Foraging Strategy of Wandering Albatrosses Through the Breeding Season: a Study Using Satellite Telemetry

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 distribution. 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 transmitters 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 transmitters 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 of wandering albatrosseswere to Crozet. In this case, if the last location was less monitoredusing the Argos satellitetracking system than 300 km from Crozet and if the bird fitted with (Fancy et al. 1988). The Argos systemuses two NOAA the transmitterwas recovered within one to two days April 1993] WanderingAlbatross Foraging Strategy 327

after the last location, the distance covered between distanceson a looping track. Birds covered an the nest and the last location was assumed to be a averageof 5,991 km during each foraging trip, direct line. Otherwise, only the maximum range was ranging as far as 2,602 km from their colony consideredfor theseforaging trips. Transmissionfail- (Fig. 2, Table 1). During the last month of the ure was causedby broken antennae, exhausted bat- incubation period (i.e. "late incubation"), max- teries, oxidation of contactsby sea water and unknown factors. imum foraging ranges and distances covered The data were analyzedusing ELSASoftware (Ar- were lessthan during the first two months (t = gos CLS, Toulouse, France). Four classesof location 3.2 and 2.8, respectively,P < 0.01) so that the can be receivedwith the Argossystem, with accuracy surface area prospectedwas reduced (Table 1, of locational information (Anonymous 1989) as fol- Figs. 1 and 2). At this time, before returning to lows: (class0) accuracyto be determined by investi- the nest, all the birds spent one or two days gator; (1) SD of 1 kin; (2) SD of 350 m; (3) SD of 150 foraging at the edge of the Crozet shelf. The m. All classesof locationswere used in the analysis, locationsof femaleshad a significantly more unlessthe locationproved to be unreliable (i.e. im- northern distribution compared to those of plying a movement between the locations of more males (Table 2, Fig. 4). than 80 km/h, the maximumspeed recorded and pre- dicted for Wandering Albatrosses;from Pennycuick During the first month after hatching both [1982] and Jouventin and Weimerskirch [1990]). In parentsalternated on the nest every one to five this case, the location was removed from the data set. days to brood the chick (Table 1). The average Statisticaltests were performedusing STATITCF and maximum range was only 256 km, with the for- LOHITHEQ software packages. aging area correspondinglyreduced (Table 1, Information on wind directionand wind strength Figs. 1 and 2). Birds covered short distances was obtained from the Bureau des PrOvisions Marines, (Table 1), and the foraging trips of males were M•t•o France,Paris. The forecastmaps of the south- interruptedby periodsover restrictedareas (Fig. ern Indian Ocean provided data twice daily on wind 5A). These areasof "active foraging" were con- strength and direction at 10-m altitude for each 1.8ø centrated at the southern edge of the Crozet square. shelf (Fig. 6). However 1 of 11 males ranged over pelagic waters more than 1,000 kilometers RESULTS from its nest (Fig. 2). It flew directly to the Ob Shoal (52øS,41-42øE), where it spent two days Changesin foragingpattern through breeding sea- before returning directly to Crozet. Unlike son.--The maximum foraging range, distance males, the four females did not forage inten- covered and surface prospectedvaried greatly sively over specificareas of the shelf and ap- depending on the stage of the breeding cycle pearedonly to moverapidly over the shelf.They (Figs. 1 and 2, Table 1). During the first two foraged over pelagic waters in the vicinity of monthsof the incubationperiod, when the two the shelf (Fig. 5B). membersof the pair alternateevery 4 to 33 days One month after hatching, the chick is left on the egg (Table 1), Wandering Albatrosses unattendedon the nest,and both parentsforage foraged over pelagic waters from polar to sub- in order to feed it. At this time the adult birds tropical latitudes (Fig. 1). However, one of the mix short trips over inshore waters with long eight males foraged mostly over the inshore trips over pelagic subantarcticand subtropical waters of the Crozet shelf and, otherwise, over waters(Fig. 7). There were no intermediatetrips the adjacentpelagic waters. Foraging trips dur- (Fig. 2) betweenlong and shorttrips. Short trips ing incubation followed a looping coursefrom had a similar pattern to those of the brooding Crozet (Fig. 3A). During the trips of the entire period (Table 1). During long trips the average incubation period, 5 of the 16 birds tracked in- foraging range reached 1,534 km and the av- terrupted their directional progress,spending erage distancecovered 6,091 km (Table 1). Dur- a period of three to six days in a restrictedarea ing these long trips the birds foraged further where they moved over short distances(Fig. north than they did during the incubation pe- 3A). For four birds, these areas were located riod, and no bird was observed in Antarctic north of the subtropical convergencein sub- waters (Figs. 1 and 4, Table 2). During the chick- tropicalwaters (see Fig. 3A); the fifth bird moved rearing period, the long looping tracks rarely continuouslyover a shoal (Skiff Bank, 50øS,64- were interrupted by short-distancemovements 66øE)west of the Kerguelen Archipelago. The lasting only one to two days (Fig. 3B). During other birds moved continuouslyover extensive these long trips, three males foraged over or at Jllillllllll IIII 40]1111JlllllIIIlllllll IIII IllJill IIIIIIIIIIIIllliJlJll. 'I•'I',l-lel. IIIIIllIll I 5011111111111 'I'I'II IIIIIIJ IIIllllllllIIII IIIII1[ '• IIIIIIJlJlIIIIIIIIII IIIIII IIIIII1

INCUBATION LATE INCUBATION

IIIIIIIIII III IIIIIIIIII .I.•1 III 50Illlllllll 'I'III I-• IllllJllJl IIII I IIIIIIIJll IIII III

