Probable Object Play Among Gulls in Staffordshire Juvenile Common

Notes Juvenile Common Coot feeding second-brood young Graham Graham Catley 42. When Common Coots Fulica atra have a second brood, the first-brood young are either driven away or remain close to the nest-site and are occasionally, as this photograph shows (at Barton Pits, Lincolnshire, in July 2010), seen feeding the chicks of the later brood (BWP). Probable object play among gulls in Staffordshire One of the most likely forms of avian play Water weed was the most regularly involves a bird carrying an object into the air manipulated object but twigs and leaves were to repeatedly drop and catch it in flight. With also used. In none of the observations of some variations, drop-catch behaviour has drop-catch or drop-retrieval was any object been observed in raptors, gulls, corvids and eaten. When dropping weed, the gulls typi- possibly hirundines (Ficken 1977). cally manipulated the weed into a roughly Observations of drop-catch behaviour in spherical shape before taking off from the Black-headed Chroicocephalus ridibundus, water. Chases of birds carrying weed would Lesser Black-backed Larus fuscus and Herring usually ensue, involving up to five gulls, both Gulls L. argentatus were made from the conspecific and non-conspecific. Gulls of all public hide at Aqualate Mere, Staffordshire, three species engaged in chases of gulls of the on three out of a total of 18 visits between 1st other species. The pursuers were never October 2009 and 28th February 2010. The observed to make contact with the leading behaviour was always performed over open birds in any way, and neither did they water and the gulls used only their bills to attempt to catch the weed in flight once it manipulate, carry and catch the objects was dropped. Drop-catches tended to occur involved. when the chasing birds had ‘given up’ the There were usually many more gulls pursuit. present when fishing boats were absent from Chases with no drops were more regular the mere. On the 15 dates when boats were than chases with drops. Often birds would present, aerial chases involving Black-headed simply return to the water surface, to repeat- Gulls carrying objects were observed only edly release, submerge and retrieve the weed. occasionally and no drop-catching/retrieving Dropping objects in flight with subsequent behaviours were recorded in any species. retrieval from the water surface (drop- 94 © British Birds 104 • February 2011 • 94–99 Notes retrieving) was quite regular, while drop- was no physical contact between the gulls catches were the least common behaviour. and also, when involved in drop-catches, However, Black-headed Gulls of all ages and drops or chases, the objects were never subse- immature Lesser Black-backed and Herring quently eaten. Gulls all drop-caught objects (in one Gamble & Cristol (2002) also found that instance, by an immature Herring Gull on immature birds were most often involved, 22nd January 2010, six times in succession). although they found that drop-catching was On each of the three visits where this behav- a solitary activity that declined in the close iour was recorded, it lasted from roughly presence of conspecifics. At Aqualate, drop- 11.00 to 13.00 hrs and drop-catches were catching and associated chasing behaviour numerous. appears to be a social activity. In particular, In all three species the behaviour appeared the interspecific chasing prior to drop- to fulfil Burghardt’s (2005) five criteria of catches may not have been documented play, namely that it had a limited immediate before. function, was voluntary, differed from ‘serious’ behaviour, was repeated and was References performed in a relaxed field. The fact that the Burghardt, G. M. 2005. The Genesis of Animal Play. behaviour was performed only in the absence Cambridge, Mass. of human disturbance (boats) may suggest Ficken, M. 1977. Avian Play. The Auk 94: 573–582. Gamble, J. R., & Cristol, D. A. 2002. Drop-catch that a relaxed field is important. The behav- behaviour is play in Herring Gulls Larus argentatus. iour differed from kleptoparasitism as there Anim. Behav. 