Demography and Populations

Measures Of Breeding Activity

Age At First Breeding

Most at 1 yr old. Some become summer floaters; most of these first breed the following summer (at age 2), and a very few begin breeding at age 3 (Smith 1991). Once a bird has entered the breeding population, it typically breeds every year.

Clutch

From 1 (Smith 1974) or more often 2 (Ramsay et al. 2003), to 13 (Bent 1946). Of 225 clutches at the Western Foundation of Vertebrate Zoology, nearly 80% are 6, 7, or 8 eggs, the three most common sizes (Smith 1991). Sample showed no evidence of geographical variation. Usually just 1 clutch/yr (second broods rare). No studies to date of clutch manipulations—changing clutch size to determine parents’ capacity to rear extra young—comparable to European studies of Great Tit (Parus major) and other parids (see synopsis in Perrins and Birkhead 1983).

Annual And Lifetime Reproductive Success

Hatching success (nestlings/clutch): 4.8 (Odum 1941b, New York); 5.0 (Kluyver 1961, Massachusetts); 4.0 and 4.6 in 2 consecutive years (Smith 1967b, British Columbia). Fledging success (fledglings/clutch): 6.6 (Nickell 1956, Michigan); 4.2 (Kluyver 1961), 3.8 and 4.1 (Smith 1967b). Number of young/successful clutch: 6.6 (Nickell 1956); 4.2 (Kluyver 1961); 4.0 and 4.6 (Smith 1967b).

Lifetime reproductive success (LRS, number of young surviving to 6 days) of Black-capped Chickadees in Ontario was 6.9 for males (range: 0 - 58.5 young) and 6.8 for females (range: 0 - 42.4 young). For those individuals who produced at least one young, lifetime reproductive success was 9.3 for males and 9.6 for females. Lifespan significantly predicts LRS (Shubert et al. 2007).

Number Of Broods Normally Reared Per Season

One in most areas; possibly more second broods in areas with lower population density (Smith 1991).

Proportion Of Total Females That Rear At Least One Brood To Nest-Leaving

Direct data not available. Due to the secretive nature of non-territorial birds during the breeding season, the non-breeding segment of the population is not known. Smith (1991) documented 4 female summer floaters (2 that did not breed and 2 that replaced females that died and went on to breed) in 9 years.

Life Span And Survivorship

No systematic study. Many young evidently disappear in their first summer (Smith 1991). Average life-span approximately 2.5 yr; the current longevity record is 12 yr 5 mo (Smith 1991). See also: http://www.pwrc.usgs.gov/BBL/homepage/long6882.cfm#Chickadee.

Annual survival in Ontario from 1997-2002 ranged from 36–73% for males (Schubert et al. 2008). Annual winter survival in Connecticut was 0.63 from 1958-1991 (range 0.43-0.95, Gould and Nichols 1998). In Massachusetts, annual survival was 59%, with winter mortality rates of 26% for females and 29% for males, and 16% summer mortality rates for breeders (Smith 1994); greater annual survivorship of higher ranked than lower ranked individuals within the sexes (Smith 1994, Schubert et al. 2008). Adult survival probabilities are higher in Eastern and Northwest regions (51, 48% respectively) than in Central, Southwest, and Alaska and Boreal/Arctic Canada regions (41, 40, 41% respectively) (Michel et al. 2006). Winter starvation is potentially serious. Both Desrochers et al. (1988) and Brittingham and Temple (1988) showed that feeding stations increased chickadee overwinter survival, especially in periods of severe weather. Young are also vulnerable to starvation during the first few weeks after leaving the nest (Smith 1991).

Mortality And Disease

See Behavior: predation. This chickadee’s habit of roosting in protected sites (dense vegetation or cavities), coupled with its ability to drop body temperature and go into regulated hypothermia on cold winter nights (see Food Habits: metabolism), helps it survive severe winter conditions (Chaplin 1974, 1976, Smith 1991). No major outbreaks of any disease reported for this species. Blood parasites (hematozoa) such as Haematoproteus spp., Plasmodium spp. (malaria), and Trypanosoma spp. reported at low levels (< 6%); recently described blood parasite Hepatozoon parus has this chickadee as type host (Smith 1991). Few ectoparasites, due at least in part to this bird’s habit of digging out new cavities each time it nests.