BROODING

[P-,Y_._14_II• I I I I I I I [ I ! ! ! ! ! ! I I I I I I ! ! • • i iiI LLLL""'"I II I I I I I I II I I.I.I'I I I II IH'I Illlllll I JIø1•,• J_l III I I I I I I I I "1.11I I I I I&l I I I I I I III •'"1II•l..i!!H IIII I IIIII !!!! !!!!1 Illll LLJJ.I III I IIIII IIIIIIIII IIII I III JALLI IIHIIIIIIIIIIIIIIIIIIIIIIII II1•1 I•.111111111111111111!111111111111111 •1111111111llllllllllllllllllllllll LLIIII III III I III II III IALLLII•111 IIII

CHICK REARING - Long lrips CHICK REARING - $horl lrips Fig. 1. Areasprospected by Wandering Albatrossesduring successivestages of breedingcycle. Each 2.5 ø square for which locationswere obtained are marked with a point. Crozet Islands are indicated by a star (incubation11 trips, 11 individuals;late incubation5, 5; brooding 15, 8; fledging 34, 16). April 1993] WanderingAlbatross Foraging Strategy 329 the border of the Kerguelen shelf, whereasthe other six malesand three femalesforaged over 28oo pelagicsubantarctic and subtropicalwaters (Fig. 8). Femalestended again to forageover more 24oo northerly watersthan males(Figs. 1 and 4, Table 2). During the short trips of the chick-rearing period,males breeding at the Baiedu Marin • 2000 colonyhad foraging zones mostly south of Pos- •

sessionIsland and East Island, whereas those • 16o0 o from the Pointe Bassecolony were foraging z mostly west of these zones (Fig. 6). •' 1200 Relationshipbetween length of stay at sea and • foragingrange.--During the long foragingtrips •_ ofthe incubation and chick-rearing periods, the ,• so0 time at seawas significantlyrelated to the maximum range and distancecovered (Fig. 9). The 4oo time spent at sea was more closely related to the distance covered than to the maximum range.In contrast,during the broodingperiod, o there was no relationship between duration of Early Late Brooding Chick alone

foraging trips and either the maximum range INCUBATION FLE DGING or distance covered for tracks with a maximum Maximum rangesrecorded for males(black rangeshorter than 500 km (Fig. 9). The rela- points)Fig.2. and females(white points) during successive tionship was significant if the longer tracks, stagesof breeding season. spent mostly over pelagic waters, were included. When the chick was left alone at the nest, there was no relationship between the time 5A). Similarly, two other individuals were spent at sea and the range or distancecovered. trackedduring the incubationperiod and there- Individualforaging tactics.--During the long after during the brooding period. Both spent trips of the incubation period, we did not fit morethan one day at specificzones on the edge the same bird with a transmitter for successive of the shelf on the way backfrom their pelagic foraging trips. During the late incubation pe- foraging trips of the incubation period. Later riod, just before its chick hatched, one male was during the broodingperiod, they returned to tracked during two successivetrips. The bird the samerestricted area of the shelf (Fig. 10B). foragedtwice over the shelf, spendingmost of During shorttrips of the fledgingperiod, nine its time over two adjacentbut distinct areas(Fig. maleswere trackedon successiveforaging trips. 10A). During the brooding period, it returned Each individual tended to return to the same four times to the secondarea visited (see Fig. specificarea, locatedat the edge of the shelf

TABLE1. Maximumforaging range, distance covered and durationof foragingtrips during successivestages of breeding cycle:œ + SD, range (n).

Maximumrange Distancecovered Length Period (km) (km) (days) Incubation (first 1,284 + 740 5,991 + 4,264 14.0 + 9.0 two months) 75-2,602 (11) 1,282-15,200 (11) 4-33 (11) Late incubation 395 + 217 2,118 + 1,068 9.6 + 4.6 110-612 (5) 908-3,664 (5) 4.2-14 (5) Chick brooding 256 + 257 923 + 698 2.8 + 0.9 74-1,030 (15) 330-3,007 (15) 1.3-5 (15) Chick rearing (long trips) 1,534 + 509 6,091 + 3,328 11.6 ñ 6.2 814-2,618 (17) 3,736-14,716 (14) 1.8-26.9 (14) Chick rearing (shorttrips) 117 + 77 532 + 325 2.4 + 1.0 34-303 (17) 279-1,327 (10) 0.7-4 (14) 330 WEIMERSKIRCHETAL. [Auk, Vol. 110

45øS

50os 40 ø E 45 ø E 50 ø E i I I sOUT•

'40os

EDWARDPRINCE 0 500 KM

ß50 os 30 øE 40oE 50øE I I Fig.3. Detailedtracks oflong foraging trips of Wandering Albatrosses during: (A) incubation period with aninterruption ofseveral days of the loop (4,372 km covered bymale BS 1989); and (B) fledging period (9,986 kmcovered by female CF 3742). White dots indicate daytime locations and black dots the nighttime locations.

