2023 Bird Observation Codes for Philadelphia County, PA
The purpose of this document is to describe the frequency with which bird species are observed in Philadelphia County, PA. Similar to the American Birding Association’s checklist codes, the observation codes listed in this document categorize bird species from the most frequently observed to the rarest:
- Code-1: species that are observed a large number of times every year; can easily be observed through casual birding
- Code-2: species that are observed a significant number of times every year; can be observed with some effort
- Code-3: species that are observed a small number of times every year; can be observed with a lot effort
- Code-4: species that are not observed every year but could be with better coverage and/or have some pattern of occurrence
- Code-5: species that are observed very rarely, twice or less in the past decade
- Code-6: species that were formerly observed in the area on a yearly basis, but have not been reported over the past 7 years
The classifications below were determined using eBird histogram data for Philadelphia County, PA from 2013 to 2022. Specifically, each species’ observation code was derived based on its “yearly sighting probability”, that is, the probability of this species being reported in at least one of 52 checklists chosen at random, one per week, from all the checklists submitted for the area in a year. This probability can also be understood as the probability of seeing this species at least once over the course of a year while birding once a week at a random location in the area.
Limitations
The present guide provides only an indication of the frequency with which each species can be observed. The accuracy of these classifications may suffer from several limitations, some of which are listed below:
- Although the codes were assigned based on objective observation data, it was necessary to make some subjective choices on how to assign these codes, such as how to distinguish between “some effort” and “a lot of effort” for Code-2 and Code-3 species.
- Species sharing the same observation code may be observed in very different situations. For instance, Code 4 may correspond, among other possibilities, to species only seen as flyovers, highly secretive species, or species only seen during irruption years.
- The observation data is biased in that observations are not evenly distributed throughout the year and throughout the area. Also, the number of observations per year is unlikely to be constant throughout the years.
- The guide only lists the species that appear in the eBird database for the area between 2013 and 2022, including naturalized, provisional, and escapee exotic species.
Acknowledgments
The present guide was inspired by Rob Fergus’ Delaware County, PA birds by finding code guide. The author thanks Rob Fergus for sharing his definitions for the different codes. The author is also grateful to everyone who has provided feedback on this project.
Contact
Please send your questions, comments, and suggestions to vldbirding@gmail.com. Happy birding!
Reference
eBird. 2021. eBird: An online database of bird distribution and abundance [web application]. eBird, Cornell Lab of Ornithology, Ithaca, New York. Available: http://www.ebird.org.
PDF version
A PDF version of this document can be downloaded here.
Code-1: Common regularly occurring
| Species | Observation code |
|---|---|
| Mute Swan | 1 |
| Wood Duck | 1 |
| Northern Shoveler | 1 |
| Gadwall | 1 |
| American Wigeon | 1 |
| Mallard | 1 |
| American Black Duck | 1 |
| Northern Pintail | 1 |
| Green-winged Teal | 1 |
| Ring-necked Duck | 1 |
| Bufflehead | 1 |
| Hooded Merganser | 1 |
| Common Merganser | 1 |
| Ruddy Duck | 1 |
| Pied-billed Grebe | 1 |
| Rock Pigeon | 1 |
| Mourning Dove | 1 |
| Chimney Swift | 1 |
| Ruby-throated Hummingbird | 1 |
