ID challenges: The Chordeiles nighthawks

By eBird Centroamérica marzo 22, 2018
Lesser Nighthawk Chordeiles acutipennis

By John van Dort & Oliver Komar

Late March marks the beginning of the passage of migrant Common Nighthawks in our region, as well as the return of this species to its Central American breeding grounds. What better month than March to highlight the identification challenge that this species poses compared to the very similar Lesser Nighthawk?

Before getting into nighthawk identification, we should start by separating the aerial nighthawks from the other, more earth-bound nightjars (also part of the Caprimulgidae family) such as pauraques and whip-poor-wills. Nighthawks do not perch on the side of the road like pauraques. A nightjar usually makes short flights to snatch an insect out of the air, before returning to the ground. Nighthawks generally fly higher and for much longer periods, sometimes for hours, and forage on the wing. Compared to nightjars, their heads are small and their wings are pointy. The rictal bristles, those hair-like feathers near the bill, are much shorter on nighthawks than on nightjars.

Confusing names

The Common and Lesser nighthawks are members of the genus Chordeiles, which means string of a lyre or harp (chorde) and dusk (deile), a reference to their vocalizations at dusk. If we look at the scientific species names, however, we immediately notice something odd: Common Nighthawk is called Chordeiles minor, and Lesser Nighthawk is called Chordeiles acutipennis. Not helpful! Minor means ‘lesser’, and acutipennis means ‘sharp-feathered’ or ‘sharp-winged’. If you already know these birds, you’ve probably realized that it’s really the other way around: Common Nighthawk is the one with the pointy wings, and Lesser Nighthawk is slightly smaller.

Size

Despite the name Lesser Nighthawk, the size difference with Common is not obvious, and generally not the best clue for identification. Sometimes, the two species can be seen foraging side by side, and a slight size difference may be visible. This should never be more than a supporting field mark, though: there are other, better field marks, which we will highlight below.

Shape

Shape is a much better ID clue than size, both in flight and on perched birds. For birds in flight, focus on the shape of the wing tips: pointy in Common, less pointy in Lesser. The outer primary (p10) of the Common Nighthawk is usually the longest, while on Lesser Nighthawk, it’s the next primary (p9) that is longest, resulting in a more rounded wing tip (Fig. 1).

Figure 1. Left: Female Common Nighthawk, August 2017, Michigan, USA. Photo © Brendan Klick / Macaulay Library. Right: male Lesser Nighthawk, April 2014, California, USA. Photo © Brian Sullivan / Macaulay Library. Note the pointy wing tip of the Common Nighthawk versus a more rounded wing tip of the Lesser Nighthawk. Also note the placement of the white wing band: roughly halfway between the ‘wrist’ and the tip of the wing of the Common Nighthawk versus closer to the wing tip (2/3 of the way) on the Lesser Nighthawk. A third field mark, visible here but usually not in the field on flying birds, is the buffy spotting on the inner half of the outer primaries of the Lesser Nighthawk, reduced or absent on the Common Nighthawk. Finally, photos this good allow us to count the feathers that show the wing band: five in Common, four in Lesser.

Wing band

Both Common and Lesser nighthawks have prominent wing bands, but these differ between the two species, providing further ID clues. In flight, the Common Nighthawk shows a white band across the wing that falls roughly halfway between the ‘wrist’ and the tip of the wing. This band is usually all-white and relatively broad on the male, and whitish with a buff tinge (or buff altogether), as well as slightly narrower, on the female. On the Lesser Nighthawk, the band is placed closer to the wing tip, about a third the length between the wing tip and the ‘wrist’ (Fig. 1). On some immature females, the wing band may be much reduced, sometimes not even noticeable in the field. Another difference, sometimes visible in high quality photos, is the number of primaries that show the white banding: five primaries in Common, four in Lesser.

The differences are less obvious on perched nighthawks. On Common Nighthawks, the wing band (if visible at all) is aligned closer to the base of the tertials. Since the band is placed closer to the wing tip on Lesser Nighthawk, it is aligned with the tips of the tertials (Fig. 2). Some field guides mention a difference in shape of the wing band on perched nighthawks, with the white band more aligned from one primary to the next on the Lesser Nighthawk, versus a more serrated or jagged distribution of this white band in the primaries of the Common Nighthawk. In Figure 2, however, we see it the other way around, illustrating the variation in this character.