(Fig. 6). For 15 pairsof successiveshort trips, in the area. The three females tracked during the birds returned to the same area as visited successiveshort trips did not return to exactly previouslyin 73%of the cases.The birdsused the samepelagic area (see caption for Fig. 5B). various routesto reach this area (sometimesfly- After the broodingperiod, the sameindividual ing overpelagic waters; Fig. 5A) and spentan appearedto mix long tripswith shorttrips. For averageof 61.2%(SD = 19.8%,n = 15, range example,male BS 6663 started with a long trip 32.0-90.7%)of the duration of the foragingtrip north of Crozet,then foragedon the shelf dur- April 1993] WanderingAlbatross Foraging Strategy 331

TABLE2. Median latitudes(and ranges)of locations obtainedfor malesand femalesduring long foragingtrips of incubationand fledgingperiods, with 25 a test on equality of medians x ranges. 20 Chi 30tA INCUBATION Males Females square Incubation 47.2 (36-68) 44.2 (32-56) 24.9*** Fledging 44.3 (30-60) 37.8 (30-48) 103.7'** Chi square 192.8'** 46.1'**

***, P < 0.001.

30 34 38 42 46 50 54 58 62 66

ing two successiveshort trips before finally re- FLEDGING

turning to pelagicwaters north of Crozet (Fig. 25 7A). Similarly, female CF 3043 started with a long trip over subtropicalwaters north of Cro- 20 zet, foraged over pelagic waters close to the shelf,and returnedthereafter to exactlythe same pelagic area (Fig. 7B). Another male returned twice to the sameextensive pelagic sector(Fig. 8A, tracks 4a and 4b). During long foraging 5 trips,some birds headed for the Kerguelenshell and one bird trackedduring two long trips re- O30 34 38 42 46 50 54 58 62 •6 turned twice to the Kerguelen shelf. LATITUDE øS Influenceof wind.--To evaluatethe hypothesis Fig. 4. Frequencydistribution of locationsof males that during long pelagic trips routesare pri- (white columns) and females (black) between 30øS marily determined by wind direction, we had and 68øSduring long foragingtrips of: (A) incubation the opportunity to track two birds leaving Cro- period (n = 285 and 1,308 locations for females and zet at the sametime for long foraging trips dur- males,respectively); and (B) fledging period (n = 306 and978 locations for femalesand males, respectively). ing the fledging period. The two birds were 60 km apart and flew so as to have the wind on the quarter (i.e. blowing from behind to one side).They followed similar coursesduring the trosses(Tickell 1968, Tickell and Pinder 1975, first six days of their respective trips, then Weimerskirchet al. 1986)and, generally,is as- changed direction when the wind direction sumedto ensurethat on hatchingthe chickre- changed(Fig. 11), suggestingthat wind was im- ceivesa mealquickly (Croxall 1984). During the portant in determining the route of the birds. brooding period, when the chick has to be fed everyday or so,Wandering Albatrosses feed at the edgeof the shelf closeto the breedingcol- DISCUSSION onies. After the brooding period parents re- sumeforaging over distantwaters. Although Our studyhas revealed several aspects of the somechanges in foraging behavior have been foragingstrategy of the WanderingAlbatross. inferred from the change in duration of for- First, length of trip varied extensivelyaccord- agingtrips, our datashow clearlyhow substan- ing to the stage of the breeding season.Al- tial and clear cut are differencesin foraging though we confirmed that Wandering Alba- patterns during the different stagesof the trossesare basicallylong-range pelagic feeders breeding season.However, pelagic feeding (Tickell 1968,Croxall and Prince 1980,Jouven- zonesprospected in summerduring incubation tin and Weimerskirch1990), their foraging move north in winter. This shift to the north strategycan changesubstantially to copewith probablyoccurs because the high latitudesare the constraintsimposed by the breedingcycle. ice coveredduring winter and there is a sig- During the incubationperiod, pelagic trips are nificantdecrease in preyavailability in antarctic reducedin rangeand durationas the hatching waters comparedto that in subantarcticor sub- of the chickapproaches. This decreasein trip tropicalwaters during the winter (Foxton1956). durationis known for severalspecies of alba- Thus,the foragingbehavior of the Wandering 332 WEIMERSKIRCHETAL. [Auk, Vol. 110

B /• (• BS4956 .

46os k -5om . -.• .A' , - "'•-$• • , /- •,-_-/•._ ?•----• ,.- 47øS• ' ,,.. .,/,• 2 (• BS4965 0 50KM

48 ø E 50 ø E 52 ø E ! t I Fig.5. Foragingtrips of (A) two individual males and (B) two individual females during brooding period. Islandsof Crozet group indicated inblack and edge of shelf with dotted line. Four successive tracks (numbered 1-4)of maleBS 5151, two successive tracks (A-B) of maleBS 4982, two successive trips of femaleBS 4957 (la and lb), andone trip of femaleBS 4965 (2) represented.Arrows indicate flight direction.

Albatrossesappears to be influencedby con- feedingfrequencies, are invalid in speciesthat straintsimposed by the breedingcycle and by mix short and long distancetrips. changesin prey availability. Third, birds are able to return to specificareas Second,in additionto being ableto vary for- in the ocean.During the shorttrips of the chick- aging tacticsin relationto the differentcon- rearingperiod, male Wandering Albatrosses re- straints of the breeding cycle, birds may mix turnedto specificareas, at the edgeof the shelf, (duringthe samestage of the season)long pe- on successivetrips. These areas are restrictedin lagictrips with shortinshore trips during chick size,and may be usedby severalbirds or by rearing.This suggests that previous deductions only one.A particularrestricted zone located concerningforaging range during the chick- at the edge of the shelf, south of Possession rearingperiod, based on the measurementof Island,appeared to be attractiveto morethan April 1993] WanderingAlbatross Foraging Strategy 333

'•i•• COCUONSß /,/ -•PO ¸BM [] 3.5 d. 1327km 1.6 d. 629 km 18.0d. 9880 km 0 4•00km

45 ø

PRINCE 47•S EDWARD •ROZET KERGUELEN 50'E 52•E I • 11.4d.4837km• 40ø Fig. 6. Map of the Crozet shelf showing location B of different oceanicsectors prospected during short trips during chick-rearingperiod by malesoriginat- ing from two colonies of PossessionIsland, Pointe Basse(PB, circles, three different birds) and Bale du Marin (BM, squares,nine different birds). When same bird tracked during successivetrips, the area pros- 40øS pected is indicated with an "a" for first trip, "b" for second, etc.

