Wednesday, 2 September 2015

Northern Goshawk flight identification and ageing in the UK

Despite an increase in the Goshawk population during the 20th Century it is still a scarce bird and this, along with its generally reclusive behaviour, make it one of the hardest of our birds of prey to see. It is perhaps the difficulty of observing the Goshawk combined with its size and striking plumage which makes it one of the most enigmatic of British birds and one that all bird watchers get a thrill from seeing.
For almost two decades I have had the opportunity to study the Goshawk through the year, and witness the various stages in the breeding, and non-breeding seasons. For such a large bird it is surprisingly elusive and whilst sightings are regular from December through March as birds start the display cycle they are very difficult to observe outside this period.

General considerations

In a reasonable view, where plumage features are discernible, the only likely confusion is with the Sparrowhawk, particularly if the observer is not familiar with Goshawk. The female Goshawk has the size and build of a Buzzard and should not normally cause a problem but males are considerably smaller and slighter and approach the size of a female Sparrowhawk. Note that even for experienced observers size can be very difficult to judge in distant birds and it may not always be possible to confirm identification unless a specific characteristic can be seen such as the flight or behavioural characteristics noted below or some plumage features.
The Sparrowhawk is a compact bird with short broad wings and a generally long square cut tail. The Goshawk tends to have a more rounded tail (Photo 4) but it can look square (Photo 1 and 10), this isn't a feature I would recommend for separating the two species.
Photo 1 Goshawk adult (© Andy Butler)
Photo 2 Sparrowhawk adult female (© Ken Smith)

The flight of the Sparrowhawk is normally very distinct with circling gliding flight interspersed with rapid flickering wing beats which are never seen in Goshawk. The Goshawk glides on flat wings, unlike the Buzzard which holds its wings in a shallow V, and flaps with deep wing beats which gives the impression of its size. 

Without the labels in the silhouette above, even though I've reproduced the birds at a similar size it's fairly obvious that the Goshawk is on the left. The silhouettes are taken from photos of birds in similar positions but clearly not exactly the same, despite this I think there are a number of differences that are useful in the field;

  • The head of the Goshawk sticks further out, similar to Honey Buzzard when compared to Common Buzzard, and the neck base is broader,
  • The Goshawk has relatively broader wings where they join the body, producing a bulkier appearance,
  • The bulkier appearance is further enhanced by the thicker tail base on Goshawk which looks more pinched on Sparrowhawk (per Paul Doherty/Mick Cunningham)
Moult
Juveniles do not start their first moult until the spring of the second calendar year although they may loose some feathers in the intervening period. 
Goshawks complete an annual moult and, in common with many other birds of prey, the females start the moult earlier then in males usually commencing during the egg laying or incubation period and losing 3 or 4 inner primaries over a short period. Males commence the moult a few weeks later and the moult is completed by the autumn.

First calendar year to second calendar year spring (Juvenile)

Photo 3 Goshawk Juvenile January (©Andy Butler)
Photo 4 Goshawk Juvenile December (©Andy Butler)


As noted above the Goshawk retains its juvenile plumage from fledging in July through to July of the second calendar year. The young Sparrowhawk shows barring on the breast when it leaves the nest and therefore looks similar to the adult. Thus an accipiter showing  a streaked, rather than barred breast must be a Goshawk.
The juvenile on Photo 6 has "flared" undertail coverts which has previously been noted as a diagnostic characteristic of Goshawk which is clearly not the case.
Photo 5 Sparrowhawk Juvenile September (©Andy Butler)
Photo 6 Sparrowhawk Juvenile (©Ken Smith)


Photo 7 Recently fledged Juvenile female July (© Andy Butler)
From fledging through to spring of the second calendar year the young Goshawk has an orangey-buff ground colour to the breast and underwing coverts with heavy black streaking on the belly and chest. This colouration can show a distinct contrast with the pale ground colour to the primaries and secondaries which are heavily barred blackish.
The iris of the recently fledged juvenile Goshawk is a blue-grey colour which turns to yellow, like the adult birds by the end of the first calendar year.
I'm not aware of any plumage characteristics that separate males from females in the first calendar year and therefore size is the only field characteristic and this should be used with caution for the reasons stated in the introduction.
Second calendar year autumn to third calendar year spring (First-adult)
Photos 8 Female Goshawk in third calendar year June (© Andy Butler)
Photo 9 same bird as Photo 8 (© Andy Butler)

Following the moult in the summer of the second year Goshawk's look very much like adults but viewed from the underside the flight feathers are rather dark, generally looking darker than the barred underwing coverts. From above the upper parts are a warm, slightly rufous brown. Barring on the tail is obvious when viewed from both above and below. 
The head pattern is inconspicuous with no obvious pale supercilium or dark ear coverts and the iris is yellow.
The bird in photos 8 and 9 photographed in early June has already started the moult to adult plumage having lost four inner primaries. 
Third calendar year autumn and older (Adult)
Photo 10 Adult February (Andy Butler)
Photo 11 Same adult as Photo 10 note flared undertail coverts (©Andy Butler)
Photo 12 Goshawk adult female (© K Smith)
Photo 13 Goshawk adult female (© K Smith)

Following the moult in the autumn of the third calendar year birds are in adult plumage. The remiges are pale and a similar colour to the underwing coverts giving a plain appearance to the underwing, this can be particularly obvious in distant views. The secondaries still show barring when seen close but the barring gets paler with successive moults.
The upper parts are a uniform grey in males and grey brown in females with blackish crown and ear coverts. The head pattern is more distinct in males with a more pronounced white supercilium.
The iris is yellow but gets more orangey with age. 

2 comments:

  1. Great blog. I was lucky enough to stumble across someone who owns one of these birds. I think it was a Northern Goshawk. Stunning bird, and quite surreal to be in the presence of at ground level.

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  2. Cheers, yes they are amazing birds

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