Weight Loss in Dunlin <I>Calidris Alpina</I> Over the High Tide Period

INTERNATIONAL WADER STUDY GROUP BULLETIN

Weight lossin Dunlin Calidris alpina over the high tide period.

Steve Dodd

Dodd,S. 2000. Weightloss in Dunlin Calidrisalpina overthe high tide period. WaderStudy GroupBull. 91:28-29

SteveDodd, WintergreenNurseries, Bringsty, Worcester, WR6 5UJ, UK.

INTRODUCTION daywith moderatewind, temperature 7.3C, cloudy,wind Many speciesof waderare forced to roostfor a number SSW force5 for 11.00a.m at RAF Valley.(Data from the of hoursover the hightide periods, when their intertidal NationalMeteorological Office). Themeasurements of feedingareas are covered. During this time, they are the two groupswere comparedusing a standardt-test. likely to be losingweight through evacuation of the gut andexpenditure of energyin orderto maintainbody temperature.The majority of coastalwaders are caught RESULTS andweighed over the high tide period, a timewhen The meanwing lengthsand total head lengths of birdsin wadersare rarely feeding, thus giving some comparabil- the two sampleswere compared,to controlfor size ity. Manypapers have been written about the weightsof differencesbetween the two catches.No significant waders,focusing on eitherseasonal changes (e.g. differenceswere found(table 1). The meanweights of Johnson1982, Johnson1985 ), or changesin responseto bothadults and juveniles were significantly lighter in the severeweather ( Norman& Coffey 1994). Rochester& secondcatch (t -- 3.46 P<0.01ads) and (t-- 2.72 P<0.01 Moss(1992) attemptedto establishthe rate of weight juvs) (Table1). Duringthe fourhours, adults had lostan lossbetween capture and weighing in orderto correct averageof2.3g (S.E.+0.66),equatingto 0.6gper hour or weightsto thoseat capture,but few havetried to relate 1.2% of bodyweight per hour. Juvenileslost a similar the weightof the bird to whenit waslast feeding. Most weight,3.0g (S.E.+0.91). Five birds (all adults)from the of the feedinggrounds for waderson the LavanSands in firstcatch were retrapped in the second.Four lost 2g in North Walesare coveredat leasttwo hoursbefore high weightbetween catches, while the fifth lost3g. These tide, duringspring tides. This paperattempts to quantify were similarto the meanweight loss. weightlosses during the high tide period,and to com- parethem to weightloss of birdsbetween capture and weighing. DISCUSSION The roostingflock wasrelatively undisturbed over the hightide period, occasionally flying for shortperiods. METHODS Therecorded weight loss of 1.2%per hour is probably On 27 January1990, SCAN RingingGroup made a catch lowerthan average in thesesituations bexcause of this of 99 Dunlinin BangorHarbour two hoursbefore high and becauseweather conditions were good. Weight tide. The groupthen made a secondcatch of 60 Dunlin lossesmight be higherin coldor windyweather (Bangor at the samesite two hoursafter high tide, givingan Harbouris relativelysheltered from a SSWwind), or on a opportunityto comparethe weights of the birdsin the sitewith high disturbancelevels, either from humansor two catches. In each case,the birds were extracted predators. quicklyfrom the net andput in hessiankeeping cages, about20 percompartment. The birds were then ringed, The resultsof this studyare similarto thosefound by aged,measured and weighed. Wing lengthwas recorded Rochester& Moss(1983) whorecorded weight losses of to 1mm, totalhead length to 0.1mm, andweight to 1g on 1.23%and 1.18%per hour while Dunlin were held in a 100gspring balance. For the first catch all birdswere captivityfor 3.5 hrsin Feb 1983.Castro, Wunder & measuredand weighed between 45mins and lhr 40mins Knopf(1991)recorded a meanweight loss of 1.5%per aftercapture; for the secondcatch the times were 40 hour,at temperaturesof between18 and29 C. This minsand lhr 20minsrespectively. Since the interval higherrate may be dueto waterloss at highertempera- betweencapture and weighing is very similarfor both tures,since they founda sharpincrease in rate of loss catchesno correctionwas made for weightloss after above30 C. It may be that,in temperateregions, the 28 capture.The two catcheswere made on a mild January weightloss after capture is verysimilar to thatexperi- Bulletin91April2000 INTERNATIONAL WADER STUDY GROUP BULLETIN

Table 1 Measurementsof adultand juvenile Dunlin from two catcheson 27 January1990

Adults Mean weight Mean wing Mean total head (95%confidence limit) (95% confidencelimit) (95% confidencelimit)

Catch1 48.85g(+0.72) 120.02mm(+0.62) ß 56.05mm(+0.57) 76 Catch2 46.55g(+ 1.08) 120.55mm(+0.99) 56.23mm(+0.80) 38 t = 3.46,p<0.01 t = 0.88, ns t = 0.36, ns

Juveniles Mean weight Mean wing Mean total head) (95% confidencelimit) (95% confidencelimit) (95% confidencelimit

Catch1 47.34g(+1.07) 119.43mm(+1.15) 55.55(+0.97) 23 Catch2 44.31(+1.42) 118.68(+1.42) 54.80(+1.37) 16 t = 2.72,p<0.01 t-- 0.78, ns t-- 0.87, ns

encedby birdsroosting during a high tide period. Care Johnson,G. 1982 Seasonalvariation in waderweights in shouldbe takenwhen comparing weights between North Wales. SCANRinging Group Report 1981-2: 45- catches,to ensurethat variationis not largely due to 55 time of capturein relationto feeding/ hightide, or weightloss after capture. Norman,D. & Coffey,P. 1994 The importanceof the Merseyfor wadersin thecold weather of February1991. Ringing& Migration 15.91-97 REFERENCT• Castro,G. Wunder,B. & Knopf,F. 1991 Temperature Rochester,J. & Moss,D. 1982 Weightloss in Dunlin and dependantloss of massby shorebirdsfollowing capture. Tumstoneafter capture. SCAN RingingGroup Report J. Field Ornithology62:314-318 1981-2: 58-59.

Johnson,C. 1985 Patternsof seasonalweight variation in waderson theWash. Ringing& Migration. 6:19-32

Bulktin 91 April 2000