SEX-SPECIFIC DIFFERENCES IN MOLT STRATEGY IN RELATION TO BREEDING IN THE WANDERING ALBATROSS

Transcription

1 The Condor 93: Q The Cooper Ornithoogica Society I99 1 SEX-SPECIFIC DIFFERENCES IN MOLT STRATEGY IN RELATION TO BREEDING IN THE WANDERING ALBATROSS H WEIMERSIURCH Centre Nationa de a Recherche ScientiJique, Centre d Etudes Bioogiques des Animator Sauvages, Beauvoir, France Abstract The extent of mot of primary feathers was studied in reation to the status and to the duration of the interva between breeding attempts in the Wandering Abatross (Diomedea exuans) The repacement of primaries asts for more than one season, birds showing a typica wave mot with one to three foci occurring on a wing Mot never occurs on the breeding grounds In breeding as in nonbreeding individuas, maes invariaby renew more feathers than femaes Breeding maes and femaes renewed each year an average of 83 and 73 primaries per wing, respectivey The extent of primary mot of breeders was directy reated to the duration of the interbreeding period in femaes but not in maes Maes and femaes breeding for the first time had fewer new feathers than did experienced birds When they visited the nesting coonies, immature birds had fewer new feathers than did breeding birds of the same sex In immature birds, the extent of mot was reated to the body condition (mass) of maes but not of femaes The extent of mot was inversey reated to mass gain from one season to the next in nonbreeding maes These resuts suggesthat moting in the Wandering Abatross is probaby an important constraint that coud compete with breeding, particuary in femaes Possibe reasons for sex-specific differences in mot extent are discussed Key words: mot; Wandering Abatross; breeding; condition INTRODUCTION In birds, mot and breeding are two major energy demanding functions and reproduction and mot are temporay separated in most species (Payne 1972) This separation of breeding and mot coud resut from a confict in energy aocation between feather renewa and breeding (Pietiainen et a 1984, Furness 1988) In abatrosses, the primary mot period never overaps the breeding period and the repacement of fight feathers can ast severa years (Harris 1973, Furness 1988, Mevie 199 1) Birds show a Staffemauser or wave mot (Streseman and Streseman 1966) The mot of primaries in abatrosses can be interrupted and severa mot foci occur on the same group of primaries (Brooke 198 1, Furness 1988) Thus, athough primary mot takes pace at sea outside the breeding season, its extent can be studied retrogressivey on the breeding grounds by inspecting the number of freshy renewed feathers (see for exampe Furness 1988) In abatrosses, where some species breed ammay and others breed every second year when successfu in fedging a chick, the extent of mot necessary I Received 30 January 1991 Fina acceptance 5 Apri 1991 I7311 to maintain fight efficiency coud be in baance with the benefits of breeding in successive seasons (Fumess 1988) The Wandering Abatross (Diomedea exuans) is one of the most sexuay dimorphic seabirds, with femaes ony 80% of the mass of maes The breeding cyce asts a compete year and pairs that are successfu in fedging a chick breed in aternate years, whie those faiing during incubation or during the eary stages of the chickrearing period breed again the next year (Ticke 1968) The interva between breeding attempts is approximatey 12 months for the successfu breeders and between 5 to 11 months (according to the period when faiure occurs) for the faied breeders If energy or time for moting is imited, the extend of primary mot coud depend on the ength of the interbreeding season In the Wandering Abatross sexua maturity is ony acquired at an average age of years and immature birds start visiting the coonies when they are 4-7 years od (Weimerskirch and Jouventin 1987) During this extended period of immaturity the pumage of both sexes becomes progressivey whiter with age (Weimerskirch et a 1989) Immatures have to attain a sufficient body condition for breeding and probaby undergo severa compete mots Litte information, however, is

