Male and female Long-billed Dowitchers are visually similar, but females are typically larger with a slightly longer bill. In breeding plumage, both have reddish underparts and a mottled brown back, with a white rump visible in flight. They have a long, straight black bill and long green legs. In winter, they appear mostly gray.

Detailed Description:
• Breeding Plumage:
• General: Both sexes have a rich, reddish-brown (rufous) color on the head, neck, and underparts, contrasting with a darker, mottled brown back.
• Bill: Both have a long, straight, black bill that is longer in females.
• Legs: Long, green legs.
• Rump: A distinctive white rump is visible during flight.

• Winter Plumage:
• Overall: Both males and females appear mostly gray.
• Underparts: The reddish tones are replaced by white on the belly and flanks, often with some barring.
• Upperparts: The back and wings are gray-brown.

• Size: Females are slightly larger and have a longer bill than males.

• Other Distinguishing Features:
• Eyebrows: Both sexes have a white eyebrow stripe.
• Flight: In flight, they show a pale trailing edge on their wings and a white blaze up their backs.
• Behavior: They feed by probing the mud with their long bills in a "sewing machine" motion.