Figure 2. Top: Common Nighthawk, June 2012, Oregon, USA. Photo © W. Douglas Robinson / Macaulay Library. Bottom: Lesser Nighthawk, May 2013, Valle, Honduras. Photo © John van Dort / Macaulay Library. Compare the position of the wing band: well short of the tertials on Common Nighthawk versus almost reaching the tip of the tertials on Lesser Nighthawk. Compare also the relative length of wing tip versus tail tip on both birds: wing longer than tail on Common Nighthawk, wing shorter than tail on Lesser Nighthawk. Note the buffy spots near the base of the outer primaries on the Lesser Nighthawk.

Relative length of wings and tail

On perched nighthawks, the wing tips extend a little beyond the tail tip on Common Nighthawk, while the wing tips on Lesser Nighthawk are about even with or can fall a little short of the tail tip (Fig. 2). Correctly assessing the relative length of wings and tail is only possible when the bird is viewed side on (not angled).

Presence or absence of buffy spots on the outer primaries

This field mark is difficult to see in the field but can be useful if you are able to get good photos of either flying or perched birds. Lesser Nighthawk nearly always shows buffy spots on the basal part of the outer primaries, between the wing band and the ‘wrist’ (Fig. 1–3). On Common Nighthawk, these spots are generally absent, or much reduced (Fig. 1–2). Note that the palest subspecies of Common Nighthawk, e.g. henryi and sennetti, show extensive buffy spotting on the inner primaries, and that most Common Nighthawks show pale barring on the underwing coverts (Figs. 1 & 6).

Figure 3. Female Lesser Nighthawk, April 2017, Texas, USA. Photo © Barbara Lindley / Macaulay Library. On perched individuals, the buffy spots on the outer primary flight feathers are usually not as obvious as on this individual, which has the wing hanging down a bit. Note that the wing band here is buffy, not white, indicating a female. On a Common Nighthawk, the wing band would be closer to the ‘wrist’, and there would be no obvious spots on the outer primary feathers except those that form the wing band.

Spotting on wing covert tips

Many Lesser Nighthawks show large, rounded pale spots on the wing coverts, forming parallel wing bars (Fig. 6); these spots tend to be smaller and less rounded on most Commons. On worn individuals, these spots may be worn off. Use this field mark with caution, as the absence of these spots does not clinch your identification in favor of Common. Some Lessers show smaller spots with dark vermiculations in the centers, similar to Common (Fig. 3). Do not confuse these strings of spots on the wing coverts with the pale spotting on the back feathers (higher up), which both species often show.

Figure 4. Lesser Nighthawk, November 2015, Honduras. Photo © John van Dort / Macaulay Library. Note three strings of large pale spots on the wing coverts, some showing darker vermiculations in the center or near the bottom. The top side of these spots is usually rounded on Lessers, while these spots are usually smaller, not rounded, and more heavily marked in the center, on Common Nighthawks.

Vocalizations

Groups of nighthawks coming out at dusk to feed over fields and forests are often silent, especially outside the breeding season. When they do vocalize, however, you will have no problem telling the nasal «peent» of the Common Nighthawk, often given in flight, from the toad-like trill of the Lesser Nighthawk, usually given while perched. Lesser Nighthawk also gives a spluttering, nasal call in social interactions, when flying low over the ground. Common Nighthawks tend to fly higher, but both species sometimes fly either high or low, so foraging altitude is not a diagnostic field mark.

Status and distribution

Lesser Nighthawk is present in Central America year-round, while Common Nighthawk is a fairly common transient, especially on the Atlantic slope, as well as an uncommon and local breeder in a variety of habitats and elevations. Common Nighthawk is sometimes reported from southern Central America during the winter months (December through February), but thus far these reports have not been supported by solid documentation. The first Common Nighthawks arrive in our region in late March, from their South American wintering grounds. Most pass through to their North American breeding grounds, and some local breeders stay, occupying pine forests, pine savannas, and other open habitats. In September and October, the same pattern occurs in reverse, with local breeders joining migrants from more northerly locales on their route south. In many areas of Central America, Lesser is more common than Common.

