Pied flycatchers in Shropshire

Dr Bob Harris has been working with bird ringer Gerry Thomas to monitor Pied flycatchers in Clunton Coppice through the installation of next boxes. Here, he gives and insight into what is involved and introduces a charismatic bird species which travels 1000's of miles to spend summer in Shropshire.

Before they start the busy time of nesting and raising young, the Pied flycatcher could be excused a small rest. It will have just completed an 8000km journey from its wintering grounds in the wooded savannah of western Africa (Sierra Leone, Liberia and Guinea). Having started with a single flight of 40 hours to cross the Sahara - it eventually arrives in our woodlands in mid-April.

The black and white males arrive several days before the brown and white females and their first task will be to find a territory, start singing and attract a mate. Territory for this flycatcher is typically mature deciduous and mixed woodland, with Oak (Quercus spp) predominating; but they will also use riparian Alder (Alnus spp) streams. In Shropshire this confines them to the North-West uplands around Oswestry, the uplands of the Stiperstones and around Church Stretton, along the River Clun into the Clun Forest; with smaller restricted populations elsewhere.

Pied flycatcher (Ficedula hypoleuca) adult male (r) and female (l) (c) Mark Hamblin/2020Vision

Individuals can be extremely site faithful so having nested successfully at one site they will return to that site again and again. When laying their typically seven sky-blue eggs in nests of dry brown oak leaves, grasses and honeysuckle, they will use holes in trees, but given a preference they will make use of nest boxes, which makes them extremely amenable to detailed study.

Pied flycatchers, like many long-distance migrants are in trouble. They are red-listed in Britain due to falling breeding numbers, but the reasons behind this are not straight-forward. Current research centres around something called the ‘mismatch hypothesis’. Under conditions of global warming the emergence of caterpillars is getting earlier each year.

These caterpillars, particularly winter moth caterpillars, are the major food source for recently hatched chicks and so the flycatchers have to make their own breeding cycles earlier to coincide with when these caterpillars emerge. Unfortunately they are not compensating quickly enough and they are missing this food peak and suffering accordingly. Besides this mismatch habitat changes and severe weather events - squally rains and frosty nights – are also having an effect. Furthermore climate events are influencing migration, and survival in west Africa.

In the 1980's when it was discovered that Pied flycatchers would make use of boxes many nest-box schemes were started throughout the country. In Shropshire one of the earliest and biggest schemes was initiated by Chris Whittles, focusing on riparian habitats around Newcastle-on-Clun. Chris erected over a thousand nest boxes and monitored them annually. Recent analysis of records from these boxes has revealed that almost from day one there has been a steady decline in the number of pairs of Pied flycatchers nesting each year; a finding which mirrors the number of breeding pairs at all sites in the county.

Pied flycatcher at nest box (c) Amy Lewis

Shropshire Ringing Group took ownership of these nest boxes from Chris in 2015 and continued monitoring. This first year, 2015, was a bad year with virtually every weather event that could affect nesting coming in to play. At the end of the breeding season the success rate was only 12%. Over the next three years success rates improved to 60% but fell back to 22% in 2019. These returns are far short of the breeding performance returned from Welsh oak woodland sites of >85%. This raises the question: is the poor performance at Newcastle a consequence of climate and riparian habitat changes around Newcastle, or is it just indicative of nationally falling numbers?

Step forward to Clunton Coppice. This Shropshire Wildlife Trust reserve is sufficiently close to Newcastle to represent a site which can be assumed to have minimal geographical differences to the existing study. It is an oak woodland and, importantly, already has Pied fllycatchers.

Will they have better breeding success here than at the Newcastle site? And if so, can we relate this to habitat and/or food availability? Although, some nest boxes are present within the woodland they are few in number and have not been monitored consistently. During the latter half of 2019, and when Covid restrictions permitted in 2020, further nest boxes were added - now making a total of 80. A small contingent of Wildlife Trust volunteers have been recruited to monitor the boxes - collecting data weekly from the beginning of May to end of June on such things as nest building, clutch sizes and chicks fledged. When Covid allows this monitoring will begin.

It is anticipated that taking end of year breeding performance figures from Newcastle, as a riparian habitat, and Clunton Coppice, as oak woodland, together with figures from other sites from across Shropshire, we hope to understand what may be the casual factors for Pied flycatcher declines in Shropshire: habitat, location, climate change, disturbance, or some mix of all.