Identification of Adult Female Northern Harrier (Circus hudsonius)...undetected in Europe???


I was recently asked by a friend whether I knew anything about the identification of adult female Northern Harrier (Circus hudsonius) after he observed a female type Hen Harrier (Circus cyaneus) in East Yorkshire with rather a-typical plumage features.

He wondered why it wasn't an adult female Northern Harrier or Marsh Hawk  as they are known over the other side of the Atlantic and sent me a message, asking me whether I had any literature or prior knowledge to the Identification criteria regarding the females of this species.

After wracking off  a few features I knew off the top of my head, as a few pointers for him to possibly work from, I sent him a few scans of various articles and plates i could find in my Nearctic raptor guides, as well as from reference material I have collected over the years.

In doing this and with a life long obsession with raptors and feathers I began to think long and hard about how to pin a female down in a European context. My mind was well and truly racing and I began to rekindle some ideas I had visited in the past. I knew a trip down to the skin collection at Tring was in order.

The following blog post are simply musings into Identification pointers for those wishing to explore 2cy+ female Northern Harriers in the Western Palearctic or help aid birders who encounter an abnormally striking female Hen Harrier whilst out and about.

I don't wish to touch on juvenile Northern Harriers too much (apart from referring to them in later comparison studies when looking at adult female ID features), given that juveniles in recent years have been the somewhat in vogue identification challenge with European birders. There is now extensive literature on the identification of juvenile/1st winter plumage.

This mainly resulted from the inspirational and extensive work the one and only late Martin Garner compiled on them, just some of this outstanding material can be found at

Others who pushed this new knowledge included the great Killian Mullarney, Dick Forsman , John Martin , Dim Wallace and  Alex Lees.

The latter gent being the major catalyst in rekindling the field identification of juvenile hudsonius after finding the first modern day record on North Ronaldsay back in 2008 

Sifting through hudsonius records in Britain and Ireland on Birdguides (post 2008 to modern day) all I could find were entries of  juvenile birds and 2cy+ males. 

The very first record of hudsonius in Britain was a juvenile, St. Mary's, Isles of Scilly, October 1982 that was possibly present until 7 June 1983.

To quote Birdforum the Northern Harrier (Circus hudsonius) breeds over most of Alaska except the far north and Canada south of the tree-line. It also breeds over much of the western and northern USA but is absent from the south, south-east and most of central USA. The southernmost breeding limit is northern Baja California. This species winters from southern Canada and throughout the USA, and from Mexico to Panama, rarely the Caribbean, Colombia and Venezuela

Circus hudsonius has also occurred as a vagrant in the Azores, the Faroes and in 2016 was recently added to Category A of the British List as a separate species from Hen Harrier (Circus cyaneus). Hudsonius is a rarity and all records must be assessed by BBRC.

Therefore the question remains why hasn't there been a British record of an adult female as yet. Are they simply undetected and get overlooked as female cyaneus, given they show a very similar female phenotype. Or is their phenology similar to cyaneus whereby females remain altogether more loyal to their natal/breeding areas. Unlike the males that tend to migrate further afield during the winter months,  as do the juveniles (including juv females) during their juvenile dispersal.

I personally think the females simply slip through the net rather than not occurring. Some of these juveniles, some of which must be females must occasional return to our shores from wherever these individuals are returning to breed (this is more food for thought for another post given some thoughts Tim Jones and I have discussed over some of adult eastern Siberian "cyaneus" we have studied).

The North Ronaldsay male hudsonius looks to have returned in his finery given what looked like a young adult bird when Mark Warren sent me pictures back in autumn 2015  and interestingly now looks a rather more handsome full adult type bird (below)...WOW!

Where did he summer in 2016? photo courtesy of Simon Davies

So before i get carried away on to another blog post here a few of my thoughts and sorry if i waffle on.


Some thoughts about identification of late 2cy to 3cy+ female Hudsonius

D.I.M Wallace Got the real ball rolling with splitting these two species and goes to show the depth in which artists seem to explore feather tracts.  

