Demography and Populations

Age At First Breeding; Intervals Between Breeding

May breed the first spring after hatching. In the Great Lakes, 8-26% of birds that fledge return to the region to breed the following year (1997-2002, n = 296). Additional birds survive but do not breed their first year (Stucker and Cuthbert unpubl. data). Although some birds do not obtain a mate each year, most birds breed each year. Determining the number, age, and sex of nonbreeding birds in local populations would be helpful in evaluating the status of local populations.

Clutch: Size And Number Per Season

Modal clutch size of four eggs. Variations (field data) as follows: Saskatchewan: 3.3 eggs (n = 38; Whyte 1985); North Dakota: 3.5-3.7 (n = 137; Prindiville Gaines and Ryan 1988); Nova Scotia: 3.96 (n = 68; Cairns 1977); New York: 3.84 (n = 526; Wilcox 1959); and New Jersey: 2.83-3.85 (n = 135; Burger 1987). Several five-egg nests found, perhaps owing to egg-dumping, but also likely a result of female laying an extra egg in second nests when first nest fails prior to clutch completion (SMH; J. Stucker pers. comm.).

Females generally lay one clutch/year unless eggs destroyed and they renest (see Sexual behavior: mating system). Replacement clutches common due to frequent nest destruction in many areas. Third, fourth, and fifth clutches in a single season are known (but uncommon) across the species’ range (SMH).

Annual And Lifetime Reproductive Success

No estimates of lifetime reproductive success.

Annual success (mean number of chicks fledged per pair per year) vaires as follows: Saskatchewan 0.7-1.1 (2 yr of data, n = 20 pairs monitored; Whyte 1985); Manitoba 0.3-1.5 (2-4 yr, depending on site, n = 53 pairs; Haig and Oring 1988c); North Dakota 0.7-1.5 (6 yr, n = 578 pairs; Prindiville Gaines and Ryan 1988; M Ryan pers. comm.); Minnesota 0.3-3.0 (6 yr, 95 pairs; Wiens 1986, Haig and Oring 1987, SMH); and averaged 1.3 for U.S. Atlantic Coast (4 years for New Hampshire, 10 yr for all other states; over all years and states n > 10,000 pairs; average ranged from 0.5 in North Carolina to 2.14 in New Hampshire), 1.6 for Eastern Canada (10 yr, n = 1,281 pairs; USFWS 2002), and Great Lakes 1.4 for Great Lakes (20 yr, n = 464 pairs; Wemmer 2000; J. Stucker and F. Cuthbert unpubl. data). 

During four-year study, only 20% of 20 Lake Manitoba breeding pairs fledged chicks vs. 48.5% of 33 pairs on West Shoal Lake (Haig and Oring 1988c). Northern Great Plains population data suggest that current reproductive success is insufficient to maintain a stable population (Prindiville Gaines and Ryan 1988). Chick survival is lower if a family is forced to move (e.g., due to disturbance) soon after hatching (Strauss 1990). In Montana and North Dakota, early nest initiation and nearby presence of other nesting pairs were both associated with an increased probability of fledging at least one chick (Knetter et al. 2002)

In New York, 13% of 159 females lived to be five years or older, while 28% of 139 males exceeded five years of age (Wilcox 1959). Twelve of these birds reached 8-11 years of age.

North Dakota birds (n = 214 adults observed during seven years of study) exhibited mean annual adult survivorship of 66.4% (Root et al. 1992). Using the same data from North Dakota, plus three additional years of data and a different estimation method, adult survival was re-estimated as 73.7%; juvenile survival  estimated as 31.8% (Larson et al. 2000). Adult survival was also estimated at 73% for Great Lakes birds (Wemmer et al. 2001).

Early descriptions of feather-chewing lice include Actornithophilus ochraceus (Nitzsch, 1818), Austromenopon aegialitidis (Durant, 1906), Quadraceps macrocephalus (Waterston, 1914), and Saemundssonia platygaster (Denny, 1842; all in Price et al. 2003). Quadraceps macrocephalus was the only ectoparasite found in a recent study, and it appears very common (K. Mehl pers. comm.).

Natal Philopatry/Dispersal

Natal philopatry reviewed by Haig and Oring (1988b). Varies from 1.6% in Nova Scotia (Cairns 1982) to 70% at Lake of the Woods, MN (Haig and Oring 1987). First-year birds may return more frequently to the local area than to a specific natal site. For example, 5.5% of s. Manitoba birds are philopatric to natal site, but 12.2% return to the local area composed of four to five breeding sites (Haig and Oring 1988b). Distances first-year birds bred from their natal sites range from 5-273 km (Haig and Oring 1988b). In Great Lakes, natal dispersal distances ranged from about 2-430 km with males traveling slightly further than females (Price 2002). No sex bias in return rates to natal sites or areas in New York (Wilcox 1959) and Manitoba (Haig and Oring 1988b), or in distances dispersed from natal sites.