two-thirds of the males tracked. These zones are likely to be areasof high food availability. The edges of shelves are often zones of turbu- • , 2•KM lence with increasedprimary and secondary production (El Sayed et al. 1979). Complemen- tary hypotheses could be that the birds from 50øE• 60• different colonies or from different islands for- Fig. 7. Successivelong and short foraging trips age preferentially over specific zones of the during chick-rearingperiod of one male and one fe- shelf.Birds from PossessionIsland could forage male. (A) Four successivetracks (a-d) of same male mostlyover the southernedge of the shelf,south (BS 6663) during chick-rearingperiod (27 May-30 of Possession Island and East Island, whereas June),with length(days) and distance covered during each trip. (B) Three successivetrips (a-c) of female the birds from the large colony of Ile des Co- CF 3043,with two long trips in samepelagic sector. chons could forage mostly over the extensive Trackfor secondlong trip is incompletebecause bat- edge located south of that island. Our results teries became exhausted. suggestthat the separationof feeding zones during the chick-rearingperiod could even oc- cur between different colonies on Possession sector,or to the inshorewaters of the Kerguelen Island (Fig. 6). Such a separationof foraging shelf. The sectorsprospected are extensive,but zones has been detected in the Black-browed the birds are able to return to a restricted area Albatross (D. melanophris;Weimerskirch et al. as shown by the successivetracks of some in- 1988)and fits with the hinterland model (Cairns dividuals (e.g. Fig. 6). 1989),which predictsthat seabirdsfrom neigh- Fourth,different individualsseem to employ boring colonies occupy nonoverlapping feed- differentforaging tactics. For example,during ing zones and that colony size is a function of the incubationperiod one bird foragedclose to the size of thesezones. If Wandering Albatross- or even over the Crozet shelf, while most other es fit this model, it suggeststhat the size of the individuals foraged over pelagic waters. Con- colonymight be determinedby the size of the versely,during the brooding period, although feedingzone exploited during a short,but con- mostmales return to specificareas at the edge straining,period (brooding) of the breeding cy- of the shelf, one male made a short-duration cle. During the long trips of the chick-rearing trip acrosspelagic watersto reacha remote shelf. period, each bird returns to the same pelagic Although the individual area prospecteddur- 334 WE•U•RSK•RCHET^L. [Auk, Vol. 110

.35 ø

40øS

,45os

t PRINCE EDWARD

-50os

40øE !

30 øS-

It AJ 4oos.

EDWARD -- CROZET

KERGUELEN •50ø. 30 øE 40øE 50 øE 60øE 70øE I I I I I Fig. 8. Long foraging trips during chick-rearingperiod. (A) Two successivelong trips of male BS 061 (4a, 4b) and three trips of three different males(BS 156 [1], BS 1308[2] and BS 4138 [3] in Kerguelen area. (B) Long foraging trips in subtropicaland subantarcticwaters of one female (1) and three males (2, 3, 4). ing the broodingperiod was the samefor two- haveto travelfrom their nestto find foodproved thirds of males, other males had distinct indi- to be true for the long pelagic trips of the in- vidual foragingzones. During the long trips of cubation and chick-rearingperiod. The close the chick-rearingperiod, mostof the birds for- relationship observedduring the latter period aged over pelagicwaters, but somevisited the probablyresults from the fact that, during in- offshorewaters of the Kerguelenshelf. cubation, birds tended to interrupt their loop- Fifth, the assumptionthat the durationof for- ing course with movements over specific oce- aging trips is related to the distancethe birds anic sectors more frequently than they did April1993] WanderingAlbatross Foraging Strategy 335 during the chick-rearingperiod. The closerre- battossescover great distancesduring daytime lationshipbetween the durationof foragingtrips and remain stationaryor move over short dis- and the distance covered than with the maxi- tancesat night (Jouventinand Weimerskirch mum range suggeststhat the foraging strategy 1990). Prolonged absenceof movements over is not basedon a simplereturn trip to a specific severaldays, when birdsdrift on the seasurface, zone but rather on continuous foraging on a is causedby the absenceof wind, which keeps looping track. The longest distancescovered albatrossesfrom flying (Jouventin and Wei- were not distancestravelled for commutingbut merskirch 1990). Birds drifting with sea cur- distancesspent foraging. For the short trips of rents are clearly different from birds foraging the chick-rearing period, the relationship be- actively (moving continuously)over a specific tween time spent at sea and the range or dis- zone asobserved during someincubation trips. tancecovered was not significantwhen trips of The interruptionsof long foragingloops when more than 500 km were disregarded. The ab- birdsforage actively on a restrictedoceanic area sence of a relationship for the inshore trips could relate to the presence of fishing boats. probablyresulted from the factthat, during short Wandering Albatrossesare well known to be inshore trips, birds foraged over a restricted ship followersand, particularly,are attractedto areaand probablylimited their maximumrange long-line fishing boats(Brothers 1990). Several in order to return rapidly to the nest. WanderingAlbatrosses from Crozet have been Sixth, although the sample size for females caughtin long-line fishing gear in the subtrop- was small, somesex-specific differences in for- ical waters of the Indian Ocean (Weimerskirch aging behavior were apparent.The sex-specific et al. 1985). These long-line fishing boats op- differences in the foraging zones prospected erateintensively in the subtropicalwaters north during the brooding period might have result- of Crozet (Brothers 1990), where three of the ed from competitive exclusion of the females four birds pausedin their foraging loops.The by the larger males.Indeed, if almost all males fourth bird foragedactively on a bank west of (ca. 1,200 breeding males at this time of year, Kerguelenwhere trawlers operateat that time calculated from Weimerskirch and Jouventin of year. 1987) foraged at the edge of the small Crozet Apartfrom theseinterruptions of severaldays shelf, intraspecificcompetition could be high observedduring incubationin somebirds, they and, consequently,access to a patchy resource are likely to forage all along the long loops. could be difficult for females. By foraging far- WanderingAlbatrosses feed mostlyon squids ther away over neighboring pelagic waters, fe- (Imber and Russ 1975, Weimerskirch et al. 1986, males may avoid competition with the larger Rodhouse et al. 1987). It was believed until re- males.During long trips of the incubationand cently that albatrossescatch live biolumines- chick-rearingperiods, females tended to forage centcephalopods at night (e.g.Imber and Russ more to the north than did males.This tendency 1975,Harper 1989).However some albatrosses has already been detectedby observationsat may feed on dead squidslocated during the sea of Wandering Albatrossessexed using dif- daytime(Weimerskirch et al. 1986).This sug- ferencesin plumage pattern (Weimerskirchet gestionhas been supported by the observation al. 1989). In the summer in the Indian Ocean, that someprocellariiforms feed more on squid there is a larger proportion of female-plumaged speciesthat floatafter death than on thosethat birds than of males at the northern edge of the sink (Lipinskiand Jackson1989). Direct mea- speciesrange, whereas at the southernedge of surementsof time of feeding in WanderingAl- the range, malesare more abundant (Weimers- batrosseshave now confirmedthat feeding takes kirch and Jouventin 1987). placemostly during the daytime,whereas at Two distinct foraging strategieswere distin- night birdsmostly sleep (Weimerskirch and guishable.They appear to be used, either alter- Wilson 1992). This fits well with our observa- nately or mixed, to copewith the different con- tion that birds never spentsuccessive nights at straintsimposed by the breeding on land of a the samelocation during the long foragingtrips. bird feedingat sea.The first strategyis that used Their routesare determinedby the wind di- during the long foragingtrips. The route of the rection that is most favorable for flight, mini- birds is strongly influenced by wind (see Jou- mizingenergy expenditure while maximizing ventin and Weimerskirch [1990], but particu- the distancecovered. Pennycuick (1982) esti- larly Fig. 11).During long trips,Wandering A1- mated that with their dynamicsoaring flight, 336 WEIMERSKIRCHEt ^L. [Auk,Vol. 110 LONGTRIPS INCUBATION CHICK REARING 730x- 43 y=66.3x+ 688 • 2000. r=0.873, P=•01• (•?o o'o 1000, _0•¸ 0 /U .o/ o 0