2 132 H WEIMERSKIRCH TABLE 1 Differences in mot pattern between wings of the same bird in 25 maes and 25 femaes Percent Number of new feathers in both wings Maes Femaes TABLE 3 Number of new primaries per wing in maes and femaes (sampes refer to the number of birds inspected) M&S FCXaeS Identica in both wings Differs by one feather Differs by two feathers 4 8 Differs by three feathers 0 4 Same number but different pattern 8 8 Nonbreeders Breeders Student s t test 54 -t f 21 (O-10,116) (O-8, 125) k 22 (2-10,273) (O-10,309) t = 88, t = 91, P < 0001 P < 0001 avaiabe on the mot pattern during this period because the status and age of the birds inspected are not generay known (Mevie 1990) In particuar, nothing is known of the mot strategy of birds passing from immature to breeding status, when energy must be aocated for the first time between moting and breeding Using a popuation with birds of known age and breeding status, in this paper I examine the mot strategy of immature and breeding Wandering Abatrosses in reation to the ength of time avaiabe between two successive breeding attempts and to the age, experience, and condition of the birds Particuar attention is paid to the differences between maes and femaes in order to examine whether sex-specific differences in the extent of mot exist in this highy dimorphic species METHODS The study was carried out on Possession Isand, Crozet Isands (46 25 S, E) in January- March 1989 and December 1989-January 1990 On Possession Isand the entire popuation of Wandering Abatrosses has been banded since 1960 and sightings of banded birds have been carried out in every year since 1966 (Weimerskirch and Jouventin 1987) Consequenty, the sex, age and previous breeding status of each bird is known (see Weimerskirch and Jouventin 1987) The extent of primary mot was studied ret- respectivey Three generations of feathers are found in the wing of Wandering Abatrosses I restricted my observations to the primaries that were cassified as new, od and very od according to the criteria described in Fumess (1988) New feathers have been renewed within the ast 12 months, od ones months earier and very od ones months earier (Harris 1973, Furness 1988) The breeding birds were weighed during incubation using the technique of Prince et a (198 1) that does not require restraining the breeder Nonbreeders were weighed in a cotton sack Weighings were performed with 10 and 20- kg spring baances accurate to 05 and 1% of capacity, respectivey During the period December-Apri, when they arrive at the coony from the sea, immature and breeding birds have empty stomachs and their mass is therefore basic body mass pus any body reserves Immature birds were weighed when they visit the coonies in December-Apri to seect their future mate (Pickering 1989) Vaues for the numbers of foci and of renewed primaries are given as the average + one standard deviation, range and sampe size RESULTS Of 8 14 immature and adut birds inspected, none was found in active primary mot between December and Apri The pattern of mot of pri- TABLE 2 Number of foci per wing (sampes refer to number of birds inspected, range for each category is - 3) Students test M&S Femaes f P Nonbreeders ns (82) (90) Breeders 151 k k (273) (310)

3 MOLT IN WANDERING ALBATROSS 133 TABLE 4 Number of new primaries per wing in maes and femaes with and without former breeding experience TABLE 6 Infuence of breeding experience of successfu breeders on the number of primaries renewed when commencing breeding the next season First breeding attempt Experienced breeders Student s t test M&S Femaes z+z 19 (-10,40) (-10,48) 86 * (3-10,233) (-10,261) t = 56, t = 41, P < 0001 P -c 001 Number of renewed primaries after Student s f test First SW%31 breeding breedings t P Maes 83? (5-10,27) (5-10, 116) Femaes ns (3-10, 31) (5-10, 132) maries was examined in 50 birds on both wings It was symmetrica in 52% of birds The number of renewed feathers was identica between wings in 52% of the birds, but coud differ by one, two or three feathers (Tabe 1) The differences between the sexes were not significant Because differences of this kind between wings in the number of feathers renewed was unikey to be significant in terms of energy requirement, ony one wing per individua was considered in the rest of the study The number of foci per wing varied from -3 It was sighty higher in breeding femaes than in breeding maes In nonbreeders there was no difference in the number of foci between the sexes (Tabe 2) Maes had significanty more renewed primaries than did femaes (Tabe 3: nonbreeders, t = 21, P < 0035; breeders t = 62,P < 0001) In both sexes nonbreeders had significanty fewer new feathers than did breeding birds (Tabe 3) Maes and femaes breeding for the first time had fewer new feathers than did birds that had bred at east once previousy (Tabe 4) Femaes that were successfu in rearing a chick two years previousy had a compete year between successive breeding attempts and they had more new primaries than did femaes that faied in breeding one year previousy or than femaes that bred for the Iirst time (Tabe 5) In maes, previousy faied and successfu breeders had simiar numbers of new primaries but more new feathers than did maes attempting