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Ibis British Ornithologists Union Blackwell Publ - PPT Presentation

The winter fattening model a test at low latitude using the Clamorous Reed Warbler OBY MEROM SUHEL QUADER YORAM YOMTOV Kibbutz Nir David Bet Shean Valley Israel Department of Zoology University of Cambridge Downing Street Cambridge CB2 3EJ UK Small ID: 67335

The winter fattening model

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, 680Ð687© 2005 British OrnithologistsÕ Unionthe Clamorous Reed WarblerOBY MEROM, Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK © 2005 British OrnithologistsÕ Union, , 680Ð687Body mass ßuctuations in Clamorous Reed Warblersdemonstrated diurnal fat accumulation, but thatthere was little seasonal variation in body mass(Ward 1964, 1969).lowered ability to withstand cold temperatures.arctic species. This implies that the increased energydemand due to the decrease in ambient temperaturein those at high latitudes. Latitude-associated differ-nces in nocturnal body-mass loss have been observedintra-speciÞcally. For example, Lehikoinen (1987) notedthat Great Tits populations at the same ambient temperature.Apart from seasonal and daily changes in mass,one might also expect longer-term changes. Globalmean surface temperatures have increased by 0.6 since the late 19th century (IPCC 1995), and inIsrael, mean minimum summer temperatures increasedby an average of 0.26 by BergmannÕs rule, which states ÔIn warm bloodedanimals, races from warm regions are smaller thanaces from cold regionsÕ (Mayr 1963). Ashton (2002)for the existence of BergmannÕs rule among birds.BergmannÕs rule was interpreted as an adaptation toambient temperature: the larger body surface arearelative to volume of the smaller races serves as anefÞcient heat dissipater in warm climates, while asmall surface area to volume ratio may help in heatconservation in cold climates. It has recently beenclaimed that global warming has affected body sizein several species of passerines (Yom-Tov 2001) and1998). Although none of thesestudies included a controlled experiment, these trendsinvestigated daily, seasonal, and long-term(32N) small passerine, the Clamorous Reed WarblerIsrael, and breeds across a continuous distributionfrom Egypt and Israel, to Australia, in reed beds andsimilar wetland habitats (Paz 1987). In Israel itbreeds between April and July, and moult takes placefrom the end of breeding until September. We used18 years of ringing data to address the followingtions: wing length) decreased during the study period, asexpected from BergmannÕs rule? (2) Are there dailyseasonal ones? (4) Does the Ôconstant mass modelÕ orthe Ôtrue winter fattening modelÕ (1987) hold? We expected both body mass and fatscore to increase from summer to winter, and dailychanges to be more pronounced than seasonal changes,as predicted from the Ôtrue winter fattening modelÕ.tested these predictions separately on Þrst-yearand adult birds, because different age-classes mayshow different patterns of fattening. Finally, we pre-Reed Warbler would be-smaller than in a similarly-Clamorous Reed Warblers were mist-netted andmeasured by one of us (K.M.) at various localities inthe Bet Shean Valley, northern Israel (32within an area of about 50 kmduring 1986Ð2003.Fieldwork was carried out on 1447 days, during which2262 individual birds were captured. On average,each bird was captured 1.75 times, but most birds1451) were captured only once. For recaptured birds,the median number of captures was 2 (maximum19). To avoid pseudoreplication, we included in ouranalysis only one record (chosen at random) fromeach individual caught more than once. Netting effortas not evenly distributed, resulting in small winteramong Þrst-year and adult birds, respectively) andand adult birds, respectively).aluminium rings, weighed with a ance to an accuracy of 0.1 g, and their wing chordmeasured to a precision of 0.5 mm using a wing rule.isible fat at the tracheal pit was scored on a scale ofPrevious work has shown that for several spe-stored fat (Rogers 1987, Rogers & Rogers 1990), andcies. Age was noted according to the EURING code.