Ibis British Ornithologists Union Blackwell Publ - PDF document

Ibis       British Ornithologists Union Blackwell Publ
Ibis       British Ornithologists Union Blackwell Publ

Ibis British Ornithologists Union Blackwell Publ - Description

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 Download Pdf


The winter fattening model

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, 680–687© 2005 British Ornithologists’ Unionthe Clamorous Reed WarblerOBY MEROM, Department of Zoology, University of Cambridge, Downing Street, Cambridge CB2 3EJ, UK © 2005 British Ornithologists’ Union, , 680–687Body mass Ŗuctuations 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-speciřcally. 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 Bergmann’s rule, which states ‘In warm bloodedanimals, races from warm regions are smaller thanaces from cold regions’ (Mayr 1963). Ashton (2002)for the existence of Bergmann’s rule among birds.Bergmann’s rule was interpreted as an adaptation toambient temperature: the larger body surface arearelative to volume of the smaller races serves as anefřcient 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 Bergmann’s rule? (2) Are there dailyseasonal ones? (4) Does the ‘constant mass model’ orthe ‘true winter fattening model’ (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 ‘true winter fattening model’.tested these predictions separately on řrst-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 1986–2003.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 řrst-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, řrst-year birds may differ from K. Merom, S. Quader & Y. Yom-Tov© 2005 British Ornithologists’ Union, , 680–687der birds in their strategies of body mass adjustment.Hence, for the purpose of this study we dividedthe birds into two age classes: řrst-year birds (fromŖedging 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 deřned asuntil 3 h later, and evening was deřned as the timefrom 3 h before sunset to sunset. Summer monthswere June–August, autumn September–November,winter December–February and spring March–May.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 řrst-year and adult birds wasrelated signiřcantly to day period, season and year ofcapture (Table 1). Controlling for season and dayperiod, řrst-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 signiřcant ( 0.0001 and002, respectively), explained only a small proportionof the variance in body mass among řrst-year (increase0.0095), and year was not used in further analyses.birds Ŗuctuated 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 řrst-year and adult birds,respectively, while the corresponding increases foradults, respectively. Among řrst-year birds, morningfrom that of summer, apparently because Ŗedglingsdid 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 řrst-year birds the daily incre-ment in winter was signiřcantly greater than that in-test, = 0.032) and summer (-test, 0.008), but hourly loss showed no signiřcant differ-ences among seasons. For adult birds there was nogniřcant difference in either measure among seasons.Fat reservesThe mean fat score was related signiřcantly 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 řrst-yearand adult birds in the winter.Controlling for season and day period, the fat scoresof řrst-year and adult birds increased at an average rate 0.002 ( se) and 0.009 0.003 ( se) unitsper year in řrst-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 Ornithologists’ Union, , 680–687Body mass Ŗuctuations 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 signiřcant,small portion of the variance in fat score among řrst-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 řrst-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 inřrst-year than adult birds in all seasons except spring.ithin řrst-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 Ŗuctuations in body massse; sample sizes) of řrst-year and adult ClamorousReed Warblers. The lines are interpolations. Upper and lowerrows are evening and morning sample sizes, respectively. Seasonal and diurnal Ŗuctuations in fat score (meansse; sample sizes) of řrst-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 Ornithologists’ Union, , 680–687 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 signiřcantly to body mass(řrst-year birds: = 181.92, adults = 91.92, 0.0001), but explained a smallproportion of the variation in body mass ( = 0.103, respectively).In both řrst-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 řrst-years andadults, respectively. This increase is equivalent toof řrst-year and adult birds, respectively.Among řrst-year birds, wing length increased asautumn towards winter, and summer wing length 0.0001), but other pair-wise com-parisons were not signiřcant. Among adults, winglength was signiřcantly shorter in summer than that 0.001), apparently due toincreased wear in the breeding season (spring), butother pair-wise comparisons did not differ signiřc-antly. Among řrst-year birds wing length increasedfrom spring through summer and autumn to winter.the Clamorous Reed Warbler Ŗuctuated 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 řrst-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 Ornithologists’ Union, , 680–687Body mass Ŗuctuations in Clamorous Reed Warblershigh in winter; fat scores increased steadily fromsummer through autumn to winter. This suggeststhat this population goes through ‘true 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 (4.6–10.8%; Nice 1938, van Balen1967, Lehikoinen 1987, Haftorn 1989, 1992). InIsrael (at about 30N), Shkedy & Safriel (1991) andava seasonal Ŗuctuations 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 řrst-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 sufřcient tocontent of the gastrointestinal system, of fat reserves,ater and uric acid. Various authors have estimatedcontents of 35–57% 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 řrst-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 7–9 C) was 0.240and 0.139 g/h for řrst-year and adult birds, respec-tively. It seems that while adult Clamorous Reedarblers lost mass at the predicted rate (Lehikoinen1987), řrst-year birds lost mass at a higher rate thanexpected (but the high winter loss-rate among řrst-year birds did not differ signiřcantly 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 Warbler’s distribution is mainlytropical or low latitude, possibly indicating pooradaptation to cold conditions. It is conceivable thattemperature higher, particularly that of řrst-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 Ornithologists’ Union, , 680–687Long-term trendsBody mass, wing length and fat score were seen toincrease signiřcantly 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 Bergmann’s 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 Israel– the Great Reed Warbler migrant (July–October and February–May) 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 latter’s 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 reŖected in alarger body size.arbler is related to climate change. This speciesoccurs mainly in warm climates, and may beneřtfrom 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 řeld metabolic rate and dietary intake in Arabianbabblers () inhabiting extreme desert.607–611.Ashton, K.G.2002. 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The breeding birds of the Hula Swamp andlake. 600–607.Received 7 May 2004; revision accepted 18 March 2005; řrst published online: 22 June 2005; DOI: 10.1111/j.1474-919x.2005.00444.x.

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