Breeding

The Connecticut Warbler is a socially monogamous breeder with one clutch per breeding season. Only the females incubates the eggs, but both male and female participate in brooding, feeding young birds and nest sanitation. Little is known about the extent of extra-pair copulations.

Winger and Pegan (52 Winger, B. M., and T. M. Pegan (2021). Migration distance is a fundamental axis of the slow-fast continuum of life history in boreal birds. Ornithology 138:1–18. Close ) calculated an average inter-migratory period of 108.5 d that birds spend on the breeding grounds. They based this calculation on eBird data and the median peak fall and spring migrations through Chicago, Illinois from 2000–2017. Incubation by females began from 20–24 June in Quebec (27 Saulnier, M-C. (2011). Biologie de la reproduction de la Paruline à gorge grise (Oporornis agilis) dans les pinèdes grises du Lac-Saint-Jean, Canada. M.S. thesis, Université du Québec à Chicoutimi, Chicoutimi, QC, Canada. Close ).

Pair Formation

Courtship and mating begin soon after arrival on breeding grounds in late May, continue into late June throughout breeding range (Figure 1), and, in Michigan, coincide with peak singing and territoriality (25 Walkinshaw, L. H., and W. A. Dyer (1961). The Connecticut Warbler in Michigan. Auk 78(3):379–388. Close ).

Nest Building

Most nesting accounts reported nesting in June; there are occasional records from July (Figure 1).

First Brood

Nesting dates are highly variable throughout the breeding range. Most egg dates (range-wide) have been recorded from mid to late June (7 Bent, A. C. (1953). Life Histories of North American Wood Warblers. Bulletin of the United States National Museum 203. Close ), mid to late June in British Columbia (91 Campbell, R. W., N. K. Dawe, I. McTaggart-Cowan, J. M. Cooper, G. W. Kaiser, M. C. E. McNall and A. C. Stewart (2001). The Birds of British Columbia, Volume 4: Passerines, Wood-Warblers through Old World Sparrows. University of British Columbia Press, Vancouver, British Columbia, Canada. Close ), 15–30 June in Alberta, some later records in mid-July (85 Salt, W. R. (1973). Alberta vireos and wood warblers: families Vireonidae and Parulidae, distribution and breeding. Edmonton Provincial Museum and Archives of Alberta, Edmonton, AB, Canada. Close ), early June–early July in Wisconsin (102 Robbins, S. D., Jr. (1991). Wisconsin Birdlife: Population and Distribution, Past and Present. University of Wisconsin Press, Madison, Wisconsin, USA. Close ), and first week of June through early July in Michigan (25 Walkinshaw, L. H., and W. A. Dyer (1961). The Connecticut Warbler in Michigan. Auk 78(3):379–388. Close , 129 Granlund, J., G. A. McPeek, and R. J. Adams (1994). The Birds of Michigan. Indiana University Press, Bloomington, IN, USA. Close ). Some specific dates for nests with eggs were summarized by Kilgore (221 Kilgore, W. (1930). Breeding of the Connecticut Warbler (Oporornis agilis) with special reference to Minnesota. Geological and Natural History Survey of Minnesota Occasional Papers 3:15–26. University of Minnesota Museum of Natural History, Duluth, MN, USA. Close ): 27 May in Michigan, 7 June, in Ontario, 12 June and 21 June in Manitoba, 13 June in Minnesota, 15 and 19 June in Alberta. Nests with eggs have also been reported on 8 June in Wisconsin (102 Robbins, S. D., Jr. (1991). Wisconsin Birdlife: Population and Distribution, Past and Present. University of Wisconsin Press, Madison, Wisconsin, USA. Close ) and 18 June in Minnesota (13 Parmelee, D. F., and R. J. Oehlenschlager (1972). Connecticut Warbler nest in Hubbard County, Minnesota. Loon 44:5–6. Close ). Nests with young have occurred on 30 June in Minnesota (221 Kilgore, W. (1930). Breeding of the Connecticut Warbler (Oporornis agilis) with special reference to Minnesota. Geological and Natural History Survey of Minnesota Occasional Papers 3:15–26. University of Minnesota Museum of Natural History, Duluth, MN, USA. Close ), 1 July and 27 July in Michigan (109 Chapman, F. M. (1907). The Warblers of North America. D. Appleton & Company, New York, NY, USA. Close , 222 Payne, R. B. (1983). A Distributional Checklist of the Birds of Michigan. University of Michigan, Museum of Zoology, Ann Arbor, MI, USA. Close ), 7 July in Wisconsin (102 Robbins, S. D., Jr. (1991). Wisconsin Birdlife: Population and Distribution, Past and Present. University of Wisconsin Press, Madison, Wisconsin, USA. Close ). Fledglings observed in July to as late as 10 August in Michigan (109 Chapman, F. M. (1907). The Warblers of North America. D. Appleton & Company, New York, NY, USA. Close ), 24 July and 15 August in Ontario (223 Peck, G. K., and R. D. James (1987). Breeding Birds of Ontario: Nidiology and Distribution. Volume 2: Passerines. Miscellaneous Publications of the Royal Ontario Museum, Toronto, ON, Canada. Close ), 6 July–27 July in Wisconsin (102 Robbins, S. D., Jr. (1991). Wisconsin Birdlife: Population and Distribution, Past and Present. University of Wisconsin Press, Madison, Wisconsin, USA. Close ). These dates suggest that nesting extends well into July, perhaps re-nesting. There is no information on the extent of parental feeding and protection after young depart the nest; deserves study.

