The Auk 113(4):830-841, 1996 ALLOCATION OF GROWTH IN FOOD-STRESSED ATLANTIC PUFFIN CHICKS HILDE STOL •JYAN • AND TYCHO ANKER-NILSSEN NorwegianInstitute for NatureResearch, Tungasletta 2, N-7005 Trondheim,Norway ABSTt•CT.--In long-lived seabirdsthat lay a single-eggclutch, allocation of growth to certain body parts may be advantageousfor the chick if food is limited. To investigatethis, 40 Atlantic Puffin (Fraterculaarctica) hatchlings were distributedin sevengroups that were raisedon differentamounts of food to 38 daysof age.When food intakewas reduced,growth rateswere depressedfor all charactersmeasured (i.e. body massand length of the wing, 2nd primary, forearm, head + bill, culmen, skull, tarsus,and middle toe). Head and wing parts grew preferentiallyrelative to the other characters,and onsetof growth was delayedin the primaries.All chicksaccumulated significant amounts of subcutaneousfat, whereasinternal fat depositswere presentonly in the chicksthat receivedthe mostfood. Received14 July1995, accepted20 March 1996. ONEWAY that parent birds adjustfor variation The wide variation in chick growth rates in food availability is to vary clutch size (Lack among speciesof alcids has been attributed to 1954,1966, 1968). In long-livedspecies that lay constraintson feeding ecology, such as spe- a single-eggclutch, alteration of chick growth cialized foraging behaviors,unpredictable and rate apparentlyis the only strategyavailable to patchy food distributions, and great distances adjust for variation in food. Slow growth re- between feeding and nesting sites (Lack 1968; duces daily energy requirements and allows Ricklefs 1968, 1984;Ashmole 1971;Sealy 1973; food to be delivered at a lower rate (Lack 1968; Nelson 1977; Birkhead and Harris 1985). Thus, Ricklefs 1968, 1979; Harris 1977; Nelson 1977; chicks of pelagic alcids often face the problem Drent and Daan 1980). Chick abandonment is of being fed at a low rate or even abandoned, likely when food demandscannot be met and because the contribution of an individual chick current offspringcontribute relatively little to to the total lifetime reproductionof its parents total lifetime reproduction (Williams 1966, is fairly small. Goodman 1974, Drent and Daan 1980, Ricklefs The burrow-nesting Atlantic Puffin is a typ- 1983). Variable growth provides a basisfor de- ical alcid. It is long-lived, has delayed sexual velopmental adaptationsin the chick, such as maturity, lays one egg per clutch, and feeds allocationof growth to parts of the body that mainly on pelagicfish (Harris 1984,Harris and would help reduce the nestling period and in- Birkhead1985). Chick-rearing is sharedby both creasethe chancesof survival after fledging. parentsand spans34-74 daysfrom hatchingto Someseabird chicks (e.g. tourres[Uria spp.]and fledging, depending on food supply (Nettle- Razorbills [Alca torda]), escape part of this di- ship 1972,Harris 1984,Harris and Birkhead 1985, lemma by leaving the nest soon after hatching Barrett and Rikardsen 1992). Puffin chicks leave to accompany(and be fed by) their parents at the nest burrow when they are about 60-80% sea(e.g. Lack 1968,Harris and Birkhead1985, of adult body mass(Harris and Birkhead 1985). Ydenberg 1989). In contrast,studies of species They are at risk to abandonmentby their par- that feed their chicks at the nest (e.g. Manx ents becauseadult puffins are specializedfeed- Shearwater[Puffinus puffinus], Harris 1966;At- ers that pursue a variable and patchy food sup- lantic Puffins [Fraterculaarctica], Tschanz 1979, ply (Anker-Nilssen 1987, 1992; Anker-Nilssen Anker-Nilssen 1987;and Yellow-eyed Penguin and Oyan 1995). [Megadyptesantipodes], van Heezik 1990) sug- Our study focusedon identifying adaptations gest that developing chicks faced with food in puffin chicks that may have evolved to re- shortagesallocate resourcespreferentially to duce the length of the nestling period when certain body parts. food supply is limited. We hypothesized that preferential allocation of growth takes place during food shortages.The allocation should E-mail: [email protected] favor body parts that enable the chick to reach 83O October1996] GrowthAllocation inAtlantic Puffins 831 the sea at an earlier physiological age or at a thawed in the eveningbefore being given to the chicks lower mass than "normal" and increase its as four portions supplied one by one at 0900, 1300, chancesof survival during the critical first time 1700 and 2100 (standardtime). A few milligrams of at sea. The charactersinvestigated were body Vitaplex© multivitamin were added to the morning massand growth of the wings, head, and feet. meal every day. The experimentalperiod ended at day 38, and at day 43 the chickswere sacrificedand Fat storagealso was measuredbecause fat could frozen. All carcasses were later dissected. serve as an energy supply during periods of In 1990, chicks were placed into two groups and erraticfood availability and during the firstdays given different amounts of food; diets (different of independence (Lack 1968, Drent and Daan amountsof capelin) were designedto simulate chick 1980, Ricklefs 1990). growth on Rost during a "bad" and a "good" year such that one group (group 3) always receivedhalf STUDY AREA AND METHODS the amount of food as the other (group 6). One stan- dardized equivalent (i.e. 3.33 g) of food was used as Study area.