The vast majority of the time,
raptors misidentified as peregrine falcons are in fact accipiters:
sharp-shinned hawks, Cooper’s hawks, or northern goshawks. This
Species Portrait will describe the identifying features, natural
history, distribution, and conservation status of each of the three
species of accipiter found in North America.
Accipiters are hawks characterized by long tails and short, broad
wings. They are the "true" hawks in that accipiter is
Latin for "bird of prey". However, the original derivation of
the word is thought to be from the Greek aci ("swift")
and pteron ("wing"), referring to the speed and agility
of these birds. The sharp-shinned hawk is named after a prominent ridge
on its tarsi (despite the tarsus being analogous to the arch of the
human foot rather than the shin). Its scientific name, Accipiter
striatus, refers to the heavily streaked underparts of the juvenile,
which was described before the adult. The Cooper’s hawk, Accipiter
cooperii, was named in honour of New York ornithologist William
Cooper. The northern goshawk derives its English name from the
Anglo-Saxon gos and havoc, meaning a hawk which hunts
geese. Its scientific name is Accipiter gentilis, meaning
"noble hawk", a reference to the fact that only those of an
elevated social stature were permitted to use this bird for falconry in
mediaeval times.
Identification: As is the case with many raptors, plumage differences between the sexes are minor at best among accipiters, however, females are significantly larger than males. All immature accipiters are brown on
the back and have whitish underparts streaked with brown. Adults are
slate blue-gray above and heavily barred with rufous (sharp-shinned and
Cooper’s) or gray (goshawk) below.
The typical flight pattern of accipiters is two or three quick flaps
followed by a brief glide. All three species also soar regularly, and
may fan their long tails out somewhat when doing so. The low aspect
ratio (length compared to width) of their wings provides them with rapid
acceleration upon takeoff, and enables them to manoeuvre quickly and
accurately when pursuing prey through wooded areas.
The sharp-shinned hawk is the smallest of the
North American accipiters, similar in size to a blue jay. In
terms of plumage, the Cooper’s hawk is virtually identical to
the sharp-shinned, often leading to frustration among observers.
Though there is a size difference between the species, this can
be very difficult to assess with any real accuracy when in the
field. A more reliable method of identification is to check
whether the head is in line with the wrists when in flight; if
so, it is a sharp-shinned, but if the head protrudes beyond the
wings, it is a Cooper’s. The tail of the Cooper’s also is
more rounded, and has a broader white terminal band. The
immature Cooper’s has less streaking on the lower breast and
belly than the sharp-shinned.
The goshawk is often recognizable simply by its shape and
large size, but adults can also be readily identified by the
gray breast which sets it apart from the smaller accipiters.
Immature goshawks are generally brown, with flecks of buff on
the back, and heavy streaking across the underparts which is
darker and more extensive than on the other two species.
Goshawks of all ages have a prominent white superciliary (i.e.
above the eye) line. |
An adult sharp-shinned hawk perching on the handle of a shovel
in a Niagara Peninsula backyard in February 2000. (Photo by
John Spirko)
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Species |
Length (M) |
Length (F) |
Wingspan (M) |
Wingspan (F) |
Weight (M) |
Weight (F) |
Sharp-shinned
hawk |
24-27 cm
(9-11") |
29-34 cm
(11-13") |
53-56 cm
(20-22") |
58-65 cm
(23-26") |
87-114 g
(3-4 oz) |
150-218 g
(5-8 oz) |
Cooper’s
hawk |
37-41 cm
(14-16") |
42-47 cm
(16-19") |
70-77 cm
(28-30") |
79-87 cm
(31-34") |
302-402 g
(10-14 oz) |
479-678 g
(17-24 oz) |
Northern
goshawk |
46-51 cm
(18-20") |
53-62 cm
(21-24") |
98-104 cm
(38-41") |
105-115 cm
(41-45") |
677-1014 g
(24-36 oz) |
758-1214 g
(26-43 oz) |
Peregrine
falcon |
37-43 cm
(14-17") |
42-50 cm
(16-20") |
70-85 cm
(28-34") |
95-105 cm
(38-42") |
450-680 g
(16-24 oz) |
720-1200g
(26-43 oz) |
Table 1: A summary of the range of dimensions for
each of the North American accipiters, as well as the peregrine
falcon. Note that the peregrine is similar in size to the Cooper’s
hawk, but is bulkier, and thus is closer to the northern goshawk in
terms of weight. Sources: W.S. Clark and B.K. Wheeler: A
Field Guide to Hawks of North America (1987), R. Monneret: Le Faucon
Pèlerin (1987)
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Distribution:
All three accipiters are distributed quite widely across North
America. The sharp-shinned hawk has the greatest range, breeding across
Canada and many northern states, and wintering from southern Canada
through Panama. The Cooper’s hawk is more southerly, breeding
regularly in all of the continental states except North Dakota, and
along the southern edges of most provinces; only individuals from the
northern edge of the breeding range tend to be migratory. The goshawk
has the most northern distribution, breeding across Canada, as well as
through much of the Rockies and northern Appalachians. Goshawks are not
strongly migratory, but will periodically winter as far south as
northern Mexico when there is a shortage of prey on their breeding
grounds.
