Field and Laboratory Metabolism and Thermoregulation in Dovekies (Alle Alle)

FIELD AND LABORATORY METABOLISM AND THERMOREGULATION IN DOVEKIES (ALLE ALLE)

GEIR WING GABRIELSEN,1'3 JAN R. E. TAYLOR,2 MAREK KONARZEWSKI,2 AND FRIDTJOFMEHLUM • 1TheNorwegian Polar Research Institute, P.O. Box158, N-1330 OsloLufthavn, Norway, and 2Instituteof Biology,University of Warsaw,Branch in Bialystok,Swierkowa 20B, P.O. Box 109, 15-950 Bialystok,Poland

AI3STRACr.--TheDovekie (Alle alle) is an abundant seabirdin the high Arctic. We studied Dovekie energeticsby measurementsof resting metabolicrate (RMR) in the laboratoryand ratesof CO2 production(with doubly labeled water, DLW) of free-living adultsduring the chick-rearingperiod. Within the thermoneutralzone, restingmetabolism was 2.42 _+0.13 ml O2.g-•.h-• (177.9 + 9.6 kJ/day). Thesevalues were 84-112%greater than predictedfor non- passetines.Thermal conductance(C) was 0.0630 _+0.0029 ml O2.g-•. h -• .øC%which was close to or lower than allometric values of birds of similar body size. Field metabolic rate (FMR) was 6.68 _+1.06 ml CO2'g-•' h -• (696.1 _+103.7 kJ/day). This is the highestFMR value, corrected for body mass,yet publishedfor seabirdsstudied by the doubly labeledwater methodduring the chick-rearingperiod. The high wing loading of Dovekiesimplies that flight costmay be high, resulting in a high FMR. Despite a high FMR, Dovekies had an FMR/RMR ratio of 3.9, similar to valuesreported for other speciesin other regionsduring chick-rearing.We estimated that the amount of plankton (mainly Calanusfinmarchicus) consumed each day by Dovekiesequaled 80% of their body mass.A colony of 70,000pairs of Dovekies(assuming one 14-day-oldchick in eachnest) would consume21.9 tons of fresh zooplanktonper day, and would addapproximately 2.1 tons (dry mass)per day of guanoto the marineand terrestrial ecosystemsover this period. Received4 January1990, accepted 13 July 1990.

ThE Dow•cm (Alle alle) is the smallest (163 g) tems by transportingorganic matter and nutri- and the most abundant seabird speciesof the ents from seato land (Norderhaug 1970, Taylor Svalbard archipelago. The largest breeding col- and Konarzewski unpubl. data). onies, which comprise several hundred thou- High-latitude seabirdsduring the chick-rear- sand pairs, are on the western coast of Spits- ing period have high values of resting meta- bergen (Lovenskiold 1964). Dovekies feed bolic rate (RMR) within the thermoneutral zone, offshoreduring the breeding season,and have and a high field metabolic rate (FMR) when been observed as far as 150 km from the colonies comparedwith tropical and temperate species (Byrkjedal et al. 1974, Brown 1976). Some Dove- (Johnson and West 1975; Ricklefs et al. 1986; kies also feed inshore (Hartley and Fisher 1936, Roby and Ricklefs 1986; Obst et al. 1987; Ga- Evans 1981). Near Hornsund, Svalbard (77øN), brielsen et al. 1987, 1988). The FMR/RMR ratio the birds feed mainly offshore (Konarzewski in high-latitude seabirdsvaries between 3 and and Taylor pers. obs.). The diet consistspri- 4, which is consistent with Drent and Daan's marily of planktonic copepods (Norderhaug (1980) proposalof a "maximum sustainedwork- 1980; Evans 1981; Lydersen et al. 1985; Wes- ing level" of 4 times basalmetabolic rate (BMR) lawski, Taylor, and Konarzewski unpubl. data). during chick-rearing.The Dovekieactivity pat- The large populationsof Dovekiesare the major tern during chick-rearing reflects a high en- avian predatorson marine copepodsin the Sval- ergy expenditure. Each parent makes approxi- bard area. Dovekies spend most of their time at mately 3-5 trips between nesting and feeding sea,and may play an important role in recycling areas daily (Norderhaug 1980, Evans 1981, nutrients in arctic marine ecosystems.They also Stempniewicz and Jezierski 1987, Konarzewski have a significantimpact on terrestrial ecosys- and Taylor pers. obs.).Dovekies have only one chick, which is broodedfor 5-7 days (Norder- haug 1980,Taylor and Konarzewskipers. obs.). 