Second/Later Broods

In a thorough study of several breeding pairs by Saulnier (27 Saulnier, M-C. (2011). Biologie de la reproduction de la Paruline à gorge grise (Oporornis agilis) dans les pinèdes grises du Lac-Saint-Jean, Canada. M.S. thesis, Université du Québec à Chicoutimi, Chicoutimi, QC, Canada. Close ) in Quebec, there was no mention of birds attempting a second brood; “probably” only a single brood in British Columbia (89 Cooper, J. M. and S. M. Beauchesne (2004). Connecticut Warbler. In Identified Wildlife Management Strategy (K. Paige, Editor). Ministry of Environment and Climate Change Strategy, BC, Canada. Close ). A single brood per year is most likely across the breeding range, but deserves further attention.

Selection Process

Information needed.

Site Characteristics

Nest site characteristics differ between the eastern and extreme western parts of the breeding range. In the eastern portion of the breeding range, the nest site is similar to that of other bog-nesting warblers, such as Palm Warbler (Setophaga palmarum) and Nashville Warbler (Leiothlypis ruficapilla) (25 Walkinshaw, L. H., and W. A. Dyer (1961). The Connecticut Warbler in Michigan. Auk 78(3):379–388. Close ). The nest is hidden on or near the ground, in thick undergrowth of saplings, among thickets, or at the base of a shrub, in a sunken clump or mound of moss, or in dry grasses sometimes covered by overhanging vegetation (83 Kells, W. L. (1889). Nesting of the Connecticut Warbler. Oologist 14:49–51. Close , 85 Salt, W. R. (1973). Alberta vireos and wood warblers: families Vireonidae and Parulidae, distribution and breeding. Edmonton Provincial Museum and Archives of Alberta, Edmonton, AB, Canada. Close , 224 Harrison, C. J. O. (1978). A Field Guide to the Nests, Eggs and Nestlings of North American Birds. Collins, Toronto, ON, Canada. Close ). Western birds tend to breed in well-drained upland sites in or near aspen forests (7 Bent, A. C. (1953). Life Histories of North American Wood Warblers. Bulletin of the United States National Museum 203. Close , 205 Hannah, K. C., E. M. Bayne, and N. V. Sanchez (2020). First description of the structure and geographic patterns in the songs of the Connecticut Warbler (Oporornis agilis). Wilson Journal of Ornithology 132:598–607. Close ). Nests in open forests with widely spaced trees, such as aspen (Populus) and balsam (Abies) (199 DeGraaf, R. M., V. E. Scott, R. H. Hamie, L. Ernst, and S. H. Anderson (1991). Forest and rangeland birds of the United States. Agricultural Handbook no. 688, U.S. Forest Service, Washington, DC, USA. Close ) or willows (Salix) (7 Bent, A. C. (1953). Life Histories of North American Wood Warblers. Bulletin of the United States National