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Pair Formation
Beginning in early spring, juvenile males that are ready to breed perform their courtship displays in the vicinity of females, often at the same time as three to four other males (Cramp, 1993). Displaying males fly straight up (roughly five to six feet) while fanning their tail feathers and then descend rapidly while emitting a twittering call. Researchers disagree on the process of pair formation: some sources report that males and females from the same winter flock pair up with each other while others report that females pair up with males from neighboring flocks (Gaston, 1973; Harrap & Quinn, 1996; Cramp, 1993). In either case pairs build their nests within the territory defended by the male’s winter flock (Cramp, 1993).
Long-tailed tits are best characterized as a monogamous species. Hatchwell, Ross, Chaline, Fowlie, and Burke (2002) obtained DNA samples from 14-53 color-ringed pairs of long-tailed tits and their offspring in order to assess the incidence of mixed parentage, which is common in most bird species. Although 8.9% of females and 7.4% of males attempted to breed with more than one partner during the breeding season, most mate switches were made after the first breeding attempt failed, so no cases of mixed parentage resulted from these switches.
Female long-tailed tits lay their clutches of 8-12 eggs inside their nests and incubate them for 12-18 days (Harrap & Quinn, 1996). Both parents tend to their young but rely on the assistance provided by “helpers,” which are adult long-tailed tits whose nests have failed. The young typically fledge within 14-18 days and return to their nests to feed for up to two weeks after fledging (Grzimek, 2003; Gaston, 1973).
Provisioning
In an eight-year observational study, MacColl and Hatchwell (2003) analyzed the provisioning behavior of 18-53 breeding
pairs of long-tailed tits. Fathers spent more time providing their nestlings with food than mothers did, which suggests that the resource defense hypothesis applies to this monogamous species. However, considering that female long-tailed tits lay their clutches and incubate the eggs by themselves, it is possible that the amount of parental investment balances out in the long run (Cramp, 1993).
Parental long-tailed tits exhibit a “hover display” after their brood hatches, which involves flying straight up from a perch, briefly hovering a couple feet above the perch, and then landing on the original perch or an adjacent one (Gaston, 1973). Birds often exhibit this behavior during feeding time, so they may have food in their beaks. Although adults who perform this eye-catching display increase their risk of predation, it appears to serve as a way for them to attract supernumerary helpers to their nests.
Divorce
Hatchwell, Russell, Ross, and Fowlie (2000) conducted a five-year observational study of 88-105 color-banded pairs of long-tailed tits in which they measured the frequency of divorce from one breeding season to another as well as breeding success, which is based on whether a brood was fledged or not. “Divorce” was said to have occurred when one member of a pair that bred during year N mated with a different partner during the following year.
Sixty-one percent of the males in the study population and 65% of the females divorced between breeding seasons. Unlike other cooperatively breeding species, however, long-tailed tits that bred successfully were significantly more likely to divorce than were those who failed to breed. Given the high mortality rate of adult male long-tailed tits (44%) and the tendency for pairs to reside with the male’s natal flock, Hatchwell et al. (2000) concluded that divorce (and the accompanying dispersion) may allow females to avoid the risk of breeding with related males; this is referred to as the inbreeding avoidance hypothesis.
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