Peregrine falcon (pealei and anatum/tundrius) COSEWIC assessment and status report: chapter 8

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Limiting Factors and Threats

Chemical pollution

Widespread use of organochlorine pesticides, most notably 1,1,1-Trichloro-2-2 bis (p-chlorophenyl) ethane (DDT), from the late 1940s through the 1970s, with subsequent bioaccumulation within the food chain, was the primary factor causing the dramatic decline of Peregrine Falcon populations (White et al. 2002). Major declines in North American populations of Anatum Peregrine Falcons occurred from the 1950s through 1970s due to egg shell thinning and the resultant reproductive failure (White et al. 2002). DDT/DDE was banned in Canada and the United States in the early 1970s and in Mexico in 2000 (G. Holroyd personal communication (pers. comm.) 2006), but is still used in other parts of the world including the winter range of some Anatum and Tundrius Peregrine Falcons (i.e. South and Central America; White et al. 2002). In addition, many prey species winter in the south where they may be exposed to and accumulate organochlorines, which may in turn be passed on to falcon predators on their breeding grounds.

Declining organochlorine levels in Peregrine Falcon eggs are encouraging and are linked with improving reproductive success. For example, in Alberta there has been a strong downward trend in DDE concentrations over the last four decades (Court et al. 1996). In the Bay of Fundy, unhatched eggs have been recovered from two sites in New Brunswick for toxin analysis. These eggs have been relatively free of the contaminants that cause reproductive failure (L. Shutt, unpubl. data in Amirault 2004).

The current impact of residual organochlorine pesticides in Canada on Peregrine Falcons is not well known. For instance, serum contaminant loads of some individual Tundrius Peregrine Falcons from Rankin Inlet, Nunavut exceed safe thresholds (e.g. 1.8-2.4 ppm in serum; Figure 4), but overall there is a general downward trend in DDE levels in serum samples of adult Rankin Inlet birds collected since 1981 (Figure 4; Franke et al. 2006). Some believe that even a minor change in agricultural practices in the peregrine's wintering grounds in Central and South America could result in another population catastrophe (Northwest Territories Wildlife and Fisheries 2004). These concerns are echoed by the Alberta Peregrine Falcon Recovery Team (2004), as they note there are strong lobbies hoping to resurrect chemicals like DDT as a short-term measure to control malaria and other insect-borne diseases in developing nations (Raloff 2000) and as new biocides are licensed for use in Canada.

A toxicological study of Peregrine Falcon prey in the Okanagan Valley, British Columbia has recently been conducted (Elliott et al. 2005). Researchers collected potential prey species in the region, analyzed the prey for chlorinated hydrocarbon residues, then used a bioaccumulation model to predict the concentration of DDE in Peregrine Falcon eggs. Due to ongoing contamination in many species found in orchards, the common habitat in the region, it was deemed unlikely that Peregrine Falcons could breed successfully in the Okanagan unless they fed on a diet primarily of doves.

Avicides are also known to kill Peregrine Falcons. Organophosphorus fenthion commonly used as an avicide to control European Starlings and other birds was implicated in the deaths of at least six Peregrine Falcons in North America (Mineau et al. 1999). This and other organophosphorus compounds are used widely in North America (Hayes and Buchanan 2002).

A recent discovery of significant uptake of PBDEs (polybrominated diphenyl ethers) by Peregrine Falcons and other raptors raises potential concerns for another DDT-like impact (Lindbergh et al. 2004). Research is underway in Ontario on this new threat (T. Armstrong pers. comm. 2006).

Human disturbance

Peregrine Falcons have adapted to urban environments and rarely experience enough disturbance from humans to cause breeding failure. However, there have been occasional nest losses associated with disturbance from construction (T. Maconachie, pers. comm. 2004), bridge maintenance, and excessive visitation by bird watchers (D. Amirault pers. comm. 2006). Adults have also been killed by hitting flares on off-shore oil rigs in Newfoundland (D. Amirault pers. comm. 2006).

Disturbance of wild nests, serious enough to cause nesting failure, is also a relatively rare event (Alberta Peregrine Falcon Recovery Team 2004). In the Northwest Territories and Nunavut, cabin building, recreation and resource exploration and development could impact pairs not habituated to human activity (Carrière et al. 2003). Management guidelines for human activities at specific sites where human recreation (rock climbers, hang gliders) conflicts with nesting Anatum Peregrine Falcons has proven successful in British Columbia (M. Chutter pers. comm. 2006). Other jurisdictions in Canada have established minimum disturbance/setback conditions (Ontario, Ontario Ministry of Natural Resources 1987; Nunavut, M. Setterington pers. comm. 2007).

Urban development

Possible hazards in urban environments may include collision with vehicles and buildings and exposure to high levels of contaminants. However, to date, no long-term adverse impacts to Peregrine Falcons living in urban centres have been noted.

Migrants are flexible in their use of foraging habitat and prey selection (White et al. 2002), so urban development is not likely a limiting factor during that phase of their life cycle.

Prey availability

For Pealei Peregrine Falcons, the abundance and distribution of seabird prey is considered the primary limiting factor (Cooper 2006). Seabirds, in turn, are strongly limited by ocean productivity, which can be affected by such diverse factors as global warming, El Nino events, and over-fishing. Populations of seabirds can also be adversely affected by other factors such as introduced mammalian predators on nesting islands and oil spills. The impact of mammalian predators on seabird colonies can be very large (Taylor et al. 2000) and has been linked to local declines of nesting Pealei Peregrine Falcons (Kirk and Nelson 1999).

In Labrador, coastal nesting Peregrine Falcons seem to be strongly associated with Black Guillemots, a potential prey source, (J. Brazil pers. comm. 2006) and are largely absent from otherwise suitable nesting areas when guillemots are absent.

Harvesting for falconry

Harvesting of Peregrine Falcons for falconry is not currently permitted in most of Canada. However, recent de-listing of the Anatum Peregrine has resulted in the lifting of falconry harvest bans in parts of the US. The Canadian Anatum Peregrine Recovery Team did not, however, endorse a proposal by the International Fish and Wildlife Agencies to reopen a harvest (Allen 2000) as there is no way to guarantee that harvested passage birds are not taken from managed, recovering populations rather than from larger, apparently stable populations from farther north (Alberta Peregrine Falcon Recovery Team 2004). Even so, Saskatchewan has allowed a small harvest of juvenile passage migrants since 2001 (Rowell 2002). Reopening a restricted harvest on the Blue-listed Pealei Peregrine Falcons in British Columbia is under consideration (Cooper 2006) and harvest of Peregrine Falcons is currently being considered for Nunavut’s new Wildlife Act Regulations (M. Setterington pers. comm. 2007).

Shooting

In decades past, shooting of adult Peregrine Falcons and destruction of nests occurred in areas occupied by people who viewed “hawks” as threats to other birds and domestic fowl (Bent 1938). This occurs much less often today, although shooting of Peregrine Falcons may occur from time to time.

Poaching

Poaching of eggs or nestlings for falconry purposes occurs, but at an unknown rate. Poaching of eggs and nestlings could impact local productivity rates and, if extensive enough, could impact recovery of some populations. However, occasional poaching would not likely be a serious threat.