Demography and Populations

Age At First Breeding; Intervals Between Breeding

Not known.

Clutch

Normally 4 eggs per clutch, but regularly 3–5 (Bent 1953b Bent, A. C. (1953). Life Histories of North American Wood Warblers. Bulletin of the United States National Museum 203. Close , Macarthur 1958 Macarthur, R. H. (1958). Population ecology of some warblers of northeastern coniferous forest. Ecology 39:599-619. Close , Peck and James 1987 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 evidence that clutch size changes during spruce budworm outbreaks (Macarthur 1958 Macarthur, R. H. (1958). Population ecology of some warblers of northeastern coniferous forest. Ecology 39:599-619. Close ). May lay second clutch if first destroyed, but no further information on total number of clutches female may lay.

Annual And Lifetime Reproductive Success

Few data; needs study and better documentation, especially comparisons among populations. Pairs regularly fledge broods of 4 (DHM). Lifetime reproductive success not known.

Number Of Broods Normally Reared Per Season

Only one brood known to be reared/pair/season. See second brood per season.

Proportion Of Total Females That Rear At Least One Brood To Nest-Leaving Or Independence, Two Broods, Etc.

Not known.

Oldest recorded bird minimum of 8 yr, 2 mo, banded as hatching year male and later recaptured at same site in Minnesota (Klimkiewicz and Futcher 1989 Klimkiewicz, K. M., and A. G. Futcher (1989). Longevity records of North American birds, Supplement 1. Journal of Field Ornithology 60:469–494. Close ). Survivorship not known, but likely to be high for small passerine, judging from survivorship of similar parulid warblers with comparable reproductive rates and migratory patterns (see Roberts 1971 Roberts, J. O. L. (1971). Survival among some North American wood warblers. Bird-Banding 42:165-184. Close , Morse 1989a Morse, D. H. (1989). American Warblers: An Ecological and Behavioral Perspective. Harvard University Press, Cambridge, MA, USA. Close ).

Peters (Peters 1936 Peters, H. S. (1936). A list of external parasites from birds of the eastern part of the United States. Bird-Banding 7:9–27. Close ) recorded two species of lice and one mite as external parasites of this species.

Exposure

Nestlings may die of exposure or starvation during cold, rainy periods (DHM). Unincubated young whose mother lost on day 4 probably died as result of lack of brooding (Lawrence 1953b Lawrence, L. de K. (1953b). Notes on the nesting behavior of the Blackburnian Warbler. Wilson Bulletin 65:135-144. Close ).

Predation

Red squirrels and Blue Jays regularly capture about-to-fledge or just-fledged young (DHM). Predation on breeding adults likely by Cooper's and Sharp-shinned hawks (DHM). Nesting female taken by Merlin (Lawrence 1953b Lawrence, L. de K. (1953b). Notes on the nesting behavior of the Blackburnian Warbler. Wilson Bulletin 65:135-144. Close ).

Human/Research Impacts

Some hit television towers and other objects in migration (Graber et al. 1983 Graber, J. W., R. R. Graber, and E. L. Kirk (1983). Illinios birds: wood warblers. Illinois Natural History Survey Biological Notes 118. Close ).

Initial Dispersal From Natal Site

Young often wander from natal site after leaving nest. No evidence of return to these sites (DHM).

Fidelity To Breeding Site And Winter Home Range

No data; probably return in subsequent years after selecting breeding site (DHM). Winter fidelity should be looked for in light of likely winter territoriality.

Dispersal From The Breeding Site Or Colony

Parents often leave territories at same time as young, in company with them. No information on subsequent return in that season (DHM).

Home Range

No information.

