dormice are emerging from hibernation. As flycatchers lay eggs a little later than the tits their timing is more likely to coincide with this dormice activity. Five pairs of Pied flycatchers lost their nests to dormice in 2022, although two of these pairs tried again (both successfully) in another nearby nestbox.

In total, 220 Pied flycatcher chicks fledged at Yarner this year. All these young were ringed with uniquely numbered rings, and one has already been found (alive) during its post-fledging dispersal period at Challacombe, 10km away. We don't often get these post-fledging movements detected, but about 10% of the ringed chicks get captured as breeding birds across Devon and Somerset in subsequent years, usually back to East Dartmoor NNR. As part of our scientific studies, we catch nearly all the adult flycatchers each year to reveal this sort of information.

Helped by funding from Natural England, we have fitted some adults with geolocator tracking devises over the last 10 years to learn about their migration. This work has revealed that our Pied flycatchers migrate to a fairly limited part of Western Africa centred on Guinea, Sierra Leone and Liberia, which they reach via stops in Portugal and brief stops after crossing the Sahara Desert. We have learnt that they usually cross the Sahara in a single non-stop flight that takes 36-60 hours. You can read more about this work in this blog. This year we fitted tags that additionally record air pressure to give us more insights. This year we retrieved 7 of these multi-sensor tags that we fitted in 2021 and fitted another 20 - this data will reveal flight altitudes as they cross the Sahara Desert on migration!

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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.

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Lead: Dr Antica Culina, Netherlands Institute of Ecology

Funding: Netherlands Organization for Scientific Research, NIOO-KNAW, Centre for Biodiversity Dynamics (NTNU, Trondheim), NLBIF, and CEFE CNRS (Montpellier).

Summary: SPI-Birds is a network of researchers who collect data on breeding, individually marked birds. The SPI-Birds Network hosts breeding data from over 175 breeding populations of individually marked birds, in the original format as stored by researchers and in a SPI-Birds standardised data format that has been developed within the community (see here). The SPI-Birds team creates tailored R code pipelines to convert any data format into the standard one. This quality checks the data to correct for any mistakes, and warns the users about potential issues when using the data, acting as a central contact point for researchers to access data.

As well as helping the development of SPI-Birds, PiedFly.Net are using it as a safe and secure way of storing and utilising the datasets we hold, and to make large efficiencies in the way our data is managed and added to each year. The first of our datasets are now available through the SPI-Birds database.

For more information see here and this paper: Connected data landscape of long-term ecological studies: the SPI-Birds data hub (2021) A Culina, F Adriaensen, L Bailey, M Burgess, A Charmantier, E Cole, et al. https://doi.org/10.1111/1365-2656.13388

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Lead: Dr David Wheatcroft, Uppsala University

Summary: Both Pied and Collared Flycatcher nestlings discriminate against the songs of the other species in a mixed-species population in Sweden. This discrimination has a largely genetic basis, which is suggested to maintain species differences in songs across species by biasing what juveniles learn. This project will determine whether co-occurrence with other species drives stronger discrimination in juveniles by collaborating with researchers across Europe, including PiedFly.Net, to evaluate song discrimination in nestlings in multiple locations. This study aims to determine the causes of geographic variation in song discrimination in flycatchers. In addition to information on responses to songs, video recordings of nestling behaviour capture begging calls, begging rates (before and during playback) and begging interactions among nestlings.