ID Challenges: the Buteogallus hawks

By John van Dort abril 16, 2018
Solitary Eagle Buteogallus solitarius

The problem is familiar: there are three black Buteogallus hawks in our region—Common Black Hawk (Buteogallus anthracinus), Great Black Hawk (B. urubitinga), and Solitary Eagle (B. solitarius)—and they are often depicted in field guides as if they were Russian dolls, i.e. each an identical larger version of the previous. While size differences do exist and would even be obvious if the three species were seen side by side, the reality is that you will usually not see the three—or even two—species in the field together. Sometimes, there may be a Black Vulture nearby to provide a size reference. But size is often difficult to assess on a single flying raptor, so it’s really better to rely on other ID clues. The purpose of this article is to help you do that.

Immatures

Let’s start with the immatures. And let’s also remember that immature and juvenile are not the same thing. Some definitions then: A juvenile hawk is in its first life year and is wearing the plumage it acquired shortly before it left the nest. An immature hawk is any hawk in a plumage that is not adult. This means that any juvenile is automatically also an immature, but not all immatures are necessarily juveniles. In many large birds, including some of the Buteogallus hawks, individuals need more than one year to reach the adult plumage. Common Black Hawk has only two plumages (juvenile and adult), but Great Black Hawk, for example, has three field-identifiable plumages: juvenile, Basic II and adult, while Solitary Eagle even has four: juvenile, Basic II, Basic III, and adult. So, an adult Common Black Hawk is more than one year old, an adult Great Black Hawk more than two, and an adult Solitary Eagle more than three. For raptors that take more than one year to reach adult plumage, the Basic II plumage refers to the first plumage after the juvenal plumage (i.e. that it wears between 1-2 years of age) and the Basic III plumage to the second plumage after the juvenal plumage (i.e. between 2-3 years of age). It’s helpful to understand the difference in meaning between juvenile and immature when talking about raptors in non-adult plumages. Check out this article if you’re interested in learning more about age terminology in raptors.

Immatures in flight

As throughout birding, it’s often valuable to learn a common species really well and to use that species as a reference for learning to distinguish similar, rarer species. In this case, the Common Black Hawk is by far the most common of the three Buteogallus in most of Central America, so let’s start there.

Figure 1: Variation in juvenile Common Black Hawks (Buteogallus anthracinus). Left a paler individual, right a darker individual. Note the shape of the broad wings and the heavy barring of the flight feathers. Both individuals show a dark malar area, and a paler panel in the primaries. Observe how the feet reach to about the middle of the tail. Left photo March 2018, Honduras © Oscar Rolando Suazo Ortega / Macaulay Library. Right photo September 2012, Honduras © John van Dort / Macaulay Library.

All three juvenile Buteogallus have pale panels in the hand of the wing, just like many juvenile Buteo hawks, like for example Red-tailed Hawk. Juvenile Common Black Hawk has broad, round wings that are heavily barred, including the darker ‘fingers’. The tail is also heavily barred. The legs reach halfway down the tail. Given close views or good photos, a dark malar region is often visible, usually—but not always—lacking in Great Black Hawk. A small percentage of Common Black Hawks have the malar area pale.

The legs extend further toward the tip of the tail on a flying juvenile Great Black Hawk, compared to Common Black Hawk. The juvenile Great Black Hawk’s tail has many thin bars, and the pale bars are usually the same width as the dark bars, unlike juvenile Common Black Hawk, which usually has wider pale bars in the tail. There is some variation in this character. At greater distances, these details cannot be appreciated, and you’re left with what most hawk watchers rely on when identifying distant raptors in flight: shape. Great Black Hawk usually has a proportionally longer tail than Common Black Hawk (although the difference can be minor when the tail is worn, as in Figure 2). What sometimes works better in such cases is the color of the uppertail coverts. If you can see the uppertail coverts, note that Great Black Hawk has white, or mottled white, uppertail coverts in all plumages, while Common Black Hawk and Solitary Eagle have dark uppertail coverts in all plumages.

Unlike the two smaller species, the flight feathers of the juvenile Solitary Eagle are barely, if at all, barred. The short tail and broad secondaries result in a silhouette similar to that of the adult. The juvenile Solitary Eagle has dark, unbarred thigh feathers (these feathers are usually barred in the other two species).