Numbers

Using data from the North American Breeding Bird Survey (BBS), the mean annual population for Blackburnian Warbler was estimated at 14,000,000 individuals for the United States and Canada for the period between 2005 and 2014 (Rosenberg et al. 2016 Rosenberg, K. V., J. A. Kennedy, R. Dettmers, R. P. Ford, D. Reynolds, J. D. Alexander, C. J. Beardmore, P. J. Blancher, R. E. Bogart, G. S. Butcher, A. F. Camfield, A. Couturier, D. W. Demarest, W. E. Easton, J. J. Giocomo, R. H. Keller, A. E. Mini, A. O. Panjabi, D. N. Pashley, T. D. Rich, J. M. Ruth, H. Stabins, J. Stanton, and T. Will (2016). Partners in Flight Landbird Conservation Plan: 2016 Revision for Canada and Continental United States. Partners in Flight Science Committee. Close ). Point-count survey data collected by state and provincial breeding bird atlas projects yielded estimates of annual population size of 360,000 singing males (95% CI: 320,000 to 405,000) for Pennsylvania, 2004–2009 (Wilson et al. 2012 Wilson, A. M., D. W. Brauning, and R. S. Mulvihill (Editors) (2012). Second Atlas of Breeding Birds in Pennsylvania. Pennsylvania State University Press, University Park, PA, USA. Close ) and XXX,XXX individuals in Ontario (Cadman et al. 2007a Cadman, M. D., D. A. Sutherland, G. G. Beck, D. Lepage, and A. R. Couturier (Editors) (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, Ontario, Canada. Close ).

Density estimates vary considerably with habitat. In Maine, up to 0.7–1.1 breeding pairs/ha in mature red spruce and white spruce growth, down to 0.4.–0.6/ha in younger red spruce and white spruce growth; numbers relatively constant over 5-yr span; not found in white spruce forest lacking emergent trees (Morse 1976b Morse, D. H. (1976b). Variables affecting the density and territory size of breeding spruce-woods warblers. Ecology 57:290-301. Close ). In n. Maine, 0.3/ha in bottomland fir-spruce forest and 0.9/ha in adjacent higher-ground, coniferous-deciduous forest (Morse 1978 Morse, D. H. (1978). Populations of Bay-breasted and Cape May warblers during an outbreak of spruce budworm. Wilson Bulletin 90:404-413. Close ).

In mountains of New Hampshire, not found above 750 m on Mt. Osceola, but regularly encountered at that height (0.5/ha) in mixed deciduous-coniferous forest (Morse 1979a Morse, D. H. (1979a). Habitat use by the Blackpoll Warbler. Wilson Bulletin 91:234-243. Close ). In primarily deciduous forest at 600 m, fluctuated between about 0.2–0.7/ha over 16-yr period; density varied more than either Black-throated Blue Warbler (Setophaga caerulescens) or Black-throated Green Warbler; and only occurred in association with small clumps of red spruce. Site probably marginal for this species, so that its fluctuations may mirror events in more central parts of range (Holmes et al. 1986 Holmes, R. T., T. W. Sherry and F. W. Sturges. (1986). Bird community dynamics in a temperate deciduous forest: long-term trends at Hubbard Brook. Ecological Monographs 56:201-220. Close ).

In e. Canada, most common in fir-spruce and hemlock forests, with maximum densities of 0.8–1.2/ha, though usually less (Erskine 1980 Erskine, A. J. (1980). A preliminary catalogue of bird census plot studies in Canada, Part 4. Ottawa, ON: Progress Notes no. 112. Can. Wildl. Serv. Close , Erskine 1984a Erskine, A. J. (1984). A preliminary catalogue of bird census plot studies in Canada, part 5. Canadian Wildlife Service Program Notes 144:1–34. Close ). Numbers may initially increase quickly with abundant budworms (Choristoneura fumiferana), but increase short-lived, perhaps because of simultaneous great increase of Bay-breasted Warblers (Setophaga castanea; Morris et al. 1958 Morris, R. F., W. F. Cheshire, C. A. Miller and D. G. Mott. (1958). The numerical response of avian and mammalian predators during a gradation of the spruce budworm. Ecology 39:487-494. Close ).

Density in jack pine (Pinus banksiana)-black spruce forest in Minnesota halved after wildfire destroyed half of canopy cover (Apfelbaum and Haney 1981 Apfelbaum, S. and A. Haney. (1981). Bird populations before and after wildfire in a Great Lakes pine forest. Condor 83:347-354. Close ). Territories in budworm-damaged spruce-fir forest in n. Maine declined from 14 to 0 between 1982 and 1987, over a period in which virtually all of the conifers, already heavily damaged in 1982, died (Oliveri 1993 Oliveri, S. F. (1993). Bird responses to habitat changes in Baxter State Park, Maine. Maine Naturalist 1 (3):145-154. Close ).

