Justification of Red List Category
This species has undergone rapid declines in the past, which seem to be slowing down now. Observational data suggests that it has not met the threshold for listing as threatened during the last decade, even though the rate of decline might accelerate slightly in the future. Consequently, the species has been downlisted to Near Threatened.
Partners in Flight estimate the global population to number 570,000 mature individuals (A. Panjabi in litt. 2017).
Rosenberg et al. (2016) estimate the population reduction between 1970 and 2014 to be 72%, which roughly equates to 26.8% over three generations (10.8 years). Short term population trends from the North American Breeding Bird Survey (Sauer et al. 2017) show an annual decline of 1.31% (3.70% decrease to 1.83 increase) between 2005 and 2015. This equates to a reduction of 13.3% (33.4% decrease to 21.6% increase) over three generations. Even when looking at year by year records from Sauer et al. (2017), the species’s rate of decline has not met or approached the threshold for Vulnerable (reduction of 30% over three generations) since 2008, and so the rate of decline has been below the threshold for Vulnerable for some time. Partners in Flight estimate the half-life of the species to be 26 years though (Rosenberg et al. 2016), which would equate to a decline of 25.0% over the next three generations.
The species breeds from Quebec and Ontario (Canada) west to Nebraska and south to northern Texas, Louisiana, Mississippi, Alabama and Georgia (U.S.A.) (AOU 1983). Within this broad range, its distribution is very patchy. Although sizeable populations can be found throughout the breeding range (Buehler et al. 2008), approximately 80% of the population breeds in the Appalachian Mountains (Wood et al. 2013). The species migrates south through the south-eastern USA, the Bahamas, Cuba, Jamaica, the Caribbean slope of Mexico, Belize, Guatemala, Honduras, Costa Rica and Panama, and winters from Colombia and Venezuela south, mainly east of the Andes, to eastern Ecuador, south-eastern Peru and perhaps occasionally to northern Bolivia (AOU 1983, Herzog et al. 2009).
The species breeds in mature deciduous forest (AOU 1983, Sibley and Monroe 1990), in both upper dry slopes and ridge tops and riparian bottomlands (Buehler et al. 2013). In general, individuals preferably establish territories in forests with higher canopy height, greater canopy cover (c.85%) and larger trees (Roth and Islam 2008). Recent evidence suggests that the species selects habitat in the vicinity of small canopy gaps, both natural and anthropogenic (Wood et al. 2005, 2006, Bakermans and Rodewald 2009, Boves et al. 2013), within these larger forested landscapes. The nest is built on the branch of a tree, and breeding takes place between May and July (Curson et al. 1994). Wintering birds are found in Andean submontane forest, mainly between 1,000 and 2,000 m (Curson et al. 1994, Buehler et al. 2013), although they have been observed at higher elevations (e.g., 3500 m in Venezuela; Rengifo et al. 2005). Traditional shade-coffee plantations are an important wintering habitat; they support densities of Cerulean Warblers 3-14 times higher than in neighbouring primary forest (Bakermans et al. 2009). Information on migratory stopover sites is limited, but the species has been recorded in primary and secondary subtropical montane forests in Belize (600-750 m; Parker 1994), at a wide range of elevations and habitats in Honduras (Welton et al. 2012) and a range of forested habitats in Costa Rica (Stiles and Skutch 1989).
Degradation of habitat through land use change is the major threat to this species. Conversion of mature deciduous forest to agricultural or urban areas, fragmentation and increasing isolation of remaining mature deciduous forest, the change to shorter rotation periods and even-aged management, and loss of key tree species to disease are the main constraints to the species on the breeding grounds (Hamel 2000, Buehler et al. 2013). Mountaintop mining constitutes a known, but as yet uncontrolled, threat on the breeding grounds, primarily in West Virginia, Virginia, Tennessee and Kentucky (G. Butcher in litt. 2003). On the wintering grounds, habitat is threatened by the conversion to other land uses such as pastureland, subsistence crops, conventional coffee plantations and coca plantations, which have a detrimental effect on the availability of suitable primary forest habitat. Conversion from shade-grown to sun-grown coffee reduces habitat quality for the species; Colombia has converted 70% of its plantations, while Venezuela lost 38% of its plantations between 1950 and 1990 (Bakermans et al. 2009). Attempts to eradicate coca plantations may also potentially damage forests (Hamel 2000, Buehler et al. 2013).
Conservation Actions Underway
In the United States, Cerulean Warblers are considered a National Species of Conservation Concern. In Canada, Cerulean Warblers are listed as Endangered by the Committee on the Status of Endangered Wildlife in Canada, and as Special Concern on Schedule 1 of the federal Species at Risk Act. In North America, current conservation activities include planning projects for habitat acquisition and protection, land protection and acquisition projects to increase the amount of forest in certain areas such as the Interior Low Plateaus and Coastal Plain of Tennessee. Forest management guidelines for the Appalachian Mountain region (based on a large-scale silvicultural experiment; Boves et al. 2013) have been recently published that should prove useful throughout the breeding range. Over one million acres of bottomland forest in the USA have been replanted with native hardwoods. ProAves Colombia established the Cerulean Warbler Bird Reserve, the first reserve in South America specifically for a neotropical migrant landbird. A conservation corridor has also been created in Colombia through reforestation to connect existing habitat. Shade-grown coffee is promoted as “bird friendly” (Jones et al. 2002, Bakermans et al. 2009, Colorado et al. 2012).
Conservation Actions Proposed
Investigate long-term population viability in response to forest management (J. Jones in litt. 2016). Protect intact primary forest ecosystems to maintain wintering populations. Urgently protect key sites for the species in its breeding range. Prevent the conversion of shade-coffee agroecosystems (which support high densities of wintering Cerulean warblers) into cattle lands (C. Rengifo in litt. 2012). Conduct thorough environmental impact assessment prior to any mining operations to ensure that measures are taken to avoid destroying habitat and to mitigate against any negative impacts. Carry out reforestation with native tree species, especially at margins of existing habitat patches (J. Jones in litt. 2016).
12 cm. Small canopy-dwelling wood-warbler. Male has sky-blue upperparts, with two white wing-bars. Underparts are mostly white with a narrow blue breast band and flank streaks. Female plumage mirrors that of the male but the blue is replaced by a greenish-blue. Voice Song is a high-pitched rather musical buzz.
Text account compilers
O'Brien, A., Benstead, P., Wheatley, H., Sharpe, C.J., Westrip, J., Hermes, C., Bird, J., Harding, M.
Butcher, G., Islam, K., Jones, J., Panjabi, A., Rengifo, C. & Sharpe, C J
BirdLife International (2020) Species factsheet: Setophaga cerulea. Downloaded from http://www.birdlife.org on 15/08/2020. Recommended citation for factsheets for more than one species: BirdLife International (2020) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 15/08/2020.