A study of certain Aythya hybrids ERIC GILLHAM, JAMES M. HARRISON and JEFFERY G. HARRISON Summary Six distinct types of drake Aythya hybrids which may be seen in Britain are described both from museum specimens and as seen in the field. These are the progeny of various combinations of four species: Pochard, Tufted Duck, Ferruginous Duck and Scaup. A description is also given of a drake hybrid between two North American species, the Redhead and Ring-necked Duck. Female Aythya hybrids must often remain unrecognised: four specimens are described. The relatively frequent occurrence of hybrids resembling species rarely found in Britain necessitates very careful scrutiny of all records purporting to be of Lesser Scaup, Ring-necked Duck and Ferruginous Duck. Introduction one or other of the parent species is so The problem of hybridisation among the close that they are likely to be overlooked. diving duck of the genus Aythya was We have, however, examined one skin of a brought into prominence in this country female Pochard X Tufted Duck and by the now famous ‘Lesser Scaup’ dispute, watched female Paget’s Pochards in the in which a bird, eventually obtained at field. Sutton Courtenay, Berkshire, was finally i . P o c h a r d A. ferina X T u f t e d D u c k identified as a hybrid, probably between a A. fuligula, o ‘L e s se r S c a u p T y p e ’ . The Pochard Aythya ferina (Linnaeus) x Sutton Courtenay specimen. (See Plates Tufted Duck Aythya fuligula (Linnaeus). 16, 17, 18 in Photographic Section I, The hybrid was described by Perrins opposite page 64.) (1961), in comparison with a Lesser Scaup The description and relevant compari­ Aythya affinis (Eyton), but no attempt was sons have already been published else­ made at that time to compare it with other where (Perrins, 1961). These include the Aythya hybrids, of which there are at least important differences of colour, pattern six types to confuse ornithologists in and measurements between this bird and Britain today. For this reason we have the Lesser Scaup A. affinis, and also a brought together a series of field observa­ description of the bill colour, stressing the tions on these and have linked them with a presence of black at the tip and base, comparative study of all the specimens we pigmentation which is absent in A . marila could assemble. and A . affinis, in which the nail only is These different types may be loosely black. The importance of the wing-bar is defined as a ‘Lesser Scaup type’ (if one stressed as this reflects the intermediate accepts the fact that the Sutton Courtenay character of the individual. Similarly the bird resembles that species to some extent) ; iris is stated to have been intermediate in a ‘Pochard type’; a ‘Tufted Duck type’; a colour. ‘Baer’s Pochard type’; a ‘Scaup type’, and There would be little point in repeating ‘Paget’s Pochard’ or a ‘Ferruginous type’. the detailed description of the plumage of As a result of our studies, we are able to the specimen which appears in the Appen­ confirm the correct diagnosis of the Sutton dix to Perrins’ paper (loc. cit. p.53). In our Courtenay bird, the parentage almost opinion the identification of the specimen certainly and rather surprisingly being is correct, i.e. it is a presumptive hybrid Pochard Ç X Tufted Duck <?. When the between A . ferina $ and A . fuligula <?. cross occurs in the reverse direction, a (See field notes, numbers 18 to 23.) completely different type of hybrid results, We would add the following particulars : as will be seen. We are also able to show Measurements (in mm.) that there is a New World equivalent of Wing: 222 the ‘Lesser Scaup type’ hybrid. Bill: length from feather margin 45 Part One: The museum specimens width at nostrils 21 Table I sets out the data of the sixteen width at widest point 21 specimens we have examined comprising nail 9 x 9 all six types of hybrid, the final column on Tarsus: 38 parentage being of considerable impor­ Middle toe without nail: 59.5 tance, when these findings are linked with Our only comment on the description the field observations. already published is that the black on the It will be noted that only four records tip of the bill appears to be more extensive, refer to females. Their resemblance to 4mm. proximal to the nail and for about AYTHYA HYBRIDS 49 T able I» Mmseuam specim ens o f Aythya hybrids examined in this study» Ref. Observations No. Hybrid and Type Data Reference re parentage I. Pochard x Tufted 3 Mar. i960. Sutton Perrins An identical hybrid of Duck (‘Lesser Scaup Courtenay, Berkshire (1961) known parentage type1) S Oxford University Pochard $ x Tufted Museum B.4171 Duck <J is alive at the Wildfowl Trust and was bred by J. P. Williams 2. Pochard x Tufted 23 Nov. 1962. ¡J * Wild shot Duck (‘Lesser Scaup Sevenoaks, Kent type’) 3. Pochard X Tufted 28 Mar. 1937. <? Lake Bezzel Wild shot Duck (‘Pochard type’) near Ismaning. (i960) Bezzel Coll. Munich Museum No. 37.106 4. Pochard x Tufted 4 Jan. 1939. $ * Wild shot Duck Hickling Broad, Norfolk. Norwich Castle Museum No. 119,939 5. Redhead x Ring- 2 Nov. 1962. Wildfowl * This hybrid was thought necked Duck. (‘New Trust collection. ¿ ad. to be Redhead x Ring­ World representative Bred in captivity necked Duck. We support of Lesser Scaup type’) this and suggest it results from Redhead $ x Ring­ necked Duck <J 6. Pochard x Tufted 30 Mar. 1959. J. M. * Duck (‘Tufted Duck Harrison collection These hybrids were of type’) o Bred in captivity the same brood of known > parentage Pochard S X 7. Pochard x Tufted 2 Mar. 1962. J. M. * Tufted Duck $ and Duck (‘Tufted Duck Harrison collection. were bred by T. Jones type’) ad. Bred in captivity 8. Scaup x Tufted Duck - Dec. i960. B. L. Sage Of known parentage (‘Scaup type’) Sage collection. <? Bred (1963) Scaup <? X Tufted Duck in captivity $ bred by J. O. D’eath 9. Scaup x Tufted Duck 10 June 1940. Voous Wild shot. Same type (‘Scaup type’) Durgedam, Holland. (1955) as 8 and therefore c? Coll. Zoological probably of same Museum, Amsterdam parentage No. 5050 10. Scaup X Tufted Duck 20 Feb. 1947. Voous Wild shot. Same type (‘Scaup type’) Landroost-Ymuiden, (1955) as 8 and 9 and therefore Holland. <J Coll. probably of same Zoological Museum parentage Amsterdam No. 28771 i i. Pochard X Ferruginous 16 April 1909. Zoologist Wild shot. An identical Duck. (‘Ferruginous Hickling, Norfolk. ¿ (1909) hybrid of known Duck type’). ad. Norwich Castle parentage Ferruginous Paget’s Pochard Museum No. 208.949 Duck $ X Pochard <? was bred by J. P. Williams in 1964. 12. Pochard X Ferruginous - Jan. 1897. Soham Riviere Wild shot Duck (‘Ferruginous Toney Mere, Norfolk. (1930) Duck type’) <J ad. Norwich Castle Museum No. 7423 13. Pochard X Ferruginous 3 Nov. 1928. Hickling Riviere Wild shot Duck. (‘Ferruginous Broad, Norfolk. ad. (1930) Duck type’) Norwich Castle Museum No. 179.928 14. Pochard X Ferruginous 8 Dec. 1933. Heigham * Wild shot Duck. (‘Ferruginous Sound, Norfolk. S imm. Duck type’) Norwich Castle Museum No. 66.934 15. Tufted X Ferruginous ‘Zoo.Soc.’ <J by Harrison Bred in London Zoo (‘Baer’s Pochard plumage. British C.J.O. type’) Museum No. 1858 (1963) 16. Tufted X Ferruginous ‘Zoo.Soc.’ $ by Sage (1962) Bred in London Zoo (‘Baer’s Pochard plumage. British and C.J.O. type’) Museum No. 71.3.20.3 Harrison *Not previously recorded 5 0 THE WILDFOWL TRUST 12mm. on the edges of the culmen on Courtenay bird grey, tipped brown.) either side (ef. sketch, loc. cit. p.51). Axillaries and under wing-coverts, white; 2. P o c h a r d A. ferina x T u f t e d D u c k fore edge of wing grey. (Sutton Courtenay A. fuligula, $, ist w. ‘L e s se r S c a u p bird paler.) T y p e ’ . (See Plates 19, 20, 21.) Primaries: sepia, outer vanes and tips November 23rd, 1962, Sevenoaks, Kent. dusky. (Sutton Courtenay specimen very Harrison collection. pale brownish-sepia, outer vanes and Crown, head and neck: strong purplish- tips dusky.) red, darker on the chin and on front of Flanks: pale grey, vermiculated white. neck ; a well marked white chin spot. (The Measurements (in mm.) Sutton Courtenay bird is possibly a little Wing: 224 brighter on these parts, but has no chin Bill: spot.) A distinct but stubby crest, which is length from feather margin 44.5 also present in the Sutton Courtenay width at nostrils 18 specimen. Upper breast: purplish-black; width at widest point 20 at lower edge, narrow whitish crescentic nail 9 X 7 markings to feathers. In the Sutton Tarsus: 37 Courtenay bird this area is a little brighter Middle toe without nail : 58 and the white crescentic markings are Specimens 1 and 2 agree very closely; more pronounced. Over shoulder regions the difference appears to be due to advanc­ blackish-slate with minimal purplish-red ing maturity in the Sutton Courtenay reflections, which are slightly stronger specimen. laterally; lower edge wedge-shaped on 3. P o c h a r d A . ferina x T u f t e d D u c k mantle, the apex somewhat brownish, A. fuligula, (J, ad. ‘P o c h a r d T y p e ’. (S e e directed towards the tail. In the Sutton P la tes 22, 23, 24.) Courtenay bird this area is brighter and March 28th, 1937.