Breeding Site Fidelity/Dispersal

Reviewed by Haig and Oring (1988b). Fidelity ranges from 24.6% in New York (Wilcox 1959) to 84% at Lake of the Woods, MN (Wiens and Cuthbert 1988). Birds not only return to specific former sites but also use nearby sites if available. Fidelity may be low in areas where breeding habitat is ephemeral (Knetter et al. 2002). Where few local options exist, may disperse 300-600 km to the next breeding site (Haig and Oring 1988b). Males return to former breeding sites only slightly more often than females in Manitoba and no sex bias was detected in dispersal distance (Haig and Oring 1988b). However, females dispersed from former breeding sites in Michigan more frequently than males, and traveled greater distances (Wemmer 2000). Site fidelity in Great Lakes population was associated with previous reproductive success.

Home Range

In Manitoba, individual breeders seen throughout the breeding season at sites that ranged from 3-102 km apart (SMH). Where sites are dispersed, pairs are often seen in more densely populated areas during their incubation recesses. The great potential for nest destruction and intrayear mate switching may explain the movement. During winter, home range size was 12.6 km² with 2.9 km² core area (based on 50% of telemetry locations) in Texas (Drake et al. 2001).

Winter Site Fidelity

Winter studies indicate 63% of marked birds return to their Dauphin I., AL, sites the following year (Johnson 1987). One banded female from Great Lakes wintered at same location in Florida for 11 out of 13 winters (T. Below unpubl. data). Birds may make small movements within a winter, but remain in the same general area throughout the season (Drake et al. 2001). Sex differences not noted.

Population Numbers

Breeding season population estimates have become reliable as biologists became increasingly concerned about the status of this species. Three complete international breeding censuses have been undertaken (Cairns and McLaren 1980, Haig and Oring 1985, Haig and Plissner 1993, Plissner and Haig 2000, Haig et al. in press; Table 1). Overall, the 2001 census total population estimate of 5,945 birds is very low for a species with such a widespread distribution (Haig et al. in press). Northern Great Plains birds may be declining owing to severe drought and inappropriate water management practices. Atlantic and Great Lakes populations have increased recently via intense human and predator management (Haig et al. in press). At Lake of the Woods, MN and ON, which is the only geographical link between the Northern Great Plains and Great Lakes, population declines continue despite intensive management practices (Maxson and Haws 2000). Allozyme data indicate that populations sampled in Saskatchewan, Manitoba, Minnesota, North Dakota, and New Brunswick are in Hardy-Weinberg equilibrium, have within-population variability equivalent to other avian populations (mean heterozygosity = 0.016 ± 0.014), and do not suffer from significant inbreeding (mean F_is= 0.049; Haig and Oring 1988a).

Population modeling. Viability models based on an initial survival estimate of 66% indicated that Great Plains and Great Lakes populations had a low probability of persisting for more than 80-100 years and would require a 31-36% increase in productivity to stabilize populations (Ryan et al. 1993, Plissner and Haig 2000). Predictions were first made considering geographic areas as single populations, but after incorporating rudimentary metapopulation dynamics, extinction was still predicted and viability appeared to decrease with increasing dispersal (Plissner and Haig 2000). However, models of Atlantic Coast populations indicate stability if management efforts continue, and contrary to inland populations, dispersal appears to increase viability (Plissner and Haig 2000). Recent census results support predicted increases in Atlantic populations; decreases observed in the Great Plains, but at a slower rate than initial model predictions (Haig et al. in press)

One problem in analyzing population viability is that all models were found to be highly sensitive to adult survival estimates yet survival is difficult to estimate accurately. This may be particularly true in the Great Plains, where ephemeral breeding habitats may reduce site fidelity, and therefore lower resighting probability. Models that were based on recent survival estimates of 73% suggest a much greater probability of persistence and recovery for Great Lakes populations (Wemmer et al. 2001) and with increased management, Great Plains populations could also persist (Larson et al. 2000, Larson et al. 2002). However, given model sensitivity to survival estimates, potential uncertainty in these estimates, and the difficulty of increasing survival through management, minimizing the risk of extirpation in the Great Plains may depend on intensive management to effect a substantial increase in productivity (Larson 2001, Larson et al. 2003).

Egg and chick predation is a significant factor limiting populations in North Dakota (Prindiville Gaines and Ryan 1988), Saskatchewan (Whyte 1985), Manitoba (Haig and Oring 1988c), Minnesota (Haig and Oring 1987), and New Jersey (Burger 1987). Frequent storms that wash out nests also affect population success in Manitoba (Haig and Oring 1988c) and New Jersey (Burger 1987; also see below, Effects of Human Activity).