Wool causing injuries to legs and feet of Oystercatchers

Transcription

1 Wool cusing injuries to legs nd feet of Oysterctchers By P. J. Dre nd A. J. Mercer Fisheries Experiment Sttion, Conwy, Cernrvonshire (Plte 38) INTRODUCTION Although mny diseses nd deformities of the legs nd bills of wild birds hve been described (e.g. Keymer 1958, Keymer nd Blckmore 1964, Pomeroy 1962), few records of leg nd foot deformities mong wders (Chrdriiformes) pper to hve been published. Wlton (1962) described n Oysterctcher Hemtopus ostrkgus found ded with the inner toe of ech foot missing; the strikingly symmetricl nture of this deformity led Dr. I. F. Keymer, quoted in n ccompnying editoril comment, to suggest tht it ws probbly congenitl. Hrris (1967) recorded the occurrence mong young Oysterctchers of virus disese, vesiculr dermtitis, which cused blistering nd swelling of the toes nd trsi, nd led to some mortlity, bout the time of first flying. Boer (1967) described, with photogrphs, the finding of mssive 'wrts' on the upper trsi of severl Oysterctchers. Post-mortem exmintion of one such specimen reveled tht chronic inflmmtion hd strted t the intertrsl or 'nkle' joint; lthough the initil cuse of these growths could not be determined, sheep's wool ws suspected. During the course of generl study of the Oysterctcher, by the Fisheries Reserch brnch of the Ministry of Agriculture, Fisheries nd Food, it soon becme cler tht not only were trsl* nd foot deformities common, but lso tht most were cused directly by cst sheep's wool. Detiled records were kept of ll such injuries. The purpose of this pper is to drw ttention to the significnce of sheep's wool s cuse of mny injuries, nd some mortlity, in the Oysterctcher. MATERIAL EXAMINED This quntittive survey of injuries is bsed on totl of 7,3 50 Oysterctchers exmined in the hnd by us between Mrch 1962 nd December Some hd been shot by fishery officers nd others trpped by us for ringing, ll between August nd Mrch, from wintering nd pssge flocks in Wles nd on the west cost of Englnd. Ctches for ringing nd colour-mrking were mde t Morecmbe By (Lnc- 257

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3 WOOL INJURING OYSTERCATCHERS shire), the Dee Estury (Cheshire/Flintshire), Conwy By (Cernrvonshire), the Burry Inlet (Glmorgn) nd the Exe Estury (Devon), but ll the shot Oysterctchers were from Morecmbe By. Additionl informtion ws provided by field observtions of deformed Oysterctchers in the bove wintering res, nd on breeding grounds in Wles, northern Britin nd the Froe Islnds. ORIGIN OF INJURIES During utumn nd winter Oysterctchers live entirely on the shore, except in few res where flocks feed or roost by dy in costl fields (Dre 1966). Mny Oysterctchers which winter on British shores, however, including those in the loclities from which our mteril ws gthered, breed inlnd in northern countries where sheep re frequently encountered, for exmple in Scotlnd nd the Froe Islnds (Dre in press). Our own experience of some of these northern popultions, nd reports from locl observers, together suggest tht, whilst some wintering Oysterctchers certinly do feed midst sheep, entnglement with wool occurs lmost exclusively on the breeding grounds. In some regions cst wool occurs so profusely in summer tht it presents considerble hzrd to dult Oysterctchers nd their broods on sheep pstures nd moorlnd. In the Froe Islnds, ccording to A. Mortensen {in litt.), mny Oysterctchers cn be seen with wool twisted round their legs, especilly lter in the breeding seson. On Eysturoy two dults which hd become shckled together with long 'ropes' of wool round their wings were cptured nd cut free (H. A. Winther in litt). Similrly, Shetlnd Oysterctchers re very prone to become ensnred in the fine wool shed by sheep. Sometimes both legs my become tied together until the bird cnnot wlk (J. Peterson in litt., Peter Dvis in litt.). R. J. Tulloch {in litt.) hs lso recorded mortlity from this cuse nd comments tht some breeding sesons re worse thn others, perhps s result of wether differences ffecting the quntity nd period of wool shedding. We hve ourselves observed breeding Oysterctchers encumbered by clumps of wool in the estern highlnds nd southern uplnds of Scotlnd. Although wool is rrely found on first-winter Oysterctchers (tble i), higher proportion of youngsters undoubtedly pick up wool before they fly, judging by our own field records nd the comments of R. J. Tulloch, but possibly the worst cses die before they cn leve for winter qurters. In the Netherlnds, too, young Oysterctchers occsionlly become entngled in wool (Boer 1967). The successive stges in the injury process hve been reconstructed from series of specimens exhibiting different degrees of wool entnglement (plte 38). Should few wefts of wool ensnre the foot 259

4 BRITISH BIRDS or trsus (strictly the trso-mettrsus), there is considerble risk tht they will grdully shrink, due to wethering nd the bird's ctivity, until tight noose is formed, which then begins to cut into the skin. On some Oysterctchers, however, the wool my form finely woven nklet which fits loosely nd hrmlessly bout the trsus so tht, from little distnce, it resembles dirty white bnd. As wool noose tightens, blood circultion is restricted nd the ffected prt swells. Lter, the distl portion of the ppendge withers nd ultimtely the tendons nd bones re severed. The mputted structure usully hels so clenly tht little or no indiction of the cuse of injury remins. Occsionlly, wool my be lost t n intermedite stge, leving swollen or incised toe or trsus. TYPES AND FREQUENCY OF INJURIES The vriety nd incidence of limb injuries which cn thus be scribed to sheep's wool re summrised in tble i for ech of the three recognisble ge groups of Oysterctchers. Trsl deformities from other cuses for exmple, shooting or ccidentl brekge re noted seprtely in the tble, but miscellneous lesser ilments, such s bent toes nd elongted or missing clws, re omitted. The symptoms of vesiculr dermtitis or of other diseses hve never been observed either mong dults or mong the 600 chicks hndled by us, nor hve we found trsl growths of the type described by Boer (1967). Injuries re grouped subjectively s either mjor or minor, ccording to whether the individul's survivl chnces seemed likely to be impired. Loss of one or two toes, or even two from one foot nd one from the other, will probbly not influence survivl significntly, but severed or grossly mis-shpen trsus or foot might well do so. Since tble 1 groups wounds only into brod ctegories, nd does not distinguish intermedite stges, further comment on types of injury is required. 'Toes lost' includes those in process of mputtion (either severely incised by wool or hnging by tendons), A foot is considered lost when ll three toes hve been severed t their bses to leve only stump; one such Oysterctcher hd lost further two toes from its other foot. Swollen feet usully result from tight wool nooses round toes. Seven dults with only loose wool round the feet re excluded. Swollen trsi sometimes occur in conjunction with swollen feet. Most stumped trsi hd been mputted bout hlf wy up, but some t just below the intertrsl joint or 'nkle'. This group includes two individuls in which trsus ws swollen nd in the process of being severed by tight wool. A further 15 (ten dults, three first-yer nd two older immtures) with loose wool nklets re omitted from the nlysis. 260

5 WOOL INJURING OYSTERCATCHERS Of the 7,550 birds exmined, 2.8% hd lost toes (clssed s minor injuries) nd 0.5% hd mjor foot or trsl injuries from -wool. Tble 1 lso shows tht those in their first-yer re rrely ffected by wool, wheres mny dults re injured. A puzzling feture of foot injuries is tht tvie inner toe is much more likely to be ffected thn the outer nd middle ones. All seven of the Oysterctchers with three toes missing hd lost their inner ones; nd 48 (88%) of the 5 5 with two toes missing hd lost their inner ones. Mny of the ltter were identicl in ppernce to the specimen illustrted by Wlton (1962). Compred with other wders, the injury rte experienced by the Oysterctcher from ll cuses combined, but especilly from wool, seems to be very high. In Britin four other species Curlew Numenius rqut, Redshnk Tring totnus, Golden Plover Vltmlis prkri nd Lpwing Vmllus vnellus commonly breed or winter in sheep country. Of these, the Lpwing is certinly ffected by wool (Wenner 1912 nd others), though precisely to wht extent is not cler, but informtion on the other three species is negtive. BEHAVIOUR AND SURVIVAL On the wintering grounds we hve wtched eleven Oysterctchers with injuries clssed s severe (six with trsus or foot severed or bdly swollen due to wool, nd five with trsus or foot mimed from other cuses). All ppered to be fending for themselves quite dequtely. In ddition, one Oysterctcher with n mputted trsus ws observed breeding in Scotlnd. In the Netherlnds, on the other hnd, Boer (1967) observed tht both the movements nd blnce of one individul were noticebly hindered by lrge growth round its 'nkle' joint, whilst two others found ded with similr deformities were extremely thin. Informtion on the body weights of incpcitted individuls is limited, but the weights of ten with mjor leg injuries re compred in tble 2 with the men weights of uninjured Oysterctchers collected on the sme dy. The results confirm our generl field impressions, for, lthough ll but one of the injured birds were below the men weight of their respective smples, most were not fr below, whilst the only two which were considerbly below were still not unduly light. If, however, the weights of injured Oysterctchers were typicl of the smpled popultions s whole, one would expect them to fll in pproximtely equl numbers bove nd below the smple mens of uninjured specimens. The observed skewed distribution, in fct, indictes tht injured individuls were significntly lighter thn the popultion s whole (P=o.oo2, pplying the sign test), nd thus presumbly t some disdvntge. It is cler, nevertheless, tht mny Oysterctchers lrgely overcome such disbilities, though to wht 261