Figure 2: Juvenile Buteogallus hawks in flight. From left to right: Common Black Hawk (Buteogallus anthracinus), Great Black Hawk (B. urubitinga) and Solitary Eagle (B. solitarius). While these are not the same size, they are shown here as if they were, to emphasize field marks other than size. Note how the silhouettes are similar between the Common Black Hawk and Great Black Hawk, while the Solitary Eagle’s triangular wing shape, created by longer secondaries versus shorter primaries, is distinctive. Another similarity between Common and Great black hawks is the strong barring of the flight feathers, virtually absent in juvenile Solitary Eagle. Note the longer legs of the Great Black Hawk, extending further down the tail in comparison with the Common. Photo Common Black Hawk, March 2018, Honduras © Oscar Rolando Suazo Ortega / Macaulay Library; photo Great Black Hawk, February 2018, Brazil © Willian Menq / Macaulay Library; photo Solitary Eagle July 2017, Peru © Brian Sullivan / Macaulay Library.

Basic II Great Black Hawk and Basic II and III Solitary Eagle

Great Black Hawk has one more immature plumage after the juvenal plumage (Basic II) and Solitary Eagle has two (Basic II and Basic III). The Basic II plumage of Great Black Hawk is similar to the juvenal plumage, except that the tail now has fewer bars, which are wider and are black and white instead of buffy. These bars are also rather irregular. The Basic II plumage of Solitary Eagle is similar to the juvenal plumage, but the tail is now shorter and instead of buffy rather whitish, with the black subterminal band more defined. The dark sides of the lower neck, present in the juvenal plumage, now connect with dark malar and auriculars. Most of the flight feathers are also darker, except for some retained juvenile flight feathers. Basic III Solitary Eagle is adult-like, with some buffy areas on the head, breast and underwing coverts.

Figure 3: Basic II Great Black Hawk (Buteogallus urubitinga). This plumage is similar to the juvenal plumage, but the tail is different: instead of very thin and regular banding on a buffy tail, the tail is now whitish with wider, irregular banding. Note that this bird has started the molt to the adult plumage and is thus probably about two years old. In the tail, the two outermost rectrices (r6) are adult, as are both r3’s; the remaining rectrices are Basic II. Likewise, some of the inner primaries have been replaced also, with p1-3 of the right (lower) wing adult, and p1-2 of the left (upper) wing adult. The belly is also turning dark. Long legs and absence of malar stripe help distinguish this individual from juvenile Common Black Hawk. Photo March 2017, Mexico © Andrew Nyhus / Macaulay Library.

Figure 4: Immature Solitary Eagle (Buteogallus solitarius), possibly juvenile molting to Basic II plumage. The darker inner primaries are new feathers, and the tail also shows a mix of different age feathers. Don’t be distracted by these plumage details when identifying raptors in flight. Focus instead on the shape of this individual, which is classic Solitary Eagle: short, square tail and broad wings, broadest close to the body. Photo January 2017, Colombia © Daniel Orozco Montoya / Macaulay Library.

Immatures perched

On perched immature black hawks, it is useful to consider primary projection, bill color, leg length and width, and plumage aspects. When visible, the primary projection, i.e. the length of the folded primaries sticking out from the folded secondaries, is a good field mark to separate Common and Great black hawks. Primary extension is very short in Great Black Hawk (Fig 5).

Figure 5: Juvenile Buteogallus hawks perched. From left to right: Common Black Hawk (Buteogallus anthracinus), Great Black Hawk (B. urubitinga), and Solitary Eagle (B. solitarius). Note the pale base of the bill of the Common Black Hawk; the other two hawks have bills that are dark on the topside all the way to the cere. Compare the primary extensions and observe how short that is on the juvenile Great Black Hawk. Note the banding of the tail: wider pale bands on the Common versus thinner pale bands on the Great Black Hawk, and a lack of banding altogether on the Solitary Eagle. This particular juvenile Great Black Hawk has darker markings in the malar area than is typical for this species. Common Black Hawk, January 2018, Costa Rica, photo © Jeffrey Thomas / Macaulay Library. Great Black Hawk, May 2015, Panama, photo © Tim Lenz / Macaulay Library. Solitary Eagle, November 2017, Peru, photo © Alex Valle Soto / Macaulay Library.