Appeared sporadically as breeder during first 50 yr of second-growth red spruce forest in West Virginia, but numbers have never increased to high levels encountered in mature red spruce forest of region. Over same period density in mature, undisturbed forest declined from 1.7–0.7/ha (Hall Hall 1984a Hall, G. A. (1984a). A long-term bird population study in an Appalachian spruce forest. Wilson Bulletin 96:228-240. Close , Hall 1984b Hall, G. A. (1984). Population decline of Neotropical migrants in an Appalachian forest. American Birds 38:14–18. Close ). Re-establishment may be similar in second-growth hemlock forests of North Carolina (Holt 1974 Holt, J. P. (1974). Bird populations in the hemlock sere on the Highlands Plateau, North Carolina, 1946 to 1972. Wilson Bulletin 86:397-406. Close ).

The most common overwintering species at some locations in Colombia (Lerner and Stauffer 1998 Lerner, S. de la Zerda and D. F. Stauffer. (1998). Habitat selection by blackburnian warblers wintering in Colombia. Journal of Field Ornithology 69:457-465. Close ), but no density estimates available for overwintering grounds.

Trends

North American Breeding Bird Survey (BBS) results (Pardieck et al. 2018 Pardieck, K. L., D. J. Ziolkowski Jr., M. Lutmerding, and M.-A. R. Hudson (2018). North American Breeding Bird Survey Dataset 1966–2017, version 2017.0. U.S. Geological Survey, Patuxent Wildlife Research Center, Laurel, MD, USA. Close ) indicated a 0.3% (95% CI: -0.3, 0.8) annual increase in the survey-wide population for 1966–2017 (n = 869 survey routes), with stable or positive trends across many Bird Conservation Regions, including: 1.7%/yr (95% CI: 0.2, 3.1; n = 75 routes) in the Lower Great Lakes and St. Lawrence Plain; 0.4%/yr (95% CI: -0.1, 0.9; n = 260 routes) in the Boreal Hardwood Transition; 0.3%/yr (95% CI: -0.2, 0.7; n = 273 routes) in the Atlantic Northern Forest; and 0.1%/yr (95% CI: -1.1, 1.4; n = 76 routes) in the Boreal Softwood Shield (Pardieck et al. 2018 Pardieck, K. L., D. J. Ziolkowski Jr., M. Lutmerding, and M.-A. R. Hudson (2018). North American Breeding Bird Survey Dataset 1966–2017, version 2017.0. U.S. Geological Survey, Patuxent Wildlife Research Center, Laurel, MD, USA. Close ). The only negative trend was in the Appalachian region where there was a -0.4%/yr (95% CI: -1.3, 0.5; n = 128 routes) decrease (Pardieck et al. 2018 Pardieck, K. L., D. J. Ziolkowski Jr., M. Lutmerding, and M.-A. R. Hudson (2018). North American Breeding Bird Survey Dataset 1966–2017, version 2017.0. U.S. Geological Survey, Patuxent Wildlife Research Center, Laurel, MD, USA. Close ). Over a 45-year period (1970–2014), BBS data indicated that the range-wide population has increased by an estimated 103% (Rosenberg et al. 2016 Rosenberg, K. V., J. A. Kennedy, R. Dettmers, R. P. Ford, D. Reynolds, J. D. Alexander, C. J. Beardmore, P. J. Blancher, R. E. Bogart, G. S. Butcher, A. F. Camfield, A. Couturier, D. W. Demarest, W. E. Easton, J. J. Giocomo, R. H. Keller, A. E. Mini, A. O. Panjabi, D. N. Pashley, T. D. Rich, J. M. Ruth, H. Stabins, J. Stanton, and T. Will (2016). Partners in Flight Landbird Conservation Plan: 2016 Revision for Canada and Continental United States. Partners in Flight Science Committee. Close ). As forest interior species, Blackburnian Warbler populations are probably underrepresented by roadside surveys, but sample sizes should suffice to provide useful trend information.