“Compared to cyaneus, hudsonius differs in showing an additional fifth, usually strong basal bar on the longest four/five primaries, with it and the other four bars also being narrower than those of cyaneus. The sub-distal line immediately inside the dark terminal band (trailing edge) being distinctly narrower than in cyaneus, with the difference in width and the whole traverse pattern also emphasised by the whiter ground  colour of the Secondaries and more heavily spotted under wing coverts"

The mighty Dick Forsman touched on this subject in his new book Flight Identification of Europe, Raptors of Europe, North Africa and the Middle East and points out that although they are very similar to adult female hen harrier they do have:

"a tendency for more strongly and distinctly marked flanks, axillaries and greater and median underwing coverts and with the longest primaries showing more bands compared to hen harrier, mirroring the differences of juveniles. Distinguished from juveniles by more distinct markings and the more spotted appearance of the underbody and underwing coverts. Upperwings are distinctly banded across the remiges and the greater upperwing-coverts, with broad dark bands on the greyish ground colour more striking compared to the uniformly dark brown appearance of juveniles and average adult Hen Harrier"

I hope i can add a little weight to the exceptional work that was pioneered by the gents above in the hope that as a country of exceptional birders we can celebrate a female hudsonius! I  must stress and further the thoughts of the heroes i look up to, that this is no easy subject and a degree of overlap in salient features could easily lead to a mis-identification of a female cyaneus.


This said, I believe if a polarised bird is observed well l  i really do believe these birds are identifiable especially with the amazing advances in telephoto lenses we all readily carry with us out in the field.

Whats reassuring is Jerry Ligouri mentions (see link below) that adults in the west are more commonly rufous which suggest birds in the east must therefore have be more polarised parts and not only more identifiable but theoretically be a more likely as a candidate for vagrancy.

My thoughts:

Underpart Feather Topography
(Left-right) Circus cyaneus by Radovan Vaclav & Circus hudsonius by Simon Richards

Adult Female Circus cyaneus
Adult Female Circus hudsonius

1-  4 occasionally 5 bars (rarely a very inconspicuous washed out 6th bar exposed before the Greater Primary Underwing coverts) on longest primaries (p8/p7).Barring usually thicker and more course

2- Tend to show subtly paler outer webbing to ventral sides of outermost primaries especially P10. (Best understood by thinking of the Pale bands of flight feathers continuing onto the outer web of feather rather than stopping at shaft)

3Broad and diffusely marked underwing primary coverts with less definition and less neatly trimmed pale proximal fringe, combining to give the bird what appears to be a thicker and more diffuse comma. Large and wide thumb prints as feather centres to the primary coverts.

4- Underwing  primary median coverts normally show a stem attached to diffuse droplets or diamonds and never seem to be as isolated or heart shaped as hudsonius.

5-  Penultimate secondary band (adjacent to trailing edge) running through under arm (although variable) is very course and mirrors the rest of the basal bands running through secondaries. Some are that thick (especially in inner arm) that they seem to merge into one another like bleeding ink. Creating a rather dirty area unlike the contrasting clear inner arm of hudsonius.

5-A more consistent trailing edge to the entire wing showing less distinction between pale primary window and Secondaries

6- Although they show spotted axillaries and lesser underwing coverts they are never as vividly spotted. They have more broad and more diffuse feather centres to the marginal coverts, which are not as spotted and are more streaked. Also shows less definition to the proximal fringe of the greater underwing coverts with less of an extensive pale edge. (see diagram below)

7- Vent markings can at times mirror hudsonius but are never as isolated from the breast as hudsonius. Cyaneus more commnoly lacks the contrasting jump from breast to vent due to more extensive and hazy feather centres of the  breast and belly.Not only is the body more greatly streaked but these streaks merge into on another making the bird look less sharp or defined. Lacks the rounder oval spot markings found in hudsonius. 'think dot to dot in hudsonius'

8/9-Certainly hooded birds do occur but the hood is not commonly as clear cut as hudsonius and the hood seems to blend away in to the underbelly more diffusely given the more heavily marked feather centres of the breast feathers that are usually more striated than spotted.

