Wonderful Wrens - PDF Document

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  1. ABOUT BIRDS Wonderful Wrens T and a regular user of the garden environment. Many books describe the Wren as being secretive but, while it is often overlooked, it certainly does not hide itself away from Man. It would, perhaps, be better described as being indifferent to us and to our activities. The Wren population is at something of a peak at the moment, thanks to a run of mild winters which have boosted overwinter survival. Monitoring work carried out by the British Trust for Ornithology has highlighted how particularly cold winters can reduce the breeding population by a quarter or more. iny, restless and pugnacious, the Wren is one of our most familiar songbirds, widespread across Britain & Ireland of the upland fringe. The species also breeds on the sea cliffs of offshore islands, where it occurs in a number of distinct island forms (see page 11), exploiting the tide line for feeding opportunities. Male Wrens establish their breeding territories in early spring, each proclaiming ownership through a surprisingly powerful song. Such territory holders are highly aggressive towards other males and use a combination of song and posture to see off their rivals. Each male will court any female that enters his territory, tempting her to use one of the nests that he has built there. Males nesting in the south of Britain will build five or six different nests, the female inspecting each in turn to determine which, if any, she wishes to use. Females appear to select nests that are the most cryptic, presumably because such nests are less likely to be predated. Once selected, the nest will be lined by the female and breeding will commence. Males nesting further north, and in particular on islands off the coast, build fewer nests (in some cases just a single nest) and are more attentive partners than those further south. Such differences in investment relate By Mike Toms GBW Organiser The nesting habit The preferred nesting habitat of the Wren is the understorey of deciduous and mixed woodland, especially the damper areas where this vegetation is particularly lush. However, when numbers are buoyant (such as following a run of mild winters), other habitats are increasingly well-used. Among these other habitats are gardens, orchards, farmland hedgerows and the sheltered scrubby valleys Wrens (this page and opposite) by Steve Round | Spring 2008 Bird Table 53

  2. WREN to the environmental conditions under which the bird is nesting. With a shorter season and less food available in the north of the breeding ranges, males here have to work harder to rear a successful brood. Males in the south have access to more resources and so can indulge in establishing relationships with multiple females, at the same time investing less in each individual nesting attempt. Similarly, the species tends to be single-brooded in the extreme north of Britain, managing two broods elsewhere within Britain & Ireland. maintaining a compost heap, turned regularly to reveal a wealth of tiny insects upon which the Wren can feed. Even so, the species tends to favour cover and is unlikely to be seen visiting bird tables. FACT BOX Common name: Wren Scientific name: Troglodytes troglodytes Family: Wrens Winter roosts The establishment of communal roosts is a means by which individual Wrens can reduce heat loss during the long winter nights. Such roosts usually involve small numbers of individuals but there are records of several dozen roosting together. There is even a record of 61 roosting together in a Norfolk nestbox during the winter of 1969. In the confined space afforded by many of these roosting sites the birds may squat on top of one another, heads in and tails towards the entrance. The establishment of communal roosts appears to be initiated by the male within whose territory the roost is located. He will attract other birds to the roost through calls and short flights out. Individuals appear to enter the roost shortly after sunset, and depart before dawn, so they may be using sites within your garden without your knowledge. Late in the winter, with the approach of spring, the resident male attempts to prevent other males from entering the roost, favouring females, one or more of whom may go on to mate with him come the breeding season. Certainly, paired females will often roost within the preferred nest prior to the initiation of egg-laying. UK population: 8 million pairs (summer) winter numbers unknown Foods and feeding Wrens feed on insects and spiders, occasionally adding small seeds to their diet. Their small size and agility mean that Wrens are able to access holes and crevices that would be out of the reach of many other birds. Many of these sites remain available during periods when snow has fallen and so provide a lifeline for these diminutive insectivores. Wrens have even be known to forage under the snow cover itself, seeking out the small invertebrates that remain active within the somewhat protected environment afforded by the snow. Being so small has its disadvantages, the most prominent of which are that the bird chills rapidly and is unable to store much in the way of body fat. Wrens can be tempted to take supplementary food by providing breadcrumbs, a little oatmeal or finely grated cheese. A more valuable service can be provided by Conservation status: Green listed Migratory status: Resident / winter visitor Breeding: Clutch size: 5–6 eggs Incubates: 16–18 days Young in nest: 15–18 days Number of broods: 1 (2) Breeding season: Mar–Aug Age at first breeding: 1 Typical lifespan: Two years Max. recorded lifespan: Seven years www.bto.org/birdfacts Bird Table 53 Spring 2008 |