Bill color

In Central America, a useful way to separate perched Common Black Hawk from Great Black Hawk and Solitary Eagle is the color of the base of the bill: pale blueish-gray or yellowish-gray in Common Black Hawk; black in Great Black Hawk and Solitary Eagle. This difference holds up at all age classes and works nearly always in Central America. Note that Great Black Hawks in South America can show a pale base of the bill as well.  Some Common Black Hawks can show a bill almost completely black to the cere, but this is unusual. It appears that an all-black bill is still rare but slightly more common in the extreme northern part of the range (i.e. United States, where Great Black Hawk does not occur), and that birds with all-black bills often have lores that are pale gray or whitish (like Great Black Hawk), lacking the yellow tinge that is more typical of Common Black Hawk. This is based on a very small sample series and needs further testing. In such cases, primary projection on perched individuals may be more reliable. Summarizing, this difference in bill and lore color generally holds up in areas with overlapping ranges, presumably because of selection pressure on those traits, while these differences may be less pronounced in areas where normally only one of the two species occurs.

Adults in flight

Given reasonable views, the adult Buteogallus hawks can be identified using wing shape, tail length, and leg extension. Proportionally, the tail seems longest on Great Black Hawk and shortest on Solitary Eagle, with the Common Black Hawk tail appearing as intermediate. Note that open tails always seem shorter than closed tails. All three species have broad wings compared to most other raptors, but the wings are especially broad on Solitary Eagle. The latter’s combination of a short tail with broad wings, an effect further heightened by bulging inner secondaries, creates a distinctive silhouette. The widest part of the wing is further away from the body in Common and Great black hawks. The adult Common Black Hawk has a whitish slash near the base of the outer two or three primaries, absent in Great Black Hawk. The Solitary Eagle has a pale area in the proximal part of the primaries contrasting with the dark primary tips. The flight feathers of Common and Great black hawks are barred, while those of Solitary Eagle are faintly barred or not at all; note that this field mark is only visible given reasonable lighting and distance (i.e. not backlit or distant). Common Black Hawk usually shows a wide band on the trailing edge of the wing, contrasting with a paler inner part. This contrast is usually absent or far less visible in Great Black Hawk and Solitary Eagle. The fine barring on the thigh feathers of the adult Great Black Hawk is sometimes visible when the bird is relatively close and not backlit. This last field mark works for adults in all of Central America except eastern Panama, where a different subspecies occurs that has the leggings unbarred.

Figure 6: Adults in flight. From left to right: Common Black Hawk (Buteogallus anthracinus), Great Black Hawk (B. urubitinga), and Solitary Eagle (B. solitarius). Note that the tail length of Common Black Hawk is almost that of Great Black Hawk, but the extension of the legs is quite different: halfway down the tail in Common Black Hawk versus past the white tail band in Great Black Hawk. The feet also reach beyond the white tail band in Solitary Eagle, but the tail is shorter, and the wings are broader than in those other two species, creating a silhouette that’s distinctive. Note the pale slashes in the outer two primaries of the Common Black Hawk, absent in the other two species. In comparison, Solitary Eagle has a wider pale area in the hand, contrasting with the black fingers. Note the white banding on the Great Black Hawk’s leg feathers. Common Black Hawk, Mexico, July 2017 © Antonio Martinez Hirtz / Macaulay Library. Great Black Hawk, Mexico, February 2018 © James Thompson / Macaulay Library. Solitary Eagle, Peru, June 2013 © Rob Martin / Macaulay Library.

Figure 7: Topside view of an adult Common Black Hawk (Buteogallus anthracinus), March 2018, Trinidad and Tobago. Note black uppertail coverts and yellow loral area and base of bill, ruling out Great Black Hawk. Photo © Pam Rasmussen / Macaulay Library.