3 Present address:Norwegian Institute for Nature Dovekiesand other alcidspractice both aerial Research,% TromsoMuseum, University of Tromso, and underwater locomotion. They use their N-9000 Tromso,Norway. wings for propulsion, and the media differ sub- 71 The Auk 108: 71-78. January 1991 72 GABRIELSENETAL. [Auk,Vol. 108 stantially in density and in buoyancy.Flying ready homeothermic(Konarzewski and Taylor pers. auksprobably represent a compromisebetween obs.). birdsadapted for locomotionin air and in water Restingmetabolic rate measurements.--RMRwas mea- (Storer 1960). Comparedwith other seabirdsof sured both during the day and at night. Metabolic the same mass,auks have reduced wing span measurementsat Ny-•lesund, were as described by Gabrielsenet al. (1988). Briefly, a metabolicchamber and wing area (Masman and Klaassen1987, (4.5 1) was placed inside a climatic chamber where Pennycuick 1987). Thus, we expect a high en- the ambient temperature could be controlled within ergetic cost of aerial locomotion and pursuit + IøC from -25 to +30øC. We measured air flow (1.5- diving in the Dovekie. The cost of flight and 2.0 1/min) with a mass flow meter (Model F 113, Hi- swimming, measuredon free-living birds by Tec) connected to a readout (Model E-0020, Hi-Tec). the doublylabeled water (DLW) method,ranged Oxygen consumptionand CO2 production were mea- between 4.8 and 11.6 times BMR (LeFebvre 1964, sured with an Applied Electrochemistryoxygen an- Utter and LeFebvre 1973, Flint and Nagy 1984, alyzer and a Leybold-Heraeus(BINOS-l) CO2 ana- Nagy et al. 1984). Becauseof the expectedhigh lyzer. Temperatures in the climatic and metabolic costof existencein Dovekies,we felt it impor- chamberwere measuredby thermocouplesconnected tant to determine whether FMR and RMR are to a Fluke thermometer.Body temperaturewas measured during metabolismtrials by a small thermo- consistent with these values, and whether the couple inserted ca. 2-3 cm into the cloaca.The first FMR/RMR ratio supportsthe "maximum sus- metabolic measurement was made within 10-12 h of tained working level" hypothesis (Drent and capture. Eight to ten hours before metabolic trials, Daan 1980). We used the DLW method to mea- birds were denied food. All birds were exposed to sure FMR of the Dovekie during the chick-rear- a given chambertemperature 1-3 times for at least ing period. To determine the FMR/RMR ratio 1.5-2.0 h. We measuredmetabolism under full light of free-living Dovekies,we alsomeasured rates conditions in the climatic chamber and while the bird of metabolismin the laboratory. We estimated was resting, as determined by inactivity of the bird foodconsumption based on water flux ratesand (observed by video). We calculated 02 consumption (ml O2.g-l.h-•), CO2production (ml CO2'g "h •), re- the chemical composition of the diet. Finally spiratory quotient (RQ), and energy expenditure (kJ/ we estimatedfood requirementsof a population day) at STPD. of Dovekies to assess their influence on the arc- We calculated thermal conductance (C) from the tic marine ecosystem. mass-specificmetabolic rate (VO2) at an ambienttem- perature (Ta) below lower critical temperature, ac- METHODS cordingto the formula:C = VO2/(Tb- Ta),where Tb is the body temperature of the bird. Thermal con- We studied Dovekies breeding in Krossfjorden ductanceis expressedas "wet" conductancebecause (79øN, 1løW) and in Hornsund (77øN, 15øW),Svalbard, evaporativeheat lossfrom respirationwas included. from July to mid-August1986. Laboratory studies were All birds used in laboratory experimentswere re- performed at the researchstation of the Norwegian leasedin the colony. PolarResearch Institute in Ny-•lesund(32 km south Doublylabeled water studies in the field.