  3. ABOUT BIRDS and we receive a small but regular passage (in autumn and spring) of birds from the near continent. Some of these birds, seemingly of Scandinavian origin reach Scotland and there is a regular passage of Wrens reported from oil platforms located in the North Sea. Further confirmation of the arrival of such birds comes from the spring recovery in Sussex of a Wren ringed the previous autumn at a Russian ringing station on the Baltic coast. Winter territoriality Many Wrens establish winter territories, which they use to defend their preferred feeding areas. Such territories clearly make an important contribution to overwinter survival, since it has been shown that territory holders have much better survival rates than birds without a territory. Presumably having a territory provides access to known food sources and accrues knowledge of where these food sources are, plus the locations of suitable roosting sites. Competition for winter territories may be fierce and can begin as early as the preceding July. Even migrant Wrens (of which more later) may establish winter territories, often returning to the same territory in subsequent winters. Many of the winter territories of these migrant individuals are associated with reedbeds and other damp habitats, presumably because they hold good populations of invertebrate prey species. Shout about it A question that is frequently asked by Garden BirdWatchers is how such a small bird can have such a loud song. In birds, the larynx lacks any vocal cords and so has little or no role in song production. Instead, birds have an organ known as a syrinx. This is located just above where the windpipe forks into the two lungs. It has several components, including a resonating chamber (the tympanum), a series of vibrating membranes and controlling musculature. Interestingly, the syrinx is far more efficient at producing sound than our own larynx and its associated vocal cords. In comparison, while the syrinx is able to vibrate just about all of the air coming out of the lungs, our vocal chords manage to utilise a mere 2% of the air passing over them. In addition, the syrinx can produce two different sounds simultaneously (one from each half) and this goes some way to explaining the complexity of sounds that a bird can incorporate into its song. On the move Within Britain & Ireland, Wrens are largely sedentary in habit. However, those birds breeding in upland areas may move to lower altitude sites for the winter. Populations on our northernmost islands are able to persist without the need to move elsewhere because of access to the tide line, a habitat that supports good numbers of invertebrate prey even in the most testing of weather conditions. Other breeding populations may be more mobile Wetland habitats, such as reedbeds and wet woodland, are well used by Wrens, especially during the winter months. They are rich in invertebrates. Wren by Steve Round 10 | Spring 2008 Bird Table 53

  4. ISLAND FORMS Some 43 subspecies of Wren are recognized globally, six of which occur in Britain & Ireland. Two occur on the mainland; troglodytes in southern England (the race also found on the near Continent) and indigenus, found across northern England, Scotland, Wales and Northern Ireland. Then there are a number of island forms; Shetland Wren (zetlandicus) on Shetland, Fair Isle Wren (fridariensis) on Fair Isle, Hebridean Wren (hebridensis) on the Outer Hebrides and St. Kilda Wren (hirtensis) on St. Kilda. These island forms typically differ from the mainland forms by being darker in the ground colour of their plumage and more heavily barred - for example, the Shetland Wren is a sooty brown colour and not the rufous brown of mainland birds. Their songs also differ and some of the subspecies are notably different in size. The development of island races or subspecies derives from their isolation. Separated from the mainland populations, there is scope for divergence in characteristics, like song or body colour. The island forms also show differences in their behaviour, with the males typically more supportive of their mates during the breeding season. Main image, Wren by Steve Round; inset Shetland Wren by Jill Pakenham – BTO Collection Wren folklore There is a great deal of folklore associated with the Wren, much of it of a related and relatively modern nature. The Latin name of the Wren is ‘Troglodytes’ which we typically translate as ‘cave dweller’. The word itself comes from ‘trogle’ (a hole) and ‘duo’ to plunge in, a more appropriate description of the bird. The word ‘Wren’ has its origins in the Anglo Saxon word ‘wrœnno’ meaning lascivious! One particularly interesting aspect of Wren folklore is that the bird is sometimes regarded as being masculine and sometimes feminine. ‘The Robin and the Wren, are God’s cock and hen’ is a good recent example of a feminine association, as are the names ‘Jenny Wren’ and ‘Kitty Wren’. Masculine associations can be seen in the German name of ‘Zaunkönig’ (‘hedge-king’) and the old Danish name of ‘Vrensk’ (‘uncastrated’). The association with kingship appears in some of the chants associated with the custom of Wren Hunts (see below) and with a legend that sees the Wren elected king of all birds. The legend goes that all the birds of the earth agreed to choose as king the one who should soar highest. This honour was bestowed upon the Wren because it remained on the back of the Eagle, the latter having soared to the limit of its power above the earth. The tradition of ‘Hunting the Wren’, still played out in parts of Ireland, shows a commonality across various parts of western Britain and Ireland. Curiously, the custom varies in its origins and enactments in the different regions. The central focus, however, revolves around groups of boys going out into the countryside to capture or kill a Wren. This is then paraded around the village where the boys demand rewards for their actions (it sounds a bit like the American custom of trick or treat). In parts of Ireland the hunt took place on St. Stephen’s Day (December 26th); the Wren taken alive and tied to a pole. As the Wren is paraded around the houses, the boys chant ‘The wran, the wran, the king of all birds’ St. Stephen’s Day was caught in the furze; Come, give us a bumper, or give us a cake, or give us a copper, for Charity’s sake.’ It is believed that this apparent victimisation stems from the Wren, at some time in the past, having betrayed the Irish to their enemies by tapping on a drum. A similar hunt took place in Kerry, though on Christmas Day, and this time the Wren was persecuted because it was thought to be a beautiful fairy, assuming Wren form, who lured the male inhabitants to a watery grave in the sea. A similar custom on the Isle of Man, resulted in the Wren being buried in the churchyard, accompanied by the singing of dirges. It is clear from such folklore that the Wren has a special association with Man, hardly surprising given its resilience and character. To me, a description from the very start of the 1900s sums up the Wren; ‘even on uninhabited island rocks ... [the Wren’s] ... lively song relieves the awful solitudes.’ Bird Table 53 Spring 2008 | 11