6 BRITISH BIRDS Tble 2. Weights of Oysterctchers Hemtopus ostrlegus with severe leg injuries compred with men norml weights Weights of injured individuls re given to the nerest 5 grms. All weights were tken fter the crop nd gizzrd hd been emptied of food, nd were therefore true weights Men weights (nd numbers weighed) of Weight uninjured individuls Dte Age nd sex Deformity (grms) of sme sex Adult (J Left foot grossly (11) deformed Adult 9 Left foot (67) mputted Adult o* Trsus mputted (52) in middle, upper leg swollen nd gngrenous due to nylon twine Adult $ Trsus mputted (36) in middle Adult <J Trsus broken, (52) foot twisted sidewys (old wound) Adult. Trsus mputted (17) in middle Adult o* Trsus severed t (54) top Adult $ Trsus severed (77) Adult $ Trsus severed (20) Adult $ Trsus severed (25) ner top extent this is chieved by modifying their feeding behviour for exmple, by extending the norml feeding times or by chnges of diet is not known. ACKNOWLEDGEMENTS We wish to express our thnks to ll those people who hve helped with trpping nd collecting Oysterctchers, but especilly to our collegue, P. E. Dvidson, to J. C. Gittins nd Dr. E. White of Liverpool University, nd to the Superintendent of the Lncshire 262

7 WOOL INJURING OYSTERC ATCHERS nd Western Se Fisheries Joint Committee nd his Fishery Officers, Cptin E. Croft nd D. G. Hrrison, for kindly supplying us with specimens from Morecmbe By. We re lso grteful to Peter Dvis, A. Mortensen, J. Peterson, R. J. Tulloch nd H. A. Winther for informtion on the incidence of wool on breeding Oysterctchers; to Dr. P. R. Evns nd Dr. C. D. T. Minton for informtion on other wders in winter; to Dr. M. P. Hrris for drwing our ttention to the unpublished mnuscript of M. V. Wenner; nd to B. T. Hepper for sttisticl dvice. SUMMARY AND CONCLUSIONS Exmintion of 7,350 Oysterctchers Hemtopus ostrhgus in costl wintering hunts in western Britin reveled tht 3.3% hd injuries to the legs nd feet cused by sheep's wool. The process of injury by wool, nd the vriety of deformities so cused, re described. Most injuries re minor, involving loss of from one to three toes (in 2.8% of the individuls exmined), but pproximtely 1 in 200 Oysterctchers (0.5%) suffers mjor deformities of foot or trsus. Entnglement with cst wool origintes lmost exclusively on the northern breeding grounds, especilly in Scotlnd nd the Froe Islnds, nd is responsible for some mortlity mong dult Oysterctchers nd their broods. In the winter qurters, however, body weights of Oysterctchers with mjor injuries to one trsus or foot re not fr below those of uninjured individuls, suggesting tht mny successfully djust to these hndicps. REFERENCES BOER, P. (1967): 'Ontstekingen n poten vn scholeksters'. Ntur, 64: DARE, P. J. (1966): 'The breeding nd wintering popultions of the Oysterctcher (Hemtopus ostrhgus Linneus) in the British Isles'. Fishery Invest. Lnd., series II, vol. 25, no. 5, 69 pp. (in press): 'The movements of Oysterctchers (Hemtopus ostrhgus Linneus) visiting or breeding in the British Isles'. Fishery Invest. Lond,, series II, vol. 25, no. 9. HARRIS, M. P. (1967): 'The biology of Oysterctchers Hemtopus ostrhgus on Skokholm Islnd, S. Wles'. Ibis, 109: KEYMER, I. F. (1958): 'A survey nd review of the cuses of mortlity in British birds nd the significnce of wild birds s dissemintors of disese*. Vet. Rec, 70: , nd BLACKMORE, D. K. (1964): 'Diseses of the skin nd soft prts of wild birds'. Brit. Birds, 57: POMEROY, D. E. (1962): 'Birds with bnorml bills'. Brit. Birds, 55: WALTON, F. (1962): 'Oysterctcher with deformed feet'. Brit. Birds, 55: 419, plte 67b. WENNER, M. V. (1912): Untitled MS in Alexnder Librry t Edwrd Grey Institute, Oxford. 263

8 PLATE 38. Feet of Oysterctchers Hemlopns oslrkgiis injured by wool. Above, the two on the left cme from the sme individul; the one in the middle shows swelling of the trsus. Below, the lower specimen illustrtes the mnner in which wool cn form loose bnd round the trsus (pges ) (photos: A. J. Mercer)