Museum 203. Close ). In Ontario, nests have been found well concealed in raspberry (Rubus) thickets in logging areas (223 Peck, G. K., and R. D. James (1987). Breeding Birds of Ontario: Nidiology and Distribution. Volume 2: Passerines. Miscellaneous Publications of the Royal Ontario Museum, Toronto, ON, Canada. Close ) and in red maple (Acer rubrum) among fallen logs near margins of woods and clearings (83 Kells, W. L. (1889). Nesting of the Connecticut Warbler. Oologist 14:49–51. Close ). The first nest in central Ontario found by Harris (225 Harris, A. (2011). First documented nest of Connecticut Warbler in Ontario. Ontario Birds 29:25–30. Close ) was in a fen with cotton grass (Eriophorum vaginatum), black spruce (Picea mariana), leatherleaf (Chamaedaphne calyculata), bog laurel (Kalmia polifolia), and sphagnum moss. In Manitoba, nests have been found on bogs with sundew (Drosera) and pitcher plant (Sarracenia) (7 Bent, A. C. (1953). Life Histories of North American Wood Warblers. Bulletin of the United States National Museum 203. Close ); in Alberta, in forbs or short grasses, or attached to rosebuds (Rosa) approximately 15 cm above ground (85 Salt, W. R. (1973). Alberta vireos and wood warblers: families Vireonidae and Parulidae, distribution and breeding. Edmonton Provincial Museum and Archives of Alberta, Edmonton, AB, Canada. Close ); and under ferns (Pteridium) among dense grasses in Michigan (25 Walkinshaw, L. H., and W. A. Dyer (1961). The Connecticut Warbler in Michigan. Auk 78(3):379–388. Close ). Nests are more common in aspen woodland than muskeg in Alberta and British Columbia (7 Bent, A. C. (1953). Life Histories of North American Wood Warblers. Bulletin of the United States National Museum 203. Close ). Nests have been found in small openings among spruce, sundew, pitcher plant, orchids (Arethusa), buckbean (Menyanthes), calla (Calla), coralroot (Corralorhiza), moccasin flower (Cypripedium), sphagnum moss, Labrador tea (Ledum), bog rosemary (Andromeda polifolia), bog laurel, and leatherleaf (7 Bent, A. C. (1953). Life Histories of North American Wood Warblers. Bulletin of the United States National Museum 203. Close ). They have been found sometimes within 30 m of swamps in Minnesota (7 Bent, A. C. (1953). Life Histories of North American Wood Warblers. Bulletin of the United States National Museum 203. Close ). Parmelee and Oehlenschlager (13 Parmelee, D. F., and R. J. Oehlenschlager (1972). Connecticut Warbler nest in Hubbard County, Minnesota. Loon 44:5–6. Close ) described a nest on dry ground in an abandoned old field among tall grasses on the edge of spruce forest near Itasca State Park in northwestern Minnesota.

Construction Process

Information needed.