(1999) have shown that in this specieswing length increases continuously with age, whileadulthood), and stays constant thereafter. In additionto these differences, Þrst-year birds may differ from K. Merom, S. Quader & Y. Yom-Tov© 2005 British OrnithologistsÕ Union, , 680Ð687der birds in their strategies of body mass adjustment.Hence, for the purpose of this study we dividedthe birds into two age classes: Þrst-year birds (fromßedging to the following 1 March) and adults.Each capture record was categorized according totime of day (morning or evening) and season (summer,autumn, winter or spring). Morning was deÞned asuntil 3 h later, and evening was deÞned as the timefrom 3 h before sunset to sunset. Summer monthswere JuneÐAugust, autumn SeptemberÐNovember,winter DecemberÐFebruary and spring MarchÐMay.The daily increment in mass and fat was calculatedby subtracting mean evening values from mean morn-ing values within each season and age-class. Standardas . We also calculated the hourly nocturnalverage night length (in hours) in the different seasons.verage night length for summer, autumn, winterand spring in Bet Shean Valley is 10.1, 12.5, 13.6 and11.2 h, respectively.time of day, season, and year of capture on bodymass, fat score and wing length. All comparisons ofmade using pair-wise -tests.RESULTSThe body mass of both Þrst-year and adult birds wasrelated signiÞcantly to day period, season and year ofcapture (Table 1). Controlling for season and dayperiod, Þrst-year and adult birds increased in mass atan average rate of 0.05 0.010 ( se) and 0.04 se) g/year, respectively, during the 18 years of thestudy. This increase is equivalent to 0.21%/year andbirds, respectively. When we compared models withand without year of capture, we found that the yeareffect, although highly signiÞcant ( 0.0001 and002, respectively), explained only a small proportionof the variance in body mass among Þrst-year (increase0.0095), and year was not used in further analyses.birds ßuctuated during the year, rising from a mini-mum in spring or summer towards autumn andwinter (Fig. 1). Mean minimum (morning) winterbody mass was 4.6% and 2.0% higher than meanminimum summer mass in Þrst-year and adult birds,respectively, while the corresponding increases foradults, respectively. Among Þrst-year birds, morningfrom that of summer, apparently because ßedglingsdid not complete their growth until the summer.Among adults, evening winter mass did not differfrom those of the autumn and spring. In both agein the autumn. All other comparisons of different 0.04 to Fig. 1).In all seasons, daily body mass was lower in the 0.001). Data onvided in Table 2. For Þrst-year birds the daily incre-ment in winter was signiÞcantly greater than that in-test, = 0.032) and summer (-test, 0.008), but hourly loss showed no signiÞcant differ-ences among seasons. For adult birds there was nogniÞcant difference in either measure among seasons.Fat reservesThe mean fat score was related signiÞcantly to dayperiod and season (Table 3). Most birds (86.9% and86.5% in evening and morning, respectively) had novisible fat (fat score = 0), and no bird was recordedwith fat score of 4. However, the proportion of fatscore = 0 was only 30.3% and 45.2% among Þrst-yearand adult birds in the winter.Controlling for season and day period, the fat scoresof Þrst-year and adult birds increased at an average rate 0.002 ( se) and 0.009 0.003 ( se) unitsper year in Þrst-year and adult birds, respectively, during seseTabResults of multiple regression of the effects of season,time of day and year of