to breed for the first time (Tabe 5) Birds faiing during incubation (January- February) had 1 O- 1 months avaiabe for the moting between the successive breeding attempts whereas those faiing during the first part of the chick-rearing period (March-Juy) had ony 5-9 months between the successive breeding attempts There was no significant difference in the number of renewed primaries between birds (maes or femaes) faiing during the incubation period and those faiing during the first three months of the chick-rearing period On returning to breed after a successfu breeding season maes that had bred ony once previousy had fewer new primaries than did more TABLE 5 Number of new primaries per wing in maes and femaes with previous experience of breeding (the status indicated is that during the previous breeding cyce) Maes Fe&S Status (period avaiabe for moting) a) Successfu breeders (12 months) b) Faied breeders (5-0 months) c) Faied during incubation (9-0 months) d) Faied during chick-rearing (5-8 months) Student s t tests: a)-b) c)-d) * 16 (5-10, 142) (3-10, 162) 83? (2-10, 53) (3-10,57) (2-10, 21) (3-10,20) 86 * (5-10, 33) (O-10, 38) t = 15, ns t = 49, P < 0001 t = 11, ns t = 07, ns

4 WEIMERSKIRCH FEMALES n = 86 MALES n = 73 r = 0141 NS 15 i r = 0181 NS 1 * L ti a I I II I I 1 1 I , * 3, a 4 I I I 1 1 I r = NS ,, I o- r = 0368 PrOX)2 y= _,b- :/ /* 2 g->:,; : : 8 + : NUMBER OF NEW PRIMARIES I I I I I 1 FIGURE 1 Number of primaries renewed per wing in immature maes and femaes in reation to age and body mass experienced breeders (Tabe 6) The difference in femaes, athough it existed, was not significant (Tabe 6) In nonbreeding maes, the number of new primaries was significanty correated with the mass of individua birds, but it was not reated to the age of the birds (Fig 1) In nonbreeding femaes, however, the number of renewed primaries was reated neither to the age of birds nor to their mass (Fig 1) When considering the number of new feathers and the mass of individua nonbreeding birds, during two consecutive years, the number of feathers renewed from one season to the next was inversey reated to the reative mass gain from the first to the second season in maes (r = -045, n = 18, P < 005) but not in femaes (r = -007, n = 16, ns) In breeding birds of either sex, there was no significant reationship between mass and extent of mot DISCUSSION Since the identification of feathers is easiest with the primaries, the mot of birds is generay described by the mot pattern of primaries This simpification appears reasonabe because primary mot usuay has a duration spanning the mot of a other feathers and requires a significant proportion of the tota amount of energy necessary for the entire repacement of the pumage (Ginn and Mevie 1983) In the Wandering Abatross, as in other species of abatrosses studied (Harris 1973, Furness 1988), the repacement of primaries can extend over three successive seasons, with up to three mot foci occurring on a singe wing Maes and femaes renewed an average of 83 and 73 primaries per wing, respectivey, between successive breeding attempts This figure is much high-

5 MOLT IN WANDERING ALBATROSS 735 er than the number of feathers renewed each year by the sma-sized Yeow-nosed Abatross (0 chororhynchos) (21 kg) that mots on average 45 feathers each year (Furness 1988) It is however ower than the 33-kg Waved Abatross (0 irrorata) where breeders renew 94 feathers each year (Harris 1973) Thus, size probaby has no infuence on the extent of primary mot in abatrosses Within each of the three species considered, but not in mae Wandering Abatrosses, the extent of mot appears to increase with the time between two successive attempts (Fig 2) However, interspecific comparisons indicated that the extent of mot is unreated to time avaiabe for moting Resource avaiabiity during the interbreeding season, which probaby depends on the feeding zones visited for moting and on migration patterns, is more ikey to have a major infuence on the extent of mot of the different species, but more comparative data are needed In abatrosses the primary moting period is ceary separated from the breeding period Very few abatrosses have been observed in active mot on the breeding grounds (Harris 1973, Fumess 1988) In the Wandering Abatross, as we, moting occurs amost excusivey during the interbreeding period However, some breeding birds start moting their primaries during the ast months of the chick-rearing period (M Saamoard, unpub) In breeders, the extent of mot coud depend on the time avaiabe between two breeding attempts (Fumess 1988) Wandering Abatrosses successfu in fedging a chick have an entire year to recover