One of the difficulties with assigning breeding codes is that the behaviors the codes describe are sometimes used by birds away from their nesting sites. Migrating birds are particularly problematic because they often engage in breeding behaviors long before they get to their breeding grounds. When a species is known to not nest in a region, it is easy to recognize that they are not local breeders. But, when some individuals of a species breed in an area, while others migrate through en route to sites farther north, it becomes harder to know how some records should be treated.
In Connecticut, for example, it is easy to determine that singing Blackpoll Warblers are migrants because the nearest known breeding grounds are well to the north. Similarly, ducks often form pairs on the wintering grounds and then migrate to breeding sites – so their late-winter courtship displays cannot be taken as evidence of local breeding. A singing Yellow Warbler in early May, or a pair of mallards in mid-April, however, is harder to interpret; they could be planning to breed nearby, or they could have hundreds of miles to go before they find a nest site.
Later in the summer, a similar problem arises, as birds begin to move away from nest sites. A Greater Yellowlegs in Connecticut in July, for example, will almost certainly be a bird that has finished breeding, probably because its nest failed resulting in an early start to its southbound migration. Similarly, a young but independent starling or swallow in August might have come from a nest far away, and not have fledged locally. Ideally, none of these records would be included in block lists, because they do not describe the breeding bird community of the block.
Like many breeding bird atlases, we attempted to address this problem by identifying “safe dates” at the beginning of the project for each species known to breed in Connecticut. Safe dates give the period during which the occurrence of a bird means that there is a high likelihood that it is breeding near to where it was seen, and that it is unlikely to be a migrant or a wandering non-breeder. Safe dates do not identify the entire period in which breeding may occur, and records of birds engaged in breeding behaviors that confirm breeding were accepted even when outside this period. Breeding codes in the possible and probable categories, however, were generally not accepted unless they lay within these dates. For example, if a Wood Thrush was seen building a nest in the second week of May, the record would be accepted because there is no doubt it was nesting. But, if one was just heard singing, even if in the same place that one was heard a week earlier, it would not be accepted because it could have been a migrant.
The table below displays safe dates for Connecticut breeding bird species, and was based on one used for the Second Atlas of Breeding Birds in Rhode Island (Clarkson et al. 2023). It is in taxonomic order by default, but it can be filtered alphabetically by clicking on the Species heading, by date by clicking the Safe Dates heading, or by taxonomic order by clicking on the Taxonomic heading.
| Species | Safe Dates | Habitat | Taxonomic |
|---|---|---|---|
| Canada Goose | 4/15-8/1 | Shore or islands in any wetland | |
| Mute Swan | 4/15-8/1 | Large ponds and marshes | |
| Wood Duck | 5/1-8/5 | Wooded swamps, freshwater marshes, streams, rivers | |
| Gadwall | 5/15-8/5 | Fresh/brackish water or saltmarsh | |