Other nighthawks

Besides Lesser and Common Nighthawks, one other distinctive nighthawk occurs, while the occurrence of one cryptic nighthawk is hypothetical. You’re not likely to mistake the Short-tailed Nighthawk (Lurocalis semitorquatus) for any of the other nighthawks—unlike the others, this one is aptly named (Fig. 5). As befits a nighthawk, it is highly aerial and does not sally forth in short flights like the nightjars. Its really short tail is obvious, even in poor light, while its vocalizations are equally distinctive. It’s usually found in lowland and foothill rainforest, from the Petén region in Mexico and Guatemala to southern Brazil, Paraguay and northern Argentina.

Figure 5. Short-tailed Nighthawk, August 2017, Brazil. Photo © Tom Johnson / Macaulay Library.

Antillean Nighthawk (Chordeiles gundlachii) replaces Common Nighthawk in the Caribbean but has never been found on the Central American mainland. It is extremely similar to Common Nighthawk—much more so than Lesser Nighthawk—and silent birds cannot safely be identified. The calls of Antillean Nighthawk are very different from those of Common, so if you find yourself on one of the Caribbean islands or coast looking at a nighthawk and hearing this call, try to record it! Like the Common Nighthawk, the Antillean migrates to wintering grounds in South America.

Don’t get too comfy

The Lesser/Common species pair can present real identification challenges, even for experts. While Lesser Nighthawks often show an overall buffy aspect to their plumage, note that there is considerable individual and subspecific variation in Common Nighthawks, from gray to buffy, and from dark to light (Fig. 8). Being aware of this color variation will help you focus on other, more helpful field marks. However, as you spend more time studying these fascinating species, you will occasionally come across birds that seem to defy easy classification, demonstrating a mix of field marks for either species. Below we have collected a few examples of such problematic birds.

Figure 6. Common Nighthawk, July 2017, New Mexico, USA. Photo © Bob Nieman / Macaulay Library. Common Nighthawk usually has the outer primary longest, but not always. The two outer primaries seem almost the same length here, creating a more rounded wing impression usually associated with Lesser Nighthawk. Wing molt in Common Nighthawk takes places on the wintering grounds, between December and February, so the potential pitfall of an incoming, and thus shorter, outer primary resulting in a more Lesser-like wing shape, is unlikely in Central America. Note that the white wing band falls halfway on the hand of the wing, and that it stretches across five primaries, not four as in Lesser.

Figure 7. Lesser Nighthawk, August 2017, Nicaragua. Photo © Jessie Stuebner / Macaulay Library. This individual seems to show a mix of characters for Lesser and Common. The wing tip appears to extend beyond the tail, and the apparent absence of buffy spotting on the basal part of the outer primaries both suggest Common. However, the wing band almost reaches the tips of the tertials; the undertail coverts are buffy, not white; and the wing coverts show three strings of large round pale spots.

Figure 8. Plumage variation in Common Nighthawks. Top: June 2017, Texas, USA. Photo © Robert Mustell / Macaulay Library. Bottom: May 2017, Massachusetts, USA. Photo © Marjorie Watson / Macaulay Library. Not surprisingly for a species that combines a cryptic plumage with a wide distribution, there is considerable plumage variation between the various subspecies. The top bird likely belongs to the pale subspecies henryi of the dry southwestern United States. Below the nominate ssp minor, the darkest subspecies, better adapted to the wetter boreal and temperate forests of Canada and the northeastern USA. Variation within the subspecies is complex, and most individuals are best left identified only to species level away from the breeding grounds.

Figure 9. Comparison of Lesser (top) and Common nighthawks (bottom). Note placement of white wing band, presence/absence of buffy spots on the outer primaries, and shape of wing tip. Photo collages like these present a rare opportunity to assess how variable these characters are, and how similar the two species can be (especially the two birds on the far right!). All photos copyrighted by the respective photographers and Macaulay Library. Photographers, from top left to bottom right: Mark Stephenson, Hans Spiecker, Alison Sheehey, Alex Lamoreaux, Ronnie d’Entremont, Brendan Klick, Daniel Irons, Dan Vickers.

Finally

We invite eBirders of the Central American region to document their observations of nighthawks, whenever possible, and suggest identifying them to the species level only when the field marks have been considered carefully. As with any identification challenge, it’s okay to leave some birds unidentified, or to report them as Nighthawk sp. (or as Lesser/Common Nighthawk).

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