- 3.9–4.3 in
- 7.1–8.3 in
- Paruline à flancs marron (French)
- Reinita de costillas castañas (Spanish)
- On the wintering grounds in Central America the Chestnut-sided Warbler joins in mixed-species foraging flocks with the resident antwrens and tropical warblers. An individual warbler will return to the same area in subsequent years, joining back up with the same foraging flock it associated with the year before.
- The Chestnut-sided Warbler sings two basic song types: one is accented at the end (the pleased-to-MEETCHA song), and the other is not. The accented songs are used primarily to attract a female and decrease in frequency once nesting is well under way. The unaccented songs are used mostly in territory defense and aggressive encounters with other males. Some males sing only unaccented songs, and they are less successful at securing mates than males that sing both songs.
- The oldest recorded Chestnut-sided Warbler was at least 6 years, 11 months old when it was found in Rhode Island in 1980. It had been banded in the same state in 1973.
- Breeds in early successional deciduous woods.
- Winters in moist tropical forest.
Insects and other arthropods, occasionally fruit.
- Clutch Size
- 3–5 eggs
- Egg Description
- Creamy white or greenish with brown speckles.
- Condition at Hatching
- Helpless with sparse down.
Nest an open cup woven of bark strips, weed stems, grasses, and plant down. Lined with fine grasses, hair or rootlets. Placed in small crotch of shrub or within a group of thin vertical stems, less than 2 m (6.5 ft) from ground.
Gleans insects from the bottom of leaves.
Chestnut-sided Warbler populations declined by about 44% between 1966 and 2015, according to the North American Breeding Bird Survey. Partners in Flight estimates a global breeding population of 19 million with 30% breeding and migrating through the U.S., 70% in Canada, and 9% wintering in Mexico. It is a U.S.-Canada Stewardship species, and rates a 12 out of 20 on the Continental Concern Score. Chestnut-sided Warbler is not on the 2016 State of North America's Birds' Watch List. Numbers have declined in part due to loss of habitat.
- Richardson, M., and D. W. Brauning. 1995. Chestnut-sided Warbler (Dendroica pensylvanica). In The Birds of North America, No. 190 (A. Poole and F. Gill, eds.). The Academy of Natural Sciences, Philadelphia, PA, and The American Ornithologists' Union, Washington, D.C.
- Dunn, J. L., and Garrett, K. L. 1997. A Field Guide to Warblers of North America. Houghton Mifflin Co., Boston.
- North American Bird Conservation Initiative. 2016. The State of North
America’s Birds 2016. Environment and Climate Change Canada: Ottawa, Ontario.
- Partners in Flight. 2012. Species assessment database.
- USGS Patuxent Wildlife Research Center. 2016. Longevity records of North American Birds.
- USGS Patuxent Wildlife Research Center. 2015. North American Breeding Bird Survey 1966–2015 Analysis.