| American Black Duck | 5/1-8/5 | Most wetlands, from beaver ponds to saltmarsh | |
| Mallard | 5/1-8/5 | All wetlands, occasionally suburban yards with swimming pools | |
| Blue-winged Teal* | 5/10-8/5 | Fresh/brackish pond or marsh | |
| Green-winged Teal* | 5/15-8/5 | Fresh/brackish pond or marsh | |
| Common Eider* | 5/15-8/1 | Coastal islands | |
| Hooded Merganser | 5/15-8/5 | Wooded swamps, freshwater marshes, streams | |
| Red-breasted Merganser* | 6/1-8/5 | Coastal marsh | |
| Common Merganser | 6/1-8/5 | Forested lakes and rivers | |
| Ring-necked Pheasant | 5/1-8/15 | Open scrub, pastures, fields | |
| Ruffed Grouse | 4/1-6/31 | Mixed upland woods | |
| Wild Turkey | 4/1-7/15 | Mature deciduous woods, edge | |
| Northern Bobwhite* | 4/30-8/15 | Open scrub, pastures, fields | |
| Pied-billed Grebe* | 5/10-8/1 | Fresh/brackish reedy pond or marsh | |
| Double-crested Cormorant | 5/10-8/5 | Islands on coast or lake | |
| American Bittern* | 5/15-8/1 | Fresh/brackish reedy pond or marsh | |
| Least Bittern* | 5/25-8/1 | Fresh/brackish reedy pond or marsh | |
| Great Blue Heron | 5/1-7/15 | Wooded swamps, beaver ponds, islands | |
| Great Egret | 5/15-7/15 | Islands on coast or lake | |
| Snowy Egret | 5/15-7/15 | Coastal islands | |
| Little Blue Heron | 5/15-7/15 | Coastal islands | |
| Tricolored Heron* | 5/15-7/15 | Coastal islands | |
| Cattle Egret* | 5/10-7/15 | Coastal islands | |
| Green Heron | 5/10-8/1 | Woody growth near marshes or open water | |
| Black-crowned Night-Heron | 5/5-7/15 | Coastal islands | |
| Yellow-crowned Night-Heron* | 5/5-7/15 | Coastal islands | |
| Glossy Ibis | 5/1-7/15 | Coastal islands | |
| Turkey Vulture | 5/10-8/15 | Woods, cliffs, caves, buildings | |
| Black Vulture | 5/10-8/15 | Woods, cliffs, caves, buildings | |
| Osprey | 5/10-8/15 | Coastal marshes; rarely large wetlands inland | |
| Bald Eagle | 4/15-8/15 | Margins of large lakes, rivers | |
| Mississippi Kite* | 5/1-8/15 | Various wooded habitats ranging from wooded suburbs to hardwood forest | |
| Northern Harrier* | 5/10-8/20 | Coastal dunes, beaches, marshes, heathlands | |
| Sharp-shinned Hawk* | 5/10-8/1 | Conifers in mature woodlands | |
| Cooper’s Hawk | 5/5-8/1 | Mixed woodlands, groves, copses | |
| Northern Goshawk* | 4/10-8/15 | Mature, mixed woodlands | |
| Red-shouldered Hawk | 4/10-8/15 | Wet mixed forests, swamps | |
| Broad-winged Hawk | 5/15-7/25 | Mature, mixed woodlands | |
| Red-tailed Hawk | 4/15-8/1 | Mature woodlands, often near edges | |
| American Kestrel | 5/10-7/20 | Open country, scattered trees, edge | |
| Peregrine Falcon | 5/15-8/1 | Cliffs, tall buildings, towers | |
| Black Rail* | 5/15-8/1 | Fresh/brackish marshes, especially along coast | |
| King Rail* | 5/15-8/1 | Fresh/brackish reedy pond or marsh | |
| Clapper Rail | 5/15-8/1 | Salt and brackish marsh | |
| Virginia Rail | 5/15-8/1 | Salt, fresh, or brackish pond or marsh | |
| Sora* | 5/15-7/25 | Fresh/brackish reedy pond or marsh | |
| Common Gallinule* | 5/25-8/15 | Fresh/brackish reedy pond or marsh | |
| Piping Plover | 5/15-8/15 | Coastal, sandy beach | |
| Killdeer | 4/20-7/1 | Open, sparsely vegetated areas; flat rooftops | |
| American Oystercatcher | 5/15-8/15 | Upper portions of coastal beach, dunes | |
| Willet | 5/15-7/15 | Coastal beach, dunes, saltmarsh | |
| Spotted Sandpiper | 5/25-7/5 | Coastal shores, shores of freshwater lakes, ponds, rivers, streams | |
| Upland Sandpiper* | 5/20-7/15 | Extensive grasslands, especially airports | |
