The Barn Owl in Ontario

Scientific Name: Tyto alba

The Barn Owl is a grassland bird and therefore of interest to people involved in the recovery of tallgrass prairie and oak savanna habitats. The Barn Owl historical status is unknown but it was probably always present in Ontario in small numbers, foraging mainly in tallgrass prairie and oak savanna habitat prior to European settlement. It likely became more common in the province (and bordering states) following the clearing of forests and replacement with pastures and hay fields, and the erection of barns and other structures that augmented the availability of nest and roost sites. 

News from the Ontario Barn Owl Recovery Project February 15, 2008 

Main threats to barn owl populations:
(Copied from the Canadian Biodiversity Project website)

Loss of habitat:
In most areas, old farms are being renewed or torn down. These usually provided the dark and undisturbed areas that barn owls prefer. However, the new farms lack these conditions and this has caused a decrease in the number of adequate roost and nest sites (Taylor, 1994. Shawyer, 1998). In Europe, churches have also made for good habitat. Now, wiring is installed at tower openings to keep out pigeons... and, consequently, barn owls. Also, Dutch Elm disease and deforestation have caused a loss of natural habitat (Shawyer, 1998). It has also been found that if a nest site is lost, a bird will also leave surrounding sites it had previously frequented. The lost of a nesting site can therefore have important repercussions (Ramsden, 1998) .

Canada has been going through a lot of industrialization, and most of it takes place in highly inhabited areas: the southern part of the country, which is exactly where barn owls live (Campbell et al, 1984). The subsequent loss of open grassland has been detrimental to neighbouring populations, both directly and indirectly. Directly because of the loss of roost and nest sites, and indirectly because of the loss of prey habitat. For example, some rodents like the woodland vole have been declared of special concern by COSEWIC (1998) in Ontario and in Quebec.

Starvation and Climate:
This is closely linked to the loss of habitat. In general, how the species fares depends greatly on prey availability, which depends on prey habitat. In traditional farming, smaller fields separated by hedges and less-than perfect storage provided habitat and food for prey. Now, with industrial farming, fields are larger, inorganic fertilizer has allowed the conversion of previously unused grassland, and storage has improved. This has caused a decrease in prey numbers and has therefore affected the barn owl (Taylor, 1994). Starvation during the winter can cause death in about 10 days (Hanrich et al, 1993). In farmlands, studies have shown that there was a connection between density of hedges around nests and breeding success (Taylor, 1994).

Another factor, highly relevant to Canada, is climate. Cold weather and high snow cover reduce number and availability of prey during the winter (Shawyer, 1998). Furthermore, the owl's physiology is not adapted to cold weather (bad insulation and low fat storage), therefore energy requirements to keep warm are high, at a time where food is low (Thouzeau et al, 1999). This causes some birds to freeze or starve. Also, cold weather reduces chances of population growth by reducing the number of breeding attempts and their success (Marti, 1993. Marti, 1997)

Pesticide or rodenticide poisoning:
Previously, when DDT was still in use, through biomagnification, it would show up in barn owls in levels high enough to disrupt its calcium metabolism. This caused egg shells to be fragile and they would break under the weight of the mother during incubation. Now, cyclodienes are used, and these compounds damage the bird's brain tissue, leading to death (Taylor, 1998). A study has found that, in England, between 1963 and 1977, 40% of reported barn owl deaths were caused by aldrin-dieldrin poisoning, and the increase in population since has been partially attributed to restrictions on the use of these compounds (Newton et al, 1991).

Rodenticides such as strychnine and anticholinesterases are used in rat-infested barns, which is where barn owls are likely to feed. Therefore these compose a fatal problem (Blus, 1996). First generation rodenticides are rarely used now because rodents have developed resistance, so second-generation rodenticides are used. These are even more dangerous to the owls, which they kill by causing haemorrhaging. Both of these products also affect fertility and the survival of the young (Taylor, 1998).
 

References:
Blus, L.J. Effects of pesticides on owls in North America. Journal of Raptor Research. 30 (4): 198-206. 1996.

Campbell, E.C., Campbell, R.W. Status report on the Barn Owl, Tyto alba in Canada. Committee on the Status of Endangered Wildlife in Canada. 1984.

Campbell, R.W., Manowal, D.A., Harestad, A.S. Food habits of the common Barn Owl in British Columbia, Canada. Canadian Journal of Zoology. 65 (3): 578-586. 1987.

Hanrich, Y., Niculss, L., LeMaho, Y. Winter starvation in captive common barn owls: physiological states and reversible limits. The Auk 110 (3): 458-469. 1993.

Marti, C.D. Barn owl reproduction and its constraints near the limit of the specie's distribution. The Journal of Raptor Research 27 (1): 76-77. 1993.

Marti, C.D. Lifetime reproductive success in barn owl near the specie's range limit. The Auk. 114: 581-592. 1997.

Newton, I., Wyllie, I., Asher, A. Mortality causes in British Barn Owls Tyto alba with discussion of aldrin dieldrin poisoning. Ibis 133 (2): 162-169. 1991.

Ramsden, D.J. Effect of barn conversion on local populations of barn owl. Bird Study. 45 (1) March, 1998. 68-76.

Shawyer, C. The Barn Owl. Arlequin Press, Essex, 1998.

Taylor, I.R. Barn Owls. Cambridge University Press, Cambridge, 1994.

Thouzeau, C., Duchamp, C. Handrich, Y. Energy metabolism and body temperature of barn owls fasting in the cold. Physiological and Biochemical Zoology. 72 (2), March - April, 1999. 170-178.
 

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