Figure 8: Adult Great Black Hawk (Buteogallus urubitinga), January 2017, Mexico. When you get views or photos this good, identification is easy: barred thigh feathers; long legs reaching well beyond the white tail band; absence of whitish slash in the outer primaries all serve to eliminate Common Black Hawk. Photo © Alan Selin / Macaulay Library.

Figure 9: Adult Common Black Hawk (Buteogallus anthracinus), February 2018, Trinidad and Tobago. This is clearly a Common Black Hawk, as the white slashes in the outer primaries confirm. But note how short the tail seems here! Solitary Eagle does not occur in Trinidad and Tobago but imagine seeing this bird in a place where all three species occur. Then further imagine it at a much greater distance, and without any birds of known size such as vultures or other raptors nearby for size comparison. An observer not familiar with Common Black Hawk might confuse this with a Solitary Eagle. However, the tail of the latter is less rounded, or when completely open as here, even less extending, and the hand is narrower. Photo © Jerome Foster / Macaulay Library.

Figure 10: Adult Common Black Hawk (Buteogallus anthracinus), April 2018, Honduras. These two photos of one individual were taken moments apart—but note how different the leg extension appears in the left photo compared the right! Compare this also to the leg extension in Figures 6, 8 and 9, and you will learn to use this field mark with caution. Head-on angles exaggerate the apparent leg extension, which in the left photo seems to reach the tip of the tail, suggestive of Great Black Hawk. The white slashes in the outer primaries and the contrast between the wing’s broad terminal band and inner wing, however, point to Common, not Great Black Hawk. Photos © John van Dort / Macaulay Library.

Adults perched

On perched adult black hawks, look for the base of the bill: pale gray or yellowish in Common Black Hawk, black to the yellow cere in Great Black Hawk and Solitary Eagle. The pale loral area between the cere and the eye often has a yellow tinge in Common Black Hawk; this area is pale gray in Great Black Hawk and usually pale gray in Solitary Eagle. Consider the primary extension beyond the folded secondaries: very short in Great Black Hawk and Solitary Eagle; longer in Common Black Hawk. Note that the wing tips almost reach the tail tip in Common Black Hawk but fall well short of the tail tip in Great Black Hawk. The wing tip often extends beyond the tail tip in Solitary Eagle. In most of Central America (except eastern Panama), the adult Great Black Hawk has the thigh feathers finely barred; this is diagnostic when visible. The legs are relatively longest on Great Black Hawk, but be aware that in certain body positions, the other two species may look long-legged as well.

Figure 11: Adult female Common Black Hawk (Buteogallus anthracinus), Honduras, January 2015. The pale grayish cheek indicates a female. The thin barring on the leg feathers should not be confused with that of the Great Black Hawk. Note how here the pale edges are very thin and are not restricted to the thigh feathers. These are simply pale edges on fresh plumage and will soon wear off. Solitary Eagle is often said to be grayer than Great and Common Black Hawks, but note the gray tones on this individual, especially the head. Photo © John van Dort / Macaulay Library.

Figure 12: A pair of Common Black Hawks (Buteogallus anthracinus), Costa Rica, January 2018. This photo illustrates that not all females have the cheek gray. Photo © Gates Dupont / Macaulay Library.

Figure 13: Photo collage of an adult Great Black Hawk (Buteogallus urubitinga), Mexico, August 2017. In the left photo, the bird helpfully sticks out its right leg, as if to say “See? Barred leg feathers.” These photos, taken moments apart, perfectly illustrate how the fine barring on the leg feathers—diagnostic when detected—isn’t always visible. Even without the left and right photos, we can still identify the bird in the middle photo as a Great Black Hawk: the bill is black all the way to the cere, and the loral area is gray, not yellowish. Note how in these photos the legs do not seem obviously longer than you would expect to see on an average Common Black Hawk, which should serve as a warning about relying on that field mark only for identification. Note also that adult Great Black Hawks in eastern Panama and South America do not have the leggings barred. Photos © Gerardo Marrón / Macaulay Library.

Figure 14: Adult Solitary Eagle (Buteogallus solitarius), June 2017, Belize. As is often the case on perched adult Solitary Eagle, the short tail is invisible, covered by the long secondaries and primaries. The subtle contrast between browner and grayer feathers indicates a younger adult. Photo © Bryce Robinson / Macaulay Library.