• ' •o ' •o ' ' 1•) ' •0 ' 3b Time 8t (days) 0

y=506x + 220 r=0.942 , P <0.0001 10,000- o.•o•,p

' • ' •o ' •o ' ' 1•) ' 2•0

0 Time ( days ) o 15,000- •x - 326. 0 r =0.945 , P . y=6.6x-r=0.936, 3554P < 0.0001 10,000-

5000' o / ./ 0 /o 1dO0 2000• 10•00 20•)0 Maximum range (kin) Fig.9. Relationshipsof time spent at sea, maximum foraging range, and distance covered during successive stagesof breedingseason for (A) longtrips and (B) short trips. Circles refer to malesand squares to females. Blacksymbols refer to the late incubationperiod. April 1993] WanderingAlbatross Foraging Strategy 337

SHORT TRIPS B

BROODING CHICK ALONE ON NEST 1000- 13 0.175 r= 0.329 200' N.S. N.S. o

500 - o o ¸ 100. o o o [] •0 o o o¸ o o oO o 0

Time at sea (days)

3000-

n=13 r = O. 506 r = 0.543 N.S. N.S.

2000- 1000-

o 0 [] o o 1000 ß 500- o o o o o

3000- 0 Time at sea (days) y= 3.4x* 147 r = 0.854 , P < 0.001 o n=13

2000- 1000 - y=6.1x - 3.6 / r = O.781 / [] P=0.01 / 0

1000 - 500 - oo/

56o 1oho 16o 260 Maximum range (km) Fig. 9. Continued. 338 WEIMERSKIRCHET^L. [Auk, Vol. 110

could increase the probability of locating the A • /' ..... , A 0 BS 5151 sparseand scatteredprey at the seasurface. Dead squid could be found in this way. Rodhouseet al. (1987) pointed out, for example, that mass mortality of squid after spawning could rep- resent considerable but sporadic opportunities for surface-feedingseabirds. During the long foraging trips, most birds probably do not try to reacha specificarea but forage continuously throughout their looping tracks. Continuous foraging during the long loops could allow the O• 50KM • predator to scana very large area. The surface area prospectedby the Crozet population during the breeding seasonis very large (several millions of square kilometers). The low prob- B /'---,, 0• BS5373 ability of finding sparseprey, thus, is offsetby the surfacearea coveredby each individual. t/ •..•LATEINCUBATION Models of optimal foraging suggestthat central-place foragers should reduce the time for commuting to a minimum and stay in feeding ,, ,, ,'/,e zonesuntil they have fulfilled their energy requirements (Charnov 1976, Orians and Pearson 1979). During long trips, Wandering Albatross- es move continuously and do not remain on /t /•/ •0 50I KM specificareas except at night, suggestingthat searchingand exploiting resourcesare not mu- tually exclusive as assumedby the models of optimal foraging (Schoener1971, Charnov 1976). Most theoretical work has concentrated on C "'.... • (• BS5373 studiesof animals facing distributions of food , BROODING in distinct patches(Krebs et al. 1983), but often animals combine travelling and feeding when .46øS i/ ß ? k-•,• • ,, .,.y...... they move acrosstheir habitat (e.g. Krebs and McCleery 1984). Excluding the resting periods at night, the entire loop could be productive for the bird. As during the fledging period, Wandering Albatrossescatch several prey during a single trip, the transportationof prey to the central place is combined with foraging. This strategyis probably very efficient in petrels and albatrossesbecause for these species the V50øE • ' 52OE'food is transformed into a lipid-rich stomach oil (Clarke and Prince 1976, Warham et al. 1976). Fig. 10. Successivetracks of: (A) male BS5151 just This adaptation reducesthe mass of the food prior to hatchingof chick (comparewith Fig. 5A for load while concentrating the dietary energy. successivetrips of samebird after hatching);and of Our results suggestthat the food exploited by male BS5373 for (B) one trip justbefore hatching and the Wandering Albatrossesduring the long trips (C) two trips just after. is probably not distributed in well-delimited distinct patches. Rather, these albatrossesforage for a resourcewith a spaceddistribution. which extractsenergy from the wind gradient, This is confirmed by direct measurementsof Wandering Albatrosseswould need to consume time of feeding showing that Wandering Al- only 1% of their body massto cover 1,000km: batrossesswallow on average one prey every foraging over long distances,consequently, 100 km (Weimerskirch and Wilson 1992). April 1993] WanderingAlbatross Foraging Strategy 339

ß MIDNIGHT LOCATION OrBS6663 • WIND DIRECTION

0 200 km I i I 6 40Os.

ov BS061

45øE ' 55 ø E

Fig. 11. Tracksof two males leaving Crozet Islands at sametime on 28 May 1990, with successive-night locationsindicated from 1 (night of 28-29 May) to 9 (night of 5-6 June). Arrows indicate wind direction.

Characteristicsof short trips (with periods alters at this time (Weimerskirch unpubl. data). spent at specific areas), in contrast to those of During the short trips, each bird has a prefer- long trips, are in closeraccord with the central- ential oceanicfeeding zone to which it returns place-foraging model. Commuting routes for irrespectiveof the prevailing winds. Thesespe- short trips are likely not to be productive, and cific zonesvisited by the birds cannotbe zones the birds remain in the same restricted area for of trawling or long-lining becauseno commer- a proportionatelylonger period. Either the birds cial fishing activity takes place in the 370-km locate their inshore feeding zones on the way (200-nautical-mile) economic zone around back from their long foraging trips of the in- Crozet. When birds are commuting they are cubationperiod, or they return each breeding likely to faceadverse winds during the few days season to the same area. However, some birds available to reach the feeding zonesand return changedfeeding area from one short trip to the to the colony. Short travelling distancesare next. This suggeststhat either the choiceof the likely to be moredemanding energetically than feeding zones could be related to proximal food the long foraging trips during which birds can availability, which is evaluated during incu- usewind optimally to reduceforaging cost. Why bation for exploitation later on during the short then do birds not foragepermanently over pe- trips, or that birds have traditional feeding lagic waters rather than alternate short inshore zones.During the brooding period, one parent trips with long pelagic trips? Regular and fre- remains on the nest while the other has to find quent feedingsincrease the growth rate of chicks food for himself/herself and for the chick, left alone on the nest (Schaffner 1990), increas- whose needs increaserapidly. For this reason, ing the chanceof a chick fledging and surviv- modelsof energeticsin breeding seabirdspre- ing. The dual foraging strategyobserved after dict that the brooding period is probably the the brooding period is probablya compromise most constraining(Ricklefs 1983). In the Wan- resulting from the necessityfor adult birds to dering Albatross,short inshore trips over the feed their chick frequently without flying far shelf area or to the neighboring pelagic waters from the colony and their need to foragewith enable parents to feed their chick frequently. a minimum of energy expenditure,and thereby However such trips could be particularly ex- maintain body condition.This secondrequire- pensive energetically, becausebody condition ment could only be achievedduring long trips. 340 WEIMERSKIRCHETAL. [Auk,Vol. 110

