The Chimney Swift

Population trends and factors of decline

On this page we provide population trends in Canada and Ontario and we highlight the possible factors of decline.

Generalities

The COSEWIC report stipulates that many authors have suggested that Chimney Swift populations may have increased with the arrival of European settlers and the multitude of nesting cavities provided by their chimneys. During this period the abundance of hollow trees decreased while the availability of chimneys increased. These new sites were rapidly adopted by Chimney Swifts. Graber and Graber (1963) supported the hypothesis that Chimney Swifts benefited from colonization arguing that they noted an increase in Chimney Swift density for Illinois between 1906-1909 and 1956-1959.
The COSEWIC report argues that it is as plausible to suggest that European colonization reduced the Chimney Swift population in North America since surveys revealed that the number of hollow trees removed was almost greater than the number of chimneys built after this event.

In 2007, the population in Canada was estimated at 11 820 indivuals (7 500 in Ontario). 

Population trends:

North America and Canada:
The North American Breeding Bird Survey stipulates that the species has declined 1.6% annually in North America since 1966.
According to the Breeding Bird Survey data, the Canadian population has declined by 7.8% per year from 1968 to 2005.

COSEWIC report data:

table Canada CS trends


CS trends in canada region


In Canada, this drastic decline has slowed to 2.37% per year over the last 15 years indicating a loss of about 28% during 13.5 years (3 generations).

In Ontario, the North America Breeding Birds Survey reveals a decrease of 5.32% to 8.01% from 1966 to 2007. During the last 15-20 years the Ontario population occupancy has decreased by 46%. This decline is underlined visually with the breeding evidence map of the species in Ontario presented below.

Ontario Breeding Birds Atlas:

Ontario Breeding Birds Atlas

A table of the data used can be downloaded here: Table Change OBBA1-OBBA2

In Ontario, the abundance peak of the species occurs in May (/migration) and August (/juveniles) as is shown in the following chart obtained from NatureCounts surveys:
 CS seasonal abundance in Ontario

If you are interested in obtaining raw data, you may want to visit the NatureCounts website which provides data from various regions, dataset surveys, and observatories: http://www.birdscanada.org/birdmon/default/main.jsp

Bird Studies Canada provides an interactive map that is very interesting to play with. This map illustrates the abundance of the species for the region you want, the year and data set you are interested in. You can consult the map with this link: http://birdmap.bsc-eoc.org/maps/birdmap/viewer.htm  

Factors of decline:

Habitat loss: decrease in nesting and roosting sites

This factor is believed to be the most significant contributor to Chimney Swift population decline:
Nowadays, the number of suitable sites continues to decline mainly due to:
- The destruction of old, large, bricked chimneys
- The closure/capping of these suitable chimneys.
- Public misconceptions: It is often believed that the presence of Chimney Swift could increase fire risks and lead owners to prevent Swifts from using their chimneys. However, Chimney Swift pairs build only one tiny nest per site and nests often fall at the end of the reproductive season, therefore it is doubtful that the presence of nests could block the chimney and enhance fire risks!
Moreover, alternative ways of heating (electric, gas...) are more and more promoted since the middle 20th century. In addition, new buildings have either no chimneys or have metal flues unsuitable for Chimney Swift: they have usually smaller diameters (<30 cm), are too narrow and can turn into fatal traps for birds that venture inside. 

Food Availability

Loss of insect prey may be a large factor in the decline. few studies of flying insects are available to help decide the importance of prey abundance changes. Research into the guano deposits in roost sites like the Fleming Hall chimney on Queen's campus may help to determine if changes in insect populations are a factor in the swift decline.

 

Chimney sweeping during breeding period

Unfortunately, the chimney sweeping season coincides with the Chimney Swift's breeding season. Sweepers could contribute to a large decrease in reproductive success by removing nests or by other kinds of disturbance. Communication and discussion can help to counteract this tendency. For example, Driftwood Wildlife Association provides a sweeper's guide and has achieved several agreements with local sweepers.  

Climatic factors

- Storms and hurricanes are believed to create high mortality during migration events.
- Abnormal temperatures during the breeding season: In spite of their torpor (see biology page) capacity, Chimney Swifts can still be very sensitive to cold temperature. Extremely warm temperatures could also severely impact juveniles mortality which unlike adults,  have no ability to cool down their body temperature by flying out of the chimney.
- Intense precipitation can play a role by diminishing food supply and leading birds to starvation. Heavy rain can also detach nests from chimney walls on occasion and contribute to egg destruction and juvenile mortality. 
- Climate change has a greater and greater impact by increasing the potential for abnormal temperatures during the breeding season and by impacting prey resources and insect emergence timing, direct abundance, shifts in insect species ranges.

Pesticides:  

 
It is a certainty that pesticides indirectly impact Chimney Swifts by directly reducing insect prey populations. In addition it is likely that Chimney Swifts could suffer from bioaccumulation resulting from eating insects that suffered from pesticide applications. This pattern has been reported for related species but evidence for the Chimney Swift's case is lacking.
Pesticides may have a greater impact in the winter range where the legislation is more flexible (wide and aerial applications, higher toxicity, etc). Research by Queen's and Ottawa Universities on the Fleming Chimney may shed some light on this.

Competition:

Intra and interspecific competition could be involved in the reduction of nesting sites availability. Competition can directly impact the breeding possibilities (no site) or indirectly by increasing the amount of energy spent for territory defences.

Predation and diseases such as the West Nile Virus are also considered as factors of decline.

Sources:
- Bird Study Canada: http://www.bsc-eoc.org/
- Cadman M.C., D.A. Sutherland, G.G. Beck, D. Lepage and A.R. Couturier. The Atlas of the Breeding Birds of Ontario (2001-2005). Bird Studies Canada, Environment Canada, Ontario Field Ornithologists, Ontario Ministry of Natural Resources, and Ontario Nature. 
- COWEWIC. 2007. Assessment and Status Report on the Chimney Swift chaeture pelagic in Canada, threatened 2007. Committee On the Status of Endangered Wildlife In Canada. Ottawa. 49pp
- McIlwraith Field Naturalists of London. 2008. Swift Fact Sheet 2008.
- Nature Counts: http://www.birdscanada.org/birdmon/default/
- Ramsey J. J. 1970. Temperature Changes in Chimney Swifts (Chaetura pelagica) at Lowered Environmental. The Condor, Vol. 72, No. 2, pp. 225-229.