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COSEWIC Assessment and Status Report on the Chimney Swift in Canada

Biology

General

Chimney Swifts spend most of the day on the wing. They are extremely gregarious, feeding and roosting in large flocks (Chantler and Driessens 2000; Snow and Perrins 1998). During migration, they congregate in flocks of thousands at roosting sites along their migration route (Groskin 1945; Michael and Chao 1973). Roosts are also used in the summer, before and after nesting by breeding birds and during all of the summer by most of the non-breeding birds and failed breeders.


Reproduction

The reproductive information in this section comes primarily from the work of Ralph Dexter (1944-83) at Kent State University in Ohio and of Richard B. Fischer (1939-53) in New York State.

The Chimney Swift is a solitary breeder and only one nest is built per nesting site (chimney, tree hollow, air shaft, etc.; Fischer 1958; Dexter 1969, 1974, 1991). Although several pairs may nest close together on the roof of a building with a number of chimneys (Dexter 1969), it is not a true colonial species (Fischer 1958). Chimney Swifts can form loose colonies in which each pair uses and defends a different site. Dexter (1969) even noted that swifts tended not to nest in air shafts that were adjacent to one already occupied by another pair. The only exception reported in the literature is of two nests inside the same barn (Fischer 1958). In that case, the building’s large size in comparison to a chimney doubtless explains the presence of two pairs in one location. It is difficult to believe that there could be more than one nest in a given chimney given the aggressiveness that nesting pairs show to neighbouring swifts when nesting is advanced (C. Garneau, pers. comm.).

Chimney Swifts normally mate for life and are monogamous (Dexter 1992). Adults have a very strong tendency to return to the previous year’s nesting site (Fischer 1958; Dexter 1992). Swifts retain the same mate as long as both return to the nesting site each year (Dexter 1971). However, if one of the birds does not appear, the remaining one will mate with another individual. Dexter (1992) recorded a mate fidelity rate of 84% (294 pairs) and 96% of these pairs occupied the same air shaft that they had used the previous year. Pairs typically build their nest in the same spot on the wall from one year to the next (Dexter 1969).

Chimney Swifts do not generally breed before their second year (Dexter 1981a), but some individuals can breed during their first summer (Dexter 1952a, 1981b, 1985; Fischer 1958; Kyle and Kyle unpublished data). Courtship takes place primarily in the air and consists of chasing and flying by the pair, with the birds engaging in “V-ing” and gliding for short distances (Fischer 1958). It was long believed that swifts copulate while in flight but in fact they copulate on the vertical surface inside the nesting site (Dexter 1950; Fischer 1958) or in the nest (C. Garneau, pers. comm.). Chimney Swifts are generally single-brooded in northern latitudes (Baicich and Harrison 1997), although there have been reports of 2 broods per year for some pairs in Texas (Kyle and Kyle unpublished data).

The nest is made of small dead twigs glued to the vertical surface and to each other to form a half-saucer (MacNamara 1918; Shelley 1929; Fischer 1958; Zammuto and Franks 1981). Dexter (1969) observed that the average depth from the chimney top was 6.1 m in 400 nests studied in Ohio. Most of the time, they were attached to the chimney’s south and west walls. Swifts do not normally reuse nests built the previous year as most fall down over the fall or winter (Dexter 1969), but some nests built in sheltered locations are in good enough condition to be renovated and reused (Amadon 1936; Fischer 1958; Dexter 1978, 1981a; Cink and Collins 2002; C. Garneau, pers. comm.).

Two to six (normally four or five) eggs are laid and the young hatch after 19 to 21 days of incubation (Fischer 1958), which is done by both parents. Hatching success is high; Fischer (1958) obtained a figure of 90.7%. These results are similar to those obtained from an artificial chimney in Lévis between 1998 and 2003 (Garneau and Gauthier, CWS-QC unpublished data) and in Texas between 1989 and 2002 (Kyle and Kyle unpublished data). Fledging success is also high (86%) and three to six young are produced (Fischer 1958). All existing data seems to show that reproductive potential is similar across the different regions and in time suggesting that when individuals reproduce, they perform well. The decline is therefore potentially caused by some other problem.

Based on numerous banding data collected across North America, between 1920 and 1950, the annual adult survival rate for Chimney Swift was about 63% (Henny 1972). This rate is similar to the 73 ± 7 % calculated from banding data from Paul and Georgean Kyle’s Chimney Swift project in Texas between 1989 and 2002 (CWS-QC Unpublished data). Mortality is highest in the first year after hatching for most swift species studied (Chantler and Driessens 2000), but data from Kyle and Kyle permitted an estimation of the survival rate for juvenile Chimney Swifts (78.8 ± 21.9%), which was not significantly different from the adults. This is particularly high considering that the Chimney Swift makes long transcontinental migrations. With such a high survival rate, it is not surprising that swifts live to an old age for birds of such a small size. The record for known Chimney Swift longevity is 14 years (Dexter 1979); the average is 4.6 years (Dexter 1969).


Movements/Dispersal

Swifts arrive in southern Ontario at the end of April and in mid-May in the more northern areas (Cink and Collins 2002). Most Chimney Swifts arrive in Quebec in the last two weeks of May (David 1996). They leave Quebec early, most of them by the end of August (David 1996). In New Brunswick, swifts have been reported from 22 April and 10 November, but most are gone by 18 September (Squires 1976, Tufts 1986).

The Chimney Swift migrates diurnally in flocks (Coffey 1936; Tyler 1940; Whittemore 1981; Chantler 1999). During the fall migration, the birds converge on the Mississippi Valley from the northern United States and Canada (Lowery 1943; Ganier 1944; Bowman 1952). The number of birds increases as they get farther south, reaching thousands of individuals in the Gulf States (Texas, Louisiana, Mississippi). Most of the swifts then cross directly over the Gulf of Mexico (Lowery 1943), passing over the Yucatan Peninsula and following the Atlantic coast of Central America (Howell and Webb 1995), reaching Peru in early November (Plenge et al. 1989). In spring, Chimney Swifts essentially repeat this route in reverse, arriving in the southern United States in mid-March.


Feeding Habits

Chimney Swifts feed on insects and spiders, taken almost exclusively in the air (Chantler 1999). Main insects taken are caddisflies (Trichoptera); mayflies (Ephemeroptera); crane flies (Diptera; Tipulidae); various other flies (Diptera); beetles (Coleoptera); wasps, ants, bees (Hymenoptera); and true bugs (Hemiptera) (Cink and Collins 2002). To drink, they skim close to the water, touching the surface lightly with their bills (Whittemore 1981; Godfrey 1986).


Physiology

Chimney Swifts can enter a torpid state when exposed to cold temperatures (Ramsey 1970). They do not exhibit any movement and their body temperature drops, rising quickly when the ambient temperature rises (Ramsey 1970).


Adaptability

Since the settlement of North America, the Chimney Swift has quickly adapted to new artificial habitats provided by man-made structures (chimneys, shafts, silos, etc.). However, the species seems to be declining as the habitats for which it is adapted (hollow trees, chimneys) are rapidly disappearing. This situation will be addressed in the section on Limiting Factors and Threats.