| American Woodcock | 4/15-7/15 | Forest edges | |
| Herring Gull | 5/1-8/1 | Coastal shores/islands, flat rooftops | |
| Great Black-backed Gull | 5/1-8/1 | Coastal islands | |
| Roseate Tern* | 6/1-8/5 | Coastal islands | |
| Common Tern | 6/1-8/5 | Coastal islands, saltmarsh | |
| Least Tern | 5/25-8/15 | Coastal sandy beach, especially dredge spoils | |
| Black Skimmer* | 6/1-8/1 | Coastal, sandy beach | |
| Rock Pigeon | 1/1-12/31 | Buildings, bridges, towers in urban areas, farms | |
| Mourning Dove | 4/1-8/15 | Suburbs, woodlots, farmlands | |
| Monk Parakeet | 6/1-8/1 | Urban streets, large trees, telephone poles | |
| Black-billed Cuckoo | 6/5/8/15 | Forested habitats, edge | |
| Yellow-billed Cuckoo | 6/5-8/15 | Forested habitats, edge | |
| Barn Owl* | 4/1-8/1 | Open habitats | |
| Eastern Screech-Owl | 4/1-8/1 | Open deciduous forests, woodlots, orchards, residential areas | |
| Great Horned Owl | 12/1-6/15 | Wide variety of habitats from forest to farmland | |
| Barred Owl | 4/1-7/15 | Moist woods, wooded swamps, bottomlands | |
| Long-eared Owl* | 4/1-8/1 | Conifers | |
| Northern Saw-whet Owl* | 4/15-8/15 | Mixed moist woods with conifers | |
| Common Nighthawk* | 6/5-8/1 | Barren habitats including river bars and flat rooftops | |
| Eastern Whip-poor-will | 5/25-7/15 | Secondary forest, copses, pine barrens, Scrub Oak, edge | |
| Chimney Swift | 5/25-8/15 | Urban chimneys | |
| Ruby-throated Hummingbird | 6/1-8/1 | Open woodland, rural and suburban gardens, edge | |
| Belted Kingfisher | 5/1-8/10 | Stream, river, lake, or bay shore with banks | |
| Red-headed Woodpecker* | 5/20-8/25 | Open country with scattered trees | |
| Red-bellied Woodpecker | 4/15-8/1 | Older-growth forest and woodlots | |
| Yellow-bellied Sapsucker | 5/20-8/1 | Higher-elevation hardwoods | |
| Downy Woodpecker | 5/1-7/25 | Forests, copses, suburbs | |
| Hairy Woodpecker | 4/25-7/20 | Forests | |
| Northern Flicker | 5/25-7/25 | Forests, parks | |
| Pileated Woodpecker | 4/1-6/31 | Matured forest, especially bottomland | |
| Eastern Wood-Pewee | 6/5-8/1 | Mature forest | |
| Acadian Flycatcher | 6/5-8/1 | Red Maple swamp and hemlock | |
| Willow Flycatcher | 6/5-8/1 | Shrubby areas near water, thickets | |
| Alder Flycatcher | 6/5-8/1 | Shrubby areas near water, thickets | |
| Least Flycatcher | 5/25-8/5 | Open deciduous forests, forest edge | |
| Eastern Phoebe | 5/1-8/15 | Ledges, bridges, porch sills, etc., usually near water | |
| Great Crested Flycatcher | 5/25-8/1 | Mature forest, edge | |
| Eastern Kingbird | 5/25-7/25 | Open habitats, including edge, copses, often near water | |
| White-eyed Vireo | 5/15-8/1 | Moist areas, thickets, tangle of vines or briers | |
| Yellow-throated Vireo | 5/20-8/10 | Open deciduous and mixed forest and riparian woodlands | |
| Blue-headed Vireo | 5/15-8/10 | Mature coniferous or mixed woods | |
| Warbling Vireo | 5/15-8/10 | Semi-open borders of river meadows, ponds, and streams | |
| Red-eyed Vireo | 6/1-8/10 | Mixed and deciduous woods | |
| Blue Jay | 5/1-8/15 | Varied; most forest types, thickets, suburban yards, parks | |
| American Crow | 3/25-7/15 | Conifers in forested areas, woodlots, suburban yards, parks | |
| Fish Crow | 5/1-7/15 | Mixed woods, woodlots, suburban yards, parks | |
| Common Raven | 3/20-7/20 | Remote forested areas | |
| Horned Lark* | 4/25-8/1 | Coastal dunes and beaches, abandoned agricultural fields, airports | |
