Northern Harrier
Circus hudsonius (Linnaeus, 1766)
Photo © By Melissa McMasters from Memphis, TN, United States - Northern harrier, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=81966052
STATUS
North America and Middle America. Monotypic.
OVERVIEW
This sub-species was split from Hen Harrier to become a full species (BOURC (2016) Ibis 158: 202).
NOT PROVEN
0). 1957 Norfolk Cley-next-the-Sea and Salthouse area, immature, October to April 1958.
(D. I. M. Wallace, British Birds 64: 537-542; D. I. M. Wallace, British Birds 65: 358-359; P. J. Grant, British Birds 76: 373-376).
[J. P. Martin, British Birds 101: 394-407].
History D. I. M. Wallace (1971) in British Birds, Vol. LXIV. pp. 537-542, says: 'This is the long-delayed story of an immature ring-tailed harrier Circus sp that wintered in the area of Cley and Salthouse, Norfolk, from October 1957 to April 1958. Plans for the co-authorship of an earlier paper foundered and with the passage of time the task was relegated to a low priority by several of the observers concerned. A chance meeting in May 1968 between two protagonists of a definite identification for this troublesome raptor revived interest and this paper is the outcome. It seeks to show that the harrier was an immature of the American race of the Hen Harrier Circus cyaneus hudsonius, called in America the Marsh Hawk.
Circumstances of the record: The Cley harrier was first seen by R. A. Richardson on 26th October 1957. His initial impression was of "a big powerful ring-tail with beautiful cinnamon-chestnut underparts...obviously too large and powerful for a juvenile Montagu's [C. pygargus]". News of the bird and its unusual combination of characters quickly spread and observers flocked to Cley for the next five weeks. At this early stage most observers formed the opinion that it was an immature Pallid Harrier C. macrourus, but some regarded its bulk as incompatible with that species. On 9th November A. E. Vine suggested to me in conversation that it was a young Marsh Hawk. This possibility was discussed at a meeting of the Cambridge Bird Club on the 15th: on the following day P. A. D. Hollom, I. J. Ferguson-Lees and other experienced observers assembled at Cley to test it. Although conditions for observation were not good, A.E.V.'s theory seemed more feasible than any other. By 4th December it had gained the tentative support of P. J. Hayman and had almost completely supplanted the earlier school in general parlance. There were questionable points, however, and the argument, as well as the bird itself, continued to receive attention throughout December. Thereafter general enthusiasm waned, though R.A.R. continued to watch the harrier throughout the winter. It was last seen on 13th April 1958.
During its stay the bird inhabited the entire coastal area between Cley and Salthouse, at first hunting over the reed-beds and marshes, but later spending more time over the fields and heaths inland. In general it was a most spirited raptor, attracting mobbing by Carrion Crows Corvus corone (which it dealt with in no uncertain manner), a Merlin Falco columbarius and a Sparrowhawk Accipiter nisus. The only prey noted was a freshly killed full-grown Moorhen Gallinula chloropus.
Description: Between October 1957 and February 1960 I collected from various sources, but particularly through the offices of I. J. Ferguson-Lees, thousands of words describing, and several drawings illustrating, the harrier. These, together with my own notes and sketches, provided a very full record. The most detailed comments, with dates of field observations, came from H. P. Medhurst (29th October), M. J. Carter and P. R. Colston (2nd November), R.A.R. (entire period) and myself (16th November and 15th December), and a careful summary of these descriptions follows (I have found it shorter and less ambiguous to use scientific names throughout, rather than the vernacular, referring to the Hen Harrier as cyaneus and to the American Marsh Hawk as hudsonius). Plate 88 is based on my final drawings, controlled by all other available information.
Size and general character: At all ranges, the impression was of a "large ring-tail". All notes included words such as "powerful" or "superior-looking". Mental comparisons with both cyaneus and pygargus were made, and it was agreed that the bird was obviously too large and powerful for juvenile pygargus and that its build was like that of cyaneus. Four of the five observers named above (all but M.J.C.) thought it at least as big as cyaneus and both H.P.M. and I noted that its silhouette also recalled Marsh Harrier Circus aeruginosas: Other points mentioned included "ponderous wing-beats", "powerful direct flight" and "more dominant appearance" in comparison with pygargus.
Wing shape and formula: All observers were impressed by the breadth of the wings. Their notes are unamimous in comparing them in shape with those of cyaneus and aeruginosus and not with the narrower remiges of pygargus. R.A.R., P.R.C., M.J.C. and I all made careful observations of the wing-formula. P.R.C.'s first sketches show that the wing-tip was made up of four well-fingered primaries and this was confirmed by R.A.R. My drawings show five, the first short but usually visible and the next four clearly separated and forming the end of the wing. The tip of the sixth could also be detected, but only in exceptional circumstances at close range. M.J.C. noted the wing-formula as "2nd visible primary longest, 3rd next, 1st and 4th next, the 2nd being about half as long again as the 1st", but he did not indicate how many separated feathers he saw.
