Northern Goshawk flight identification and ageing in the UK - Revised and updated

This is a fully revised version of a blog I first posted in September 2015 with more photographs, particularly of sub-adult plumages. To make comparison easier and to facilitate the increase in the number of photos used I have copied individual photos on to a common background for the main illustrations. Whilst this may be less aesthetically pleasing I think it assists the identification purpose of the blog. 
I'm always happy to receive feedback and comments to andysbutler@aol.com or via the comments section at the end of the blog.

Despite an increase in the Northern 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 Northern Goshawk combined with its size and striking plumage which makes it one of the most enigmatic of British birds and one that all birdwatchers get a thrill from seeing.

For more than two decades I have had the opportunity to study the Northern Goshawk through the year in the Derbyshire Peak District, 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.
Despite seeing Northern Goshawks most days when I'm out in the first few months of each year I still get an incredible thrill from watching them. 
This article is aimed at helping those who are less familiar with them to confirm their identification and also for those with a deeper interest in bird identification and ageing to share my thoughts on the various plumages that can be identified in the field.

Figure 1 Northern Goshawk juvenile male (first plumage) Feb 2019

General considerations

To avoid repetition from this point forward I will refer to Northern Goshawk as Goshawk and Eurasian Sparrowhawk as Sparrowhawk other than in the Figure captions.

In order to clarify the various plumages associated with a Goshawk's age I have referred to First, Second, Third etc. Plumages, where First Plumage is the juvenile plumage the bird has when it fledges from the nest. I find the use of other terms such as the calendar year age of a bird confusing since in each calendar year after the bird has fledged it will have two plumages (either side of the summer moult). 

In a reasonable view and good light 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 (Figure 3) and should not normally cause a problem but males are considerably smaller, similar to Carrion Crow (Figure 2) and more likely to be confused with female Sparrowhawk although the latter is closer to Kestrel in size. 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 additional characteristics can be seen such as the flight or structural details noted below or some plumage features. I have watched very distant birds circling without flapping and have been uncertain which species I was watching. Clearly it helps if there are birds nearby to make a direct size comparison. 

Figure 2 Male Northern Goshawk with Carrion Crow

Figure 3 Female Northern Goshawk with Common Buzzard Feb 2019

The Sparrowhawk is a compact bird with short broad wings and a generally long square cut tail. 

The Goshawk has a more rounded tail, as the feather length decreases moving out from the longest central feathers (Table 1).  Although the closed tail can look square on the Goshawk (see Figure 11a for example) it is often possible to see the shorter outer tail feathers, particularly on photographs. Compare the tails on Figures 1 and 7 b & d for Goshawk with the Sparrowhawks on Figure 4 b & c. 

Note that moult may also affect the relative length of the feathers particularly in the autumn when feathers may be still growing. The central feathers are the first to be replaced so the outer feathers may still be growing after the central feathers are at full length. 

The Goshawk will often circle with the tail closed when it has a distinctive cross like silhouette with long wings and tail whilst the square ended tail of the Sparrowhawk can often be seen even in fairly distant views.

Table 1 Difference in length between central and outer tai feathers

Figure 4 Eurasian Sparrowhawk a, b, f, e juvenile, c adult male, d adult female

The flight of the Sparrowhawk is normally very distinct with circling and gliding interspersed with rapid flickering wing beats which are never seen in Goshawk. Both Goshawk and Sparrowhawk glide on flat wings (Figures 4e, 7f & 10b), unlike the Buzzard which holds its wings in a shallow V, and flaps with deep wing beats which gives the impression of its size.

Figure 5 Flight silhouette of Northern Goshawk and Eurasian Sparrowhawk not to scale

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;

• Where plumage details can be seen Sparrowhawk always shows barred secondaries. In Goshawk these are only present in First (juvenile) and Second Plumages. First Plumage Goshawk has a heavily streaked not barred breast but identification of Second Plumage Goshawk requires additional features,  
• 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,
• The shorter outer tail feathers of the Goshawk produce a rounded tail rather than the square ended tail of the Sparrowhawk.

The shape of Goshawk can also recall Hen Harrier and on more than one occasion I have seen a female Goshawk flying low over the moors where my first thought was that I was watching a Hen Harrier.

Moult

The Goshawk has a complete moult each year mainly during June to October. Females start the moult earlier than 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.
In common with other large raptors not all the flight feathers are moulted each year. Figure 5 below gives a diagrammatic representation of a study of the moult in a captive female obtained as a juvenile in autumn 1982 under license in Germany. The moulted feathers were collected in each subsequent year (except 1983 when only primaries and tail feathers were collected) and the feathers moulted or retained identified.

Figure 5 Diagrammatic representation of the main flight feathersin the Northern Goshawk A=alulas, P= primaries, S= secondaries. The bar codes show which feathers were moulted (open cells) or retained (solid cells) each year between 1983 and 1989. The stippled cells represent those feathers for which no moult data were obtained.

