I decided to post my answer here. Such a limited set of identification choices should aim to cover the most common birds that people are likely to see. The following is a list of the 40 most commonly reported bird species of Middlesex County, New Jersey, according to eBird data. All of them have a solid case for inclusion because all are very common and very widespread outside of this area.
- Mourning Dove
- Northern Cardinal
- Canada Goose
- American Robin
- House Sparrow
- American Goldfinch
- European Starling
- House Finch
- Blue Jay
- Downy Woodpecker
- Common Grackle
- Song Sparrow
- Dark-eyed Junco
- White-throated Sparrow
- American Crow
- Red-bellied Woodpecker
- Tufted Titmouse
- Black-capped Chickadee
- Mallard
- Northern Mockingbird
- Ring-billed Gull
- Red-winged Blackbird
- White-breasted Nuthatch
- Gray Catbird
- Herring Gull
- Carolina Wren
- Northern Flicker
- Great Black-backed Gull
- Red-tailed Hawk
- Killdeer
- Great Blue Heron
- Brown-headed Cowbird
- Rock Pigeon
- Double-crested Cormorant
- Carolina Chickadee
- Turkey Vulture
- Barn Swallow
- Great Egret
- Tree Swallow
- House Wren