Basedon a detailedstudy of feedingfrequencies ing successvaries so little from one seasonto of males and females,a similar dual foraging the next (Weimerskirch and Jouventin 1987) and strategyhas been identified recentlyin another is not affectedby local decreasesin food avail- pelagic seabird, the Blue Petrel (Halobaenaca- ability (Croxall et al. 1988b). erula;Chaurand and Weimerskirch in press)and supports this hypothesis. It may be that this ACKNOWLEDGMENTS dual foraging strategy is a general feature of the ecology of pelagic procellariiforms (Wei- This study was supported by Terres Australes et merskirch et al. in press),but has not been iden- AntarctiquesFran•aises. We thank L. Ruchonfor help with the figures,as well asY. Gouedardand the mem- tified previouslybecause studies have not been bers of the 27th missionon Crozet for valuable help able to determine which of the two parentsare with the field work. D. G. Ainley, F. Cezilly, J.P. feeding the chick. The dual strategyprobably Croxall, S. Hall, J. C. Haney, W. L. N. Tickell, R. P. alsoresults in provisioningthe chickwith fresh Wilson, and G. D. Schnell gave helpful commentson food after the short trips and with a mixture of the manuscriptand improved the English. stomachoil and semidigestedprey after the long trips. The prey caught during the two types of LITERATURE CITED foraging trips are likely to be different, since one involves inshore foraging and the other AINLEY,D. G., AND R. J. BOEKELHEIDE.1990. Seabirds occursin pelagic waters. Thus, Croxall et al. of the Farallon Islands. Stanford Univ. Press, Stanford, California. (1988a) were surprised to find that the fish AINLEY, D.C., E. F. O'CONNOR, AND R. J. BOEKELHEIDE. caughtby a pelagicseabird like the Wandering 1983. The marine ecology of birds in the Ross Albatrosswere mostly speciesfrom the shelf. Sea, Antarctica. Am. Ornithol. Union Monogr. Conversely,Rodhouse et al. (1987) found that No. 2. mostof the squidwere taken in pelagicwaters. ANONYMOUS.1989. Guide to the Argos system.Ar- Given our results,we suggestthat during short gos Collecte Localisation Satellites, Toulouse, inshore trips Wandering Albatrossesfeed on France. fish,whereas during long pelagictrips they for- BROTHERS,N. 1990. Albatross mortality and associ- age for squid. ated bait lossin the Japaneselong line fishery in the Southern Ocean. Biol. Conserv. 55:255-268. The existenceof a dual strategysuggests that CAIRNS,D.K. 1989. The regulationof seabirdcolony in pelagic seabirdsthe averagerate of food in- size: A hinterland model. Am. Nat. 134:141-146. take is probablynot maximized(Schoener 1971), CHARNOV,E. L. 1976. Optimal foraging, the mar- but rather adjustedthrough a stereotypedfor- ginal value theorem. Theor. Popul. Biol. 9:129- aging strategyso that the condition of the adult 136. neverdeteriorates sufficiently for the bird'ssur- CHARNOV,E. L., ANDH. WEIMERSKIRCH.In press. The vival to be at risk. Models of life-history strategy regularalternation of shortand long trips in the predict that this risk is low in long-lived birds BluePetrel (Halobaena caerulea): A previouslyun- (Williams 1966, Weimerskirch et al. 1987), and describedstrategy of food provisioningin a pe- the dual strategycould be one way of reducing lagic seabird. J. Anim. Ecol. CLARKE,g., AND P. g. PRINCE. 1976. The origin of this risk, while providing regular food loadsto stomachoil in marinebirds: Analysis of the stom- the chick. This strategy is therefore a compro- ach oil of subantarcticprocellariiform birds. J. mise between the needs of the adult and those Exp. Mar. Biol. EcoL 23:15-20. of the chick. It differs from the strategy pre- CROXALL,J.P. 1984. Seabirds.Pages 533-619 in Ant- dicted for long-lived vertebratesoperating as arctic ecology,vol. 2. (R. M. Laws, Ed.). Academic long-distance,central-place foragers (Orians and Press, London. Pearson1979) that presumablyforage until they CROXALL,J.P., ANDP. A. PRINCE.1980. Food,feeding have met their own requirements before col- ecologyand ecologicalsegregation of seabirdsat lecting food for their chick (Charnov 1976, South Georgia. Biol. J. Linn. Soc. 14:103-131. Croxall et al. 1988b). Mixing foraging in two CROXALL,J. P., t. S. MCCANN, P. A. PRINCE,AND P. ROTHERY.1988b. Reproductive performance of distinct water massesfor two different types of seabirdsand seals at South Georgia and Signy prey could permit individuals to compensate Island, South Orkney Islands,1976-1987: Impli- for any decreasein food availability in one area cationsfor SouthernOcean monitoring studies. by increasingforaging effort in the other area Pages 261-285 in Antarctic ocean and resources or on another type of prey. This tactic could variability (D. Sahrhage,Ed.). Springer Verlag, explainwhy, in Wandering Albatrosses,breed- Berlin. April 1993] WanderingAlbatross Foraging Strategy 341

EL SAYED, S. Z., D. A. STOCKWELL,H. A. REHEIM, S. Georgia and its vicinity. Philos. Trans. R. Soc. TAGUSHI,AND M. A. MEYER. 1979. On the pro- Lond. B Biol. Sci. 300:75-106. ductivity of the southwestern Indian Ocean. PENNYCUICK,C. J., J.P. CROXALL,AND P. A. PRINCE. Comit• National Fran•aisdes Recherches Antarc- 1984. Scalingof foraging radiusand growth rate tiques 44:83-110. in petrelsand albatrosses(Procellariiformes). Or- FANCY, S. G., L. F. PINK, D.C. DOUGLAS,C. H. CURBY, his Scand. 15:145-154. G. W. GARNER,S. C. AMSTRUE,AND W. L. REGELIN. PRINCE, P. A., AND R. A. MORGAN. 1987. Diet and 1988. Satellitetelemetry: A new tool for wildlife feedingecology of Procellariiformes.Pages 135- researchand management.U.S. Fish Wildl. Serv. 171 in Seabirds:Feeding ecologyand role in ma- Publ. 172:1-54. rine ecosystems(J.P. Croxall, Ed.). Cambridge FOXTON,P. 1956. The distribution of the crop of Univ. Press,Cambridge. zooplankton in the Southern Ocean. Discovery RICKLEFS, R. E. 1983. Some considerations on the Rep. 28:1-108. reproductiveenergetics of pelagicseabirds. Stud. FRESSANGESDU BOST, D., AND M. SEGONZAC. 1976. Avian Biol. 8:84-94. Note compl•mentairesur le cycle reproducteur RODHOUSE,P. G., M. R. CLARKE,AND A. W. A. MURRAY. du Grand Albatros (Diomedeaexulans) de l'•le de 1987. Cephalopod prey of the Wandering Al- la Possession,Archipel Crozet. Comit• National batrossDiomedea exulans. Mar. Biol. (Berlin) 91:1- Fran•ais des RecherchesAntarctiques 40:53-60. 10. HARPER,P. C. 1989. Feeding behaviour and other SCHAFFNER,F.C. 1990. Foodprovisioning by White- notes on 20 speciesof Procellariiformesat sea. tailed Tropicbirds:Effects on the developmental Notornis 34:169-192. pattern of chicks.Ecology 71:375-390. HARRISON,C. S., AND M.P. SEKI. 1987. Trophic re- SCHOENER,T. W. 1971. Theory of feeding strategy. lationship among tropical seabirds at the Ha- Annu. Rev. Ecol.Syst. 11:369-380. waiian islands.Pages 305-327 in Seabirds:Feeding STAHL,J. C., P. JOUvENTIN,J. L. MOUGIN, J.P. ROUX, ecologyand role in marine ecosystems(J.P. Crox- ANDH. WEIMERSKIRCH.1985. The foragingzones all, Ed.). Cambridge Univ. Press,Cambridge. of seabirds in the Crozet Islands sector of the IM1)ER,M. J., AND R. RUSS. 1975. Some foods of the Southern Ocean. Pages478-486 in Antarctic nu- Wandering Albatross(Diomedea exulans). Notor- trient cyclesand food webs (W. R. Siegfried, P. his 22:27-36. R. Condy, and R. M. Laws, Eds.).Springer Verlag, JOUVENTIN,P., AND H. WEIMERSKIRCH. 1990. Satellite Berlin. tracking of Wandering Albatrosses.Nature 343: TICKELL,W. L. N. 1968. The biology of the great 746-748. albatrosses,Diomedea exulans and Diomedeaepo- KREBS,J. R., AND R. H. MCCLEERY.1984. Optimiza- mophora.Antarct. Res. Ser. 12:1-55. tion in behavioural ecology.Pages 91-121 in Be- TICKELL,W. L. N., AND R. PINDER. 1975. Breeding haviouralecology: An evolutionaryapproach (J. biology of the Black-browedAlbatross Diomedea R. Krebs and N. B. Davies, Eds.). Sinauer, Sun- melanophrisand Grey-headedAlbatross D. chryso- derland, Massachusetts. stomaat Bird Island, South Georgia. Ibis 117:433- KREBS,J. R., D. W. STEPHENS,AND W. J. SUTHERLAND. 451. 1983. Perspectivesin optimal foraging. Pages WARHAM, J., R. WATTS, AND R. J. DAINTY. 1976. The 165-216 in Perspectivesin ornithology (A.M. composition,energy content and function of Brush and G.A. Clarke, Eds.). Cambridge Univ. stomachoil of petrels (order Procellariiformes). Press,Cambridge. J. Exp. Mar. Biol. Ecol. 23:1-13. LACK,D. 1968. Ecologicaladaptations for breeding WEIMERSKIRCH,H., J. A. BARTLE,P. JOUVENTIN,AND J. in birds. Methuen, London. C. STAHL. 1988. Foraging rangesand partition- LIPINSKI,M. R., AND S. JACKSON.1989. Surface feeding of feeding zonesin three speciesof southern ing on cephalopodsby procellariiform seabirds albatrosses. Condor 90:214-219. in the southern Benguelaregion, South Africa. WEIMERSKIRCH,H., O. CHASTEL, L. ACKERMAN, T. J. Zool. (Lond.) 218:549-563. CHAURAND, F. CUENOT-CHAILLET,X. HINDERMEYER, ORIANS, G. H., AND N. E. PEARSON. 1979. On the ANDJ. JUDAS.In press. Mixed foraging strategy theory of central place foraging.Pages 154-177 in pelagic seabirds.Anim. Behav. in Analysisof ecologicalsystems (D. J. Horn, G. WEIMERSKIRCH,H., AND P. JOUVENTIN.1987. Popu- R. Stairs,and R. D. Mitchell, Eds.).Academic Press, lation dynamicsof the Wandering Albatross,Di- New York. omedea exulans, of the Crozet Islands: Causes and PEARSON,T.H. 1968. The feeding biology of seabird consequencesof the population decline. Oikos speciesbreeding on the Farne Islands, North- 49:315-322. umberland. J. Anim. Ecol. 37:521-552. WEIMERSKIRCH,H., P. JOUVENTIN,J. L. MOUGIN, J. C. PENNYCUICK,C. J. 1982. The flight of petrels and STAHL,AND M. VAN1)EVEREN.1985. Banding re- albatrosses(Procellariiformes) observed on South coveriesand the dispersionof seabirdsbreeding 342 WEIMERSKIRCHETAL. [Auk, Vol. 110

in French austral and antarctic territories. Emu ments in the Wandering Albatross. Pages 185- 85:22-33. 198 in Wildlife telemetry (I. G. Priede and S. M. WEIMERSKIRCH,H., P. JOUVENTIN,AND J. C. STAHL. 1986. Swift, Eds.). Ellis Horwood, Chichester, United Comparativeecology of the six albatrossspecies Kingdom. breeding on the Crozet Islands.Ibis 128:195-213. WEIMERSKIRCH, H., AND R. P. WILSON. 1992. When WEIMERSKIRCH,H., B. LEQUETTE,AND P. JOUVENTIN. do Wandering AlbatrossesDiornedea exulans for- 1989. Development and maturation of plumage age?Mar. Ecol. Progr. Ser. 86:297-300. in the Wandering Albatross,Diornedea exulans. J. WILLIAMS, G.C. 1966. Natural selection, the costs of Zool. (Lond.) 219:411-421. reproduction, and a refinement of Lack's prin- WEIMERSKIRCH,H., M. SALAMOLARD,AND P. JOUVEN- ciple. Am. Nat. 100:687-690. TIN. 1992. Satellitetelemetry of foragingmove-