from breeding, whereas birds that fai in their breeding before Juy have a shorter period (Ticke 1968) In maes, the extent of primary mot is not significanty infuenced by the ength of the interbreeding period In contrast, femaes renew more primaries after a successfu breeding season than after faiing to breed Consequenty, the extent of mot in femaes is reated to the time avaiabe during the nonbreeding season Faied and successfu breeders from Crozet spend the interbreeding period at sea, in feeding zones that are different from those used during breeding period, particuary aong the Austraian coasts (Weimerskirch et a 1985) In these oceanic zones, Wandering Abatrosses have to renew their feathers and, in addition, have to restore breeding condition for the next season The repacement of feathers represents an increased energy requirement that coud compete with the rebuiding of body re- ; P 5 5 z 4 3, Time avaiabe for moting (months) f Mae Wandering Ab _) Yeow nosed Ab FIGURE 2 Number of primaries renewed per wing in reation to the ength of the period between two breeding attempts (data for Yeow-nosed Abatross from Fume 1988 and for Waved Abatross from Harris 1973) serves necessary for the next breeding season This competition coud occur in femaes where the extent of mot is dependent on the time avaiabe between two breeding attempts, but not in maes The difference between the sexes coud resut from the additiona energy demand associated with egg formation However, egg formation occurs in December in the Wandering Abatross, when the breeding femaes have aready competed their mot If energy is more imited for femaes than for maes during the nonbreeding period, femaes coud repace fewer feathers than do maes in order to be abe to breed the next season However, moting may aso increase the difficuty of obtaining food because of the reduced fight abiities incurred during the active repacement of fight feathers (Masman et a 1988) Abatrosses are aso subject to a higher mortaity during the active renewa of fight feathers, being particuary vunerabe to storms (Kinsky 1968) Thus, in the ife history of peagic seabirds, moting coud constitute an important constraint and very few reevant data on this topic are avaiabe on other species Immature birds have different constraints than do breeding birds Athough not concerned with breeding duties, they do visit their future breeding grounds reguary for pair formation (Pick-

6 136 H WEIMERSKIRCH ering 1989) and attain breeding condition and mot outside the breeding grounds The smaer number of new primaries in immatures compared to breeding birds indicates that immatures probaby have more difficuties in moting than do breeders This difference probaby resuts from a imitation in energy required for moting rather than in time avaiabe Utimatey, the difference between immatures and aduts resuts probaby from young birds having not attained the same foraging skis than breeders (Burger 1988) When increasing their skis, immatures progressivey increase their mass with age (Weimerskirch, unpub data), but not the number of renewed primaries The significant reationship between the number of renewed primaries of nonbreeders and body mass observed in maes, but not in femaes, indicates that body condition and mot coud be more antagonistic in femaes than in maes In addition, moting during the period spent at sea and the abiity to increase body mass from one season to another coud be in confict because at east in maes the extent of mot is negativey reated to the mass gain from one season to the next The onset of breeding coud be favored at the expense of moting in femaes because, when they start breeding, they are in the same body condition as are experienced birds (Weimerskirch, unpub data) but have fewer new feathers During the period preceding their first nesting attempt, future breeders renewed more feathers than other immatures but ess than did breeders This indicates that, athough they have a simiar time avaiabe for moting, inexperienced birds breeding for the first time have not attained simiar skis or met simiar energy requirements as have experienced birds After they have fedged a chick for the first time, maes and femaes repace sighty fewer feathers than do successfu experienced birds This difference coud resut from the fact that during a first breeding attempt, inexperienced birds coordinate food provisioning to the chick much ess effectivey than do experienced birds (Lequette and Weimerskirch 1990) To recover from this first breeding season, consequenty, they coud have a higher energy requirement during the interbreeding season that coud reduce the extent of mot Through this