| Purple Martin | 5/25-7/1 | Open areas; edge of saltmarsh, coastal farmland, and golf courses | |
| Tree Swallow | 5/15-7/1 | Open areas or woodland edge near wetlands; including saltmarsh | |
| Northern R-winged Swallow | 5/20-7/1 | Often near water, in cavity, pipe, or excavated burrow | |
| Bank Swallow | 5/25-7/1 | Earthen embankments | |
| Cliff Swallow | 5/25-7/1 | Eaves and sides of old barns and other buildings, bridges | |
| Barn Swallow | 5/25-7/1 | Structures offering access to interior; barns, garages, porches, | |
| Black-capped Chickadee | 4/1-8/15 | Woodlands, orchards, shade trees, yards, and city parks | |
| Tufted Titmouse | 4/5-8/1 | Deciduous forest, riparian woodlands, and residential areas | |
| Red-breasted Nuthatch | 5/15-8/10 | Coniferous forest | |
| White-breasted Nuthatch | 4/25-8/10 | Deciduous forest | |
| Brown Creeper | 5/20-8/1 | Mature, mixed, and swampy forest | |
| Carolina Wren | 4/1-8/15 | Wet woods, stream edges with dense thickets, tangles, brush piles, etc. | |
| House Wren | 5/20-8/15 | Open forests, wood edges, farms, orchards, suburbs, parks, gardens | |
| Winter Wren | 5/1-8/5 | Cool, moist, coniferous or mixed woods, swamps, bogs, streams, brooks | |
| Sedge Wren* | 5/15-8/15 | Overgrown wet fields, edges of freshwater marshes, bogs and wet meadows | |
| Marsh Wren | 5/15-8/15 | Cattail and other tall marshes, including saltmarsh edges | |
| Golden-crowned Kinglet | 5/10-8/1 | Coniferous woods | |
| Blue-gray Gnatcatcher | 5/15-8/1 | Wooded edges along ponds, rivers, streams, swamps, beaver ponds | |
| Eastern Bluebird | 5/1-8/15 | Fields with scattered trees; farmland, orchards, pastures, etc. | |
| Veery | 5/25-8/10 | Moist mixed forest | |
| Hermit Thrush | 5/10-9/10 | Damp mixed forest with dense undergrowth including pine barrens | |
| Wood Thrush | 5/25-8/10 | Mature forest | |
| American Robin | 5/1-9/1 | Almost anywhere except the most open habitats such as marsh, grasslands | |
| Gray Catbird | 5/20-8/15 | Dense tangles and thickets | |
| Northern Mockingbird | 5/5-8/15 | Suburban or semi-rural habitats with thickets, forest edges, hedgerows | |
| Brown Thrasher | 5/15-8/10 | Dry second-growth; powerlines, overgrown pastures, coastal thickets | |
| European Starling | 4/10-6/15 | Everywhere except remote rural areas | |
| Cedar Waxwing | 6/10-8/15 | Second-growth forest, parks, orchards, gardens, and margins of waterways | |
| Blue-winged Warbler | 5/20-8/1 | Old, brushy fields, copses, edge with low undergrowth, powerline cuts | |
| Golden-winged Warbler* | 5/20-8/1 | Damp brushy fields, powerline cuts | |
| Nashville Warbler | 5/25-8/15 | Open Scrub Oak woodlands, overgrown pastures, bogs | |
| Northern Parula* | 6/1-8/10 | Woodlands with Usnea lichen | |
| Yellow Warbler | 5/25-8/1 | Margins of freshwater marsh, other wet brushy areas, farmland | |
| Chestnut-sided Warbler | 5/25-8/1 | Brushy, open second-growth, edges | |
| Magnolia Warbler | 6/5-8/10 | Coniferous forest | |
| Black-throated Blue Warbler | 5/25-8/10 | Mixed woods with dense understory, esp. Mountain Laurel | |
| Yellow-rumped Warbler | 5/25-8/10 | Mature White Pines, coniferous forest | |
| Black-throated Green Warbler | 5/25-8/5 | Coniferous and mature mixed forest | |
| Blackburnian Warbler | 5/25-8/5 | Coniferous forest | |
| Pine Warbler | 5/1-8/5 | Variety of pine forest types | |
| Prairie Warbler | 5/25-8/1 | Brushy fields, powerline cuts, edges | |
| Cerulean Warbler | 6/1-8/1 | Mature, moist deciduous forest | |