Structure and Composition

Cup nest, composed of fine, dry grasses, dry leaves, stalks of weeds, sedge stems, rootlets and other plant fibers, and horsehairs (83 Kells, W. L. (1889). Nesting of the Connecticut Warbler. Oologist 14:49–51. Close , 7 Bent, A. C. (1953). Life Histories of North American Wood Warblers. Bulletin of the United States National Museum 203. Close , 203 Harrison, H. H. (1984). The Wood Warblers' World. Simon and Schuster, New York, NY, USA. Close , 223 Peck, G. K., and R. D. James (1987). Breeding Birds of Ontario: Nidiology and Distribution. Volume 2: Passerines. Miscellaneous Publications of the Royal Ontario Museum, Toronto, ON, Canada. Close ). The first documented nest in Ontario was a cup nest near the base of a black spruce, made up of sedges (225 Harris, A. (2011). First documented nest of Connecticut Warbler in Ontario. Ontario Birds 29:25–30. Close ). In Quebec, similar cup nests lacking domes were found in depressions on the ground and always near openings in the canopy; nesting materials included roots, herbaceous plant twigs, and pine needles (27 Saulnier, M-C. (2011). Biologie de la reproduction de la Paruline à gorge grise (Oporornis agilis) dans les pinèdes grises du Lac-Saint-Jean, Canada. M.S. thesis, Université du Québec à Chicoutimi, Chicoutimi, QC, Canada. Close ).

Dimensions

One nest from Minnesota (interior dimensions) measured 3.8 cm deep, 5.1 cm wide; outer dimensions 12.0 × 14.2 cm across and 5.5 cm deep; nest wall 1.3 cm thick (7 Bent, A. C. (1953). Life Histories of North American Wood Warblers. Bulletin of the United States National Museum 203. Close ). In Ontario, a nest found by Harris (225 Harris, A. (2011). First documented nest of Connecticut Warbler in Ontario. Ontario Birds 29:25–30. Close ) had an inner diameter of 7 cm. Seven nests found in Quebec had the following average dimensions (27 Saulnier, M-C. (2011). Biologie de la reproduction de la Paruline à gorge grise (Oporornis agilis) dans les pinèdes grises du Lac-Saint-Jean, Canada. M.S. thesis, Université du Québec à Chicoutimi, Chicoutimi, QC, Canada. Close ): dry weight 5.3 g (range 2.0–8.3); inner diameter 5.5 cm (range 4.7–6.2), inner depth 2.8 cm (range 2.0–4.4); outer diameter 8.0 cm (range 7.1–9.5), outer depth 4.9 cm (range 3.4–7.1).

The dry mass of a nest in Michigan was 19.8 g (25 Walkinshaw, L. H., and W. A. Dyer (1961). The Connecticut Warbler in Michigan. Auk 78(3):379–388. Close ).

Microclimate

Information needed.

Maintenance or Reuse of Nests

Not known to occur.

Nonbreeding Nests

Not known to occur.

Shape

Short, ovate.

Size

Mean length (mm) × breadth (mm): 18.9 (range 17.6–20.2) × 14.5 (range 13.8–15.2, n = 27; Western Foundation Vertebrate Zoology [WFVZ]); 19.5 (range 17.3–21.3) × 14.3 (range 13.2–15.6, n = 39; 7 Bent, A. C. (1953). Life Histories of North American Wood Warblers. Bulletin of the United States National Museum 203. Close ); 19.0 (range 17.4–21.0) × 14.2 (range 13.4–15.2, n = 20) from Quebec (27 Saulnier, M-C. (2011). Biologie de la reproduction de la Paruline à gorge grise (Oporornis agilis) dans les pinèdes grises du Lac-Saint-Jean, Canada. M.S. thesis, Université du Québec à Chicoutimi, Chicoutimi, QC, Canada. Close ).

Mass

Average weight of eggs from Quebec: 1.7 g (range 1.2–2.3, n = 16); average weight of empty egg shells abandoned by female 0.098 g ± 0.0003 SD (27 Saulnier, M-C. (2011). Biologie de la reproduction de la Paruline à gorge grise (Oporornis agilis) dans les pinèdes grises du Lac-Saint-Jean, Canada. M.S. thesis, Université du Québec à Chicoutimi, Chicoutimi, QC, Canada. Close ).