--The study was carried out in the ar- the basisfor the design of the diets. One group was chipelagoof Rost in northern Norway during the startedwith three equivalents,the other with six. In summers of 1990 and 1991. Chicks were collected (un- 1991, five groupswere establishedand given 2, 4, 5, der license from the Directorate of Nature Manage- 6, and 7 equivalents,respectively, from day 1 (Table ment) from nest burrows on the island Hernyken 1). At days 4, 10, and 19, chick diets were increased (67ø26'N, 11ø52'E),which had approximately 55,000 by a number of equivalentscorresponding to their occupiedburrows in 1990.The puffin colony of Rost groupnumber. Due to insufficientsupplies of capelin, amountsto about660,000 pairs and constitutesalmost each chick was fed 50 g of capelin per day from the one-third of the total Norwegian population of At- end of the experimentto day 43, resemblingthe "nor- lantic Puffins(Anker-Nilssen and •lyan 1995). mal" ageat fledgingat Rost(Anker-Nilssen and Oyan Chicks.--In the beginning of each June, 100 acces- 1995). Groupsgiven equal amountsof food (group 6 sible nests containing an egg were checkedevery in both years) acted as controls for possiblediffer- evening throughout the hatching period. When ap- encesin experimental conditionsbetween the years. proximately one-third of the eggs had hatched, 20 Due to a temporaryproblem with saltedcapelin being chicks (less than 24 h old) were collected and ran- given to chicks in group 6 on days 17 to 19 in 1990, domly distributedbetween the experimentalgroups this group was excludedfrom further analysis. (see below). Chicks were collected between 23 June Most chicks ate willingly throughout the experi- and 3 July in 1990 and 25 and 27 June in 1991. The ment, except that chicks in groups 6 and 7, which first day after collectionwas defined as day 1, and were provided with the most abundant food supply, chick massat this day prior to their first meal was occasionallyhad to be force-fedduring the first and taken as the hatching mass.Chicks weighed lessat last 2 to 4 days. This reluctanceto feed probably was hatching in 1990 than in 1991 (t = 2.30, df = 37, P = a consequenceof excessivefeeding, as severalstudies 0.027), but the differencewas only 2 g (i.e. <5% of indicatemuch lower daily food requirementsof wild body mass).Therefore, data from both years were puffin chicks early and late in the nestling period pooled for subsequentanalyses. (Harris 1976, Harris and Hislop 1978,Ashcroft 1979, Experimentaldesign.--Five blocks of four one-chick Anker-Nilssen 1987). cages(21 x 30 x 20 cm) were built of waterproof The quality of random samplesof the capelinwas plywood and wire netting. Aluminum profiles with det•erminedatthe Agricultural University of Norway built-in heatingelements made up the crosswalls of at As (1990) and the State Food Control Authority at the cages.The surfacetemperature of the profileswas Kv•il (1991) accordingto standardmethods for water, regulatedby a voltage regulator (Liibcke R52-220b) crude fat (HC1), protein (Kjeldahl-N), and total ash and kept within the range 34-37øC for the first 10 content. Sample sizes were small, but there was no days,to compensatefor brooding.During the restof indication that protein and fat content of the fish the experiment it was kept at 20-22øC to keep the differed between the two years (Table 2). The mean chicks dry, as excreted salty water tended to accu- energeticvalue for the capelin was about 5.3 kJ/g of mulate on the inner walls of the cages.The roomwas wet mass,which is well within the rangeof 3-11 kJ/g kept dark exceptduring a few hoursof cleaningevery reported by Bradstreetand Brown (1985) and others 1-3 days,and temperaturewas approximately 12-15øC (e.g. Barrett et al. 1987) for food brought to puffin throughoutthe experiment.Disturbance was kept to chicksby their parents. a minimum. Measurements.--In 1990, chicks were measured ev- Chicks were fed on capelin (Mallotusvillosus) that ery morning for the first 26 days,and thereafterevery were caughtand frozen in the BarentsSea each May. secondmorning. In 1991,chicks were measuredeach Capelin were transportedto Rost in blocks of 15-25 morning throughout the experimental