Other than in 1985 all the primaries were moulted each year. There are no years when all of the secondaries are replaced and thus any bird older than juvenile will have at least some feathers in the wing grown the prior year. This is helpful in ageing immature birds.
The secondary feathers in the first post juvenile moult are dark tipped and more strongly barred than in subsequent moults. This makes these birds, which also have more coarsely barred underparts fairly easy to identify but a Goshawk encountered which has a one or two of these more heavily barred feathers most have completed it second post juvenile moult and is therefore in the second half of its third calendar year or the first half of its fourth calendar year.

Figure 6 Comparison of female Northern Goshawk in its 4th calendar year with an adult

The pattern of the barring on the primaries also changes with age in juveniles and birds having completed the first post juvenile moult the primaries have 5 or six visible bars, the barring is darker towards the tip and forms an even band in subsequent moults the bars become more triangular, broadest on the leading edge and narrowing to the rear.

First or Juvenile Plumage, first calendar year to second calendar year summer

Figure 7 Northern Goshawk in juvenile or first plumage b,c,d are males; a,g,e female

The Goshawk retains its juvenile plumage from fledging in July through to September of the second calendar year. I have seen a male in late June/ early July of its second calendar year still with a full set of juvenile remiges and retrices so there is a short period when recently fledged juveniles and 2nd calendar year birds still in juvenile plumage could be in the air together.

The young Sparrowhawk shows barring on the breast, although there may be some streaking on the upper 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 in 7d has a single moulted breast feather just above its left leg which shows Second Moult barring.

The juvenile 7e has "flared" undertail coverts which has previously been noted as a diagnostic characteristic of Goshawk which is clearly not the case and may be seen in both species and sexes during the display period (see Sparrowhawk in 4a).

From fledging through to summer of the second calendar year the young Goshawk has an orangey-buff ground colour to the breast and underwing coverts with heavy dark brown streaking on the breast and underwing coverts. This colouration can show a distinct contrast with the pale ground colour to the primaries and secondaries which are heavily barred dark brown and forming a dark trailing edge to the wing.

The iris of the recently fledged juvenile Goshawk is a pale blue-grey colour which turns to yellow, like the adult birds by the end of the first calendar year.

Second Plumage, second calendar year autumn to third calendar year summer

During the moult in the summer of the second year the Goshawk's sheds its juvenile plumage and starts to look  much more like an adult. but viewed from the underside the flight feathers are heavily barred, similar to a juvenile. The breast is rather coarsely barred with barring coalescing on the upper breast. The colour of the underparts is generally browner than in the adult. From above the upperparts are a warm, slightly rufous brown. Barring on the tail is obvious when viewed from both above and below. 

The head pattern is less conspicuous than the adult with limited or no pale supercilium or dark ear coverts and the iris is yellow.

The bird in photo 8d photographed in early June of its third calendar year has started the moult to adult plumage having lost four inner primaries.

Figure 8 Northern Goshawk Second Plumage 

In Second Plumage the Goshawk is in its most Sparrowhawk like plumage with barred secondaries and breast. Identification is still fairly straightforward based on size, structure and absence of the 'flickering' wing beats shown by Sparrowhawk.

Third Plumage, third calendar year autumn to fourth calendar year summer 

Figure 9 Northern Goshawk Third Plumage

As noted under Moult above after the second post juvenile moult some individuals may be tentatively aged due to the retention of secondaries from the Second Plumage. Note however that the appearance of the underwing varies significantly depending on how it is lit. In strong light the underwing variations look muted but may be quite distinct in less direct sunlight. The head pattern is also less distinct and the barring on the underparts tends to be slightly coarser (the bars are wider) than in subsequent plumages. 

The iris is yellow.

Fourth Plumage, Adult, fourth calendar year onwards
After the third post juvenile moult birds are in adult plumage although with subsequent moults the secondaries become paler and more silvery, the primary barring becomes less distinct, barring on the underparts become finer, the ear coverts and crown darken in males and some females and the iris becomes more orange rather than yellow.

Figure 10 Northern Goshawk Adult Male 

There are no plumage characteristics that reliably separate males from females but in adult plumage males tend to have blacker ear coverts and a more distinct white supercilium but some females may also show these features.

Females are significantly larger as noted at the start of this article, they are also more bulky with broader chest and base of the wing and have a more aggressive look.

Figure 11 Northern Goshawk adult female

The females in photos 11a and 11b are the same bird taken in subsequent years, interestingly it has retained a gap in the secondaries so perhaps these feathers weren't moulted?

References

Reading C J, Molt Pattern and Duration in a Female
Northern Goshawk,  (Accipiter gentills),] Raptor Res. 24(4):91-97, 1990
Forsman D, Raptors of Europe North Africa and the Middle East, Helm Identification Series.