Natural history:
All of the accipiters prey primarily on smaller birds, though the
Cooper’s will also take some small mammals and herptiles on occasion,
and the goshawk hunts medium-sized mammals (e.g hares) quite regularly.
The typical hunting strategy is to wait silently on an inconspicuous
perch until prey comes near, then attack with a rapid burst of flight.
The goshawk, and to a lesser extent the Cooper’s hawk, will also
actively search for prey by flying relatively close to the ground and
trying to use the element of surprise to their advantage. Both species
will occasionally chase their quarry on foot if the vegetation is too
thick to allow pursuit by flight.
Accipiters tend to nest in medium to large forests,
and in general show a preference for areas relatively undisturbed by
human activity. They may use either existing nests (often those of
crows), or construct their own out of sticks, strips of bark, grasses,
and feathers. Nests are normally situated near the trunk of a tree; the
sharp-shinned and goshawk prefer conifers, while the Cooper’s is less
particular. Courtship generally takes place relatively near the nest,
and may involve a variety of aerial dives and swoops, performed alone or
as a pair. Though rarely heard through the rest of the year, accipiters
can be quite vocal during courtship. All three species give a variation
of a call consisting of sharp "kak" notes. Once nesting has
begun, accipiters tend to be very shy and reclusive. Even when an active
terrritory is discovered, it can be difficult to pinpoint the actual
nest. All accipiters are very protective of their territories, but none
more than the goshawk, which is absolutely fearless and does not
hesitate to strike any intruders, including humans.
The eggs of accipiters are off-white, usually with a
faint bluish or greenish tinge and spotted or lightly streaked with
brown. Those of the sharp-shinned and Cooper’s hawks average 39 mm
(1.5") in length, while the goshawk’s eggs are 59 mm (2.3")
long. Incubation requires 32 to 36 days for the smaller species, and 36
to 38 days for the goshawk. Fledging times are also related to the size
of the species: 24 to 27 days for sharp-shinned, 27 to 34 days for
Cooper’s, and 35 to 42 days for goshawks. Sharp-shinned hawks may be
independent within less than a month of fledging, but juvenile Cooper’s
and goshawks remain with their parents for four to six weeks. Like
peregrines, accipiters acquire adult plumage toward the end of their
second summer. Only a small fraction of accipiters breed before reaching
full maturity, and as many as half of goshawks wait until their third
year.
Though seldom seen by most people during the spring
and summer because of their retiring habits, accipiters become quite
conspicuous during the fall when sharp-shinned hawks in particular
migrate south in large numbers. Those accipiters which remain in the
north for the winter are frequently sighted, as they often stake out
bird feeders for easy hunting. A backyard with an active feeder and
nearby cover in the form of a dense bush or tree is ideal. Of the
"backyard peregrines" reported to CPF, 95% or more are in fact
accipiters, mostly Cooper’s hawks because of the close similarity in
size. While the peregrine is a highly skilled hunter, it is adapted to
aerial pursuits, and would actually have very little success if it
attempted to hunt from a low perch in the manner of an accipiter.
Conservation:
The populations of all three accipiters decreased as a result of
eggshell thinning due to DDT contamination in the 1960s and 1970s. The
sharp-shinned and Cooper’s hawks were both placed on the National
Audubon Society’s Blue List in 1972, indicating that they were in
serious decline. However, accipiter populations have recovered well, and
are currently stable or increasing over most of their range. The
sharp-shinned hawk is the most common of the three accipiters, and is
seen in large numbers each fall at raptor migration watches across North
America. The Canadian population is estimated to be between 500,000 and
1,000,000 pairs, making it Canada’s most abundant raptor of any kind.
The Cooper’s hawk remains less common (10,000 to 50,000 pairs in
Canada), but is increasingly being found in some urban areas. The
northern goshawk is the least frequently seen member of the genus,
though this is largely because it frequents more remote areas; its
Canadian population is also estimated to be 10,000 to 50,000 pairs. |