63: 339–345. Stephen Hewitt, 13 Bowen’s Manor, Lurgan, Co. Armagh BT66 7RT Marks on the iris of the Black Woodpecker In recent years I have spent much time variable shape, occasionally giving the observing Black Woodpeckers Dryocopus impression of a ‘double pupil’. It soon martius at nesting and roosting cavities, became clear that such marks were the norm mainly in Hungary but also elsewhere in for both males and females, typically (as far central and eastern Europe. With a telescope, as I could determine) found in both eyes. I have been able to obtain close and pro- Black Woodpecker nestlings have bluish- longed views of individual birds and was sur- black eyes, in which it is difficult to distin- prised to note that many birds seemed not to guish the pupil from the iris, but it is clear have a circular pupil, but rather a pear- that many older, fully feathered chicks shaped or teardrop-shaped one. Intrigued, already show a dark mark on the iris as it I began to focus systematically upon the eyes becomes paler. of all the Black Woodpeckers I encountered, I examined over 100 close-up photo- noting the colour and shape of the pupil and graphs of the eyes of adult male and female iris. Black Woodpeckers, taken across the Gradually, it became apparent that the Palearctic range of the species, and including irregular shape of the pupil was actually both races: nominate martius (most of range) created by dark marks on the iris, i.e. the and khamensis (southwest China, Tibet). pupil was circular but the dark marks created Approximately 85% of Black Woodpeckers in an impression that it was pear-shaped. these photographs had some form of dark Indeed, BWP (1985) mentions that adult mark on the iris while 15% did not. There Black Woodpeckers have a ‘black spot in was no evidence that such marks were con- front of the pupil’. Most of the birds I fined to a particular population, region, race observed, however, showed rather more than or gender, and there was no clear evidence of a simple spot on the iris. In many cases there an irregularly shaped pupil. was a dark, elongated slit between the edge of Marks on the iris may not be unique to the pupil and the bill base, sometimes Black Woodpeckers, but seem to occur much stretching across the iris and being of rather more frequently in this species than in most British Birds 104 • February 2011 • 94–99 95 Notes showed such marks. What, if any, is the function of these dark marks on the iris? In some animals, irregular pupil shapes modulate the amount of light reaching different parts of the retina that may have different sensitivi- ties or resolution – so the shape is adaptive for vision. Iris pigmentation patterns have little effect on vision but perhaps act as signals, perhaps in terms of fitness or mate recognition. In some species iris pattern indicates gender (for example, American Lee Mott Black Oystercatchers Haematopus bach- mani, in which the iris of adult females is patterned but that of adult males is not; Guzzetti et al. 2008), but this is clearly not the case with Black Woodpeckers, nor is it likely that the marks are colobomas or other optical defects. Rather, the high pro- portion of birds showing dark iris marks (Picidpics) could suggest that it confers an advantage of some sort and has been selected for. Indeed, the presence of two forms of iris shape within the same population may be an example of a polymorphism which is heritable; and it would be interesting to Julio Pérez Cañestro know whether this is the case. There is 43 & 44. Adult male (43, Hungary, January 2010) clearly more to find out about the function and female (44, Barcelona, Spain, March 2007) Black of these distinctive dark iris marks in the Woodpeckers Dryocopus martius. Both photographs clearly show a dark spot on the pale iris, adjacent Black Woodpecker. to the pupil and extending from the pupil towards the base of the bill. Reference Guzzetti, B. M., Talbot, S. L., Tessler, D. F., Gill, V. A., & other picids; they are much less common Murphy, E. C. 2008. Secrets in the eyes of Black in the other (six) Dryocopus species. For Oystercatchers: a new sexing technique. J. Field Orn. 79: 215–223. example, I examined many photographs of both White-bellied D. javensis and Pileated Acknowledgments Woodpeckers D. pileatus and found that I thank Martin Collinson and Richard Chandler for very few White-bellied and no Pileated commenting extensively on a first draft of this note. Gerard Gorman, Budapest 1511, Pf: 4, Hungary; e-mail [email protected] Female song in the Ring Ouzel Although bird song is generally considered to species was it stipulated that females do not be a largely male phenomenon, studies have sing (Garamszegi et al. 2007). Among British revealed a considerable number of species in passerines, female song is seemingly frequent which the females sing, and that song in both in Robins Erithacus rubecula and Dippers sexes may be the ancestral condition (Riebel Cinclus cinclus. et al. 2005). Indeed, a search of the vocalisa- The Ring Ouzel Turdus torquatus is one of tions texts in BWP revealed that, of 233 the 124 species for which there is no mention passerine species covered, female song was of female song in BWP. (In terms of a com- recorded in 101 species and in just eight parison with the Ring Ouzel’s closest rela- 96 British Birds 104 • February 2011 • 94–99 Notes tives, BWP shows that 8 song by female Black- birds T.

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