A land manager's guide to conserving habitat for forest birds in ...

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Brown-headed Cowbird Molothrus ater parasitism rates may be as high as 50 percent, the pressure on some host populations can be substantial. See pages 16 and 25 for additional photos of Brown-headed Cowbirds. Diet Brown-headed Cowbirds depend on open fields, crop and pasture lands for foraging. They feed primarily on weed seeds (grasses and crop grains) and insects (primarily grasshoppers and beetles). Female Brownheaded Cowbird (foreground) with males — Photo: Greg Lavaty Identification (17–22 centimetres) Originally a bison-following bird of the Great Plains, the Brownheaded Cowbird spread eastward in the 1800s as forests were cleared. Notorious as a brood parasite that lays its eggs exclusively in other birds’ nests, it never raises its own young. It is a mediumsized songbird with a stout pointy bill and dark eyes. Males are shiny black with a brown head and neck, while females are dull grey-brown with faint streaking. Conservation Status The Brown-headed Cowbird breeds throughout southern Canada and across the United States. It is often seen near short-grass fields and lawns. Though previously restricted to the short-grass plains, its range expanded widely as European settlement opened forests and created large regions of agricultural and suburban habitat. In Ontario, the distribution of the cowbird is limited by the northern edge of the Canadian Shield. Populations have decreased continentally in recent decades due to the abandonment of farms, urbanization, agricultural intensification, and blackbird control programs. In particular, the disappearance of pastureland over the past 25 years has been implicated in the decline of the cowbird in Ontario. Breeding Biology The Brown-headed Cowbird is a brood parasite that depends on hosts to care for and raise its young. Females are prolific breeders, laying up to 40 eggs each breeding season. Though 89 host species have been documented in Ontario, Cowbirds seem to have a preference for shrub and tree nesters with eggs smaller than their own. Frequent host species include the Red-eyed Vireo, Yellow Warbler, Northern Cardinal, and Song Sparrow. Females tend to exploit forest-field edges, where they typically remove one to two eggs from the nests they parasitize. Once hatched, the cowbird young are reared alongside the hosts, but tend to be larger, more aggressive and faster growing. Because of this unfair advantage, the cowbird may be the only nestling to survive, often suffocating, starving, or ejecting the weaker host young out of the nest. Because Management Guidelines In Ontario, reduction of large, contiguous tracts of forest to small, isolated fragments has benefited the Brown-headed Cowbird at the detriment of a large suite of host species that have had no historical exposure to cowbirds. These species have not evolved mechanisms for rejecting cowbird eggs and are particularly vulnerable to parasitism. As edge specialists, cowbirds respond favourably to all types of forest harvest. Intensive harvesting, such as diameter-limit cuts, particularly result in higher densities of cowbirds. By maintaining higher tree densities (basal area) post-harvest and creating fewer edge habitats, the frequency and intensity of parasitism will decline. As such, efforts should be made not only to follow silviculture standards but to conserve, expand and preserve large, mature forest tracts to benefit host species with small populations. How to find You can spot cowbirds most easily when small groups of males gather to court a single female. Listen for the gurgling sounds of the birds while displaying. Did you know? Brown-headed Cowbird egg in parasitized Veery nest — Photo: Mark Peck • Brown-headed Cowbirds have been known to return to ransack the nests of host species when their egg was removed. • Cowbirds also destroy nests as a type of “farming behavior” to force hosts to build new ones, subsequently laying their eggs in the new nests. • The Brown-headed Cowbird lays eggs in the nests of many different species of birds. Though some female cowbirds will use a number of different hosts, they often specialize on a particular host species. • Some species, like the American Robin and Blue Jay, are cowbird egg “ejectors.” These species can recognize foreign eggs and usually throw any cowbird eggs out of their nest. • Few species can escape Brown-headed Cowbird parasitism, since commutes between feeding and breeding areas often range from two to seven kilometres and up to 15 kilometres. • Fledgling cowbirds eventually leave the host parents and find groups of adult and other juvenile Brown-headed Cowbirds by mid-late July. These flocks can be easily spotted in agricultural fields in late summer. 134 Bird Species Accounts
List of Photographers Al Woodliffe Algonquin Park Museum B.Henry c/o VIREO Bill Hubick Bob McBroom Brad Woodworth Brandon Holden Dan Kaiser Daniel Cadieux Dawn Burke Doug Tozer Eric Boysen F. Truslow c/o VIREO G.K. Peck Garth McElroy Greg Lavaty Harold Lee J.Fuhrman c/o VIREO Jarrid Spicer Jayne Gulbrand Jeff Nadler Ken Elliott Kyle Aldinger Larry Watkins Lindsay MacLean-Abbott Lucas Foerster L. Walkinshaw c/o VIREO Marie Read Mark Marek Mark Peck Michael Patrikeev Nick Bartok OMNR Peter Burke R.Curtis c/o VIREO Robert McCaw Scott Gillingwater Scott Reid Teresa Piraino Terry John Myers Terry Schwan Terry Sohl Thomas Whelan Visual Resources for Ornithology (VIREO) W.Greene c/o VIREO Trout Lily — Photo: Robert McCaw List of Photographers 135