capture on body mass.AgeVariabledfMean sq-valueSeason3168.552.5Time of day1764.3237.9Year165.420.3Residuals11973.2Season375.923.1Time of day1434.6132.4Year131.59.6 0.0020Residuals7963.3 © 2005 British OrnithologistsÕ Union, , 680Ð687Body mass ßuctuations in Clamorous Reed Warblersthe 18 years of the study ( 0.004 and 0.0001,respectively). This increase is equivalent to 0.6%/adult birds, respectively. As effect, although highly signiÞcant,small portion of the variance in fat score among Þrst-0.0088), and was not further analyses.at scores in both age categories were generallylower in the morning than in the evening (Fig. 2).Among Þrst-year birds, the mean fat score increasedwinter. Among adults, fat scores were minimal duringsummer and increased through autumn to winter.are provided in Table 2. Fat changes were greater inÞrst-year than adult birds in all seasons except spring.ithin Þrst-year birds, the daily fat increment was 0.05 for all three comparisons), and hourlyloss was greater in winter than in spring ( Seasonal and diurnal ßuctuations in body massse; sample sizes) of Þrst-year and adult ClamorousReed Warblers. The lines are interpolations. Upper and lowerrows are evening and morning sample sizes, respectively. Seasonal and diurnal ßuctuations in fat score (meansse; sample sizes) of Þrst-year and adult Clamorous Reedarblers. The lines are interpolations. Upper and lower rows areening and morning sample sizes, respectively. K. Merom, S. Quader & Y. Yom-Tov© 2005 British OrnithologistsÕ Union, , 680Ð687 0.006). In adults, the summer fatchange was smaller than in spring and autumn, both 0.001 and = 0.033, respectively). Other differences wereat score was related signiÞcantly to body mass(Þrst-year birds: = 181.92, adults = 91.92, 0.0001), but explained a smallproportion of the variation in body mass ( = 0.103, respectively).In both Þrst-year and adult birds, wing length wasurement (Table 4). Controlling for season, the yearlyincrease in wing length was 0.13 0.017 mm ( se) among Þrst-years andadults, respectively. This increase is equivalent toof Þrst-year and adult birds, respectively.Among Þrst-year birds, wing length increased asautumn towards winter, and summer wing length 0.0001), but other pair-wise com-parisons were not signiÞcant. Among adults, winglength was signiÞcantly shorter in summer than that 0.001), apparently due toincreased wear in the breeding season (spring), butother pair-wise comparisons did not differ signiÞc-antly. Among Þrst-year birds wing length increasedfrom spring through summer and autumn to winter.the Clamorous Reed Warbler ßuctuated daily andseasonally, reaching minima in the morning and sum-and maxima in the evening and winter. MorningTabDaily increment and hourly loss of mass and fat in adults and Þrst-year birds in relation to time of year. Standard errors areshown in parentheses.VariableAgeSummerAutumnWinterSpringDaily mass increment (g)Adult1.479 (0.23)1.355 (0.29)1.892 (0.51)1.827 (0.26)First-year1.493 (0.13)2.009 (0.23)3.260 (0.65)1.558 (0.45)Hourly nocturnal mass loss (g/h)Adult0.147 (0.02)0.109 (0.02)0.139 (0.04)0.163 (0.02)First-year0.148 (0.01)0.161 (0.02)0.240 (0.05)0.139 (0.04)Daily fat score increment (fat units)Adult0.002 (0.03)0.233 (0.10)0.282 (0.17)0.335 (0.07)First-year0.133 (0.02)0.328 (0.05)0.775 (0.21)0.052 (0.05)Hourly nocturnal fat loss (units/h)Adult0.0002 (0.002)0.019 (0.01)0.021 (0.01)0.030 (0.01)First-year0.013 (0.002)0.026 (0.004)0.057 (0.01)0.005 (0.004) TabResults of multiple regression of the effects of season,time of day and year of capture on fat score.Age dfMean sq-valueSeason36.145.7Time of day112.593.7Year12.317.2Residuals13570.1Season36.533.4Time of day14.221.4Year11.68.2 0.0042Residuals8800.2 TabResults of multiple regression of the effects of season,time of day and year of capture on wing length.AgeVariable dfMean