| American Coot | 1 |
| Laughing Gull | 1 |
| Ring-billed Gull | 1 |
| Herring Gull | 1 |
| Great Black-backed Gull | 1 |
| Caspian Tern | 1 |
| Double-crested Cormorant | 1 |
| Great Blue Heron | 1 |
| Great Egret | 1 |
| Green Heron | 1 |
| Black Vulture | 1 |
| Turkey Vulture | 1 |
| Osprey | 1 |
| Cooper’s Hawk | 1 |
| Bald Eagle | 1 |
| Red-shouldered Hawk | 1 |
| Red-tailed Hawk | 1 |
| Belted Kingfisher | 1 |
| Yellow-bellied Sapsucker | 1 |
| Red-bellied Woodpecker | 1 |
| Downy Woodpecker | 1 |
| Hairy Woodpecker | 1 |
| Northern Flicker | 1 |
| American Kestrel | 1 |
| Peregrine Falcon | 1 |
| Eastern Wood-Pewee | 1 |
| Willow Flycatcher | 1 |
| Eastern Phoebe | 1 |
| Great Crested Flycatcher | 1 |
| Eastern Kingbird | 1 |
| Warbling Vireo | 1 |
| Red-eyed Vireo | 1 |
| Blue Jay | 1 |
| American Crow | 1 |
| Fish Crow | 1 |
| Carolina Chickadee | 1 |
| Tufted Titmouse | 1 |
| Northern Rough-winged Swallow | 1 |
| Tree Swallow | 1 |
| Barn Swallow | 1 |
| Ruby-crowned Kinglet | 1 |
| Golden-crowned Kinglet | 1 |
| White-breasted Nuthatch | 1 |
| Brown Creeper | 1 |
| Blue-gray Gnatcatcher | 1 |
| House Wren | 1 |
| Winter Wren | 1 |
| Marsh Wren | 1 |
| Carolina Wren | 1 |
| European Starling | 1 |
| Gray Catbird | 1 |
| Northern Mockingbird | 1 |
| Hermit Thrush | 1 |
| Wood Thrush | 1 |
| American Robin | 1 |
| Cedar Waxwing | 1 |
| House Sparrow | 1 |
| House Finch | 1 |
| American Goldfinch | 1 |
| Chipping Sparrow | 1 |
| Field Sparrow | 1 |
| Fox Sparrow | 1 |
| Dark-eyed Junco | 1 |
| White-throated Sparrow | 1 |
| Song Sparrow | 1 |
| Swamp Sparrow | 1 |
| Eastern Towhee | 1 |
| Orchard Oriole | 1 |
| Baltimore Oriole | 1 |
| Red-winged Blackbird | 1 |
| Brown-headed Cowbird | 1 |
| Rusty Blackbird | 1 |
| Common Grackle | 1 |
| Ovenbird | 1 |
| Black-and-white Warbler | 1 |
| Common Yellowthroat | 1 |
| American Redstart | 1 |
| Northern Parula | 1 |
| Magnolia Warbler | 1 |
| Yellow Warbler | 1 |
| Blackpoll Warbler | 1 |
| Black-throated Blue Warbler | 1 |
| Palm Warbler | 1 |
| Yellow-rumped Warbler | 1 |
| Northern Cardinal | 1 |
| Indigo Bunting | 1 |
Code-2: Uncommon regularly occurring
| Species | Observation code |
|---|---|
| Blue-winged Teal | 2 |
| Canvasback | 2 |
| Greater Scaup | 2 |
| Lesser Scaup | 2 |
| Common Goldeneye | 2 |
| Common Gallinule | 2 |
| Killdeer | 2 |
| Least Sandpiper | 2 |
| Spotted Sandpiper | 2 |
| Solitary Sandpiper | 2 |
| Greater Yellowlegs | 2 |
| Lesser Yellowlegs | 2 |
| Great Cormorant | 2 |
| Little Blue Heron | 2 |
| Northern Harrier | 2 |
| Sharp-shinned Hawk | 2 |
| Pileated Woodpecker | 2 |
| Merlin | 2 |
| Acadian Flycatcher | 2 |
| Blue-headed Vireo | 2 |
| Common Raven | 2 |
| Brown Thrasher | 2 |
| Eastern Bluebird | 2 |
| Veery | 2 |
| Swainson’s Thrush | 2 |
| White-crowned Sparrow | 2 |
| Savannah Sparrow | 2 |
| Northern Waterthrush | 2 |
| Tennessee Warbler | 2 |
| Cape May Warbler | 2 |
| Bay-breasted Warbler | 2 |
| Chestnut-sided Warbler | 2 |
| Pine Warbler | 2 |
| Black-throated Green Warbler | 2 |
| Scarlet Tanager | 2 |
Code-3: Rare regularly occurring
| Species | Observation code |
|---|---|
| Snow Goose | 3 |
| Cackling Goose | 3 |
| Tundra Swan | 3 |
| Muscovy Duck | 3 |
| Redhead | 3 |
| Long-tailed Duck | 3 |
| Red-breasted Merganser | 3 |
| Wild Turkey | 3 |
| Horned Grebe | 3 |
| Yellow-billed Cuckoo | 3 |
| Black-billed Cuckoo | 3 |
| Common Nighthawk | 3 |
| Virginia Rail | 3 |
| Sora | 3 |
| Semipalmated Plover | 3 |
| Pectoral Sandpiper | 3 |
| Semipalmated Sandpiper | 3 |
| American Woodcock | 3 |
| Wilson’s Snipe | 3 |
| Bonaparte’s Gull | 3 |
| Iceland Gull | 3 |
| Lesser Black-backed Gull | 3 |
| Glaucous Gull | 3 |
| Forster’s Tern | 3 |
| Red-throated Loon | 3 |
| Common Loon | 3 |
| American Bittern | 3 |
| Least Bittern | 3 |
| Snowy Egret | 3 |
| Black-crowned Night-Heron | 3 |
