Visual Identification of Illinois Nightjars

Introduction

Although singing nightjars are obvious to birders and familiar even to non-birders, identifying these cryptically colored birds by sight is less straightforward. The emphsis in this article will be on visual characteristics that can be used to separate Chuck-will's-widow from Whip-poor-will and these two from Common Nighthawk. For the sake of this article, the term "rounded-wing nightjar" refers collectively to Chuck-will's-widow and Whip-poor-will.

Chuck-will's-widow vs. Whip-poor-will

The Chuck-will's-widow (Caprimulgus carolinensis) is restricted as a breeder to southern Illinois, though it does occur rarely, mostly as a spring overshoot, in the northern part of the state. Its close cousin the Whip-poor-will (Caprimulgus vociferus) is more widespread, breeding in appropriate habitat throughout Illinois.

Size

• The Chuck-will's-widow is a larger bird than the Whip-poor-will, not only being longer but also heavier and bulkier with a head that looks massive; the difference in size between them is roughly equal to the difference in size between a Herring and Ring-billed Gull.

General Color

• Although both species are superficially similar in color, the Chuck-will's-widow tends to be a duskier, brownish-gray overall, especially on the underparts. It is also sometimes described as being red or reddish; the study skins I examined did not exhibit this trait. The Whip-poor-will is a paler, grayer, and more contrasty bird, particularily on the crown, tail, and underparts.

Throat Color

• The throat of the male Whip-poor-will is black, bordered below by a prominent, narrow white band or necklace. Females have browner throats with a buffy necklace. Both sexes of the Chuck-will's-Widow have buffy-brown throats; because of the darker underparts there is a noticeable contrast between these two areas. In addition, the throat of the Chuck often appears barred, a trait not shown by the Whip.

Tail Pattern

• On the male Whip-poor-will, there is white on both vanes of the three outer tail feathers; on the male Chuck-will's-widow the white on these same feathers is restricted to the inner vanes.When the tail is spread (on the upperside) the Whip-poor-will will show large, unbroken white corners (even if the tail is folded, the white is still sometimes visible, a trait never shown by a Chuck). On the spread tail of a Chuck-will's-widow the white will be discontinuous and separated by the brown outer vanes. The tails of females lack any white being essentially brown or buffy with dark bars. There are however differences in pattern that can be seen when the tail is spread. The outer three tail feathers of the Whip-poor-will are dark with boldly contrasting pale tips. These same feathers on the Chuck-will's-widow are mostly buffy-brown, thus lacking the strong contrast.

Crown Color and Streaking

• The crown of the Whip-poor-will is pale gray, paler than the crown of the Chuck-will's-widow which is usually more brownish. In addition, the contrast between the crown and back is more pronounced on the Whip-poor-will. Both species also have their crowns overlaid with darker longitudinal streaks, the shapes of which are often a good clue to identity. On the Whip-poor-will the streaks, especially toward the center, tend to be thick and blotchy, while on the Chuck they are narrower.

Facial Bristles

• Both the Whip-poor-will and the Chuck-will's-widow possess modified feathers known as rictal bristles that run along the side of the face bordering the mouth. These bristles resemble stiff hairs and their shape can be used to separate the two species. On the bristles of the Chuck-will's-widow there are smaller side-hairs which give them a branched look. Conversely, the bristles of the Whip-poor-will are unbranched and bare.

Bill Color

• The bill of the Chuck-will's-widow is often bicolored, the pale bases of both mandibles contrasting with the dark tip. The bill of the Whip-poor-will is mostly dark, although the lower mandible may be pale.

Common Nighthawk vs. The Rounded-Wing Nightjars*

The Common Nighthawk (Chordeiles minor) is a summer resident in Illinois, arriving in late spring and departing in August, often in large numbers; stragglers are encountered into October. There is regional variation, the form occuring in our area being C.m.minor. As mentioned previously, the rounded-wing nightjars possess modified feathers known as rictal bristles that run along the side of the face from the corner of the mouth, giving these birds a whiskered appearence that is obvious even from some distance. The Common Nighthawk (all nighthawks in fact) at all ages and in all plumages lacks these bristles, the facial region appearing bare and clean-shaven.

*Chuck-will's-widow and Whip-poor-will collectively

Primary Pattern and Color

• The color and pattern of the primaries offers an excellent clue in separating these two groups; on Common Nighthawk the primaries minus the wingbar are a solid, unmarked blackish-brown, contrasting strongly with the grayish-mottled body; on the rounded-wing nightjars the primaries are, like the rest of the body, mottled-brown, showing little contrast between them.

Tail Length

• The relative differences in tail length between these two groups can also be used to tell them apart. Actually, the tails of both appear long, but the differences in wing length are obvious on resting individuals. The Common Nighthawk has longer wings which just reach the end of the tail, sometimes concealing it. The rounded-wing nightjars on the other hand have shorter wings which fall noticeably short of the end of the tail, leaving the outer part exposed.

Crown Streaking

• Briefly, the crowns of the rounded-wing nightjars have prominent longitudinal streaks; Common Nighthawk has a dark crown with sparse spotting that does not form streaks.

Conclusion

I hope this article provides you with the necessary information to confidently identify this difficult and challenging group of birds. I would like to thank Dr. Dave Willard of the Field Museum for allowing me to use their specimens. §

*******