sq-valueSeason3428.479.0Time of day16.81.2 0.2630Year1536.398.9Residuals11705.4Season387.814.7Time of day110.61.8 0.1832Year1582.797.2Residuals8296 © 2005 British OrnithologistsÕ Union, , 680Ð687Body mass ßuctuations in Clamorous Reed Warblershigh in winter; fat scores increased steadily fromsummer through autumn to winter. This suggeststhat this population goes through Ôtrue winter fatten-Lehikoinen (1987). The seasonal increasein morning body mass was about half of the dailyone, and as a percentage of body mass, the seasonalincrease was similar to those for species studied athigher latitudes (4.6Ð10.8%; Nice 1938, van Balen1967, Lehikoinen 1987, Haftorn 1989, 1992). InIsrael (at about 30N), Shkedy & Safriel (1991) andava seasonal ßuctuations of three passerines, and althoughtheir studies did not test winter fattening, they foundthat body mass was higher in the winter than in summer.ards winter and declined towards summer,season. Although winter fattening is a general phe-nomenon, it is interesting to note that in the Arabianstudied in the Arava Valley in Israel where tempera-(Anava 2000). However, we found no seasonaleither Þrst-year or adult birds.In both juveniles and adults, fat scores increasedfrom summer to winter, probably due to the decreasein ambient temperature. Fat score was relatively low,visible fat, but this proportion was much smallerduring winter evenings. For these birds the energeticalue of the food in their guts, plus fat stored in otherbody compartments, was apparently sufÞcient tocontent of the gastrointestinal system, of fat reserves,ater and uric acid. Various authors have estimatedcontents of 35Ð57% compared to the mass at dawnHelms 1963, Kontogiannis 1967, Lehikoinen 1987).is due to the consumption of invertebrates, its energyenergy needs of a warbler. The energy content of 0.9and 1.63 g (half of the daily mass increment duringwinter for adult and Þrst-year birds, respectively) canbe calculated as follows: invertebrates yield of metabolized energy per g dry matter, and the watercontent of invertebrates is 67%, i.e. the energycontent of fresh invertebrates is 6.8 kJ/g (Anava2000). Thus, the energy of 0.9 g and 1.63 ginvertebrates is 11.1 kJ, respectively,but the daily BMR of a 25 g bird is 41 kJ (Calder1998), or 20.5 kJ for a 12 h night. Hence, at leasthalf of the nocturnal mass loss of the warblers is thatthe day.than that of birds living in warm environments (vanBalen 1967, Gosler 2002). Lehikoinen (1987; Fig. 2)land and the other from Russia; Dolnik 1967, quotedby King 1971) to show that the rate of nocturnalbody mass loss of a 25 g bird at 0 0.111 g/h, respectively. We found that the meannocturnal mass-loss rate during winter (when themean minimum temperature is 7Ð9 C) was 0.240and 0.139 g/h for Þrst-year and adult birds, respec-tively. It seems that while adult Clamorous Reedarblers lost mass at the predicted rate (Lehikoinen1987), Þrst-year birds lost mass at a higher rate thanexpected (but the high winter loss-rate among Þrst-year birds did not differ signiÞcantly from the ratesat other seasons, possibly due to the small number ofbirds caught in winter). If indeed hourly nocturnalin other seasons, this phenomenon needs explana-tion. Such an explanation might be provided by theobservation that insulation and the lower criticaltemperatures of tropical birds are much less effectiveand lower, respectively, than those of arctic ones1950). Israel lies at a lower lati-tude than Europe and has a warmer climate, and theClamorous Reed WarblerÕs distribution is mainlytropical or low latitude, possibly indicating pooradaptation to cold conditions. It is conceivable thattemperature higher, particularly that of Þrst-year birds,than that of its high latitude counterparts.the night mainly on fat rather than on food stored inthe alimentary system (Gosler 2002, Broggi 2003), the Clamorous Reed