Figure 15: Adult Solitary Eagles (Buteogallus solitarius). Some field guides state a difference between grayish plumage of the Solitary Eagle versus blackish plumages of the two black hawks. These differences only apply in the southernmost range of the Solitary Eagle, where it is indeed paler gray and more easily told from the black hawks. However, in most of the range, including Mexico, Central America and northern South America, there is no appreciable difference in overall coloration between the three Buteogallus hawks. Left: July 2017, Peru, photo © Brian Sullivan / Macaulay Library. Right: March 2017, Bolivia, photo © Tini & Jacob Wijpkema / Macaulay Library.

Common versus Mangrove Black Hawk

Subspecific divisions in the Common Black Hawk have been unclear for a long time and remain so to this day. Mangrove Black Hawk (Buteogallus anthracinus subtilis) is a form of the Common Black Hawk that occurs in mangroves, and is characterized by a smaller size, stronger rufous wash on the secondaries and inner primaries, and a wider pale slash in the outer primaries, compared to the nominate form. Our understanding of the range of this subspecies remains incomplete. Many of the Common Black Hawks found in the mangroves of Central America look no different from the ones found further inland. For a full discussion of the taxonomy and distribution of the Mangrove Black Hawk, see this article.

Zone-tailed Hawk

The three Buteogallus hawks get confused far more with each other than with any other species, although for some observers, Zone-tailed Hawk (Buteo albonotatus) is similar. While Zone-tailed Hawk shares with the black hawks an overall dark plumage with one or more white tail bands, their silhouettes in flight are so different that once you learn how to factor shape into your raptor identifications, you are unlikely to mistake a Zone-tailed Hawk for any of the black hawks. In a glide, the wider hand of the Zone-tailed Hawk is a good field mark, together with the longer, thinner tail, which is often held closed. The trailing edge of the Common Black Hawk’s wings bulges, while that of the Zone-tailed Hawk is straighter. Common Black Hawk soars on wings held flat, while Zone-tailed often holds the wings in a shallow V, like a Turkey Vulture. Perched, the two species are more similar. Common Black Hawk likes to use exposed perches; Zone-tailed Hawk prefers to perch in a hidden spot. Zone-tailed Hawk often shows a small pale area on the forehead, just above the bill; Common Black Hawk does not.

Figure 16: Comparison between adult Common Black Hawk (Buteogallus anthracinus, left) and adult Zone-tailed Hawk (Buteo albonotatus). The wings and tails are held in the same position here, which highlights the shape differences: broad bulging wings of the Common Black versus narrower and straighter wings of the Zone-tailed. Note also the longer, thinner primary tips (‘fingers’) of the Zone-tailed, as well as its longer tail. Some plumage differences are also visible: thick band on the trailing edge of the wing of the Common Black versus a thinner band on the Zone-tailed; rufous tinge to secondaries and primaries in the Common Black versus a gray tinge in the wing of the Zone-tailed. White slashes in the outer primaries present in the Common Black, absent in the Zone-tailed. Common Black Hawk, Mexico, July 2017 © Antonio Martinez Hirtz / Macaulay Library. Zone-tailed Hawk, United States, November 2017 © David McQuade / Macaulay Library.

Vocalizations

Common Black Hawk is a vocal species, and especially in areas where they are common (like mangroves), they are often heard calling. The most commonly heard vocalization is this high-pitched rising and falling laughter. Great Black Hawk gives different vocalizations, like this drawn-out call (here’s another example), or this series of shorter notes. The Solitary Eagle gives a slightly lower-pitched, nasal drawn-out call.

Finally

There are several field marks for each of the age classes that work well in combination, but as this article hopefully has made clear, practically none of these field marks is 100% infallible. For best results, try to use a combination of field marks when identifying these majestic creatures, and don’t be afraid to leave some unidentified.

About ID Challenges

ID Challenges is a series of articles on the Central American eBird portal that delve deeper into bird identification challenges in a Central American context. The purpose of these articles is to provide ID help on groups of birds that can present real challenges in the field for birders of all skill levels. Each article is available in a Spanish and an English version. Topics thus far covered include:

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