1- More banding in longest primaries namely P8/P7 (as in juveniles) but average 5+ bars thin linear bars between primary coverts and primary tip

2-  Appear to show subtly darker outer webbing to ventral side of outermost primaries. As if the pale bands crossing the feather stop at shaft (supportive feature don’t rely like your life depends on it from photos as light artifact in pics varies, subject to light) In the hand this was noticable 

3Each of the Underwing Primary coverts have isolated dark centres (small & sharp thumb prints) with cleaner proximal fringing usually thinner and more neatly bordered. This creates a thinner, cleaner and sharper looking comma and that can even looking perforated at times

4- Underwing primary median coverts akin to juvenile goshawk greater underwing coverts: distinctive equally spaced isolated hearts.

5-  A thin penultimate secondary band running through entire underarm (as in juvenile hudsonius) “marmite sandwich”. Appearance of broader terminal bar in Secondaries arisen from weaker sub -erminal bar in Secondaries The inner barring of the Secondaries that transcends the length of the wing and is thinner and more refined, giving a cleaner more open secondary area.

5-  Terminal band of inner primaries pale diffuse exacerbated by broad dark trailing edge to Secondaries, swollen terminal band as in males, especially true in old adults. (above pic not the best to illustrate this point)

6- Axilliaries and lesser underwing coverts are much more contrastingly patterned due to larger spotting. Recalling a female Monty’s underwing in this area. The marginal coverts on the leading edge of arm are very spotted with spots joined by a very weak central feather streak/stem. Proximal tips of greater underwing coverts (in arm) appear to more commonly show a more proximal tip that runs further around the feather and meets a larger side spot that pinches the feather centres making them all together more contrasting.

7Vent is interspersed with lovely  hearts (akin the breast of a 1st winter male sparrowhawk and some of the young indo-chinese accipiters) merging into little oval spots on the belly & flanks leading into a more densely marked (at times extensive) breast and head giving them a hooded impression which a lot more subtle than juv hudsonius but noticable when compared to adult cyaneus. (be aware of variation in populations in east and west). The fact the body is so weakly marked exacerbates the vent markings making them even more striking. Caution vents are VARIABLE!

8/9-Striking Hooded appearance. More commonly Demarcated division between hood and breast due rapid change in feather centres. Very thick streaking or spots in breast and more extensive centres in throat and orbital area.  Dense gorget of spots in area of head/breast. In some birds (olderbirds?) this spotting can be entirely restricted to the head and breast creating a more marked hood.

Upperpart Feather Topography

Adult Female Circus cyaneus

Adult Female Circus hudsonius

 10-3-4 bars in tail between terminal bar and rump. Usually thicker and more diffuse in their pattern and not as ordered in defined in arrangement. Banding Less contrasting against duller brownish grey feather, rarely the intense blue grey of hudsonius and the orange ghosting combo.

11- Although mature females do show grey casting to dorsal side of remiges they are uncommonly as powdery grey. Barring through these greyish feather tracts i.e alula , primary coverts and Secondaries is diffuse and  generally less distinct than hudsonius

 10- Dorsal side of Central Tail feathers (T1) appear much more gun metal blue on average not blue/brown, with more distinct-demarcated transverse banding, at times with subtle orange ghosting.

On average always 4 bars between terminal bar and rump and shows a sneaky 5th bar just protruding from white upper tail coverts  

 11- Grey alula, primary coverts and Secondaries become very pastel grey and can even get as grey/blue as the tail. They seem powdery grey and somehow look dusty like a moths wing if this make any sense. Barring through these feathers tracts seems very demarcated and contrasting most likely as a result of less diffuse edges to the feather barring.

All of the awesome female Northern Harrier pics seen in this post were kindly sent to me by Simon Richards from an album of his called Northern Harriers . Please check out this Flickr link if your as obsessed with harriers as me.

I chose these pictures to help illustrate the above points. Yes it is a textbook individual and that is entirely the point of this post.

I think these are the only feasible birds we could consider claiming in the UK and we need a polarised bird to make it happen and tick off the features one by one.

You can find pictures of Northern Harriers that look like cyaneus but you cant find any pictures of cyaneus that look quite like a bird like this!