Warbler seems to dependlargely on the latter source (this study). This food hasa lower energy content than fat, and its energy tomass ratio is low: probably half that of fat. Thusrelying on it has the disadvantage of greater wingloading, perhaps resulting in higher predation risk. K. Merom, S. Quader & Y. Yom-Tov© 2005 British OrnithologistsÕ Union, , 680Ð687Long-term trendsBody mass, wing length and fat score were seen toincrease signiÞcantly over the 18 years of this study.adults, respectively, the total increase in wing lengthas 2.4% and 3.2%, respectively, and the totalincrease in fat score was 9.0% and 7.5%, respectively.These increases are contrary to our predictions ofa decrease in body mass due to climate change, asexpected from BergmannÕs rule. The increases in bodymass, wing length and fat score indicate not only alarger body, but also increased reserves. A possibleexplanation for these increases is character release.The Clamorous Reed Warbler has a larger (by about20% of body mass; Cramp 1992) congener in IsraelÐ the Great Reed Warbler migrant (JulyÐOctober and FebruaryÐMay) and wasa rare breeding summer visitor in the Bet Sheanalley and Hula Valley, north of our study site (Inbar1976, Shirihai 1996). In recent decades it expandedits range in northern and eastern Europe, while insome areas of the Western Palearctic, particularly inthe south, it decreased, and these changes have beenattributed to recent climate change (Cramp 1992).Israel hosts the most southern of all Great Reedarbler populations, and one of the most northernresident populations of the Clamorous Reed Warbler.Zahavi (1957), who studied these species in theHula Swamp in northern Israel, observed that theGreat Reed Warbler bred exclusively in reed beds,while the Clamorous Reed Warbler bred in bothreed and papyrus beds, and suggested that they werecompeting for breeding sites. After the draining ofthe swamp, the papyrus habitat was largely destroyedor replaced by reed beds, and this may have increasedhabitat competition between the two species. TheClamorous Reed Warbler appears to have been themore successful and to have supplanted the GreatReed Warbler, causing the latterÕs almost total dis-appearance as a breeder (Shirihai 1996). The samealley, as no breeding pairs of Great Reed Warblershave been observed there in the last 15 years. It islation, as well as a decrease in the transient popula-tions of the Great Reed Warbler, has enabled theClamorous Reed Warbler to use a greater range ofresources and this might have been reßected in alarger body size.arbler is related to climate change. This speciesoccurs mainly in warm climates, and may beneÞtfrom the higher temperatures at high latitudes thathave resulted from global warming. An increase inbody size in the Great Japanese Wood-Mouse was attributed to improved dietarming (Yom-Tov & Yom-Tov 2004). However, onlyin body size of the Clamorous Reed Warbler.conclude, our results show that the body massand wing length of the Clamorous Reed Warblerpossibly due to character release; body mass and fatscore changed daily and seasonally, and daily changeswere more pronounced than seasonal ones, as pre-thank the Israel Meteorological Service for permissionto use their climatological data. We thank Eli Geffen, MikiKam, Shai Markman, Uzi Paz, the late Amiram Shkolnikmanuscript, Naomi Paz for editing the manuscript, andNick Davies for his hospitality. This work was partiallysupported by the Israel Cohen Chair for EnvironmentalZoology to Y.Y. and by a Marie Curie postdoctoral fellow-ship from the European Community to S.Q.Anava, A., Kam, M., Shkolnik, A. & Degen, A.A.Seasonal Þeld metabolic rate and dietary intake in Arabianbabblers () inhabiting extreme desert.607Ð611.Ashton, K.G.2002. Patterns of within species body size varia-tion in birds: strong evidence for BergmannÕs rule. 