Color

Creamy white ground color is speckled, spotted, and blotched with auburn, bay, and chestnut, with underlying spots of brownish drab, light vinaceous drab, and light Quaker drab. More boldly marked than the egg of the Kentucky Warbler (Geothlypis formosa). Sometimes heavily blotched or clouded with wood brown (7 Bent, A. C. (1953). Life Histories of North American Wood Warblers. Bulletin of the United States National Museum 203. Close ) speckling and markings on either end, but concentrated near the larger, round end (83 Kells, W. L. (1889). Nesting of the Connecticut Warbler. Oologist 14:49–51. Close , 224 Harrison, C. J. O. (1978). A Field Guide to the Nests, Eggs and Nestlings of North American Birds. Collins, Toronto, ON, Canada. Close ); almost identical to the eggs of Mourning Warbler (Geothlypis philadelphia) (83 Kells, W. L. (1889). Nesting of the Connecticut Warbler. Oologist 14:49–51. Close ). In Quebec, eggs were predominantly a creamy color with "old rose" spots concentrated towards the end of the egg (27 Saulnier, M-C. (2011). Biologie de la reproduction de la Paruline à gorge grise (Oporornis agilis) dans les pinèdes grises du Lac-Saint-Jean, Canada. M.S. thesis, Université du Québec à Chicoutimi, Chicoutimi, QC, Canada. Close ).

Surface Texture

Smooth (7 Bent, A. C. (1953). Life Histories of North American Wood Warblers. Bulletin of the United States National Museum 203. Close ).

Eggshell Thickness

Mean empty eggshell weight: 0.11 g (range 0.09–0.13, n = 27; WFVZ); 0.09 g ± 0.01 SD, n = 5 (27 Saulnier, M-C. (2011). Biologie de la reproduction de la Paruline à gorge grise (Oporornis agilis) dans les pinèdes grises du Lac-Saint-Jean, Canada. M.S. thesis, Université du Québec à Chicoutimi, Chicoutimi, QC, Canada. Close ).

Clutch Size

Clutch size is 3–5 eggs (10 Curson, J., D. Quinn, and D. Beadle (1994). Warblers of the Americas: an Identification Guide. Houghton Mifflin Company, New York, NY, USA. Close ); mean 4.0 eggs (n = 6; WFVZ, JB, DJ). Clutch size in eastern Quebec averaged 4.4 eggs (range 4–5, n = 7) (27 Saulnier, M-C. (2011). Biologie de la reproduction de la Paruline à gorge grise (Oporornis agilis) dans les pinèdes grises du Lac-Saint-Jean, Canada. M.S. thesis, Université du Québec à Chicoutimi, Chicoutimi, QC, Canada. Close ). First nest described in British Columbia had 5 eggs (reported by Phinney in 94 Preston, M., F. Bunnell, and P. Vernier (2007). Identification of habitat variables and information gaps for providing scale-dependent management recommendations to monitor Black-throated Green Warbler and Connecticut Warbler in northeast British Columbia. Technical Report for Ministry of Environment, British Columbia and Louisiana-Pacific Canada Ltd. Close ).

Egg Laying

Information needed.

Onset of Broodiness and Incubation in Relation to Laying

Beginning of incubation is unknown, but was assumed to start before the clutch is complete in Quebec (27 Saulnier, M-C. (2011). Biologie de la reproduction de la Paruline à gorge grise (Oporornis agilis) dans les pinèdes grises du Lac-Saint-Jean, Canada. M.S. thesis, Université du Québec à Chicoutimi, Chicoutimi, QC, Canada. Close ).

Incubation Patch

Female has a single incubation patch (109 Chapman, F. M. (1907). The Warblers of North America. D. Appleton & Company, New York, NY, USA. Close ).

Incubation Period

Eleven days in Quebec (27 Saulnier, M-C. (2011). Biologie de la reproduction de la Paruline à gorge grise (Oporornis agilis) dans les pinèdes grises du Lac-Saint-Jean, Canada. M.S. thesis, Université du Québec à Chicoutimi, Chicoutimi, QC, Canada. Close ).

