Justification of Red List Category
Since 1987, conservation action has successfully increased the population of this species. Numbers exceeded 500 singing males in 1994 following doubling of suitably aged habitat between 1987 and 1990. Numbers continue to increase, but its population remains small, hence its classification as Near Threatened.
The population size continues to increase, with latest estimates (2015) putting it at around 2,365 singing males (Michigan Department of Natural Resources 2015). The population is estimated at 4,500-5,000 mature individuals (D. Ewert in litt. 2016), which equates to 6750-7,500 individuals, rounded here to 6.800-7,500 individuals.
Following major declines in c.1900-1920 and 1961-19715, numbers have recovered from 167 singing males in 1974 to 1,478 singing males in Michigan in 2006, the highest since surveys began in 1951 (Wunderle et al. 2006).
Almost the entire population of Setophaga kirtlandii breeds in north and central Michigan (Anon. 2008), with small numbers breeding in Michigan's Upper Peninsula and Wisconsin, U.S.A. and Ontario, Canada (Eskelsen 2007, Richard 2013). Breeding habitat has declined by 33% since the 1960s, but is more extensive than the 18 km2 occupied in 1994 (Nelson and Buech 1996). It has a very small winter range in the Bahamas and the Turks and Caicos Islands (to U.K.), with recent studies demonstrating that most overwinter in the central Bahamas islands of Eleuthera, San Salvador, Cat and Long Islands (J. M. Wunderle in litt. 2016). There were major declines in c.1900-1920 and 1961-1971 (Haney et al. 1998), with the population numbering just 167 singing males in 1974 and 1987 (Anon. 1996). Numbers have recovered to 2,365 singing males in Michigan, Wisconsin and Ontario in 2015 (Michigan Department of Natural Resources 2015), the highest since surveys began in 1951 (National Wildlife Refuge Association in litt. 2006); 97.5% of the singing males were in the lower peninsula of Michigan.
Its optimal breeding habitat is large, fire-maintained homogeneous stands of 1-5 m tall jack pines Pinus banksiana on sandy soil (Mayfield 1992, Sykes 1997, Anon. 2008). Eggs are laid in May and June (Curson et al. 1994). It winters in early-successional disturbed habitat (Wunderle et al. 2010), either stands of Caribbean pine P. caribbaea (Haney et al. 1998), or, more commonly, in natural and secondary scrub, and saline/upland ecotone (Sykes and Clench 1998; Wunderle et. al. 2010; Wunderle et. al. 2014). Stands of Caribbean pine, P. caribbaena were believed to be important winter habitat (Haney et al. 1998), but more recent surveys indicate that although warblers may use pine stands during migration, most of the wintering population is found on the non-pine islands of the central Bahamas (unpublished data from J. Wunderle, D. Ewert, & N. Cooper). It feeds on arthropods and abundant fruit during winter (Wunderle et al. 2010, 2014). Some birds move from patch to patch in the wintering grounds as food supplies are depleted and areas dry out, eventually concentrating in small patches where they maintain small and overlapping home ranges (Wunderle et al. 2014). Following dry winters, birds arrive relatively late on the breeding grounds, which is associated with lower reproductive success (Rockwell et al. 2012).
Parasitism by brown-headed Cowbird Molothrus ater is a threat in breeding areas (Sykes and Clench 1998). Wintering area threats include droughts and habitat disturbances that eliminate early successional habitats with favoured fruit plants (J. M. Wunderle in litt. 2016). Studies have demonstrated that late winter droughts can eliminate fruit, causing reduction in warbler body condition, annual survival and reduced reproductive success in Michigan (Wunderle et al. 2014, Rockwell et al. 2012, Rockwell 2013). Climate change is a major concern in wintering grounds, especially the potential increase in drought conditions and sea level rise, which threatens the warbler’s coastal habitats as well as limiting availability of freshwater required by warbler’s fruit plants (J. M. Wunderle in litt. 2016). Fire suppression also poses a threat (Sykes and Clench 1998).
Conservation Actions Underway
CMS Appendix I. Management replicating the effects of natural fires has expanded potential breeding habitat to c.516 km2 (Richter 1996, Sykes 1997). Since 1972, a cowbird trapping programme has reduced parasitism from 70% to 3% (Anon. 1996). Efforts are underway to evaluate cowbird parasitism rates in selective Kirtland's Warbler breeding areas where cowbirds are not removed (Nathan Cooper, pers. comm.). Education and ecotourism initiatives in Michigan include an annual Kirtland's Warbler Festival (Richter 1996). Surveys have been undertaken in the Bahamas since 1998 (Haney et al. 1998, D. Ewert in litt. 1999, R. Phillips in litt. 2016) and most recently from 2010 - 2016 throughout the Bahamas and Turks and Caicos (R. Phillips in litt. 2016). Migration routes and stopover sites are being evaluated with birds fitted with geolocators (Nathan Cooper, pers. comm.). Breeding success and carry-over effects have been studied by Rockwell et al. (2012) and others. Potential effects of climate change are being modeled. Virtually the entire population breeds within the 219,000-acre Kirtland's Warbler Management Area which includes the Huron National Forest, the Kirtland's Warbler National Wildlife Refuge and various Michigan state forests.
14.5 cm. Large grey-and-yellow warbler. Male, blue-grey above with diffuse black streaking on the mantle. Black lores and split white eye-ring. Yellow underparts with black streaking on flanks. Female, similar but paler with brown tinge to mantle and lacks black lores. Immature has greyish streaking and spots on throat. Voice Song an emphatic chip-chip-che-way-o.
Text account compilers
Khwaja, N., Pople, R., Wheatley, H., Benstead, P., Bird, J., Harding, M.
Ewert, D., Wunderle, J., Hilton, G., Rustem, R.
BirdLife International (2020) Species factsheet: Setophaga kirtlandii. Downloaded from http://www.birdlife.org on 21/09/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 21/09/2020.