The Auk 110(2):325-342, 1993 FORAGING STRATEGY OF WANDERING ALBATROSSES THROUGH THE BREEDING SEASON: A STUDY USING SATELLITE TELEMETRY HENRI WEIMERSKIRCH, MARC SALAMOLARD, FRANCOISSARRAZIN, AND PIERREJOUVENTIN Centred'Etudes Biologiques des Animaux Sauvages, Centre National de la RechercheScientifique, 79360 Beauvoir, France ABSTRACT.--Satellitetelemetry of Wandering Albatrosses(Diomedea exulans) breeding on the Crozet Islands, southwesternIndian Ocean, revealed two distinct foraging strategies during successivestages of the breedingseason: systematic foraging over extensivedistances; and useof specificareas close to the colony.During early incubation,Wandering Albatrosses foragedover pelagicwaters at an averagerange of 1,284kin. The length of the foraging trips decreasedtowards the end of the incubation period. During the first month of chick rearing when parentsbrood alternately for short periods,the foraging range, distancecovered, and area prospectedwere further reduced.Males tended to return to an individual foraging area, locatedat the edge of the continental shelf, that had previouslybeen visited during the long trips of the incubation period. Femalesmostly prospectedpelagic waters just off the shelf. After the chick had been left alone on the nest,birds exhibited a two-fold strategy,combining long foraging trips over pelagic waters with short trips over the shelf. Generally, both sexes headed for and foraged over an extensivepelagic sector.Some males also foraged over the Kerguelen shelf. Females tended to forage over more northerly waters than males. The duration of the foraging trips was most closelyrelated to the total distancecovered, but also to the maximumrange during the long trips of the chick-rearingperiod and to a lesserextent during the incubation period. There were no such significantrelationships in the caseof short trips. During long pelagic foraging trips, the birds had a looping coursethat was determined by the wind direction, suggestingrandom foraging with respectto prey distri- bution. We were able to show that Wandering Albatrossesuse two foraging strategiesto cope with the constraintsimposed by the different stagesof the breeding cycle, the availability of prey, and the distribution of the prey. Use by Wandering Albatrossesof two foraging strategiesmay be a compromisebased on the simultaneousneed to satisfythe different food requirementsof chicksand parents.Received 20 February1992, accepted 23 October1992. DURINGTHE breeding season,pelagic seabirds utility of satellitetelemetry for very large birds foragefrom a central place(often an island)and hasbeen demonstratedin a studyshowing that travel outward to feeding areas, where their four male Wandering Albatrosses(Diomedea ex- foraging behavior is impossibleto observeby ulans)moved during the early incubation pe- island-basedresearchers. Heretofore, the only riod over thousandsof kilometers, taking ad- easily measurablefeature of their foraging has vantageof the prevailing winds (Jouventinand been durations of foraging trips, determined Weimerskirch 1990). This preliminary work from incubationbouts and chick feeding fre- supported the previous simplistic suggestions quencies.Usually, it has been assumedthat the that albatrosseshave an extensiveforaging range duration of foraging trips depends on the dis- during the breeding season(Tickell 1968, Crox- tance an adult has to travel from its nest to find all and Prince 1980,Pennycuick et al. 1984,Wei- food (Lack 1968, Pearson 1968, Croxall and merskirch et al. 1986). Observations at the nest Prince 1980,Pennycuick et al. 1984).Ainley and alsohave shown that foraging trips are reduced Boekelheide (1990), however, showed that oth- in duration as the hatching of the chick ap- er factorscan complicatethis relationship. The proachesand are very short when the chick is virtual absenceof time/energy budgetsduring brooded (Tickell 1968, Weimerskirch et al. 1986). foraging of pelagicseabirds has led to extensive This pattern suggeststhat foraging parameters speculation that requires confirmation with change during the breeding season. telemetric studies (e.g. Ricklefs 1983, Harrison Further information on the pelagic ecology and Seki 1987, Prince and Morgan 1987). The of albatrosses has come from observations at sea 325 326 WEIMERSKIRCI-IET^I•. [Auk,Vol. 110 that give indications concerning the distribu- (National Oceanicand AtmosphericAdministration, tion of seabirds in relation to their environment USA) satellitesto receivea signalsent by transmitters. (e.g. Ainley et al. 1983, Stahl et al. 1985). These The data stored on the satellitesare sent to ground studieshave shown, for example,that Wander- telemetry stations at the end of each orbit cycle and relayed to CNES (Centre National des Etudes Spa- ing