Over a 45-year period (1970–2014), BBS data indicated that the range-wide population has increased by an estimated 10% (Rosenberg et al. 2016 Rosenberg, K. V., J. A. Kennedy, R. Dettmers, R. P. Ford, D. Reynolds, J. D. Alexander, C. J. Beardmore, P. J. Blancher, R. E. Bogart, G. S. Butcher, A. F. Camfield, A. Couturier, D. W. Demarest, W. E. Easton, J. J. Giocomo, R. H. Keller, A. E. Mini, A. O. Panjabi, D. N. Pashley, T. D. Rich, J. M. Ruth, H. Stabins, J. Stanton, and T. Will (2016). Partners in Flight Landbird Conservation Plan: 2016 Revision for Canada and Continental United States. Partners in Flight Science Committee. Close ).

Long-term studies in spruce forests along Maine coast (Morse 1968a Morse, D. H. (1968a). A quantitative study of foraging of male and female spruce-woods warblers (Parulidae). Living Bird 3:9-43. Close , Morse 1976b Morse, D. H. (1976b). Variables affecting the density and territory size of breeding spruce-woods warblers. Ecology 57:290-301. Close ; DHM, unpublished data) showed little change in numbers in the 1960s and 1970s.

Needs study; population regulation of Neotropical migrants in general an open question (Morse 1980c Morse, D. H. (1980c). "Population limitation: breeding or wintering grounds." In Migrant birds in the neotropics., edited by A. Keast and E. S. Morton, 505-516. Washington, D.C: Smithson. Inst. Press. Close ). Influences on numbers include: whether currently in equilibrium or still rebounding from impacts of chlorinated hydrocarbon pesticides; responding to afforestation in North America and resulting succession; responding to tropical deforestation; responding to habitat fragmentation on breeding grounds; or responding to parasitism by Brown-headed Cowbirds (Morse 1993 Morse, D. H. 1993. Black-throated Green Warbler (Dendroica virens). In The Birds of North America, No. 55 (A. Poole and F. Gill, Eds.). Philadelphia: The Academy of Natural Sciences; Washington D.C.: The American Ornithologists' Union. Close ). Climatic factors such as late snow or cold, or extensive rain during breeding season, may temporarily depress numbers (Morse 1976b Morse, D. H. (1976b). Variables affecting the density and territory size of breeding spruce-woods warblers. Ecology 57:290-301. Close ). Other warbler species may potentially depress Blackburnian numbers, but this species is last of spruce-woods warblers to occupy these sites, so not possible to investigate whether numbers greater where other species absent (Morse Morse 1976b Morse, D. H. (1976b). Variables affecting the density and territory size of breeding spruce-woods warblers. Ecology 57:290-301. Close , Morse 1977 Morse, D. H. (1977). The occupation of small islands by passerine birds. Condor 79:399-412. Close ). Populations could be depressed by predation on young by red squirrels and Blue Jays, but frequency of “surplus” breeders at some sites (Stewart and Aldrich 1952 Stewart, R. E. and J. W. Aldrich. (1952). Ecological studies of breeding bird populations in northern Maine. Ecology 33:226-238. Close ) suggests that they do not control numbers. One site in Maine initially had 9 pairs of apparent breeders. Stewart and Aldrich (Stewart and Aldrich 1951 Stewart, R. E. and J. W. Aldrich. (1951). Removal and repopulation of breeding birds in a spruce-fir forest community. Auk 68:471-482. Close ) collected 15 males (and 1 female) from site during that year; the following year 13 pairs present (Hensley and Cope 1951 Hensley, M. M. and J. B. Cope. (1951). Further data on removal and repopulation of the breeding birds in a spruce-fir community. Auk 68:483-493. Close ). Where present, Accipiter hawks take large numbers of small birds (Mueller et al. 1981c Mueller, H. C., N. S. Mueller and P. C. Parker. (1981c). Observations of a brood of Sharp-shinned Hawks in Ontario, with comments on the functions of sexual dimorphism. Wilson Bulletin 93:85-92. Close ) and may affect local densities.