Pic: Lisa Geoghehan / Alamy Stock Photo
Words: Kate Risely, of the British Trust for Ornithology (BTO)
For a few weeks in autumn, Jays seem to be everywhere, and according to BirdTrack they are twice as likely to be recorded at this time of year than in the spring and summer. They are eye-catching birds, noticeable for their pink, black, blue and white colours that are so unusual for a crow.
What’s behind this flurry of activity? In autumn, Jays collect acorns and store them for the winter, and this is a massive operation. Birds can travel long distances out of their home ranges to productive oak trees and spend hours every day ferrying acorns back and forth.
They are able to carry several acorns at a time in their gullet, as well as a larger one in their bill, and these are secreted in nooks and crannies in trees, under roots and moss and in the ground. It has been calculated that a single Jay can relocate 5,000 acorns in a few short autumn weeks, and with a British population of 170,000 pairs of Jays, it’s no wonder they intrude on our consciousness during this busy time.
Over the course of the winter the birds will revisit their many little hiding places and eat the acorns, but a proportion are never retrieved; this is the part of the process that benefits the oak tree, as millions of acorns are dispersed and planted by willing helpers.
Acorn crops can vary hugely from autumn to autumn, or even fail entirely, depending on weather conditions earlier in the year and pest levels. Jays are by nature sedentary, but if they realise they won’t have an acorn store to see them through the winter they can move long distances, and in large numbers.
Jays often make these ‘eruptive’ migrations in Scandinavia, where they are unlikely to survive without a winter larder, and in years of particularly poor acorn crops across Europe these movements may even be noticeable in Britain. One such year was 1983, when thousands of birds were observed migrating into and across Britain and even reaching Cornwall, where 800 Jays were seen together in a single field.
Responses to crop failure are not always so noticeable, but with modern online tools, patterns can clearly be seen. The BTO Garden BirdWatch results pages show how numbers of Jays visiting garden bird feeders in autumn vary from year to year, and it’s interesting to compare these to the reports of tree seed crops on the Nature’s Calendar website. In years when reports of acorns in the countryside are low, more Jays are seen in gardens, demonstrating how birds fall back on human-provided foods when their preferred natural foods are in short supply.
While Jays are mainly reliant on acorns and other seeds in winter, at other times of year they mainly forage on the ground for invertebrates, and have been known to take small mammals, other birds, bats and even fish. This generalist lifestyle has enabled them expand from their woodland strongholds into more suburban areas, following the general decrease in human persecution.
This success has led to an increased population, with numbers at their highest levels since population monitoring began in the 1960s.
by Ed Hutchings
First things first – I must nail my colours to the mast. The Wren is my favourite British bird. Indeed, I recently voted for it in the National Bird poll. I did feel a searing twinge of guilt, as if I were cheating on the Robin, but the Wren sums up the nation for me.
It is small, but fearless and full of character. It punches above its weight, though, admittedly, we rarely do as a whole these days. It sings all year; even in the depths of winter, its machine gun rattle of a song resonates through the thickest of thickets. It is found everywhere and anywhere. Most common in deciduous woodland, I have seen it up mountains and even beachcombing on the coast.
The Wren is the only member of the wren family Troglodytidae found in Eurasia and North Africa. It was once lumped together with Troglodytes hiemalis of eastern North America and Troglodytes pacificus of western North America as the Winter Wren. ‘Our’ Wren only occurs in Europe and a belt of Asia from northern Iran across to Japan. It is only migratory in the northern areas of its range, where birds will move considerable distances.
The scientific name is taken from the Greek word ‘troglodytes’, meaning ‘cave-dweller’, and refers to its habit of disappearing into cavities while hunting or to roost. This second smallest of our birds (it is only a quarter of an inch larger than the Goldcrest) has long been a national favourite and it is easy to appreciate why. The Wren is instantly recognisable as a small, warm brown bird with a restless nature, often seen holding its short, stubby tail cocked.
Although the Wren has a smaller wing length than our native duo of crests, it is a surprisingly stocky bird and is considerably heavier. When seen at close range, the delicate tones of the rufous-brown plumage become visible, as does the longish bill and pale-coloured supercilium.
The Wren is a widely distributed and successful species but, according to the BTO, it is less commonly reported from gardens than one might expect. Although tiny, inconspicuous and skulking, Wrens are not difficult to locate, at least when in full voice between February and July. Then, the song is shrill and delivered with much force. It consists of a cascading warble of clear notes that last for about five seconds, ending in a flourish.
The Jenny Wren – an epithet applied to the cock as well as the hen – has an absorbing life history. The breeding season runs from March to August. The male builds a number of ball-shaped nests, made of leaves, dried grass and moss, with an entrance at the side near the top. These are sited in hedges, ivy-covered walls, tree trunks, outbuildings and even in the old nests of other birds. The male may also make ‘dummy’ nests, which are not actually used but may help to divert potential predators.
Having lined her chosen nest with hair and feathers, the female normally lays five to six eggs, white in colour and speckled with black or reddish-brown at the larger end, which she incubates for 16 to 18 days. The young are fed by both parents (but only brooded by the female) and fledge at 15 to 18 days.
Two broods are normal and the male may take the first brood to roost in one of the ‘rejected’ nests while the female is incubating the second clutch.
Wrens are highly polygamous; that is to say a male can have, at any one time, more than one female with an active nest on his territory. However, they can be monogamous when the food supply is poor. The adaptability of the Wren underlines its success.
Typical day of a Wren
Feeding is frantic. The Wren forages in dense undergrowth for insects, mainly larvae, as well as for spiders and a few berries. Many garden nesters favour moth larvae in particular, destroying huge numbers of pests such as the dreaded Winter Moth, only emerging in the coldest weather to take small scraps of food from the ground beneath bird tables. They have even been seen paddling to reach tadpoles and small fish.
Although they are usually seen feeding low down in the undergrowth, Wrens sunbathe whenever they can find a sunlit spot to bask in. They spread their wings and raise the feathers on their head to ensure that most of their plumage is exposed to the sunlight.
Being such a diminutive bird, the Wren can be vulnerable to cold weather. Hard winters deny it food, and because of its size it chills much more rapidly than larger birds.
Bird species factfile:
Common name: Wren
Scientific name: Troglodytes troglodytes
UK numbers: 8 million pairs
Habitat: Woodland, gardens
Diet: Insects, spiders