The Cerulean Warbler is a small warbler, weighing only about 8-10 grams. They have long wings and a short tail. Adult males have deep blue colouring on top, with a distinct blue-black band across their throat. Females have light blue-green colouring on top, yellow-white eyebrows, and a whitish underbelly that has a yellow tint to it. They are more likely to be heard than seen- their call is buzzy and rapid, and ends a high note.
They eat a range of insects from the upper canopy of forests, hopping from branches to pick their meal off of the leaves. They feed mainly on insects during breeding season, and feed their young primarily butterfly larvae. Their diet includes flies, beetles, weevils, and caterpillars. During migration they will forage in groups with other birds, and they have been known to eat plant matter in the winter to supplement their diet.
Biology and Behaviour:
The males arrive at the breeding territory by mid-May, and the females will arrive a week or two later. They often return to the same nest site, and will nest in loose colonies. The female Cerulean Warbler builds her nest high in a deciduous tree, using materials such as bark strips, grass, lichen, fur, moss and spider webs. She will lay 2-5 eggs, incubate them for 11-12 days, and then nestlings will be ready to fly 10 days after hatching, which usually starts in July. Cerulean Warblers can be aggressive towards other song birds, especially during the breeding season.
When migration begins, Cerulean Warblers have a long journey south. It takes them about four months to fly from Ontario to the Andes Mountains. While the spring journey north only takes about two months, their long migration periods make them more susceptible to exposure.
- Black-throated Blue Warblers are similar but have black extending across their eyes, cheeks, and throat, and neither sex has double wing bars
- The Blackpoll Warbler, Bay-breasted Warbler, and Pine Warbler look like the female Cerulean, but they have more yellow than green along their backs
Conservation and recovery strategies:
- Habitat suitability maps have been created for the Thousand Islands Ecosystem to ensure that Cerulean Warblers have the proper breeding and nesting grounds
- Several surveys have taken place in Ontario Parks across the province in order to get an idea of where our Cerulean Warbler populations are able to thrive
- Ontario has developed Best Management Practices for forestry operations, giving specific practices to improve habitat for Cerulean Warblers. However, these practices are optional for forest managers
- Cerulean Warblers will re-nest if the first one fails, and they will often recycle the materials from their old nest, especially the coveted spider webs
- This bird is very hard to study because they live high up in the tree canopy and are often hard to spot
- Female Cerulean Warblers have a unique way of leaving their nest. They will often “bungee jump” off the side, only spreading their wings once they have passed the nest
Cadman, M.D, D.A. Sutherland, G.G. Beck, D. Lepage, and A.R. Couturier (eds.). 2007. Atlas of the Breeding Birds of Ontario, 2001–2005. Bird Studies Canada, Environment Canada, Ontario Field Ornithologists, Ontario Ministry of Natural Resources, and Ontario Nature, Toronto, xxii + 706 pp.
COSEWIC. 2010. COSEWIC assessment and status report on the Cerulean WarblerDendroica cerulea in Canada. Committee on the Status of Endangered Wildlife in Canada. Ottawa. x + 40 pp.
COSSARO. 2011. https://www.ontario.ca/page/cerulean-warbler-evaluation
Environment Canada. 2011. Management Plan for the Cerulean Warbler (Dendroica cerulea) in Canada. Species at Risk Act Management Plan Series. Environment Canada, Ottawa. iii + 19 pp.
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