Peregrine falcon (pealei and anatum/tundrius) COSEWIC assessment and status report: chapter 6

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Biology

Nest-building

Nests are simple scrapes in substrates that range from 17-22 cm in diameter and 3-5 cm deep. No nest material is added, but debris may accumulate around the scrape. Nests may be placed on bare ridges, ledges on cliffs or buildings, caves, or stick nests of other birds (White et al. 2002). Scraping in the substrate begins early in courtship and continues until egg-laying, the timing of which varies with latitude (Nelson 1977).

Number of broods annually

One brood is raised annually, although re-nesting may occur if the nest fails early in the incubation period (Beebe 1974). Some pairs may renest up to three times if eggs are lost early in incubation (Bent 1938).

Clutch size

Clutch sizes show a clinal trend ranging from a mean of 2.9 in Arctic regions to 3.7 in mid-latitudes (Hickey 1969; Palmer 1988), although Court et al. (1988a) reported a mean clutch size of 3.62 (n = 84 clutches) for Rankin Inlet. In British Columbia (BC), clutch sizes for Peale's and Anatum Peregrine Falcons ranged from 1-5, with 3-4 being most common (Campbell et al.1990). In Alberta, mean clutch sizes for Anatum Peregrines were 3.6 for southern Alberta (Stepnisky 1998) and 3.7 for northern Alberta (Moore 1995). In Ontario, mean clutch size from various areas was 3.4 eggs (n = 35, range 2-5; Peck and James 1993). On Banks Island, Nunavut (NT), Tundrius Peregrine Falcons laid an average of 2.9 eggs (n = 9, range 2-4) in 2000 (Anonymous undated).

Incubation and fledging

The female does almost all of the incubating while the male feeds her, although experienced males may share a significant portion of the incubation duties (Endersen et al. 1972). Incubation begins with the penultimate egg and lasts between 32 and 35 days (Campbell et al. 1990; Baicich and Harrison 1997). In the Arctic, however, cold temperatures require that incubation begin with the first egg resulting in asynchronous hatching, with as many as six days between oldest and youngest nestlings (Court et al. 1988b). The female does most of the brooding, which is nearly continuous for the first ten days. Nestlings leave the nest after about 40 days, with males typically fledging three to five days earlier than their female siblings. Young are fed by adults and may remain in the vicinity of the nest site for three to six weeks after fledging (Beebe 1974).

Age of first breeding

Peregrine Falcons typically begin breeding at two years of age, although there are records of breeding in one year old birds. Age of first breeding often varies depending on territory availability, with earlier breeding in areas with abundant unoccupied habitat. Females tend to breed a year earlier than males (Cade and Fyfe 1978; Ratcliffe 1993). In Rankin Inlet, Nunavut, mean recruitment age in a Tundrius population was four years (range 2-8) for males and three years (range 3-5) for females (Johnstone 1998).

Productivity

Productivity (number of fledged young/territorial pair) for Anatum Peregrine Falcons varied greatly from region to region and year to year between the 1970s and 1990s as populations recovered from the effects of pesticides on reproduction. Before the 1980s, declining populations generally suffered depressed annual productivity rates of <1.0 to <0.5 fledglings/territorial pair (Cade et al. 1989; Ratcliffe 1993), but after 1984, in association with reintroductions, annual productivity generally increased (Mesta 1999).

Most studies report 1-2 young fledged/territory (White et al. 2002), but there are frequent exceptions. For example, in some “good” years, about three young Pealei Peregrine Falcons/territory are produced on Langara Island, British Columbia (Nelson 2001). Productivity for coastal Anatum Peregrine Falcons in British Columbia is also relatively high, as 2-4 fledglings are the norm in recent years for most pairs (D. Doyle personal communication (pers. comm.) 2004). In southern Ontario, many successful Anatum Peregrine nests fledge three young (T. Armstrong pers. comm. 2006). For Tundrius Peregrine Falcons in Rankin Inlet the 25-year average number of young produced per productive pair is 2.5 ± 0.4 (GNDOE unpublished data, 2006; M. Setterington pers. comm. 2006).

