The Wren is one of our most widespread breeding birds, found in all but some of the most remote and high-altitude parts of the UK. Despite its abundance – an estimate of 7.7 million breeding territories was made for the population in 2009 – this is a bird that is more often heard than seen. The trilling song, which is surprisingly loud for such a small bird, makes up for the fact that this species spends much of its time foraging within cover.
Six subspecies of Wren are known from Britain and Ireland, four of which are island races, found on Shetland (zetlandicus), Fair Isle (fridariensis), St Kilda (hirtensis) and the Outer Hebrides (hebridensis). A fifth indigenus is found across the northern and western mainland, intergrading with a sixth, troglodytes, in the south-east of England. That we should have so many races underlines that this is a species that is rather sedentary in habits. Interestingly, these forms appear to have evolved rather rapidly, certainly since the last ice age.
Research by BTO, working in collaboration with the University of East Anglia, revealed that Wrens vary in their resilience to winter weather depending on where in Britain they occur. We know that severe winter weather can have a dramatic impact on Wren populations, causing numbers to collapse, but we didn’t realise that each Wren population is closely adapted to its local climate. The research found that there is a close correlation between the historic regional climate and the degree to which the population is resilient to severe winter weather. Wrens living in the north of Britain are more resilient than those in the south. Information collected by bird ringers reveals that Wrens living in the south-west (the warmest region in winter) had a body mass that is roughly 5% lower than that recorded in east Scotland (the coldest region). Larger bodied individuals can potentially carry more body fat and have what is known as a ‘thermal advantage.’
Small size and an insectivorous diet makes winter a challenging time for the Wren, which is the reason why individual Wrens establish and maintain territories outside of the breeding season. These are often located in damp habitats, such as reedbeds, where there are usually some insects and spiders to be found. Despite this territorial behaviour, individuals may come together at night to roost communally; some in a nest box or roosting pouch, while others make use of a natural cavity. Most roosts contain just a handful of birds but up to 60 Wrens have been recorded in a single nest box. This behaviour is easily overlooked, the birds typically arriving shortly after dusk and departing before first light.
The Wren in folklore
There is a surprising amount of folklore surrounding the Wren, some of which was still active until fairly recently. One common tradition in Ireland (and elsewhere) was ‘hunting the Wren’ in which a group of boys would seek out and capture a Wren, sometimes keeping it alive, sometimes killing it, but invariably parading the unfortunate bird around the village. The Wren was sometimes targeted for having ‘betrayed’ the Irish to their enemies, the boys who captured and paraded the bird being rewarded with cakes and sweets by other villagers.