study, sex-specific differences in moting strategies have been highighted In Wandering Abatrosses, maes and femaes differ significanty in severa important aspects of their morphoogy, behavior, and ife history Femaes are 20-30% smaer in size and ighter than maes Maes incubate sighty onger than do femaes (Fessanges du Bost and Segonzac 1976, Croxa and Ricketts 1983) and femaes probaby take a smaer share than maes in provisioning chicks towards the end of the chick-rearing period (Croxa and Prince 1990) The current study sug- gests that breeding and nonbreeding femaes have more difficuties in renewing their primaries than do maes because they have invariaby fewer new feathers Each sex forages over different oceanic water masses (Weimerskirch and Jouventin 1987) Maes favor the cod Antarctic waters whereas femaes are observed mosty over subantarctic and sub-tropica waters (Weimerskirch and Jouventin 1987) Food avaiabiity and weather conditions, particuary wind conditions that extensivey infuence foraging strategies in this species (Jouventin and Weimerskirch 1990), are very different between these two oceanic sectors Consequenty, differences in foraging zones are ikey to be associated with sex-specific differences in foraging and food avaiabiity that inevitaby affect the patterns of primary mot ACKNOWLEDGMENTS The Administration of Terres Austraes and Antarctiques Franpises provided the ogistic and financia supports for this study on the Crozet isands This study is part of the programs on the ecoogy of birds and mammas of French southern territories directed by P Jouventin J P Croxa, P A Prince and WLN Ticke improved the Engish I am gratefu to WLN Ticke, J Laemand, C A Bost and B Lequette for hep with the preparation of the manuscript and to J P Croxa, Y Handrich and P A Prince for their extensive comments J Cooper and an anonymous referee gave hepfu comments on the manuscript LITERATURE CITED BROOKE, R K 1981 Modes of mout of fight feathers in abatrosses Cormorant 9: 13-8 BURGER, J 1988 Effects of age on foraging in birds Proc XIX Int Congr (1986): CROXALL, J P, AND P A PRINCE 1990 Recoveries of Wandering Abatross Diomedea exuans ringed atsouthgeorgia ringingandmigr11: Caoxw, J P, AND C R~cxm-rs 1983 Energy costs of incubation in the Wanderina Abatross Diomedea exuans Ibis FRESSANGES DU Born, D, AND M SEGONZAC 1976 Note comptmentaire sur e cyce reproducteur du grand abatros (Diomedea exuans) de e de a Possession, archipe Crozet Corn Nat Franc Rech Ant 40:53-60 FURNFSS, R W 1988 Infuences of status and recent breeding experience on the mout strategy of the

7 MOLT IN WANDERING ALBATROSS 131 yeow-nosed abatross Diomedea chororhynchos J Zoo (Lond) GINN, H B,AND D S MELVILLE 1983 Mout in birds British Trust for Omithooav _< 1 Trina HARRIS, M P 1973 The bioogy of the Waied Abatross Diomedea irrorata of Hood Isand, Gaapagos, Ibis JOWENTIN, P, AND H WEIMERSKIRCH 1990 Sateite tracking ofwandering abatrosses Nature 343: KINSKY, F C 1968 An unusua seabird mortaity on the southern north isand (New Zeaand) Apri 1968 Notomis LEQUE-I-~E, B, AND H WEIMERSKIRCH 1990 Infuence of parenta experience on the growth of wandering abatross chicks Condor 92: MASMAN, D, S DAAN, AND C DLJSKRA 1988 Time aocation in the Kestre (Fake tinnuncuus) and the principe of energy minimization J Anim Eco 57: MELVILLE, D S 1991 Primary mout in Back-browed and Shy Moymawks Ndtornis 38:5-53 PAYNE R 1972 Mechanisms and contro of mot p In D S Famer and J R King [eds]; Avian bioogy Vo 2 Academic Press, New York, London PIETIAINEN, H, P SAUROLA, AND H KOLUNEN 1984 The reproductive constraints on mout in the Ura Ow Strix uraensis Ann Zoo Fenn PICKE~UNG, S P C 1989 Attendance patterns and behaviour in reation to experience and pair-bond formation in the wandering abatross Diomedea exuans at South Georgia Ibis 131: PRINCE P A C RICKETTS AND G THOMAS 1981 Weight oss in incubating abatrosses and its impications for their energy and food requirements Condor 83: STRESEMAN, E, AND V STRESEMAN 1966 Die Mauser der Voege J fti Omith (Berin) 107: TICKELL, W L N 1968 The bioogy of the great abatrosses, Diomedea exuans and Diomedea epomophora Ant Res Ser 12:1-55 WEIMERSIURCH, H, B LEQUETTE, AND P JOUVENTIN 1989 Deveopment and maturation of pumage in the wandering abatross Diomedea exuans J Zoo (London) 219: WEIMERSKIRCH, H, P JOWENTIN, J L MOUGIN, J C STAHL, AND M VANBEVEREN 1985 Banding recoveries and the dispersion of seabirds breeding in French austra and antarctic territories Emu 85:22-33 WEIMERSKIRCH, H, AND P JOUVENTIN 1987 Popuation dynamics of wandering abatross, Diomedea exuans, of the Crozet isands: causes and consequences of the popuation decine Oikos 49: