April 2001] ShortCommunications 519 CHASE, M. K., N. NUR, AND G. R. GEUPEL. 1997. Sur- RAPPOLE,J. H., E. S. MORTON, T. E. LOVEJOYIII, AND vival, productivity, and abundancein a Wilson's J. L. RUOS.1983. Nearctic Avian Migrants in the Warblerpopulation. Auk 114:354-366. Neotropics.U.S. Department of the Interior, Fish COOPER,B. A., AND R. J. RITCHIE. 1995. The altitude and Wildlife Service,Washington, D.C. of bird migration in east-centralAlaska: A radar RIMMER,C. C. 1988.Timing of the definitiveprebasic and visual study. Journalof Field Ornithology molt in Yellow Warblers at JamesBay, Ontario. 66:590-608. Condor 90:141-156. DWIGHT,J., JR. 1900. The sequenceof plumagesand SOGGE, M. K., W. M. GILBERT, AND C. VAN RIPER III moults of passerinebirds of New York. Annals 1994. Orange-crownedWarbler (Vermivoracela- of the New York Academyof Sciences13:73-360. ta). In The Birds of North America, no. 101 (A. HUSSEL,D. J. T. 1991a. Fall migrations of Alder and Pooleand E Gill, Eds.).Academy of Natural Sci- Willow flycatchersin southernOntario. Journal ences, Philadelphia, and American Ornitholo- of Field Ornithology 62:260-270. gists' Union, Washington,D.C. HUSSEL,D. J. T. 1991b. Spring migrations of Alder WINKER, K., D. W. WARNER, AND A. R. WEISBROD. and Willow flycatchers in southern Ontario. 1992. Migration of woodlandbirds at fragment- Journalof Field Ornithology62:69-77. JOHNSON,M.D., AND G. R. GEUPEL.1996. The im- ed inland stopoversite. Wilson Bulletin 104:580- 598. portance of productivity to the dynamics of a Swainson'sThrush population.Condor 98:133- WOODREY,M. S., AND C. RAYCHANDLER. 1997. Age- 141. relatedtiming of migration:Geographic and in- KESSEL,B. 1984. Migration of Sandhill Cranes,Grus terspecificpatterns. Wilson Bulletin 109:52-67. canadensis, in east-central Alaska, with routes Received31 January2000, accepted27 November2000. through Alaska and westernCanada. Canadian Associate Editor: E Moore Field-Naturalist 98:279-282. MCINTYRE,C. L., AND R. E. AMBROSE.1999. Raptor migrationin autumn throughthe Upper Tanana River Valley,Alaska. WesternBirds 30:33-38. The Auk 118(2):519-524, 2001 Growth Rate and Energeticsof Arabian Babbler (Turdoidessquamiceps) Nestlings AVNER ANAVA, 1'2MICHAEL KAM, 2 AMIRAM $HKOLNIK, 3 AND A. ALLAN DEGENTM lDepartmentof Life Sciences,Ben-Gurion University of theNegev, Beer-Sheva 84105, Israel; 2DesertAnimal Adaptations and Husbandry, Wyler Department of DrylandAgriculture, JacobBlaustein Institute for DesertResearch, Ben-Gurion University of theNegev, Beer-Sheva 84105, Israel; and 3Departmentof Zoology,George S. WiseFaculty of Life Sciences,Tel Aviv University,Tel-Aviv 69978, Israel ABSTRACT.--ArabianBabblers (Turdoidessquami- lings was 0.450,which was 18%higher than that pre- ceps)are territorial, cooperativebreeding passerines dicted for a passerineof its body mass.Asymptotic that inhabit extreme deserts and live in groups all body mass of fledglings was 46 g, which was only year round. All membersof the group feed nestlings 63% of adult body mass,a low percentagecompared in a singlenest, and all group membersprovision at to other passerines.Energy intake retained as energy similar rates. Nestlings are altricial and fledge at accumulatedin tissuedecreased with age in babbler about 12 to 14 days,which is shortfor a passerineof nestlingsand amountedto 0.29 of the total metabo- its body mass. Becauseparents and helpers feed lizable energyintake over the nestlingperiod. How- nestlings,we hypothesizedthat the growth rate of ever, energy content per gram of body mass in- nestlingsis fast and that they fledge at a body mass creasedwith age and averaged4.48 kJ/g body mass. similar to other passerinefledglings. Using a logistic We concludedthat our hypothesiswas partially con- growth curve, the growth rate constant(k) of nest- firmed. Growth rate of babbler nestlingswas rela- tively fast comparedto other passerinespecies, but fledgling masswas relatively low. Address correspondenceto this author. E-mail: Desertsare characterizedby unpredictablerainfall [email protected] and unpredictable, often sparse, food availability 520 ShortCommunications [Auk, Vol. 118 (Evenari et al. 1982), which can lead to a relatively Doublylabelled water measurements.--Field metabol- slow growth rate of nestlings.The Arabian Babbler ic rate (FMR) and water flux of babbler nestlings (Turdoidessquamiceps) inhabits extreme deserts, were measuredfrom Februaryto August, 1996.Nes- which suggeststhat the growth rate of babblernes- tlings (n = 65) were injectedsubcutaneously with 70 tlings would be slow.However, that doesnot appear Izl/g water whose oxygen was 95% •80 and whose to be the casebecause nestlings fledge at 12 to 14 tritium produced 1.85 MBq/mL. Injections were days (Zahavi 1990), which is short comparedto pas- done between 0900 and 1100 (GMT + 2 h). One hour serinesof similar body mass(Ricklefs 1968). Conse- was allowed for equilibrationof the isotopeswith quently,nestlings have either a fast growth rate or body fluids (Degen et al. 1981), after which time a they fledge at a low body mass,or both. blood samplewas collectedfrom a