Kirtland's warbler (Dendroica kirtlandii) COSEWIC assessment and status report: chapter 6
Biology
Reproduction, life cycle and diet
Kirtland’s Warblers are generally monogamous, but polygyny does occur (perhaps up to 15% of males). The mean clutch size is 4.63 (range 3-6; Mayfield 1992) and first breeding occurs at one year of age. Life expectancy has been calculated at four years (Mayfield 1960; Walkinshaw 1983), with maximum longevity recorded at 11 years for males and eight years for females (Walkinshaw 1983).
Annual adult survival (from June) is estimated at about 65% (Mayfield 1992). Mortality rates for different parts of the life cycle have not been evaluated. Kirtland’s Warblers nest in loose colonies and the social need for adjacent nesting pairs may limit populations in some areas.
Kirtland’s Warblers feed on spittlebugs and aphids (Homoptera), ants and wasps (Hymenoptera), beetles (Coleoptera), moth larvae (Lepidoptera; DeLoria-Sheffield et al. 2001) and blueberries.
Predation
Although predation on adult Kirtland’s Warblers has not been observed directly, circumstantial evidence suggests that Sharp-shinned Hawks (Accipiter striatus), Northern Harriers (Circus cyaneus), Great Horned Owls (Bubo virginianus) and domestic cats (Felis domesticus) prey on adults. Eggs and young may be taken by Blue Jays (Cyanocitta cristata), thirteen-lined ground squirrels (Spermophilus tridecemlineatus), raccoons (Procyon lotor), striped skunks (Mephitis mephitis), domestic cats, and Garter Snakes (Thamnophis sirtalis; Walkinshaw 1983; Mayfield 1992). Brown-headed Cowbirds may also prey on eggs and nestlings (Lowther 1993).
Physiology
There is no information on the physiology of this species.
Dispersal/migration
Juvenile males have been shown to disperse from natal sites to potential breeding sites up to 350 km away (Probst et al. 1993). In early autumn, all birds migrate from breeding areas mostly to the Bahama Islands where they spend 40-60% of the annual cycle (Probst et al. 2003). On the return migration in the spring, birds migrate in a narrow band through South Carolina, North Carolina, western Virginia, West Virginia, Ohio, and southern Michigan (see references in Mayfield 1992) and Ontario.
Males banded in 1977 and 2006 in Petawawa, Ontario both returned the following year to Petawawa (D. Coulson, M. Oldham, A. Dextrase, pers. comm. 2008).
Interspecific interactions
Relatively few bird species use young jack pine forests, so the potential for interspecific interactions with other species is quite low. One obvious interspecific interaction is between Kirtland’s Warblers and Brown-headed Cowbirds, which is a major threat to the species in Michigan.
Adaptability
The Kirtland’s Warbler has very specialized habitat requirements (fire-regenerated, early successional jack pine with specific tree densities and habitat structure; Nelson 1992), but shows some adaptability in using plantations of jack pine (and more rarely red pine), which are specifically managed for the species.
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