NT
Common Grackle Quiscalus quiscula



Justification

Justification of Red List Category
The species has undergone a population reduction of about 50% since 1970 (Rosenberg et al. 2016). Even though the rate of decline appears to be slowing down recently and the species's range might be larger than previously assumed, the population reduction is projected to continue. It is therefore precautionarily listed as Near Threatened.

Population justification
The population has been estimated at 69 million mature individuals (Rosenberg et al. 2016), equating to 103.5 million individuals.

Trend justification
This species has undergone a large and statistically significant decrease over the last 40 years in North America (-61.4% decline over 40 years, equating to a -21.1% decline per decade; data from Breeding Bird Survey and/or Christmas Bird Count: Butcher and Niven 2007). Some extrapolated trends over three generations that include both time in the past and in the future do imply a reduction that approaches the threshold for Vulnerable. For instance, data from 2005-2015 show an annual decline of 1.87% (1.47-2.26% decline) (Sauer et al. 2017). This would equate to a reduction of 27.2% (22.0-31.9% reduction) over 3 generations. However, some more recent annual declines appear to be lower, and so declines of this rate are not suspected to continue into the future.

Distribution and population

The species is found in North America, where it occurs from northern central Canada and the U.S.A. east of the Rocky Mountains to northern Mexico. Recent records of the species in northern Manitoba (Canada) suggest that its range reaches further north than previously assumed (C. Artuso in litt. 2018, Taylor 2018). In the south of its range, near the Gulf of Mexico, it is resident, but other populations will make short to medium range (up to 500 km) seasonal migrations (Peer and Bollinger 1997, Fraga 2018). It migrates in very large mixed-species flocks (often with Red-winged Blackbirds Agelaius phoeniceus, European Starlings Sturnus vulgaris and Brown-headed Cowbirds Molothrus ater) (Peer and Bollinger 1997).

Ecology

The species has likely benefited from the clearance of woodland and agricultural expansion since European settlement in North America. It may have originally occupied wooded habitats near watercourses and swamps, but can now be found in large numbers in a range of habitats (Peer and Bollinger 1997, Fraga 2018). It prefers open or partially open habitats with scattered trees, but is well adapted to human-modified habitats and occurs in large numbers in suburban and residential areas, parks and plantations (Peer and Bollinger 1997).

Threats

Following the large increase in numbers, possibly due to agricultural development, the Common Grackle is now one of the most abundant species in North America (Peer and Bollinger 1997). They occur in large flocks and dense roosting aggregations in parks and agricultural areas, where they damage grains, seeds and fruits and are now regarded as an economically significant pest species (Peer and Bollinger 1997). Moreover, its roosting sites can hold the fungus Histoplasma capsulatum, which can cause the lethal human respiratory disease histoplasmosis (Peer and Bollinger 1997). Consequently, the species has been subject to extensive deterring and population control measures, which may include chemical repellents (Methiocarb) or lethal surfactants (PA-14) (Peer and Bollinger 1997).

Conservation actions

Conservation Actions Proposed
Monitor the population trend. Investigate the causes for the reduction and assess the impact of population control measures on the population size.

Identification

c.28 cm. A medium-sized blackbird with long keel-shaped tail, yellow irides, long bill; plumage iridescent black with head, breast, neck and tail purple-blue or blue-green. Female smaller than male with shorter tail.

Acknowledgements

Text account compilers
Hermes, C., Ekstrom, J., Westrip, J., Butchart, S.

Contributors
Artuso, C.


Recommended citation
BirdLife International (2019) Species factsheet: Quiscalus quiscula. Downloaded from http://www.birdlife.org on 26/03/2019. Recommended citation for factsheets for more than one species: BirdLife International (2019) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 26/03/2019.