--Metabolic of Krossfjorden).Adult Dovekies(n = 23) were stud- rates(CO2 production) and water flux rateswere mea- ied in the laboratory during their incubation period. sured by the DLW method (Lifson and McClintock Birds were either trapped in the nest or caught with 1966,Nagy 1980,Nagy and Costa1980) in one or both a mist net. Birds used in the laboratory study were membersof a breeding pair. The mean error of this kept in an outdoor cagefor 1-1.5 days and fed frozen method ranged between -4.9 and +6.5% (Williams Parathemistosp. and Prints 1986). The field studies were conducted at the Dovekie We trapped 28 adults at the nest. We injected 0.5 colony(Ariekammen) on the northern shoresof the ml H21sO,containing 97.11 atom % oxygen-18and Hornsund Fjord (Norderhaug 1980; $tempniewicz 0.4 mCi tritium, into the pectoral muscle.The birds 1980, 1981). Approximately 70,000 pairs of Dovekies were held in a woodenbox for 1.0 h while the isotopes breed annually in the Ariekammen colony (Taylor equilibratedwith body water (Degen et al. 1981,Wil- and Konarzewskiin prep.), and 400,000 pairs are es- liams and Nagy 1984). Birds were weighed to the timated to breed on the northern mountains of the nearest1 g on an Ohaus (C 501) digital balance.Each Hornsund Fjord (Bakken pers. comm.). During the bird was marked on the breast with individual pat- last days of incubation, we fitted 25 nestswith traps. terns in india ink. Blood samples (3 x 70 •1) were These nestswere inspecteddaily before the DLW taken from a wing vein. We retrapped15 birds within experimentsto determinethe dateof hatching.Chicks one or two days, someof them more than once; and were 7-20 days old when we performed the DLW a second blood sample was taken. The colony was measurementson adults. At that age chicks are al- monitored continuouslyto establishthe presenceof January1991] DovekieEnergetics 73 experimental birds. Two backgroundsamples were taken from control birds at the start and at the end of the experimentalperiod. The backgroundfor oxygen-18was 0.2030atom % and 30.0 cpm for tritium. Measurementsof FMR by DLW becomeunreliable as final oxygen-18value approachesbackground. We ex- cluded all blood sampleswith final oxygen-18 en- -2'0 -1'0 0 10 20 30 richments within 8% of background. AMBIENT TEMPERATURE (oC) Blood sampleswere stored in flame-sealed,hepa- rinized microhematocritcapillary tubes, and were Fig. 1. Oxygenconsumption rates of Dovekiesat different ambient temperatures. vacuum-distilledto obtain pure water. Isotopelevels in the water were measuredby liquid scintillation spectrometry(for tritium) and protonactivation anal- temperatures,horizontal visibility, and wind speed ysis(for oxygen-18)(Wood et al. 1975)by Ken Nagy, were measuredevery third hour. Precipitation was Universityof California,Los Angeles, California, USA. recordedfour times daily. For each bird usedin the Ratesof CO2 productionwere calculatedwith eq. 2 field experiment,precipitation and the meanvalues in Nagy (1980).Water flux rateswere calculatedfrom of all of the above weather factors were calculated for eq. 4 in Nagy and Costa(1980). Body water volume theperiod of measurementof fieldmetabolic rate (i.e. was estimated from the regression equation: between the first and secondblood sampling). Mean values are +SD unless noted otherwise. body water (ml) = 7.70 + 0.589 (wet body mass,g) (r2 = 0.89, P < 0.0001, n = 27). We dried carcassesof adult birds caught in the colony during feeding of RESULTS the chicks to constant weight (Taylor and Konar- zewski in prep.). We used this equation to estimate Restingmetabolic rate.--The lower criticaltem- the massof water in the body of each bird at each perature, defined as the intersectionbetween sampling time. the RMR line and the line that describes the Foodconsumption.--We collected food samplesfrom dependenceof metabolicrates on Ta,was 4.5øC the gular pouchesof adult Dovekiesthat fed chicks (Fig. 1). The regressionfor Dovekies was y = in the colony. We assumedthat the diet given to the 2.61 - 0.05x (y = ml O2.g-•-h •, x = ambient chick was the same for adults. The copepod (Calanus temperature;T• range from -20 to + 1.5øC;n = finmarchicus)made up 8.5%of freshmass of food(105 21). Conductance(C) was 0.0630 ml O2'g •'h '. food samples);other crustaceanscontributed the rest (Weslawski,Konarzewski, and Taylor unpubl. data). øC • (SD = 0.0029, n = 25). The division of the Field metabolic rates (FMR) were converted from units points(Fig. 1) into two segmentsgives the low- of CO• production to units of energy by the factor est residual sum of squaresfor all points when 26.5 J/ml CO2. This factor was calculated from the the intersection of these lines falls on ambient chemicalcomposition of Dovekies'food samples (76% temperatureca. +5øC (as in Fig. 1). water in fresh mass;36.8% of lipid, 47.9%of proteins, The mean(+ SD) restingmetabolic rate (RMR) and 15.3%of mineralsin dry mass[Taylor and Konar- of Dovekies at thermoneutrality was 2.42 + 0.13 zewski unpubl. data]).Energy equivalentsfor fat and ml O2'g •'h -• (n = 16) or 177.9 + 9.6 kJ/day protein were from Schmidt-Nielsen(1975). For our (Fig. I). The mean respiratory quotient (RQ), calculation, we assumedthat the proportions of as- within the thermoneutral zone, was 0.75 + 0.02, similated dietary fat and protein were the same as their proportionsin the diet. We calculatedthe amount (n = 16), and body temperature was 40.1 + 0.4øC of food an adult Dovekie would have to consume to (n = 10). Just after the capture in the colony, satisfyits daily energyrequirement (as measured with the mean body mass of birds used for RMR DLW) from the energy content of food samplesand measurements was 162.3 + 12.2 g. Body mass energy assimilationefficiency. Because there are no droppedsignificantly because of starvationbe- assimilationefficiency studies of adult Dovekies,we fore metabolic trials (P < 0.0001, t-test), and used the value of 0.80 obtained in fledglings (Taylor during the metabolic measurementsmass av- and Konarzewskiunpubl. data).The food of Dovekies eraged 152.5 + 12.2g. The latter mean was used contains 28.1 kJ/g dry matter (Taylor and Konar- for calculationof the mass-specificRMR. zewski unpubl. data). Thus, with a water contentof Field metabolic rate.--Field metabolic rate 76%, the food contains 6.75 kJ/g of wet mass,or 5.3 kJ metabolizableenergy per gram of fresh matter. (FMR) of free-ranging birds averaged 6.68 ml Weather.--Weatherconditions during the field ex- CO2'g •'h-', or 696.1kJ/day (Table 1). The mean periments were obtained from the Polish Polar Re- body massof birds in FMR measurementswas search Station, 1 km from the Dovekie colony. Air 164.3 + 9.5 g (n = 13), and was not different 74 GABRIELSENEt AL. [Auk,Vol. 108 from initial body massof birds used in labo- DISCUSSION ratorymeasurements (P > 0.65,t-test). The FMR/ RMR ratio (basedon whole-body ratesof me- Basal metabolic rate (BMR) refers to mea- tabolism) was 3.9. surements of resting organisms in a postab- The weather during the study period was sorptivestate within their thermoneutralzones characterizedby high precipitation, fog, and (Blight and Johnson1973). Our measurements strongwinds. Mean air temperaturewas 4.4øC were similar to BMR measurements,but they (range, 2.6-7.0øC),mean daily precipitationwas were done under full light conditions.This sim- ulated arctic summer conditions. We measured 4.1 mm (range, 0-41 mm), and