Factors influencing annual productivity include: (1) egg and chick mortality from cold, wet, and late spring weather (White and Cade 1971; Court et al. 1988b; Mearns and Newton 1988; Ratcliffe 1993; Bradley et al. 1997); (2) local yearly variation in prey abundance (Court et al. 1988b; Bradley and Oliphant 1991); (3) regional differences in overall prey availability (Ratcliffe 1993) and (4) predation/disease: not quantified for any population but can be locally significant (Cade et al. 1989; Tordoff and Redig 1997).

Differences in productivity at individual territories within local populations is an important aspect of Peregrine Falcon ecology. For example, for Tundrius Peregrine Falcons at Rankin Inlet, Nunavut, at regularly occupied (high-quality) sites, productivity over 14 years averaged 1.4 young; at infrequently occupied (poor quality) sites, the average was 0.8 young/pair (Johnstone 1998). At Langara Island, British Columbia, half of all nestlings were produced by 21% of nesting pairs, one-quarter of nestlings were produced by just 9% (Nelson 1990).

Data from the 2000 survey of Peregrine Falcons in Canada found that productivity ranged from 0.6-2.5 young/territorial pair and 1.2-4.0 young/successful pair (successful defined as a pair that produces at least one fledgling; Tables 4-6). Anatum Peregrine Falcons had higher productivity than Tundrius Peregrine Falcons, which had higher productivity than Pealei Peregrine Falcons. The 2005 data indicate that productivity/ territorial pair ranged from 0–2.8 young and from 0–4.0 young/successful pair. As in 2000, Anatum populations exhibited the highest productivity/successful pair while Pealei populations exhibited the highest productivity/territorial pair (U. Banasch pers. comm.).

Table notes

Table note a

six additional pairs not included as nests not observed

Table note b

calculated from 7 pairs that produced 18 young. Other 3 pairs had 1-2 young

Table notes

Table note c

Productivity only observed at 2 nests for a total of 3 young

The unweighted average for Anatum Peregrine Falcon productivity over the eight national surveys through to 2005 is 2.2 fledglings/successful pair (Rowell et al. 2003; U. Banasch pers. comm.; Table 7). Productivity for Anatum Peregrine Falcons in 2005 (2.2 young fledged/successful pair and 1.3 young fledged/territorial pair) was at the lower end of the range from 1970-2005 (Table 7). It is difficult, however, to make meaningful comparisons on productivity across sites and years using unweighted data because of differences in survey methods and effort (e.g. surveys can vary from complete coverage of core zones to checks on known nest sites).

Models predicting population trends for northern and southern Alberta in the early 1990s required >1.7 fledglings/territorial pair for population growth (Court 1994; Stepnisky 1998). The national average has remained at 1.5 fledglings/territorial pair (i.e. lower than required by the models) for the last decade. Rowell et al. (2003) suggest a slower rate of increase for southern populations through to 2005 because fostering of new birds was discontinued.

Long-term productivity

Long-term reproductive success has been reported for Peregrine Falcons at some Canadian locations. At Langara Island, BC, a male Pealei Peregrine Falcon raised 22 young in 7 years and one female raised 18 young in 8 years. At Rankin Inlet, Tundrius Peregrine Falcons at frequently occupied nest sites had mean breeding life spans of 2.7 years for males and 2.9 years for females, with mean lifetime production of 4.7 young (Johnstone 1998). A more recent example of long-term productivity is of a female Anatum Peregrine from Wisconsin that fledged 41 young over 15 years (Septon 2004).

Life span and survivorship

Maximum longevity records for banded birds range from 16 to 20 years. In captivity, few live beyond 20 years, although a maximum of 25 years has been reported (White et al. 2002). Banded Peregrine Falcons in Alberta are known to return for at least 11-12 years (Rowell and Stepnisky 1997). First-year survival is not well known but is generally assumed to be 40–50% (see Ratcliffe 1993 for higher estimates in Britain). Tordoff and Redig (1997) estimated a minimum of 23% fledgling survival in Anatum Peregrine Falcons in midwest USA. Beebe (1960) proposed that survival among yearling Pealei Peregrine Falcons was low due to their harsh maritime environment. A minimum of 63% of breeding female and 74% of breeding male Peale’s Peregrines are estimated to survive annually (Nelson 1988, 1990). In Rankin Inlet, survivorship estimates of adult Peregrine Falcons ranges from 0.71 to 0.85 for males and 0.69 to 0.81 for females, depending on the analytical technique used and cumulative data availability (Court et al. 1989 using Turnover; Johnstone 1998 using Turnover and Cormack-Jolly-Seber and Franke et al. 2005 using Cormack-Jolly-Seber). Court (1994) estimated the average annual mortality of adult Anatum Peregrine Falcons in northern Alberta to be 16.4 %, and Stepnisky (1998) estimated 14% annual mortality for adult Anatum Peregrine Falcons in southern Alberta.

Known population growth rates in recent years and well-known productivity rates indicate true adult survival rates of 80–85% for migrant and 85–90% for resident Peregrine Falcons (White et al. 2002).

Diet

Peregrine Falcons prey primarily on birds (Sherrod 1983) ranging in size from hummingbirds to geese (White et al. 2002). Birds are typically caught in flight so Peregrine Falcons require an ample supply of suitable prey species in areas that permit aerial hunting (Beebe 1974). Burrow-nesting and cliff-nesting colonial seabirds, shorebirds, waterfowl, other waterbirds, pigeons and songbirds are important prey for all subspecies. Other prey may include bats, rodents, other mammals and, rarely, insects and fish (White et al. 2002).

Peregrine Falcons that nest on tundra can take ptarmigan (Lagopus spp), shorebirds, small songbirds such as longspurs and Snow Buntings (Plectrophenax nivalis) and ducks. Small mammals, particularly lemmings and juvenile arctic ground squirrels (Spermophilus parryii), can comprise a major portion of the diet in some parts of the range (Court et al. 1988a, Bradley and Oliphant 1991). In Labrador, for instance, male peregrines have been observed delivering small mammals such as lemmings and deer mice to the nest (J. Brazil pers. comm. 2007). In taiga areas, they take shorebirds, woodpeckers, jays, and thrushes. Anatum Peregrine Falcons in the interior of North America tend to take doves, pigeons, waterfowl, rails, gulls (G. Holroyd pers. comm. 2006) and songbirds. In Labrador, coastal nesting female Peregrine Falcons appear to  favour Black Guillemots (Cepphus grille, D. Amirault, J. Brazil pers. comm. 2006). Shorebirds are the favoured food in the Bay of Fundy where nest sites are close to shorebird migration habitat (D. Amirault pers. comm. 2006) and in the Fraser River estuary, British Columbia, where predation on sandpipers by increasing Peregrine Falcon populations has apparently caused a shift in sandpiper migratory behaviours (Ydenberg et al. 2004).

In the Strait of Georgia region of British Columbia, European Starlings (Sturnus vulgaris) account for a large proportion of Anatum Peregrine’s diet (R.W. Campbell pers. comm. 2006). Pealei Peregrine Falcons usually nest near a seabird colony and seabirds comprise a high percentage of their diet. These peregrines most frequently take auklets, murrelets, and storm-petrels, with the Ancient Murrelet (Synthliboramphus antiquus) being the most important prey species (Nelson and Myres 1976). Peregrine Falcons show great flexibility in prey use and some researchers believe it is impossible to link declines in prey with declines in Peregrine Falcons (Ratcliffe 1993). However, a decline of Pealei Peregrine Falcons on Langara Island, BC, is considered by some researchers to be linked to corresponding declines in preferred seabird prey abundance (Nelson and Myres 1976), even though seabirds remain relatively abundant and available compared to bird prey in other peregrine habitats.