LaDeau et al (2007) documented decreasing population size of chickadees (Black-capped and Carolina were combined because of difficulty separating where range overlaps) following West Nile Virus infestations, even though populations were expected to increase during that time period. The effect was particularly prominent at the Eastern, but not the Western, range limit.

In the past two decades an alarming number of bill deformities have been reported among Black-capped Chickadees in Alaska (1400 individuals), including grossly elongated mandibles (Handel et al. 2006). Other local bird species also show deformities, although in much lower numbers. The causes and consequences of these deformities are poorly understood.

Range

Initial Dispersal From Natal Site

Sudden onset of juvenile dispersal 2–4 wk after young leave the nest (Odum 1941b, Glase 1973). Direction is random; median distance for males, 211 m; for females, 198 m, with some individuals dispersing up to 11.2 km away from their natal sites (Weise and Meyer 1979). Once dispersed, the young settle down and enter local flocks. Individuals ending the winter as members of high-ranked pairs usually obtain breeding territories within their winter flock range. Lower-ranked birds may be driven away in the spring due to territorial behavior of higher-ranked pairs (Smith 1967b, 1984; Desrochers et al. 1988). Data on distances such birds travel are rare; I have one record of a low-ranked female driven away from my study area in the spring and settling into a breeding population over 20 km away (SS).

Fidelity To Breeding Site And Winter Home Range

Under most circumstances, a chickadee remains near its initial breeding territory for the rest of its life (chickadees being non-migratory). Some adult chickadees participate in irruptions, perhaps because the food-supply in their area crashed or the land was cleared by humans (Bock and Lepthien 1976, Smith 1991).

Home Range

Few direct data on chickadee home ranges; these best obtained by radio telemetry. Brewer (1978) found winter ranges of individuals varied from 5.7 to 38.9 ha. Odum (1942) found flock ranges of 8.8 to 22.6 ha (av. 14.5 ha), and Glase (1973) reported flock ranges of 8–11 ha (av. 9.5 ha). Local food supply an important factor determining size of range (Smith 1991), but birds with largest home ranges are likely either floaters or dominant wanderers (high-ranked flock regulars with expanded home ranges, Smith 1984).

Population Status

Estimates of breeding density vary considerably (Fig. 6). West coast: 0.20 pairs/ha and 0.15 pairs/ha in consecutive years, Vancouver, B.C. (Smith 1967b). East: 0.06 pairs/ha in upstate New York (Butts 1931). In w. Massachusetts, 0.24 to 0.30 pairs/ha, with an 9–yr average of 0.25 (Smith 1991). Variation likely due in part to habitat differences (this is a forest edge species), to related food supplies, and also to availability of suitable nest sites.

Five BBS regions (physiographic strata) with highest densities are: Glaciated Coastal Plain, s. New England, Adirondack Mountains, n. New England, and the Black Hills, SD (Fig. 6).

Overall population trends, from the BBS data (Sauer et al. 2008), indicate that Black-capped Chickadee populations seem to be increasing in much of the eastern part of their range, more or less stable in central regions, and showing a significant, decline in the west (see http://www.mbr-pwrc.usgs.gov/cgi-bin/atlasa99.pl?07350&1&07; also Brennan and Morrison 1991; also Fig. 7). Annual survival rate shows a long-term decline from 1959-1991 in Connecticut (Loery et al. 1997). Future changes in the northeast, where the Tufted Titmouse (Baeolophus bicolor) is currently undergoing a range extension, will be of interest; Black-capped Chickadee populations may be adversely affected by initial contact with Tufted Titmouse (Loery and Nichols 1985; Smith 1991). In Connecticut, survival rates were lower immediately following establishment by Tufted Titmice.

Population Regulation

Territorial behavior regulates breeding populations in many regions (e.g. Smith 1967b, Desrochers et al. 1988, Smith 1984, 1991), especially areas of prime habitat. Probably the norm in most areas of high quality. There is some evidence that other factors (not yet identified) may hold numbers down below the level where territoriality has an effect, especially in the midwest (e.g. Brittingham and Temple 1988; see discussion in Smith 1991)

Nonbreeding populations are less well-known. Food level has an effect; flock sizes are larger in supplemented areas (Desrochers et al. 1988, Brittingham and Temple 1988), but not known is what determines if a recruit will be accepted or rejected from a newly-forming winter flock; this is a wide-open area for future research.