Parental Behavior

Incubation is by the female only (83 Kells, W. L. (1889). Nesting of the Connecticut Warbler. Oologist 14:49–51. Close , 27 Saulnier, M-C. (2011). Biologie de la reproduction de la Paruline à gorge grise (Oporornis agilis) dans les pinèdes grises du Lac-Saint-Jean, Canada. M.S. thesis, Université du Québec à Chicoutimi, Chicoutimi, QC, Canada. Close ). The female approaches the nest by landing 10–13 m away and quietly walking the remaining distance through the underbrush (203 Harrison, H. H. (1984). The Wood Warblers' World. Simon and Schuster, New York, NY, USA. Close ). During the night, females spent an average of 9 h 4 min incubating eggs in Quebec, arriving at the nest around 20:38 and departing at 05:42 the next day (n = 7 nests, 27 Saulnier, M-C. (2011). Biologie de la reproduction de la Paruline à gorge grise (Oporornis agilis) dans les pinèdes grises du Lac-Saint-Jean, Canada. M.S. thesis, Université du Québec à Chicoutimi, Chicoutimi, QC, Canada. Close ). Total daily incubation lasted an average of 9 h 43 min per day from 06:00–20:00, with an average bout of 51 min 54 s. An average of 3 h 13 min was spent away from the nest per day; these times were consistent throughout the period of incubation. Females tended to spend more time at the nest in the morning and late evening, and this trend was consistent throughout incubation (27 Saulnier, M-C. (2011). Biologie de la reproduction de la Paruline à gorge grise (Oporornis agilis) dans les pinèdes grises du Lac-Saint-Jean, Canada. M.S. thesis, Université du Québec à Chicoutimi, Chicoutimi, QC, Canada. Close ).

Hardiness of Eggs against Temperature Stress; Effect of Egg Neglect

Information needed.

Information needed.

Condition at Hatching

Information needed. Altricial and nidicolous, on basis of descriptions of birds that were 2 to 3 days in age (13 Parmelee, D. F., and R. J. Oehlenschlager (1972). Connecticut Warbler nest in Hubbard County, Minnesota. Loon 44:5–6. Close ).

Growth and Development

Average measurements of nestlings at 6 and 7 days of age (n = 3): tarsus 18.4 mm (range 15.0–20.0); wing 27.8 mm (range 18.0–35.0); culmen 6.3 mm (range 5.1–7.4); tail 3.6 mm (range 2.0–7.0); mass 10.9 g (range 9.8–12.4) (27 Saulnier, M-C. (2011). Biologie de la reproduction de la Paruline à gorge grise (Oporornis agilis) dans les pinèdes grises du Lac-Saint-Jean, Canada. M.S. thesis, Université du Québec à Chicoutimi, Chicoutimi, QC, Canada. Close ). Nestlings achieved thermoregulation in 7 days (27 Saulnier, M-C. (2011). Biologie de la reproduction de la Paruline à gorge grise (Oporornis agilis) dans les pinèdes grises du Lac-Saint-Jean, Canada. M.S. thesis, Université du Québec à Chicoutimi, Chicoutimi, QC, Canada. Close ). Information needed on development and growth rate of nestlings.

Sex Ratios and Sex Allocation

Information needed.

Brooding

Brooding was originally thought to be by the female only (83 Kells, W. L. (1889). Nesting of the Connecticut Warbler. Oologist 14:49–51. Close ). We now know that males and females participate in parental care of nestlings, but in different capacities. Only females brood young at night. In one study, females (n = 16) averaged 7 hr 48 min on the nest, arriving around 21:01 h and departing the next morning around 4:49 h (27 Saulnier, M-C. (2011). Biologie de la reproduction de la Paruline à gorge grise (Oporornis agilis) dans les pinèdes grises du Lac-Saint-Jean, Canada. M.S. thesis, Université du Québec à Chicoutimi, Chicoutimi, QC, Canada. Close ). Although both sexes participated in brooding, females spent more time brooding and less time away from the nest than males; males spent less time brooding and more time feeding (see Feeding). Brooding behavior by both sexes declined with increasing age of the nestlings; males stopped brooding around 5 days after hatching and females stopped after 7 days (27 Saulnier, M-C. (2011). Biologie de la reproduction de la Paruline à gorge grise (Oporornis agilis) dans les pinèdes grises du Lac-Saint-Jean, Canada. M.S. thesis, Université du Québec à Chicoutimi, Chicoutimi, QC, Canada. Close ). When startled, the female walks stealthily away from nest (7 Bent, A. C. (1953). Life Histories of North American Wood Warblers. Bulletin of the United States National Museum 203. Close ).

