Several years ago, I saw my first chestnut-sided warbler (Setophaga pensylvanica) during breeding season in the mountains of North Carolina. It was a somewhat fleeting sighting but long enough for me to recognize the male’s beauty. My next sighting was a couple years ago when a pair stopped by a local creek during their south-bound migration in the fall. They were still attractive, but I had fallen for their mating season colors. What I didn’t know then was that when they reached their winter destination in some Central American area, they would be likely associating with the same birds with whom they had spent previous winters foraging.
Lucky me, therefore, when I noted that many chestnut-sided warblers were part of the spring migratory crowd in Quebec a couple weeks ago. I saw them in at least five sites and was able to get some nice photos of these beauties.
The Cornell Lab’s All About Birds website advises: “Stay around clearings, road edges, or other disturbed sites with young deciduous trees to find Chestnut-sided Warblers.” They did indeed appear in such places, looking for insects.
They appear to really like early successional deciduous habitats, e.g., terrains affected by logging, fire, storms and flooding. Clearing of people’s land around their houses may also qualify as a habitat-forming place for these little birds. We also discovered that these colorful warblers look for food among stones, rocks and boulders along bodies of water.
At the St. Irénée quay, a species mate was popping in and out among the large boulders on either side of the pier.
Seeing these beautifully colored birds as they hunted for insects was quite enjoyable. The Rev. Leander S. Keyser, who attended the 1896 World Congress on Ornithology, remarked that the chestnut-sided and blackburnian warblers were like “a sonnet in feathers – lightness of air and sunshine embodied – rhythm caught in a living form” – what a beautiful way of describing them!
Besides the chestnut-sided warbler, I saw another species which I’d seen with more muted colors in North Carolina – the bay-breasted warbler (Setophaga castanea). In the autumn, they have a yellow-green head and only slight chestnut-colored wash on their flanks; they look very similar to blackpoll warblers during that season and winter.
When I saw their breeding plumage in Quebec, it was a real surprise – and a most pleasant one! The bay-breasted warblers immediately became one of the birds I’ve most enjoyed seeing. And as I saw more and more during the week, I never tired of watching (and photographing) them!
During breeding season, these birds eat many more insects than fruit and they were very busy gleaning in the conifers.
In the spring, they specialize in seeking out spruce budworm moth (Choristoneura fumiferana) caterpillars. It was shown in one study that the bay-breasted warblers ate more than 13,000 budworms per 2.5 acres (one hectare) in a period of 41 days. These moths produce larvae that can decimate spruce and fir forests in Canada when their numbers increase greatly. The populations of bay-breasted warblers then fluctuate in conjunction with those of the budworms, which have an “outbreak” every 30-40 years.
In 2004, Boulanger and Arseneault studied this phenomenon and concluded that: “data suggest that outbreak frequency has remained quite stable, with a mean interval of about 40 years between the midpoint of successive outbreaks since the mid-16th century.” It would be interesting if another study could be done to see if the outbreak frequency is changing with climate change. The current population explosion of the budworms began in 2006 and could last until 2021; the government of Quebec is spending $30 million this year to eradicate the moth so the warblers may lose a food source. Their numbers may therefore also decline as a result.
While the fluctuations in their numbers have risen and fallen together with the spruce budworms, their summer habitats may be affected by human interventions. It is estimated that only 4% of these areas are stable so conservation efforts should take this into consideration, especially because their global population numbers have fallen about 74% since 1966.
As these birds forage on tree branches, they tend to move more slowly than some of the other warbler species, taking their time to seek out juicy tidbits. In addition to caterpillars, they eat beetles, flies, moths, leafhoppers and grasshoppers.
The female bay-breasted warblers can be distinguished from their male counterparts by the fact that they lack the black face mask and have lighter bay coloring.
Both sexes seemed to be fairly comfortable with me watching them. They seemed much less shy than some other species of birds. To my complete delight, of course!
An interesting observation is that they tend to like foraging on lichen-covered branches.
In contrast to some of the other warblers, they tend to build their nests in the mid-level tree canopy; that is also where they do a lot of their food hunting. However, as my walks in St. Irénée showed, they are not averse to foraging on the ground!
Since they mostly breed in Canada and spend their winters in Central and South America, seeing them in North Carolina during migration is a treat. Interestingly, the adults tend to migrate along routes west of the Appalachian mountain range and immature birds often migrate along the Eastern US seaboard and coastal areas.
These birds of waxing and waning populations have inspired poets and I can see why. Seeing them in their breeding plumage in Quebec was a wonderful gift. I hope to see them there again one day as they have joined my list of special species that I love. 😊