Malcolm Burgess posted: "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." PiedFly.Net The 2022 nestbox season at Yarner Wood Malcolm Burgess Oct 22 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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