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Ministry of Natural Resources A lan
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A land manager’s guide to conserv
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Male Scarlet Tananger — Photo: Je
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Photo: Algonquin Museum INTRODUCTIO
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Southern Ontario has a landscape ty
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Gray tree frog — Photo: Scott Gil
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Researcher removing bird from net
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Sugar maples — Photo: Robert McCa
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of other wildlife including America
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Male Chestnut-sided Warbler — Pho
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Female American Redstart — Photo:
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Male Black-throated Blue Warbler
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Male American Redstart — Photo: G
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Artwork: Peter Burke Forest Birds i
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Flock of Brown-headed Cowbirds —
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Photo: Scott Gillingwater Source an
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Imagery produced by the Provincial
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destroy nests, and lawns that provi
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Northern Cardinal — Photo: Daniel
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Photo: Larry Watkins FOREST HARVEST
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Tree species Additional Carolinian
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Photo: Lucas Foerster normally perf
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Logging damage — Photo: Lucas Foe
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This table illustrates the structur
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Conifer plantation — Photo: Ken E
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Silvicultural system or method Clea
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Female Pileated Woodpecker —Photo
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Hairy Woodpecker Northern Flicker P
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Louisiana Warbler Mourning Warbler
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Elderberry — Photo: Robert McCaw
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Male Northern Flicker in cavity wit
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Cedar Waxwings Mourning cloak butte
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Photo: Doug Tozer GUIDELINES FOR FO
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Barred Owl — Photo: Dan Kaiser Ol
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Redwoods —Photo: Jarrid Spicer so
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Photo: Lucas Foerster 6. Retain cav
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Types of Cavity Trees escape or roo
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9. Limit timing of harvesting activ
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Blackberry — Photo: Robert McCaw
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that are similar to the historic va
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Great Crested Flycatcher — Photo:
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hazards, harvest during winter on f
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potential. In these cases, the mana
Page 87 and 88: Male Blue-winged Warbler — Photo:
Page 89 and 90: Trembling aspen — Photo: Robert M
Page 91 and 92: M. C. Brittingham and S. A. Temple.
Page 93 and 94: Glossary of Terms abiotic — non-l
Page 95 and 96: conk — hard bracket or shelf fung
Page 97 and 98: ground cover — the layer of veget
Page 99 and 100: nurse crop — any tree, shrub, or
Page 101 and 102: site preparation — chemical (e.g.
Page 103 and 104: Chestnut-sided Warbler — Photo: B
Page 105 and 106: Diet The Ruffed Grouse diet is comp
Page 107 and 108: Red-headed Woodpecker Melanerpes er
Page 109 and 110: Yellow-bellied Sapsucker Sphyrapicu
Page 111 and 112: Hairy Woodpecker Picoides villosus
Page 113 and 114: Pileated Woodpecker Dryocopus pilea
Page 115 and 116: Acadian Flycatcher Empidonax viresc
Page 117 and 118: Red-eyed Vireo Vireo olivaceus 19 m
Page 119 and 120: Black-capped Chickadee Poecile atri
Page 121 and 122: Brown Creeper Certhia americana The
Page 123 and 124: Wood Thrush Hylocichla mustelina Di
Page 125 and 126: Gray Catbird Dumetella carolinensis
Page 127 and 128: Golden-winged Warbler Vermivora chr
Page 129 and 130: Cerulean Warbler Dendroica cerulea
Page 131 and 132: Ovenbird Seiurus aurocapilla In Ont
Page 133 and 134: Hooded Warbler Wilsonia citrina Fem
Page 135 and 136: Northern Cardinal Cardinalis cardin
Page 137: Indigo Bunting Passerina cyanea Fem
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