| Black-and-white Warbler | 5/25-8/1 | Mainly deciduous forest | |
| American Redstart | 6/1-8/1 | Secondary forest, copses | |
| Prothonotary Warbler* | 6/1-8/1 | Deciduous/mixed forest, saplings at forest edge, wooded swamps | |
| Worm-eating Warbler | 5/20-8/1 | Brushy undergrowth of rocky, wooded hillsides and ravines, usually near water | |
| Ovenbird | 5/20-8/5 | Open forests with little or no understory vegetation and ample leaf litter | |
| Northern Waterthrush | 5/20-7/25 | Wooded swamps, bogs, backwaters | |
| Louisiana Waterthrush | 5/10-7/20 | Rocky streams in deciduous or mixed forest | |
| Common Yellowthroat | 6/1-8/10 | Brushy areas, thickets, powerline cuts, preferably wet | |
| Hooded Warbler | 6/1-8/1 | Moist thickets in woodlands | |
| Canada Warbler | 6/5-8/1 | Thick undergrowth in moist deciduous/mixed forest; cedar swamp, Red Maple | |
| Yellow-breasted Chat* | 6/1-8/5 | Thickets, esp. regenerating fields and pastures | |
| Scarlet Tanager | 5/25-8/10 | Mature deciduous forest | |
| Eastern Towhee | 5/1-8/10 | Dry, open forest, edge, brushy habitats, coastal thickets, powerline cuts | |
| Chipping Sparrow | 5/1-8/15 | Open mixed forest, suburbs, parks, and cemeteries with conifers | |
| Field Sparrow | 5/1-8/5 | Brushy areas, weedy fields, powerline cuts | |
| Vesper Sparrow* | 5/10-8/5 | Short grass areas, agricultural fields, clearings in pine barrens, coastal moors | |
| Savannah Sparrow | 5/10-8/1 | Grasslands, including airports, hayfields | |
| Saltmarsh Sparrow | 5/25-8/10 | Saltmarsh | |
| Seaside Sparrow | 5/25-8/10 | Saltmarsh | |
| Song Sparrow | 5/1-8/10 | Forest edge, brushy areas, marsh edges, suburbs | |
| Swamp Sparrow | 5/1-8/5 | Freshwater wetlands including swamps, river meadows, and pond edges | |
| White-throated Sparrow | 5/20-8/20 | Scrubby habitats esp with conifers; Red Maple, Atlantic White Cedar | |
| Dark-eyed Junco | 5/1-9/5 | Edges in coniferous/mixed woodlands; brushy thickets at higher elevations | |
| Northern Cardinal | 4/15-8/20 | Suburban or semi-rural areas; forest edge, woodlots, thickets, parks, gardens | |
| Rose-breasted Grosbeak | 5/25-8/5 | Deciduous and mixed forest, woodlots, shade trees of parks and suburbs | |
| Indigo Bunting | 5/25-8/10 | Brushy habitats including forest edge, overgrown fields, powerline | |
| Bobolink | 6/1-8/1 | Grasslands, including airports, hayfields | |
| Red-winged Blackbird | 5/1-7/15 | Wide variety of densely vegetated marsh habitats | |
| Eastern Meadowlark* | 5/5-7/25 | Extensive grasslands, including airports, margins of saltmarsh | |
| Common Grackle | 5/15-7/10 | Variety of urban and rural habitats from open forest to marshes, parks, etc. | |
| Boat-tailed Grackle* | 5/1-7/10 | Various habitats close to coastal marshes | |
| Brown-headed Cowbird | 5/1-7/15 | Virtually all habitats; anywhere host species are found | |
| Orchard Oriole | 5/25-7/15 | Open, patchy forest, copses, often near river, stream, or pond | |
| Baltimore Oriole | 5/25-8/1 | Open deciduous forest, shade trees in urban or rural areas | |
| Purple Finch | 5/25-8/10 | Conifers in mixed woods, suburbs, parklands | |
| House Finch | 4/15-8/1 | Scattered trees- especially conifers- mainly in residential areas | |
| American Goldfinch | 6/1-8/1 | Forest edge, copses, brushy areas, marsh edges, residential | |
| Evening Grosbeak* | 5/25-8/15 | Mixed forest | |
| House Sparrow | 3/10-8/15 | Residential, farms |
[INSERT LEGEND]