(The bird I have used to illustrate my ideas looks to be a young adult oppose to a really mature bird given her iris colour looks amber coloured rather than strikingly hot metal yellow irides seen in old birds. There appears to be a retained inner median underwing covert that looks like a 1st generation feather. The bird looks to have a retained innermost secondaries that looks to be 2nd generation+ indicating to me she is at least 3cy years old )

3cy+ Female Northern Harrier by Simon Richards, Canada 
Nicely illustrating the Primary coverts with neat and relatively isolated dark centres (small & sharp thumb prints) with cleaner less diffuse proximal fringing, that is usually more demarcated and noticeably bordered leading to thinner, cleaner and sharp looking comma that can even look perforated at times. Also note how the median primary coverts  that resemble juvenile Goshawk (Accipiter gentilis) greater underwing coverts.

Illustrations of individual underwing primary coverts from 8 different adult female hudsonius (pc's corresponding to Primary 9 & Primary 8 (descendantly)) showing how demarcated and clean the feather centres are. Sometimes the proximal fringe travels around the feather and makes the feather centre look even more isolated. Birds that have primary coverts of  the last three birds (7,8 & 9) tend to show a thin comma at the base of the hand and you can see why times can look almost perforated.

Illustrations of indivudal underwing primary coverts from 8 different adult female cyaneus (underwing pc's corresponding to Primary 9 & Primary 8 (descendantly)) showing how broad & ill-defined  the feather centres are. The border between the proximal fringe and feather centre is more diffuse and the feather fringe is more restricted when compared to hudsomius. These larger and more diffusely patterned primary underwing coverts give cyaneus a larger, thicker and more diffuse comma. 

Above is an illustration of the greater underwing coverts of both cyaneus and hudsonius. Showing why hudsonius shows a more spotted underwing. Note how the greater underwing coverts are almost adult female Circus pygargus esque in the picture below.

Note the difference in ground colouration of hudsonius central tail feathers. Within the birds i studied hudsonius was always noticeably bluer. The tail bands looked all together more contrasting, neater, slightly darker and were more regular. 3-4 bands in cyanues and 4-5  in hudsonius with the 5th (basal band) just emerging from the white Upper tail coverts.  Photo © Natural History Museum, Tring (courtesy of NHM , Tring Staff).



First of all assessing age in both species and what warrants adult female identification is the first piece to the puzzle. I have seen numerous pictures throughout my years labelled as an adult female which a lot of the time depict 1st winter males.

Ageing is crucial when assessing any identification of any ring-tail harrier, and any raptors for that matter and 1st and foremost in order to ascertain the species. Numerous plumage traits can be confusing when assessing age on both an inter and intra-specific level but their are a few rules of thumb that can be applieds

The following excellent photos of two 1st winter birds were taken by Yorkshires very own Richard Willison and depict two very popular individuals that wintered along the Humber and clearly show the relevant feather tracts that need to be explored. Please don't get me wrong, this species is usually hard to photograph and nine times out of ten they have flashed past you or are too distant to photograph. However if a bird offers you good views take the time to break them down in to parts.

The more I look at raptors the less i look at the whole bird and tend to departmentalize each feather tract which really helps me to further my understanding of this group of birds. 

1st Winter Female Circus cyaneus by Richard Willison, Yorkshire, England

1st Winter Female Circus cyaneus by Richard Willison, Yorkshire, England

This  bird above was what initially got this blog post in full swing and it takes  a-typical birds to make you question the norm and I'm very thankful to a friend for bringing it to my attention.

Closer inspection reveals that this is a 1st winter female cyanues but why is she?

  • Secondary greater underwing coverts are a good starting point , they are concolourous. uniform and unmarked forming a band that runs the arm. 
  • Dark irides that is almost indicative of young female until the hormones kick in
  • Rufous-orange underlying wash to entire plumage as oppose to the cold/paler basal tones usually seen in more mature birds. 
  • Underwing coverts and marginal coverts (especially in the arm) on the leading edge of underwing usually covered in more longitudinal streaking than in adults akin to the juv buteos
  • A diffuse sooting to the secondaries that looks gives the arm a dusky wash, especially prominent in juvenile females  
  • The distal tips of the remiges are a washed out brown colour and more diffusely bordered 
  • I personally find juvs show a greener cere that differs in colour to talons (although bare parts variable- depending light, on health of bird, diet and time of year) 
  • Plumage altogether more diffuse, less clean cut and defined as adults
  • Collar less prominent and clearly defined and white in orbital zone striking and stands out due to more uniform head feathering
  • The lateral banding in underside of tail less defined (more diffuse)

1st winter male Circus cyaneus by Richard Willison, Yorkshire, England

The bird the 1st winter female associated with during the winter was the above bird 
which is a 1st winter male cyaneus but why?