Tail length and shape: The distance from the tip of the tail to the forward edge of the rump patch was equal to that from the latter to the bill. The tail was rounded: in general it was regarded as not particularly long and rather broad compared with that of pygargus.
Head: Generally "dark rusty brown" (appearing totally dark at long range), but supercilia and cheek patches paler, "off-white" to "buff" (obvious at closer ranges). Facial ruff or hood well developed, giving owl-like appearance at certain angles. Nape flecked white (forming an inverted horseshoe mark from behind). Chin and upper throat also dark, the whole area contrasting strongly with the underparts (cf. adult male Stonechat Saxicola torquata).
Upperparts: Mantle from neck to rump "chocolate brown", slightly darker than head (the tone recalling female or immature aeruginosas) and fairly uniform (though P.R.C. noted in sunlight "a lighter area above the shoulders" and "some feathers elsewhere appeared to have broad buff edges"). Scapulars as mantle but "with lighter margins." Rump patch "clear white" and "very conspicuous" (H.P.M. and P.R.C. described it as "very square-shaped and extending right across base of tail"). Wings "generally uniform with back", but lighter edges to median and greater secondary coverts "fairly conspicuous" (forming panel along midwing visible in flight and when perched), primary bases "paler", "some cross-barring on all flight feathers" at closer ranges. Tail "light brown", but with "central feathers darker" and with at least five bands of "darker brown" (the basal one partly obscured).
Underparts: Generally "rich rufous" or "cinnamon-chestnut" and unmarked, but area immediately below hood paler rufous (sometimes showing as faint collar) with a suggestion of streaking or barring. Undertail coverts "rufous shading to off-white" at base of tail. Wings strikingly patterned, axillaries "rufous with a few small darkish brown streaks," coverts "rufous with some cross-barring" and with "well-defined dark tips" to primary coverts, secondaries "noticeably darker" than primaries (contrast varying with light, most marked when dull) with at least three dark bands, primaries "whitish at base darkening towards tips" and well-marked with "seven dark brown concentric bands" (reminding M.J.C. of Goshawk A. gentilis). Tail "golden-brown" or "orange" with at least five dark bands ("orange glow" strongest in outer feathers), looking strikingly chequered when fully spread. Soft parts: Bill dark, cere bright yellow; irides, legs and feet yellow.
Identification: Five species of harrier inhabit the northern hemisphere. All occur in the Palearctic, but only cyaneus (hudsonius) is also found in the Nearctic. The Cley harrier was patently not aeruginosus, and the Pied Harrier C. melanoleucos of eastern Asia which winters south to Ceylon, the Malay peninsula and Borneo (Vaurie 1965), can be safely excluded on geographical grounds and plumage characters. The choice was obviously between those forms whose immatures have wholly rufous underparts, that is pygargus, macrourus and hudsonius. Although pygargus rarely winters north of tropical Africa and macrourus regularly winters in Europe only in the south-east (Vaurie 1965, Peterson et al. 1966), the colour of the Cley bird's underparts led naturally to the conclusion that it was one or the other of these two species. Since observers were unanimous in rejecting pygargus on size grounds, the initial majority view that it was macrourus was understandable. It began to founder when size considerations were shown to be partly against that species too. Then the discovery that immature hudsonius also possessed rufous underparts provided an alternative solution. The following discussion concentrates, therefore, on the distinctions between immature macrourus and hudsonius, and I am grateful to P. J. Hayman and H. P. Medhurst for help in its preparation.
Size and general character: The majority of observers, three of whom had had previous experience of cyancus, pygargus, aeruginosus and macrourus, and one of hudsonius as well, were certain that the Cley harrier was equal in size to cyaneus. P.R.C., who was able to study both male and female cyanceus on the Isle of Sheppey, Kent, within a week of watching the Cley bird, thought it was at least as large as a male; R.A.R., H.P.M. and myself rated it as large as a female. Skin examination by P.J.H. and H.P.M. in November 1957 confirmed that cyaneus and hudsonius are close in size and wing-length, both exceeding macrourus in the latter dimension by about 10% (and most pygargus by rather more). A few macrourus approach hudsonius in size, but on balance the bulk of the Cley bird was more compatible with the latter. In particular its tail appeared rather short for macrourus, which has a longer tail than hudsonius.
Wing shape and formula: Skin examination confirmed also that macrourus and pygargus share relatively narrow wings. Thus the unanimous impression of broad wings in the Cley bird was incompatible with either of those species, but fitted both cyaneus and hudsonius. P.J.H. prepared accurate flight diagrams of the precise wing-formulae of macrourus and hudsonius: these were compared with the field evidence and again found to favour the latter.
Plumage: Following the same detailed skin examination, P.J.H. commented that juveniles of hudsonius and macrourus looked practically identical at a glance, but that there were many minor differences. Features of juvenile macrourus compared with those of the Cley bird were as follows: colour tone of upperwings and mantle pale earth-brown, even greyish; upper secondary coverts much better marked; white rump usually oblong and more restricted; clouded, poorly marked undersides to primaries; inconspicuous barring on secondaries. Thus all these differences favoured identification as hudsonius. Other features, such as the facial pattern and colour of the outer tail-feathers, fell in areas of overlap between the two species. One character was against hudsonius: both P.J.H. and H.P.M. observed that, while the underparts of immatures of that form were rufous, they were usually paler than in macrourus and were variably (but often markedly) streaked below the head, over the upper breast and along the flanks. Since only P.R.C. and I had seen faint marks on or near those areas, and even these were limited to throat and axillaries, a major stumbling block arose. None of us could explain it away, and M.J.C. felt that a large macrourus remained the most economical theory after all. Two years later, however, P.J.H. and I enlisted the aid of Dr I. C. T. Nisbet, then working in North America. Equipped with all the important details and P.J.H.'s diagram, he spent some time looking at skins of hudsonius for us. After checking as many as 111 in one day, he commented at some length principally to the effect that "everything [seen] on the [Cley] bird was right for hudsonius, especially [the fact] that the breast streakings do not show on the immature in the field - I think never". He added that, to his mind, "the rufous underparts were absolutely diagnostic once you were sure that it was cyaneus subsp.". These comments seemed to clear the matter up, but the fact remained that no-one who had seen the Cley harrier had personal experience of young hudsonius. In 1962 I was able to rectify this while on business in New York. On 7th March I found two first-winter hudsonius hunting over the reed-beds and marshes of Jamaica Bay. Having seen a female or immature cyaneus only three weeks earlier, I was able to confirm the essential similarities in size and character and, importantly, I failed utterly to see streaking on the underparts, even at 30 yards. The sketches that I made of these two hudsonius showed an identical wing-formula and a very similar plumage pattern to those in the drawings that I and others had made of the Cley harrier.
Range, habitat, and plumage of adults: Hudsonius has a wide breeding range in North America, from Alaska and Mackenzie across the continent to Newfoundland and south to the Gulf of Mexico. Like cyaneus it can withstand the rigours of hard weather and snow, commonly wintering as far north as New England and even around the Great Lakes. Its breeding habitat differs from that of cyaneus, the American form having taken advantage of the absence there of pygargus and aeruginosus: thus it nests in meadows, swamps and bushy marshes. Otherwise its breeding biology is apparently similar to that of cyaneus. The distinctions between the adult females of the two subspecies are very slight, hudsonius being usually more rufous on the underparts, crown and nape; it is extremely doubtful whether they would be separable in the field. The adult male hudsonius is easily separated by the rufous cross-barring on its flanks and 'trousers' and the more distinct barring on its tail. (Data from Taverner 1949, Meinertzhagen 1959, Peterson 1961, Hanzak 1967 and skins).
Associated records: Unfortunately the Cley harrier occurred three months before rarity records became subject to assessment and reporting at national level with the setting up of the Rarities Committee, and it is therefore difficult to relate its arrival to those of other Nearctic species. It is worth noting, however, that it was shortly preceded at Cley by the fourth British Short-billed Dowitcher Limnodromus griseus (Brit. Birds, 54: 357) and by up to three Pectoral Sandpipers Calidris melanotos (Norfolk Bird Report 1957: 32). Elsewhere in Britain, September and October 1957 produced an above-average crop of transatlantic vagrants, notably the first Summer Tanager Piranga rubra (Brit. Birds, 56: 49-52).
Summary: The identification of the strange harrier Circus sp. that wintered at Cley and Salthouse, Norfolk, from October 1957 to April 1958, is fully discussed. The colour of its underparts indicated that it was an immature, either a Montagu's Harrier C. pygargus or a Pallid Harrier C. macrourus or the American race of the Hen Harrier C. cyaneus hudsonius, called in America the Marsh Hawk. Its size and build eliminated the first of these three and researches over the four years that followed finally showed that it was, in fact, the last. Brief notes on this subspecies are given.'
D. I. M. Wallace (1972) in British Birds, Vol. LXV. pp. 358-359, in a Letter, says: 'Following the publication of my paper on a young American Marsh Hawk Circus cyaneus hudsonius near Cley, Norfolk, in the winter of 1957/58 (Brit. Birds, 64: 537-542), R. A. Richardson wrote to point out that such a bird could not have had yellow irides since these are marks of adult-hood in harriers. Subsequent correspondence with E. Balfour through R.A.R. confirmed that, in the closely related Hen Harrier C. c. cyaneus, only adult males have bright yellow irides. Thus, since all the details of the Cley bird's plumage indicated that it was in its first winter, the presence of yellow eyes was a total discrepancy. I therefore re-examined the several series of notes and sketches. Only one refers to yellow irides, most make no overt mention of eye colour (while usually stressing the darkness of the head) and my field sketches made on 15 th December 1957 show the eyes as dull, if not dark. My drawings of young hudsonius near New York, U.S.A., on 7th March 1962 also show dark eyes. With memories of the Cley bird now 15 years old, it is impossible completely to explain the discrepancy, but I must now follow R.A.R. in doubting that the bird had yellow irides. I apologise for not spotting the point before publication.'
P. J. Grant (1983) in British Birds, Vol. LXXVI. pp. 373-376, says: 'A "ringtail" harrier at Cley, Norfolk, from October 1957 to April 1958 was identified as a first-year Hen Harrier Circus cyaneus of the Nearctic subspecies hudsonius (previously known as Marsh Hawk in North America, but now called Northern Harrier) because, after lengthy research, it was found to resemble immatures of that subspecies seen in the USA (Brit. Birds, 64: 537-542). As noted by D. I. M. Wallace subsequently, however, the Eurasian subspecies C. c. cyaneus can apparently also occasionally produce first-years with rufous underparts (Brit. Birds, 67: 518). In July 1980, in a further effort to clarify the long-standing confusion, and as part of a review of the Cley record and consideration by the Rarities Committee of two further claims of hudsonius, I requested (1) good photographs of immature hudsonius, (2) suggestions as to field characters other than underparts coloration which might distinguish the two subspecies, and (3) firm evidence that immatures with unstreaked rufous underparts really do occur in the Eurasian population (Brit. Birds, 73: 318). The response was good, but it has not really helped the central problem of distinguishing the two subspecies in immature plumages. The following summary may, however, provide a base-line for some future advance. It is clear that juvenile (the plumage from fledging until the post-juvenile moult) hudsonius probably always has uniform or faintly streaked rufous underparts and underwing-coverts. The tone of colour may vary, individually or through fading, from rich to pale. The post-juvenile moult of head and body feathers (which apparently takes place during the first autumn and winter) seems to be variable in extent: some individuals apparently retain the uniform rufous underparts throughout the first year (either because the post-juvenile moult is partial or because the new first-winter feathers are also rufous), whereas others acquire streaked, adult female-like underparts in their first-winter plumage. The underparts of a typical juvenile cyaneus are streaked, like those of the adult female. Some hudsonius, apparently always unmoulted juveniles, have a uniform or heavily-streaked dark brown neck-band or breast-band, extending from the hindneck onto the sides of the neck and almost joining across the foreneck or upper breast. Viewed in profile, this gives the effect of a complete dark hood, contrasting with the uniform rufous remainder of the underparts. It is uncertain whether all juveniles have this hood effect, or whether it is also a mark of those juvenile cyaneus which have rufous underparts. The hood effect is apparently lost during the post-juvenile moult. The hood effect has been suggested as a further distinction of hudsonius from cyaneus. So, too, have (a) its stronger and more contrasting head markings (but variation - probably connected with age - evident in photographs apparently clouds the value of this feature); (b) pervasion with rufous markings of the whole upperparts and upperwing on hudsonius (but does this also occur in rufous-phase cyaneus?); and (c) the presence of a dark patch on the underside of the inner secondaries (but this is certainly also a feature of some cyaneus)....
I suggest that reasonable doubt now hangs over the real provenance of the Cley harrier, and that a firmer case for its identification as hudsonius needs to be made. The difficulty of obtaining proof, one way or the other, is obvious. If rufous-phase first-year cyaneus is proved to be other than an extreme rarity, the field identification problems will, of course, also embrace all harriers which have rufous underparts in juvenile or first-year plumages (namely Pallid C. macrourus, Montagu's C. pygargus, and Pied Harriers C. melanoleucus), as well as hudsonius. The best proof will come from observations of recently fledged rufous-phase juvenile cyaneus in Europe. It is perhaps surprising that there has so far been only one such case; should this situation persist, it would begin to suggest that the rufous-phase is an extreme rarity, and European claims of hudsonius would then have to be viewed in a different, more favourable light.'