wind speed was 3.4 m/s (range,0-18 m/s). Accordingto satellite resting metabolic rate (RMR) rather than basal metabolic rate. Nevertheless we believe our maps,the mean oceansurface temperature was 2.6 (50 km) and 4.7øC (100 km) between Horn- measurementsare comparableto BMR. sund and the open sea. We used published regressionequations (al- We analyzed possibledependence of FMR pha-phase) for nonpasserine birds to predict (kJ/day) on weather conditions(average hori- resting metabolic rate (RMR) in Dovekies with- zontal visibility [km], average air temperature in the thermoneutral zone (Lasiewski and Daw- [øC],average and maximumwind velocity[m/s], son 1967, Aschoffand Pohl 1970). For a Dovekie precipitation[mm]), and body mass.We used (153 g) the measuredRMR value was 212%and the body massas an independentvariable to 184%of the predicted values. Similar predicted avoid statisticalproblems with analyzing ratios values were obtained by Roby and Ricklefs suchas mass-specific metabolic rates (Blem 1984). (1986) in their study of Least Auklets (Aethia The wind speed appeared to be the only sig- pusilla)and diving petrels (Pelecanoidesspp.), nificant weather factor: whose ecology is similar to that of Dovekies. The RMR value obtained for Dovekies agrees FMR (kJ/day)= 3.81.•V + 17.07.V with earlier observations (Weathers 1979, Hails 1983, Ellis 1984), which showed that BMR is a where 17V= meanbody mass(in g; partialre- function of breedinglatitude. Speciesthat breed gressioncoefficient significant at P < 0.0001), at high latitudes have a higher BMR than those V = wind speed (m/s, P < 0.05). For FMR, SE in temperate and tropical areas.However, fac- = 94.7, n = 13. Similar analysisof dependence tors other than relative size, diurnal phase,and of FMR on body masschange (between the first climate may contribute to the high RMR in the and secondblood sampling) and the age of Dovekie.Roby and Ricklefs(1986) and Gabriel- chicks was not significant (P > 0.05). sen et al. (1988) suggestedthat the birds' phys- Water influx rate in Dovekies was 136.6 + ical activity or their modeof life may influence 31.7 ml/day (n = 18) (Table 1). the RMR. Ellis (1984) proposeda closelinkage Foodconsumption.--Daily energy expenditure between BMR and maximum power output. This in free-rangingbirds averaged696 kJ/day. At means that a high field metabolic rate (FMR) a metabolizableenergy yield of 5.3 kJ/g fresh may correlatewith a high RMR. mass of food, the Dovekie must consume 131.3 We calculatedthermal conductance(C) as 98% g fresh food or approximately80% of its body of that predictedby Herreid and Kessel's(1967) massper day.We checkedthis estimateof feed- equation for dead birds (dry conductance)and ing rate by calculatingwater influx rate, and 76%of Aschoff's(1981) value (alpha-phase)pre- comparedthis value with the actual influxes dicted for a 152.5 g bird. After compensating measured with tritiated water. A mass of 131.3 for respiratory heat loss (Herrled and Kessel's g of food,with a water contentof 76%,contains equation), we found that the C value in Dove- 99.8 ml of water. Metabolic water production kieswas higher than predictedfrom mass.When from oxidationof assimilatedproteins and lip- compared with temperate seabirds of similar ids would provide an additional0.122 ml water body size, conductanceof Dovekieswas low. per gramof freshfood (conversionfactors from This implies greater insulation than in the Schmidt-Nielsen 1975), or 15.7 ml water. This Georgian Diving Petrel (Pelecanoidesgeorgicus; yieldsa total of 115.5ml water when consuming Roby and Ricklefs 1986).The averageambient 131.3g of food, which is about 15%lower than temperature in the Svalbard approached the the measuredwater influx of 136.6 ml water per birds' lower critical temperature (TLc= 4.5øC), bird (Table 1). which implies that these birds may not be cold- January1991] DovekieEnergetics 75