brachialvein and Arabian Babblersare cooperativebreeders and the nestling was weighed on an electronicbalance parentsand helpersparticipate in the feedingof nes- (+0.2 g). Further blood sampleswere taken daily for tlings. All group membersprovision at similar rates, the next one to two daysat the samehour. irrespective of sex or dominance rank within the Blood sampleswere microdistilled under vacuum group (Wright 1997, 1998) and, therefore,we hy- until drynessto obtain pure water. Specificactivity pothesizedthat the growth rate of nestling• is fast. of tritium in the water was measuredby liquid scin- To test that hypothesis,we determinedgrowth rate tillation spectrometry(Nagy 1983).Level of •80 spe- of babbler nestlingsusing a logistic growth curve cific activity was measuredby an autogammacount- and comparedresults with other passerines.We also ing system (Packard) after converting •sO to measuredenergy use in babbler nestlingsand esti- gamma-emitting•SF by cyclotron-generatedproton mated body-energyaccumulation during growth. activation (Wood et al. 1975). Blood samplesfrom Materials and Methods.--Studyspecies and study three noninjectednestlings from differentnests were site.--The Arabian Babbler(65 to 85 g) is a passerine treated similarly to measurebackground levels of •sO speciesdistributed in Saudi Arabia, Sinai, and in and tritium. someof the extremedeserts of Israel, and is the only Total body water (TBW) of eachnestling was cal- bird speciesin Israel that lives in groupsyear round. culated from the initial dilution volume of isotopic Thosegroups are territorialwith the numberof birds water, and water fluxes were calculated from the per group generallybetween 3 and 5 individuals,but subsequentdecline in specificactivity of tritium over the range is between 2 and 22 (Zahavi 1990). time (Degen et al. 1981).We were suspectof the exact Egg laying in eachgroup of babblerstakes place in injection volume in some nestlingsand, therefore, one nest usually between February and August. there were 48 TBW measurementsof the 65 injected Three clutchesare possible.Breeding females lay be- nestlings.In nestlingswithout TBW measurement, tween 3 and 5 eggs during each clutch and, where TBW valuesfrom the regressionanalysis of TBW on more than one female lays, the total number of eggs body masswas used (see results) to calculatewater can reach 13. Maximum number of fledglingsfrom flux and FMR (Anava et al. 2001). Total body solids one nest is about six. All membersof the group par- were calculatedas the differencebetween body mass ticipate in all phasesof nesting and rearing young and total body water.Rates of CO2production were (Zahavi 1989, 1990). estimatedfrom the declinesin specificactivities in All birds, including nestlings,were color banded. tritium and •80 over time (Nagy 1980).Eight samples To determine growth rate of nestlings,77 chicksfrom could not be measured for •80 and, therefore, there 24 nestswere used; all nestswere attendedby par- were 57 FMR measurements. ents and helpers.Five nestshad a brood of two, 10 Treatmentof data.--A logisticequation was usedto had a brood of three, 8 had a brood of four, and 1 describe the growth curve of nestlings (Ricklefs had a brood of five. All nests were observeddaily, 1968). We calculated the age of maximum growth and time of hatchingwas determinedin each.Age of rate (in days) and maximum growth rate (in grams nestlings was measured in days. Changes in body per day) at the inflection point. To compare the mass of nestlings were followed by periodically growth rate of Arabian Babblernestlings with other weighing them over the nestingperiod and pooling bird species,we determined the time required to the total of 547 measurementsthat were made (De- grow from 10 to 90% (t•0_90)of asymptoticbody mass gen et al. 1992). (Ricklefs 1968). The study was done at the Nature Reserveat Hatz- Ratesof CO2 production of babbler nestlingswere eva (30ø45'N; 35ø15'E) in the Arava, -30 km south of convertedto ratesof heat productionand energyin- the Dead Sea.That site is characterizedby long, hot, take on the basis of an insect diet: 25.7 J were ex- dry summers.It has a winter rainfall that averages pended per milliliter of CO2 produced (Nagy 1983) 35 mm annually,but there are large variationsin to- and metabolizableenergy was 0.75 of grossenergy tal rainfall and in its temporal and spatial distribu- (Robbins1983). We assumedwater influx equalled tion. Average daily air temperature for the hottest metabolic and preformed water from food. For in- (August)and coldest(January) months are 30øCand sects, a volume of 0.660 Izl of metabolic water was 15øC,respectively (Stern et al. 1986). generated per milliliter of CO2 produced (Nagy April 2001] ShortCommunications 521 40 o oo 35 30 o 5o •, 25 øøø•o 30 [ 2o 2O 0 2 4 5 8 10 12 14 10 20 30 40 50 Age (days) Body mass (g) FIG.1. Bodymass of Arabian Babblernestlings in FIc. 2. Total body water volume of Arabian Bab- relation to age. The line representsthe logistic bler nestlingsin relationto body mass. growth curve (seetext). body mass and mean adult mass (72 g) was 0.63. 1983).