505Ð523.Baldwin, S.P. & Kendeigh, S.C.1938. Variations in the mass ofbirds. Auk416Ð467.an Balen, J.H.1967. The signiÞcance of variations in bodymass and wing length in the Great Tit 1Ð59.Ben-Gal, T., Bitan, A., Manes, A., Alpert, P. & Rubin, S.emporal and spatial trends of temperature patterns in Israel.163Ð177.Blem, C.R.1990. Avian energy storage. Ornith59Ð113.Broggi, J., Koivula, K. & Lahti, K.2003. Seasonality in dailybody mass variation in a hoarding boreal passerine. Behav627Ð633.Calder, W.A.Size, Function and Life History. New York:Mineola Publishers.The Birds of the Western Palearcticol. 6. Oxford: Oxford University Press.Gosler, A.G.1996. Environmental and social determinants ofwinter fat storage in the great tit © 2005 British OrnithologistsÕ Union, , 680Ð687Body mass ßuctuations in Clamorous Reed WarblersGosler, A.G.2002. Strategy and constraint in the winter fatten-ing response to temperature in the great tit Haftorn, S.1989. Seasonal and diurnal body mass variation intitmice, based on analyses of individual birds. Haftorn, S.1992. The diurnal body mass cycle in titmice Parusspp. Ornis Scand435Ð443.Helms, C.W.1963. Tentative Þeld estimates of metabolism inuntings. Auk318Ð334.Houston, A.I. & McNamara, J.M. 1993. A theoretical investiga-tion of the fat reserves and mortality levels of small birds inwinter. Ornis Scand205Ð219.Hughes, L.2000. Biological consequences of global warming:is the signal already apparent? EvolInbar, R.The Handbook of the Birds of Israelel-Aviv:Ahiasaf [In Hebrew].Intergovernmental Panel on Climate Change (IPCC).Houghton, J.T. Climate Change 1995: theCambridge: Cambridge UniversityJenni, L. & Jenni-Eiermann, S.1986. Body mass and energyreserves of Bramblings in winter. 271Ð284.endeigh, S.C., Kontogiannis, J.E., Mazor, A. & Roth, R.1969. Environmental regulation of food intake by birds.Physiol941Ð957.King, J.R.1972. Adaptive periodic fat storage by birds. In Voous,Proc. Int. Ornith. Congr.200Ð217.ontogiannis, J.E. 1967. Day and night changes in body massof the White-throated Sparrow, Zonotrichia albicollisAuk390Ð395.Lehikoinen, E.1987. Seasonality of the daily mass cycle inwintering passerines and its consequences. Ornis Scand216Ð226.Mayr, E.opulation, Species and EvolutionCambridge,MA: Harvard University Press.Merom, K., McCleery, R. & Yom-Tov, Y.1999. Age-relatedchanges in wing length and body mass in the Reed WarblerAcrocephalus scirpaceusand Clamorous Reed WarblerA. stentoreus249Ð255.Nice, M.M.1938. The biological signiÞcance of birds weights.az, U.The Birds of IsraelLondon: Christopher Helm.Rogers, C.M.1987. Predation risk and fasting capacity: dowintering birds maintain optimal body mass? Rogers, C.M. & Rogers, C.J.1990. Seasonal variation in dailymass amplitude and minimum body mass: a test of a recentmodel. Ornis Scand105Ð114.Scholander, P.F., Walters, V., Hock, R. & Irving, I.1950. Body225Ð236.Shirihai, H.The Birds of IsraelLondon: Academic Press.Shkedy, Y. & Safriel, N.U.1991. Fat reserves of an opportunist andof a specialist species in the Negev desert. Auk556Ð561.Smith, F.A., Browning, H. & Shepherd, U.L.1998. The inßuenceof climate change on the body mass of woodrats arid region of New Mexico, USA. Ecography140Ð148.Ward, P.1964. Fat reserves of Yellow Wagtail Motacilla ßavawintering in southwestern Nigeria. 370Ð375.Ward, P.1969. Seasonal and diurnal changes in fat contents inan equatorial bird. Physiol. Zool: 8Witter, M.S. & Cuthill, I.C.1993. The ecological costs of avianat storage. : 7om-Tov, Y.2001. Global warming and body mass decline inIsraeli passerine birds. 947Ð952.om-Tov, Y. & Yom-Tov, S.2004. Climatic change and bodysize in two species of Japanese rodents. 263Ð267.Zahavi, A.1957. The breeding birds of the Hula Swamp andlake. 600Ð607.Received 7 May 2004; revision accepted 18 March 2005; Þrst published online: 22 June 2005; DOI: 10.1111/j.1474-919x.2005.00444.x.