T^BI,E 1. Ratesof body masschange, water influx, and field metabolismof breedingDovekies in Hornsund. Bodymass Waterinflux Metabolicrate Measure-Age of Mean Change rate (ml CO2- ment period chicks Bird No.a (g) (g/day) (ml/day) g '.h -l) kJ/day (days) (days) 86A 154.3 -2.4 99.1 6.90 677.3 1.06 7 94A 168.0 -5.8 131.7 7.58 809.6 1.74 11 94A 159.0 7.8 138.4 8.48 857.4 0.90 16 94A 162.5 0.0 115.3 4.91 507.3 0.88 17 94B 167.5 -4.9 131.6 6.43 685.5 1.01 15 94B 162.5 -6.7 133.9 6.10 630.6 1.64 20 13A 166.0 -4.4 108.6 -- -- 2.27 12 13B 167.0 -0.5 122.2 6.42 681.5 2.07 16 45A 160.5 7.7 182.1 8.65 882.6 1.17 11 18A 188.5 0.8 100.4 5.63 674.5 1.30 12 85A 158.0 7.3 212.8 -- -- 1.91 11 33A 150.5 - 4.0 91.2 6.54 625.6 1.25 8 48A 157.3 4.0 169.4 6.74 673.8 1.88 12 48B 174.3 - 1.5 145.7 -- -- 2.94 16 84A 173.5 -2.9 128.1 6.64 732.9 1.05 7 67A 164.5 0.0 128.1 5.83 610.0 1.63 15 81A 153.5 -1.1 143.2 -- -- 2.64 15 RSA 160.0 3.0 176.5 -- -- 2.01 20

Mean 163.7 - 0.2 136.6 6.68 696.1 SD 9.0 4.6 31.7 1.06 103.7 n 18 18 18 13 13

and B indicate two birds of the samepair. stressed while on land. However, when for- body massto wing area). The wing loading in aging at sea,water may compressfeathers. This Dovekies (0.98 g/cm2; Stempniewicz 1982), is increases thermal conductance, and results in 243%of that predictedfor a "typical" bird (Vis- increased metabolism at the 2-4øC water tem- cor and Fuster 1987). This, together with the perature. presumablyhigh energeticcost of flying long The FMR in auks and petrels, is elevatedin distances to feeding areas (Brown 1976), may comparisonwith other seabirds(Birt-Friesen et accountfor high FMR in Dovekies. al. 1989).However, auksand diving petrelsalso Dovekies as well as Kittiwakes (Rissa tridac- use their wings for underwater locomotion. Be- tyla; Gabrielsen et al. 1987) showed increased causethe optimum design of wings is different FMR with increasedwind speed.There is a neg- for flying in air and swimming underwater, an ative effect of wind speed on the increase in intermediate stage would involve a loss of ef- body massand lipid reservesof Dovekie chicks ficiencyin eachmedium. The wing area of auks (Konarzewskiand Taylor 1989). It is unlikely is approximately 40% that of Procellariiformes that chick growth is directly affectedby wind and 30% below marine larids. Wing length is becausechicks are relatively well protectedin only 60% of Procellariiformesand 50% of ma- nest crevices (Konarzewski and Taylor 1989). rine larids (Jouventin and Mougin 1981). The Presumablyunder windy conditions the FMR same tendency--but carried to extremes--is of adults is altered sufficientlyto changethe present in penguins, where the wing is pre- chicks' food intake. sumably optimized for swimming (Jouventin In seabirdsthe breeding period representsa and Mougin 1981). period in which the energy demandsupon the The FMR of Dovekies,corrected for body size, parent are thought to be at a maximum (Ricklefs is the highest among all seven cold-water sea- 1983).We found no relationshipbetween adult bird speciesthat use wings for propulsion in FMR and the age of their chicks 7-20 days of water (Table 2). The wing area of auks falls in age. Food consumptionby chicks is relatively the lower extreme of the range of all flying birds stableduring this period(calculated from water (Greenwalt 1962). Very low wing area in Dove- influx; Taylor et al. unpubl.). The food con- kies produceshigh wing loading (the ratio of sumptionof Dovekie chicksincreased only 35% 76 GABRIELSENETAL. [Auk,Vol. 108

T^BI,E 2. Field metabolicrates (FMR) of cold-waterseabirds that usewings for propulsionin water, measured by doubly labeledwater during chick-rearingperiod.

