Long-tailed tit

Voice

This species is often identified in the field through hearing its distinctive vocalisations. When they are in flocks, they issue constant contact calls, so they are often heard before they are seen. They have three main calls, a single high pitched pit, a 'triple trill' eez-eez-eez, and a rattling schnuur. These calls become faster and louder when the birds cross open ground or if an individual becomes separated from the group.^[16]

Migration and dispersal

The long-tailed tit is generally resident, only moving short distances, with the exception of the white-headed northern nominate Ae. c. caudatus; this is significantly more mobile, with some moving long distances south or west to escape the harsh winters of its breeding range.^[18] In Great Britain, recoveries of ringed long-tailed tits showed the median distance travelled was just 2 km. Immatures were more mobile than adults; of recoveries of birds ringed as adults, 95% were within 20 km of the ringing site, while for birds ringed as juveniles, 95% were within 60 km of the ringing site.^[19]

Food and feeding

The long-tailed tit is insectivorous throughout the year. Its diet consists predominantly of arthropods, with a preference for the eggs and larvae of moths and butterflies. It occasionally takes vegetable matter such as seeds in autumn and winter.^[20][21]

Nest

The nest of the long-tailed tit is constructed from four materials; lichen, feathers, spider egg cocoons, spider silk, and moss, with over 6,000 pieces used for a typical nest^[22]. The nest is a flexible sac with a small, round entrance at the top, suspended either low in a gorse or bramble bush or high up in the forks of tree branches. The structural stability of the nest is provided by a mesh of moss and spider silk; the tiny leaves of the moss act as hooks and the spider's silken thread provides the loops, thus producing a natural form of velcro.^[23] The tit lines the outside with hundreds of flakes of pale lichens to provide camouflage. The inside of the nest is lined with more than 2,000 downy feathers to provide insulation.^[23] The nests suffer a high rate of predation, with only 17% success.^[22][24]

• 
  A long-tailed tit in its nest
• 
  Egg, Collection Museum Wiesbaden
• 
  Aegithalos caudatus – MHNT

Social behaviour

Outside of the breeding season, long-tailed tits form compact flocks of six to seventeen birds. These flocks are composed of family parties (parents and offspring) from the previous breeding season, along with any additional adults who helped raise a brood.^[25] These flocks will occupy and defend territories against neighbouring flocks.^[16] The driving force behind the flocking behaviour is thought to be that of winter roosting, being susceptible to cold; huddling increases survival through cold nights.^[26] When the breeding season begins, the flocks break up, and the birds attempt to breed in monogamous pairs.^[27] Males remain within the winter territory, while females have a tendency to wander to neighbouring territories.^[16]

Since long-tailed tits are cooperative breeders, where opposite sex adult relatives are spatially clustered, they risk inbreeding fitness costs.^[28] However, such inbreeding fitness costs are avoided by active kin discrimination during mate choice.^[28] Kin discrimination appears to be based on distinguishing between the vocal calls of close kin and nonkin.^[28]

Pairs whose nests fail have three options: they can try again, abandon nesting for the season, or help at a neighbouring nest. Studies have shown that failed pairs tend to split up and assist with the nest duties of male relatives,^[26][29][30] recognition being established vocally.^[29] The helped nests have greater success due to higher provisioning rates and better nest defence.^[26] At the end of the breeding season, in June and July, the birds reform the winter flocks in their winter territory.^[16]

Helpers

There is a high nest failure rate due to high predation.^[22] If a nest fails after the beginning of May, the failed breeders will not attempt to re-nest, but they may become helpers at the nest of another pair, who are usually related. One study found that around 50% of nests had one or more helpers. By helping close relatives, helpers indirectly benefit in terms of fitness by increasing the survivability of related offspring. They may also gain greater access to mates and territories in the future. Helpers also gain experience in raising young, meaning that their future offspring have a better chance of survival.

Both males and females are equally likely to become helpers. Parents may supplement their own efforts with the help of others, or, at the other extreme, reduce their own efforts in favour of the helpers' efforts. Although the survival rate for adults of both sexes is the same, juvenile males have a higher survival rate than juvenile females. Offspring raised with helpers have a higher survival rate than those raised without. Failed breeders who became helpers had a higher survival rate than those who did not. This may be due to the reduced energy expenditure involved in sharing a nest. This is similar phenomenon to that observed in acorn woodpeckers and green wood hoopoes. However, failed breeders that did not help are more likely to breed successfully in subsequent years, so there may be a cost of helping. This may be due to helpers having relatively poorer body conditions at the end of the breeding season, similar to pied kingfisher and white-winged chough. Successful breeders have a survivability rate around the survivability of failed breeders who became helpers.^[27]