| Glossy Ibis | 3 |
| Broad-winged Hawk | 3 |
| Eastern Screech-Owl | 3 |
| Great Horned Owl | 3 |
| Barred Owl | 3 |
| Northern Saw-whet Owl | 3 |
| Red-headed Woodpecker | 3 |
| Olive-sided Flycatcher | 3 |
| Yellow-bellied Flycatcher | 3 |
| Least Flycatcher | 3 |
| White-eyed Vireo | 3 |
| Yellow-throated Vireo | 3 |
| Philadelphia Vireo | 3 |
| Black-capped Chickadee | 3 |
| Horned Lark | 3 |
| Purple Martin | 3 |
| Bank Swallow | 3 |
| Red-breasted Nuthatch | 3 |
| Gray-cheeked Thrush | 3 |
| American Pipit | 3 |
| Purple Finch | 3 |
| Pine Siskin | 3 |
| Clay-colored Sparrow | 3 |
| American Tree Sparrow | 3 |
| Vesper Sparrow | 3 |
| Lincoln’s Sparrow | 3 |
| Yellow-breasted Chat | 3 |
| Bobolink | 3 |
| Eastern Meadowlark | 3 |
| Worm-eating Warbler | 3 |
| Louisiana Waterthrush | 3 |
| Blue-winged Warbler | 3 |
| Prothonotary Warbler | 3 |
| Orange-crowned Warbler | 3 |
| Nashville Warbler | 3 |
| Connecticut Warbler | 3 |
| Mourning Warbler | 3 |
| Kentucky Warbler | 3 |
| Hooded Warbler | 3 |
| Blackburnian Warbler | 3 |
| Yellow-throated Warbler | 3 |
| Prairie Warbler | 3 |
| Canada Warbler | 3 |
| Wilson’s Warbler | 3 |
| Summer Tanager | 3 |
| Rose-breasted Grosbeak | 3 |
| Blue Grosbeak | 3 |
| Dickcissel | 3 |
Code-4: Casual
| Species | Observation code |
|---|---|
| Black-bellied Whistling-Duck | 4 |
| Brant | 4 |
| Eurasian Wigeon | 4 |
| Surf Scoter | 4 |
| White-winged Scoter | 4 |
| Black Scoter | 4 |
| Red-necked Grebe | 4 |
| Eastern Whip-poor-will | 4 |
| Sandhill Crane | 4 |
| Black-bellied Plover | 4 |
| American Golden-Plover | 4 |
| Upland Sandpiper | 4 |
| Stilt Sandpiper | 4 |
| Sanderling | 4 |
| Dunlin | 4 |
| White-rumped Sandpiper | 4 |
| Short-billed Dowitcher | 4 |
| Black-headed Gull | 4 |
| Least Tern | 4 |
| Gull-billed Tern | 4 |
| Black Tern | 4 |
| Tricolored Heron | 4 |
| Cattle Egret | 4 |
| Yellow-crowned Night-Heron | 4 |
| Golden Eagle | 4 |
| Snowy Owl | 4 |
| Long-eared Owl | 4 |
| Alder Flycatcher | 4 |
| Cliff Swallow | 4 |
| Evening Grosbeak | 4 |
| Common Redpoll | 4 |
| Grasshopper Sparrow | 4 |
| Lark Sparrow | 4 |
| Golden-winged Warbler | 4 |
| Cerulean Warbler | 4 |
Code-5: Accidental
| Species | Observation code |
|---|---|
| Ross’s Goose | 5 |
| Greater White-fronted Goose | 5 |
| Tundra Bean-Goose | 5 |
| Pink-footed Goose | 5 |
| Barnacle Goose | 5 |
| Trumpeter Swan | 5 |
| Egyptian Goose | 5 |
| Northern Bobwhite | 5 |
| Chukar | 5 |
| Allen’s Hummingbird | 5 |
| King Rail | 5 |
| Clapper Rail | 5 |
| Purple Gallinule | 5 |
| American Avocet | 5 |
| American Oystercatcher | 5 |
| Piping Plover | 5 |
| Hudsonian Godwit | 5 |
| Marbled Godwit | 5 |
| Red Knot | 5 |
| Baird’s Sandpiper | 5 |
| Buff-breasted Sandpiper | 5 |
| Western Sandpiper | 5 |
| Long-billed Dowitcher | 5 |
| Wilson’s Phalarope | 5 |
| Red-necked Phalarope | 5 |
| Red Phalarope | 5 |
| Little Gull | 5 |
| Franklin’s Gull | 5 |
| Common Gull | 5 |
| White-winged Tern | 5 |
| Common Tern | 5 |
| Arctic Tern | 5 |
| Royal Tern | 5 |
| Brown Booby | 5 |
| Anhinga | 5 |
| Brown Pelican | 5 |
| White Ibis | 5 |
| Mississippi Kite | 5 |
| Northern Goshawk | 5 |
| Swainson’s Hawk | 5 |
| Rough-legged Hawk | 5 |
| Short-eared Owl | 5 |
| Monk Parakeet | 5 |
| Vermilion Flycatcher | 5 |
| Ash-throated Flycatcher | 5 |
| Tropical Kingbird | 5 |
| Western Kingbird | 5 |
| Scissor-tailed Flycatcher | 5 |
| Cave Swallow | 5 |
| Sedge Wren | 5 |
| Scaly-breasted Munia | 5 |
| Hoary Redpoll | 5 |
| Red Crossbill | 5 |
| White-winged Crossbill | 5 |
| Snow Bunting | 5 |
| LeConte’s Sparrow | 5 |
| Seaside Sparrow | 5 |
| Nelson’s Sparrow | 5 |
| Yellow-headed Blackbird | 5 |
| Black-throated Gray Warbler | 5 |
| Lazuli Bunting | 5 |
Code-6: Formerly observed regularly
| Species | Observation code |
|---|---|
| Ring-necked Pheasant | 6 |
| Northern Shrike | 6 |