Observed Body FMR vs. mass FMR predicteda Species (g) (kJ/day) (%) Source Least Auklet (Aethia pusilla) 84 358 125 Roby & Ricklefs 1986 South GeorgiaDiving Petrel (Pelecanoides 109 464 134 Roby & Ricklefs 1986 geor gicus ) CommonDiving Petrel (P. urinatrix) 137 557 137 Roby & Ricklefs 1986 Dovekie (Alle alle) 164 696 149 Present study Black Guillemot (Cepphusgrylle) 381 863 100 Mehlum, Gabrielsen & Nagy unpubl. Common Murre (Uria aalge) 940 1,871 113 Cairns unpubl. Thick-billed Murre (U. lomvia) 1,119 2,080 110 Flint et al. prelim. unpubl. data Predictedfrom the equationof Birt-Friesenet al. (1989) relating FMRs of cold-waterseabirds that use flapping flight to their body weight. between days 8 and 14, and it remainedstable matter) of nitrogen-rich guano are added to the until day 21 (Konarzewski et al. in prep.). The Hornsund marine and terrestrial ecosystems lack of dependenceof adult FMR on chicks'age each day. agreeswith data obtained for two speciesof The amount of food consumedby adult Dove- diving petrels (Roby and Ricklefs 1986). kies may be even larger. We found that water In many breeding birds, free-living parents influx calculated from water content of the use energy at 3.1-4.3 times their RMR (Hails plankton and oxidation of its fat and protein and Bryant 1979, Bryant and Westerterp 1983, was 15% lower than water influx measured with Utter 1971, Utter and LeFebvre 1973, Williams DLW. However, the higher measured values and Nagy 1984,Nagy et al. 1984,Gabrielsen and may be due to the mode of foraging of Dovekies Mehlum 1989; but see Williams 1988). Drent (presumablythey consumesome sea water while and Daan (1980) proposed a maximum sus- feeding on copepods).The food is carried by tained working level of 4 x RMR during chick the parents in an extensible gular pouch. This rearing. Dovekies show the sameratio, despite may allow water exchangebecause the food is the fact that these birds differ in other ways in contact with the mucous membrane. from mostspecies studied in othergeographical The Dovekie is the only Atlantic seabird that regions. We strongly support Drent and Daan's feeds mainly on copepods.The specieshas a (1980) hypothesisof the maximum sustained high energy demand balanced by high food working level. consumption,and may therefore have an im- We estimatedfood consumptionfrom energy pact on both the marine and the terrestrial eco- requirementsof free-ranging Dovekies.We cal- systems,where it depositsa large amount of culated that adult Dovekies eat approx. 131 g nutrients. of plankton daily during chick rearing. This ACKNOWLEDGMENTS includesonly the adult needsand excludesfood given to the young. Basedon the water influx We thank Kenneth A. Nagy for his help in analyz- rate in growing Dovekie chicks,water content ing the DLW samples.We alsothank the staffat Horn- of their food, and its energetic value (Konar- sundand Ny-,•lesund for their assistance and accom- zewski et al. unpubl.), we calculatedthat a 14- modationduring the summerof 1986.Elizabeth Flint, day-old chick consumes51 g fresh plankton KennethA. Nagy, J. B. Williams,and two anonymous eachday. Foodrequirements of two adultsand reviewers made helpful comments on this manu- script. The study was supportedby the Norwegian one chick would total 3J3 g fresh plankton per ResearchProgram for Marine Arctic Ecology (PRO- day. There are approx.70,000 pairs of Dovekies MARE), the NorwegianResearch Council for Sciences in the Ariekammen colony (Taylor and Konar- and the Humanities, and by the Polish Academy of zewski unpubl.), and we estimatethat the col- Sciences(Project CPBP 03.03.A 5.6). This is Contri- ony will consume 21.9 tons of C. finmarchicus bution No. 257 from the Norwegian Polar Research each day. We estimatethat approx.2.1 tons(dry Institute. January1991] DovekieEnergetics 77

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