Albatrossesforage from antarctic to sub- tiales) in Toulouse,France. At CNES the data are pro- tropical waters and that males forage in more cessedand the exact position of the transmitter is northerly waters than females (Weimerskirch determined. The locations are made available within and Jouventin 1987). However, because the birds 2 h of the transmitter being located. observedwere of unknown statusand origin it Study dateswere from 10 January 1990to 28 August was impossibleto concludewhether the pattern 1990,and 10 January 1991to 14 February 1991.Results observedconcerned the breeding or nonbreed- obtained in 1989 for six males (Jouventin and Wei- ing parts of the population. Satellite telemetry merskirch 1990) are included to increasesample size can addresssuch questions. during the incubationperiod. In 1990-1991nine dif- We report a study using satellite telemetry of ferent 185-g2028C Toyocom transmitters (Toyo Com- municationEquipment Ltd, Minato-ku, Tokyo,Japan) the foragingstrategy of WanderingAlbatrosses were used. Only two were used in 1991-1992. The throughoutthe different stagesof the breeding original transmitters were modified so that the total cycle.We have addressedthree main questions: length was reduced from 180 to 110 mm, with the (1) What are the foraging characteristicsof the battery pack being relocatedto the side of the elec- Wandering Albatrossand do these character- tronics.Thus, the packagewas broaderthan the orig- isticsvary accordingto the different stagesof inal, but its mass was reduced to 160 g. The lifetime the breedingcycle? (2) Is foraging-tripduration of the batteriesdepends on the interval between two relatedto the rangeor the distancecovered? (3) messages.In 1990-1991the transmissioninterval was Do the birds foragerandomly or do they return adjustedto 90 s, giving a battery lifetime of about 35 to specificareas during each trip? Resultsare to 40 days. The transmitterswere fitted on the birds discussedin relation to the predictions and hy- usinga 10-mm-wideharness made of fine goatleather with elastic sections(Weimerskirch et al. 1992). When pothesesconcerning the foraging strategiesof fitted on the bird, the harness(24 g) was completely pelagic seabirds. coveredby feathers.Experiments with dummy trans- mitters were carried out in 1989 (Jouventin and Wei- merskirch 1990);comparison of time spent at seadur- METHODS ing incubation and brooding by birds fitted with The field study was carried out on PossessionIs- transmittersand by other birds suggestthat the pres- land, Crozet Islands, in the southwestern Indian Ocean ence of the transmitter probably did not alter the on a population of Wandering Albatrosseswhose age behavior of the birds (Weimerskirch et al. 1992). and statushas been studied since 1966 (Weimerskirch Birdsfitted with transmitterswere breeding at two different colonies on Possession Island: Baie du Marin and Jouventin 1987). The birds fitted with transmit- ters for this study were individuals who had bred located at the eastern extremity of the island; and successfullyin at least three previous seasons. Pointe Basseon the northwestern coast (for descrip- tion of colonies, see Weimerskirch and Jouventin Wandering Albatrossare among the largestpelagic seabirds.They havea massbetween 8 and 10 kg, with 1987). Transmittersfitted on birds incubating eggsor malesbeing 20%heavier than females(Tickell 1968). brooding young chicks were recovered after one (in- The breeding cyclelasts a completeyear. At the Cro- cubation period) or several(brooding period) forag- zet Islandslaying occursfrom late Decemberto early ing trips at sea.After the chick was left alone on the January(Fressanges du Bostand Segonzac1976). The nest (chick-rearing period), birds visiting the chick egg is incubatedalternately by the male and the fe- for feeding were capturedand fitted with transmitters male for 80 days.While one bird incubates,usually (until end of August).These transmitters were left in for 4 to 33 days, the partner foragesat sea to replace place for a period of one month and then recovered the body reservesused during the fast on the nest. during a feeding visit. After hatching, the chick is brooded alternately by Nine transmitterswere used successivelyon a total eachparent for one month and, thereafter,is left alone. of 30 individual birds, which included both sexes. The chick is fed regularly by both parentsduring the Sixty-five foraging trips (17 by 9 individual females, australwinter and spring, and fledging occursin No- 48 by 21 individual males) were built up from the vember-December.Parents successful in rearing the 4,468locations received. During someof the foraging chick breed in alternate years (Tickell 1968). trips, the unit stoppedtransmitting on the way back The movements