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.
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.
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.
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).
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.
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).
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.
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.
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.
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.
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.
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.
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.
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: