the Nest Files – Chestnut-sided Warbler

Adult male Chestnut-sided Warbler (Derbyshire)


Chestnut-sided Warbler (Dendroica pensylvanica)

Nidiologicals – Peck and James (1987) and Richardson & Brauning (1995)
Habitat – Early successional deciduous forest, regenerating clearcuts/fields and woodland edges
Microhabitat – Open cup nest built in crotch of understorey shrub, usually less than 2m from ground.
Spring arrival – Early to late May (Ontario)
Average nest height – .6m
Nest builder – Female only
Average # of broods/season – 1
Average egg laying date – 7 June-17 June (Ontario)
Average clutch size – 4 eggs
Incubation period – Average 11-12 days
Egg colour – White to pale greenish with variable markings concentrated at larger end.
Incubation – Female only
Brown-headed Cowbird host – Yes

CSWA nest with eggs

The Chestnut-sided Warbler (CSWA) is a fairly common breeder here in Frontenac County and across much of the southern half of Ontario. This species was a North American rarity in the early 19th century before much of the forests were cleared and the young successional habitats became widespread. Populations of Chestnut-sides exploded and now occupy scrubby margins of woodland and overgrown fields from central Saskatchewan to Nova Scotia and south to Georgia along the Appalachian Mountains. In our region they are typically associated with woodland borders of small farms, roadsides, bogs and rock barrens.

This nest was discovered by the observation and tracking of a female carrying nest material on May 28, 2010 at our Blue Lakes MAPS station near Sharbot lake, ON. There are about ten pairs in the immediate area of the station that are occupying scrubby shoreline edges of lakes and ponds. At least part of the site was burned over at some point within the last century or so, which has slowed regeneration and created appropriate conditions for the species. The nest pictured above was less than half complete on May 28 and was finished by June 4 when three eggs were photographed.

Full clutch (Seabrooke Leckie)

A clutch of five eggs is unusual for this species. This picture was taken on June 8 during our first visit to Blue Lakes. We captured and banded two males and the female responsible for this clutch on that date. The males have an interesting song repertoire and vocal development biology. Two song classes are evident; an Accented Ending (AE) class and an Unaccented Ending (UE) class. The AE song (Please, please, pleased to meetcha) is given on arrival and is primarily used to attract females. The UE song is given later on in the breeding season and seems to be mostly employed for territorial defense and intraspecific aggression. Lab studies have indicated that AE songs are developed with little social interaction while UE songs are learned through direct observation of “tutor” males (Byers and Kroodsma 1992).

Chestnut-sided Warbler nest site

Here is a photograph of the nest site context along the shore of a small unnamed lake. The Chestnut-sided Warblers are nesting in this low, dense shrub layer beneath scattered clumps of young-mid successional oak and maple. Gray Catbird, Warbling Vireo, Yellow Warbler and Indigo Bunting also occupy this habitat type, although the latter is mysteriously absent from the site. We have about five more weeks of fieldwork in 2010 and a lot yet to learn about the “Chestnuts” at Blue Lakes. We are suspecting that the forthcoming post-breeding dispersal will consist of a large dose of young Chestnut-sided Warblers.

Young CSWA at MABO in 2009 (S.Leckie)


MAPS Visit 1 – Blue Lakes

Chestnut-sided Warbler (D.Derbyshire)

Our roster of Monitoring Avian Productivity and Survivorship (MAPS) stations has grown in 2010! Our new site called Blue Lakes is the northernmost of the three and is about nineteen kilometres north of Maplewood Bog. The site fills a key gap for us both spatially and in species coverage. Finding this site was quite an exercise that involved several weeks of map study and reconnaissance. I found lots of other sites that had potential but there was always a negative factor or two with them. Access, terrain, edge conditions and species mix were key considerations that were finally met when the Blue Lakes site was discovered about two weeks ago. A satellite view of the “AXIS” network is included below. Each of the three stations provides coverage of an area up to a four kilometre radius of the station centre, which means that we are now generating productivity statistics for 150 square kilometres of the Frontenac region – very exciting.

FBS MAPS network (Google Earth)
Lake edge at banding station (Leckie)

This is the view from the banding station, which is situated on a scrubby peninsula that bisects a horseshoe-shaped lake full of emergent vegetation, amphibians and a small heronry as well.

Net 9 in mature deciduous (Leckie)

The Blue Lakes is probably the most varied of the three stations in terms of habitat. A circuit of the ten net lanes passes through rocky scrub edge along the shores of small lakes, mature deciduous forest, deciduous swamp thickets, areas of young balsam fir/shrub thicket and grass/lichen outcrops. Also distinct here is the presence of a dense understorey – not represented at our Rock Ridge or Maplewood Bog sites further south.

Net 5 in fir swamp (Leckie)

Balsam Fir occurs throughout the area but is quite dense along a wet draw through mixed age forest with an uneven canopy. The conifers attract species such as Hermit Thrush and Magnolia Warbler, among others. The firs and the odd spruce here and there add a nice northern feel, which becomes more noticeable as you approach Highway 7 from the south. The Blue Lakes site is at the edge of the Boreal Hardwood Transition zone.

rocky clearing (Leckie)

These clearings are our main modes of traversing the site. They provide stable footing and a relatively flat, unobstructed path through the station. Field Sparrow and Sweetfern are dominant species in the rocky clearings where evidence of a rock flipping Black Bear was also found.

Net 1 in edge scrub (Leckie)

This is the important edge habitat that will (hopefully) attract large numbers of dispersing young and adult birds in the latter half of the breeding season. Both of the edge nets on the peninsula performed very well today, which was very pleasing.

Seabrooke banding Yellow-throated Vireo

We banded a Yellow-throated Vireo (YTVI) that was captured in net 1 on first check! This fellow has been singing from the oaks above the net lane for at least two weeks. This is the first capture of a YTVI for the MAPS program. They are a Frontenac Arch specialty of sorts, quite common in deciduous forest with clearings, so it was great to finally band one!

Black-throated Blue Warbler (Seabrooke Leckie)

Black-throated Blue Warblers are a dominant species at Blue Lakes, largely due to the dense undergrowth found in the forests. Seabrooke and I estimated that between 5-7 territorial males are present in the core area of about 8 hectares. It is unclear as to whether these males are mated as no females were observed or captured today. The capture and banding of this second-year male was also a first for our MAPS program. Black-throated Blues are wonderful birds and we can look forward to their buzzy tones for years to come!

Hermit Thrush (S.Leckie)

The other dominant species at Blue Lakes are Veery and Chestnut-sided Warbler but a very diverse community of breeding birds was evident this morning. Singles of Hermit Thrush, Scarlet Tanager and Warbling Vireo (1st banded by FBS) were banded along with several Common Grackles and a lone Red-winged Blackbird (1st banded by FBS).

Mink Frog (one of many today)

I’ve only just barely scratched the surface of all that was enjoyed and discovered today. Visits to Rock Ridge and Maplewood Bog are imminent and the 3 A.M wake-up calls beckon me to cut this summary a bit short. We will have six more mornings of banding at Blue Lakes this summer and we are looking forward to each of them – a great study site indeed.

Here are the stats…


Blue Lakes – Visit 1 of 7

New birds banded (24 of 14 species)

Common Yellowthroat – 1
Veery- 4
Rose-breasted Grosbeak – 3
American Robin – 1
American Redstart – 1
Chestnut-sided Warbler – 3
Black-throated Blue Warbler – 1
Warbling Vireo – 1
Ovenbird – 2
Yellow-throated Vireo – 1
Scarlet Tanager – 1
Hermit Thrush – 1
Red-winged Blackbird – 1
Common Grackle – 3