Feeding

Both parents feed young at nest and after fledging (25 Walkinshaw, L. H., and W. A. Dyer (1961). The Connecticut Warbler in Michigan. Auk 78(3):379–388. Close ). It is difficult to observe feeding because parents approach the nest with food, but walk the final 10–15 m to the nest (203 Harrison, H. H. (1984). The Wood Warblers' World. Simon and Schuster, New York, NY, USA. Close , 129 Granlund, J., G. A. McPeek, and R. J. Adams (1994). The Birds of Michigan. Indiana University Press, Bloomington, IN, USA. Close ). After fledging, both adults continue to feed fledglings, with reported food items including moths, green insect larvae, caterpillars, and raspberries (7 Bent, A. C. (1953). Life Histories of North American Wood Warblers. Bulletin of the United States National Museum 203. Close , 25 Walkinshaw, L. H., and W. A. Dyer (1961). The Connecticut Warbler in Michigan. Auk 78(3):379–388. Close , 13 Parmelee, D. F., and R. J. Oehlenschlager (1972). Connecticut Warbler nest in Hubbard County, Minnesota. Loon 44:5–6. Close ). However, there are differences between the sexes with regard to feeding. Soon after hatching, females continue to brood while males spend more time feeding nestlings. Later, females spend less time brooding and join the males in feeding young. Male visits with food are frequent and do not change as the nestlings age (27 Saulnier, M-C. (2011). Biologie de la reproduction de la Paruline à gorge grise (Oporornis agilis) dans les pinèdes grises du Lac-Saint-Jean, Canada. M.S. thesis, Université du Québec à Chicoutimi, Chicoutimi, QC, Canada. Close ).

Families remain together at least 2 weeks after fledging (7 Bent, A. C. (1953). Life Histories of North American Wood Warblers. Bulletin of the United States National Museum 203. Close ). Young stay close to the ground, but come out into the open to be fed by parents, then disappear again into dense thickets. Feeding rates, amount of food brought to the young, and apportionment among nestlings are unknown.

Nest Sanitation

Although both parents usually carry fecal sacs away from the nest (25 Walkinshaw, L. H., and W. A. Dyer (1961). The Connecticut Warbler in Michigan. Auk 78(3):379–388. Close ), nest sanitation is carried out primarily by males (27 Saulnier, M-C. (2011). Biologie de la reproduction de la Paruline à gorge grise (Oporornis agilis) dans les pinèdes grises du Lac-Saint-Jean, Canada. M.S. thesis, Université du Québec à Chicoutimi, Chicoutimi, QC, Canada. Close ). Both parents were observed eating fecal sacs. Fecal sac ingestion by parents decreased over time, especially after nestlings reached 4 days of age; more efficient digestion by older nestlings may have lessened the nutritional value of the sacs to the parents (27 Saulnier, M-C. (2011). Biologie de la reproduction de la Paruline à gorge grise (Oporornis agilis) dans les pinèdes grises du Lac-Saint-Jean, Canada. M.S. thesis, Université du Québec à Chicoutimi, Chicoutimi, QC, Canada. Close ). Females were observed eating empty eggshells (27 Saulnier, M-C. (2011). Biologie de la reproduction de la Paruline à gorge grise (Oporornis agilis) dans les pinèdes grises du Lac-Saint-Jean, Canada. M.S. thesis, Université du Québec à Chicoutimi, Chicoutimi, QC, Canada. Close ).

Not known to occur.