Peregrine Falcons are thought to eat carrion only rarely (Holland 1989). On Triangle Island, BC, however, an island with very high seabird populations, Pealei Peregrine Falcons have been observed foraging on dead seabirds that perished due to mid-air collisions (L. Savard pers. comm. 2004). Similarly, in Rankin Inlet in 2006, a Tundrius Peregrine Falcon was trapped in a gill net while feeding on dead char (M. Setterington pers. comm. 2006).

Predationand mortality

Predation is not an important limiting factor for Peregrine Falcons. Of 455 peregrine fatalities in the mid-west USA, only 15 were known to be caused by predators. The majority of deaths where the cause was known were due to collisions with buildings (17%), collisions with vehicles (11%), other accidents (7%), disease (6%) and by other Peregrine Falcons (4%; Tordoff et al. 2000). Great Horned Owl (Bubo virginianus), Northern Goshawk (Accipiter gentilis) and red fox (Vulpes vulpes) are the main known predators of wild Peregrine Falcons (Rowell 2002). Hacked young falcons have also been taken by Golden Eagle (Aquila chrysaetos), cougar (Puma concolor), and American marten (Martes americana), although these predators probably do not often take wild-reared young (Hayes and Buchanan 2002).

In Alberta, mortality of young results primarily from climatic factors (cold, wet weather), predation by red foxes, Golden Eagles and Great Horned Owls or collisions with man-made structures and vehicles when young birds first fledge (Sherrod 1983; Stepnisky 1996). In Ontario, non-breeding females have been observed to kill resident females and young in the nest (A. Dextrase pers. comm. 2006).

Physiology

Peregrine Falcons proved highly susceptible to chemical contamination, as evidenced by the widespread reproductive failure, particularly in Anatum Peregrine Falcons from uptake of organochlorine pesticides.

Dispersal/migration

Peregrine Falcons are largely migratory although Pacific coastal pairs and some southern interior pairs are resident and may remain at nest sites through winter if food supplies are adequate (White et al. 2002). This is especially true for Pealei Peregrine Falcons and for urban-dwelling Anatum Peregrine Falcons across southern Canada, east of Manitoba. Migration occurs across broad fronts but there are some general routes where Peregrine Falcon movements concentrate (Cade et al. 1988). In Canada, one noticeable movement is along the eastern front of the Rocky Mountains. Another is the fall migration of Tundrius Peregrine Falcons from western Greenland west across Davis Strait, then south through Canada to the US east coast (White et al.2002).

In the fall, Peregrine Falcons typically migrate south to the southern USA, Central America and South America. Continental populations migrate in a “leap-frog” fashion, with northernmost birds tending to migrate the furthest south and mid-latitude birds migrating to a lesser extent (Schmutz et al. 1991; McGrady et al. 2002), but this is not entirely consistent. Individuals on wintering grounds in coastal Mexico and Central America with satellite transmitters were found breeding in the Canadian Arctic and Greenland (McGrady et al. 2002). One Peregrine Falcon nestling banded in the Thelon River area, NT, was recovered 14,500 km south in India Muerta, Argentina, 4 months after fledging (Kuyt 1967). Peregrine nestlings banded in Labrador have been recovered in Brazil, Peru, and the eastern and Texas coasts of the USA (J. Brazil pers. comm. 2007). Three satellite-tagged birds from Rankin Inlet migrated to coastal southern Brazil in 1994. Bands have also been returned from Peru (2), Uruguay (1) and Argentina (1; Court et al. 1988a; Seegar et al. 1997; M. Setterington pers. comm. 2007). A male Anatum Peregrine from Toronto, Ontario was tracked for three successive years to his winter area in Cartagena, Columbia (McGill University 2002).

For Pealei Peregrine Falcons on the Queen Charlotte Islands, it appears that all immatures migrate south and spend the winter between the Fraser River estuary (near Vancouver, BC) and California, whereas adults remain near nests (W. Nelson pers. comm. 2006). However, two radio-tracked adult Pealei from extreme northern Vancouver Island, BC, wintered in Oregon. Three radio-tracked adult Anatums in south coastal British Columbia remained close to their nest sites all year, except for one bird, which went to Washington for about two months before returning (D. Doyle pers. comm. 2006).