  • Secondary greater underwing coverts again uniform, russet and con colourous lacking the prominant spots of adults and colder buff tips of adults, juvs usually show a more buff-rusty/orange proximal fringe to the guwc's
  • Struturally more compact and more accipiter like than female birds owing to smaller size and structure
  • Small little compact face, less beaky
  • Barring is more cleanly cut throughout remiges and trailing edge to secondaries is thinner
  • Secondaries tend to show a reduced dusky wash to the secondary area
  • Tends to show more barring in p10 than juvenile females 
  • Basal area of hand more open, owing to weaker and more linear barring (at times even absence)
  • Pale irides
  • From experince usually thinner body streaking and they look much more streaked as the streaks seem to align along the flanks more neatly
  • Colder undertones to body compared to 1st winter female yet more rufous buff than adult female and feather barring and feather tips usually browner and more diffuse than in adult females.
Caution must be taken with 1st winters males because they seems to be the most variable sex and age combination and variation is diverse. 

I have only just touched on ageing criteria above but if you wish to make more notes please visit

Which is ace at getting the message across about ageing as its mainly imaged based which for me works well.


Applying these ideas

When making raptor notes or sketching I spend a lot of time starring at photos of raptors, so it soon becomes clear if something looks a little anomalous.

Whilst reading, what i think was the 2015 Portland Bird Obs report i noticed an interesting female harrier which i thought may be worth a closer look. I noticed it has been photographed by Brett Spencer, so i looked to see if it he had a blog. Not only did have a blog but he also taken a sequence of very good photos of the same bird and had posted them up.

The bird had my adrenaline racing momentairly until i broke the bird down tract by tract. Although the bird showed some pro hudsonius features it also showed some plumage traits well within variaiton for cyaneus which is not want you want to make a claim for female hudsonius.

You really need to tick all the boxes in my honest opinion to substantiate a claim given the crossover of plumage details between the species.

The bird above is a very interesting individual. Again i think this is a relatively recent adult female, given the subtle pale Iris colour and some rather ambiguous outer underwing coverts that are suggestive of immaturity

Yes the bird shows a good penultimate secondary band  'marmite sandwhich' and 5 bars between the proximal tip of longest primaries and underwing primary coverts (although the basal bar is rather faint) plus the very contrasting spotted appearance shown in hudsonius, yet something doesn't sit quite right.

If you look closely at the feathering on the body then the feather centres from the breast towards the vent are more streaked rather than the classic oval like spots. Yes they begin to drip off the breast towards the talons but the spots seem stretched rather than isolated or circular not the 'dot to dot' look of hudsonius.

The vent markings are diamond shaped and again stemmed, rather than isolated neat little rounded hearts.

The underwing primary covert tips appear somewhat intermediate between the two species. They are neatly shaped but have rather broad feather centres and are lacking the sharp look attributed to the clear cut and extensive proximal fringing of these feathers, shown in hudsonius giving the comma an altogether more hazy look.

The underwing median coverts are not like juvenile Goshawk greater underwing primary coverts and this bird seems to show marginal and lesser wing coverts similar to those shown by juvenile cyaneus with extensive longitudinal streaking.

Again this reinforces my thoughts and nicely concludes the blog post, demonstrating the need to closely analyse female harriers in order to find that one bird that shows the entire suite of features fitting the hudsonius featured above. You need a bird that lies right at the other end of the spectrum to the middle-of-the-road birds that remain relatively unidentifiable such as this bird above.

I will just have to keep on looking

I wish to thank all of the staff at Tring, Natural History Museum, especially Mark Adams for the assistance during my visit to the skin collections.

Thanks for taking the time to read this and sorry for my 1st post being a bit of hard read.

Eyes to the skies!