Identity of the Parasitic Species

Has been parasitized by the Brown-headed Cowbird (Molothrus ater) (226 Ehrlich, P. R., D. S. Dobkin, and D. Wheye (1988). The Birder's Handbook. A Field Guide to the Natural History of North American Birds, Including All Species That Regularly Breed North of Mexico. Simon and Schuster Inc., New York, NY, USA. Close ). Anderson found a nest with a Brown-headed Cowbird egg near Moberly Lake, British Columbia (reported in 94 Preston, M., F. Bunnell, and P. Vernier (2007). Identification of habitat variables and information gaps for providing scale-dependent management recommendations to monitor Black-throated Green Warbler and Connecticut Warbler in northeast British Columbia. Technical Report for Ministry of Environment, British Columbia and Louisiana-Pacific Canada Ltd. Close ).

Frequency of Occurrence

Information needed. The geographic extent of brood parasitism is unknown.

Seasonal or Geographic Variation Timing of Laying in Relation to Host's Laying

Information needed.

Response to Parasitic Female, Eggs, or Nestlings

Information needed.

Effects of Parasitism on Host Success of Parasite with this Host

Information needed.

Departure from Nest

Two of 7 nests in Quebec produced 8 fledglings (from 9 eggs) that left the nest when they were 8 days old (27 Saulnier, M-C. (2011). Biologie de la reproduction de la Paruline à gorge grise (Oporornis agilis) dans les pinèdes grises du Lac-Saint-Jean, Canada. M.S. thesis, Université du Québec à Chicoutimi, Chicoutimi, QC, Canada. Close ). In Michigan, nestlings depart the nest during the day (25 Walkinshaw, L. H., and W. A. Dyer (1961). The Connecticut Warbler in Michigan. Auk 78(3):379–388. Close ).

Growth

Mass of 2 nestlings about to leave nest in Michigan was 10 g each (25 Walkinshaw, L. H., and W. A. Dyer (1961). The Connecticut Warbler in Michigan. Auk 78(3):379–388. Close ). Nestlings that are 9–10 days old have paler, light pinkish legs; yellow tomia; inside of mouth is pinkish orange (25 Walkinshaw, L. H., and W. A. Dyer (1961). The Connecticut Warbler in Michigan. Auk 78(3):379–388. Close ).

Association with Parents or Other Young

Both adults remain with the young soon after fledgling (223 Peck, G. K., and R. D. James (1987). Breeding Birds of Ontario: Nidiology and Distribution. Volume 2: Passerines. Miscellaneous Publications of the Royal Ontario Museum, Toronto, ON, Canada. Close ). No specific data on period of association with parents, but families remain together at least 2 weeks after fledging (7 Bent, A. C. (1953). Life Histories of North American Wood Warblers. Bulletin of the United States National Museum 203. Close ).

Ability to Get Around, Feed, and Care for Self

Fledglings stay hidden and dependent on parents during the first week after fledging; they become somewhat more independent during the second week out of the nest (7 Bent, A. C. (1953). Life Histories of North American Wood Warblers. Bulletin of the United States National Museum 203. Close ).

Information needed. A small flock of 20–25 birds in late August on breeding grounds in northern Wisconsin (7 Bent, A. C. (1953). Life Histories of North American Wood Warblers. Bulletin of the United States National Museum 203. Close ) presumably included juveniles and adults that bred locally.

Skull ossification complete in first-fall individuals by 1 November (10 Curson, J., D. Quinn, and D. Beadle (1994). Warblers of the Americas: an Identification Guide. Houghton Mifflin Company, New York, NY, USA. Close ). Similarly, McKinney (227 McKinney, R. G. (2004). Skull pneumatization in passerines: a table of last dates many passerines in the northeast can be aged safely by skulling. North American Bird Bander 29:164–170. Close ) cautioned bird-banders against aging all Connecticut Warblers with fully ossified skulls as adult (Definitive Basic) individuals after mid-October, because many first-fall birds will have completed skull pneumatization by this date.