Adult Peregrine Falcons demonstrate a high degree of breeding site fidelity (Ambrose and Riddle 1988 in Hayes and Buchanan 2002) and are often known to reuse the same nest site for several successive seasons (Beebe 1974; Court et al. 1989; Ratcliffe 1993). Established pairs may also use alternate nest sites within their breeding territory, either on the same cliff or on alternate cliffs, over successive seasons (White et al. 2002). In recovery efforts, Anatum Peregrine Falcons often re-occupy traditional nest sites that have been vacant for many years (Ratcliffe 1993). Many nest sites are occupied continuously through successive generations and at least one nest site in Labrador has been occupied (not necessarily continuously) for up to 145 years (J. Brazil pers. comm. 2006).

Young birds are known to disperse widely to new breeding areas. A wild-reared Anatum Peregrine chick from the Bay of Fundy nested as an adult in Buffalo, New York, a distance of about 1,200 km (D. Amirault pers. comm. 2006). In the southern prairies, immature captive-raised and released Anatum Peregrine Falcons returned an average distance of 130 km from their natal site; females returned an average of 263 km and males an average of 52 km (Holroyd and Banasch 1990). On Langara Island, BC only 6 of 140 banded Pealei Peregrine Falcon nestlings have returned to breed, with others known to have settled up to 300 km away (R.W. Nelson pers. comm. 2001). At Rankin Inlet, 37 (5.5%) of 668 nestling Tundrius Peregrine Falcons banded from 1981 through to 2003 have returned to the study area to breed, but none have been found breeding elsewhere (GNDoE, unpublished data, M. Setterington pers. comm. 2006).

Gregariousness

Peregrine Falcons are solitary breeders and are highly territorial towards other peregrines, although relatively high densities may occur. For example, several pairs of Peale’s Peregrines nested as close as 400 m apart on Langara Island (6 km x 10 km), BC (Beebe 1960; Nelson 1977).

Interspecific interactions

Populations of Pealei Peregrine Falcons on the Queen Charlotte Islands were thought to be larger in the past and may have declined due to reduced seabird prey, as seabird numbers declined in response to changing oceanographic conditions and reduced availability of fish prey (Nelson and Myres 1976).

Peregrine Falcons may come into conflict with other cliff-nesting birds. Cliff-nesting Great Horned Owls are known to harass and kill Peregrine Falcons at some sites (Tordoff and Redig 1997; Tordoff et al. 2000), but at other sites both species nest in close proximity. Peregrine Falcons do not nest on the same cliff in the same year as Golden Eagles or Gyrfalcons but will nest at those sites when the other species are absent. Peregrine Falcons tend to take over Prairie Falcon nest sites when both are present, and Peregrine Falcons attack passing Prairie Falcons (White et al. 2000).

Common Ravens can negatively affect Peregrine Falcon breeding success if nests are close (White et al. 2000), although in a European study, Peregrine Falcons selected nest sites nearer to ravens than Golden Eagles (Sergio et al. 2004).

Adaptability

The Peregrine Falcon is a remarkably adaptable bird given its wide geographic range and its use of a diversity of habitats. In the last 2-3 decades, many Anatum Peregrine Falcons have acclimatized to nesting in urban habitats where they use buildings, towers or bridges as surrogates for cliffs (Cade et al.1996). Some Peregrine Falcons in Ontario even nest on cliffs in active mine sites and rock pits (A. Dextrase pers. comm. 2006). Another example of adaptability in choosing nest sites is the apparent increased use of old nests of Common Raven, Bald Eagle, Pelagic Cormorant (Phalacrocorax pelagicus) (Campbell et al. 1990), and Osprey (Pandion haliaetus) (T. Antifeau pers. comm. 2003).

The adaptability to breeding in urban environments has proven to be a key in the recovery of North American populations of Anatum Peregrine Falcons. This adaptability may ultimately allow Peregrine Falcons to exceed their known historical abundance (Cade et al. 1996).