F25: The diet of the Redbilled Quelea Quelea quelea. Soobramoney, S., Baker, C.M. & Berruti, A.

Boegel, R., Prinzinger, R., Karl, E. & Walzer, C. 1998. A multisensor telemetry system for studying flight biology and energetics of free-flying Eurasian Griffons. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban. Ostrich 69: 368.

In the study of flight energetics, several approaches are common: (1) Measuring oxygen consumption. (2) Measuring turn-over-rates using double-labelled-water. (3) Adapting models of flight mechanics to the dimension of birds, and (4) Using heart rate as an estimate of metabolic rate. All of these approaches have specific disadvantages: method (1) Is restricted to lab conditions. (2) Delivers only average turnover rates within a defined period. (3) Is a purely theoretical approach with little experimental evidence, and (4) Delivers relatively coarse estimates, which are influenced by other factors. However, several studies showed that heart rate can be a reliable indicator of metabolic rate, especially if regression functions are individually correlated to different activities. To study flight energetics of free-flying birds under natural conditions, a multisensor telemetry system has been developed, which measures heart rate, body temperature, plumage temperature and air pressure/flight altitude. The method is appropriate for long-term-monitoring (two years) under field conditions (5 km range). Flight profiles of Eurasian Griffon Gyps fulvus, corresponding metabolic rates and patterns of body and plumage temperatures were recorded at the northern European Alps. The results are compared with flight conditions as predicted by GIS-models of thermals and dynamic updrafts.

Key words: thermoregulation, physiology, migration, Gyps fulvus, GIS-modelling

 

Bosque, C., Pacheco, M.A. & Siegel, R.B. 1998. Maintenance energy costs of two partially folivorous passerines. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban. Ostrich 69: 369.

Food habits influence the rate of maintenance energy expenditure in birds, but the relationship between a diet consisting of leaves of woody plants and avian BMR is not fully understood. In this work we report on the maintenance energy costs and thermal response to ambient temperature of two species of passerines (Saltator coerulescens (47 g), and S. orenocensis (32.7 g) that regularly include leaves and other tissues of plants in their diet. Passerines are of interest because of their small body size and because folivory is particularly scarce among them. We measured oxygen consumption (VO₂) in relation to ambient temperature during the non-active phase of post-absorptive birds with an open flow analyser. In accordance with expectations, both species of Saltator had substantially lower BMR than predicted from body size. Proportional reduction of resting metabolism was slightly greater in S. coerulescens (aprox. 37%), the more folivorous species, than in S. orenocensis (aprox. 33%). This reduction of resting metabolism should contribute to an economy of daily energy expenditure.

Key words: folivory, energetics, BMR, Saltator, Venezuela

Coria N.R., Soave, G.E., Montalti, D. & Vivequin, S. 1998. Diet of the Adélie Penguin Pygoscelis adeliae at the South Orkney islands. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban. Ostrich 69: 370.

Of all Antarctic birds, Adélie Penguins constitute the greatest biomass and are the most important consumers. There has been much interest in the vertebrate consumers of krill, especially around the continent of Antarctica, as a result of human harvesting of krill for food. The diet of the Adélie Penguin Pygoscelis adeliae was studied at Laurie Island, South Orkney Islands, Antarctica, during three creche periods (1989, 1990, and 1992) by quantitative analysis of adult stomach contents (n = 103). Samples were obtained by the stomach lavage technique. Euphausiids represented the predominant prey in terms of frequency of occurrence, mass and number, while fish and amphipods were present in small amounts. Antarctic krill Euphausia superba was the only species present in all samples. The only fish species identified was the myctophiid Electrona antarctica. Amphipods found mostly belonged to four taxa, Themisto gaudichaudii, Cyllopus lucassi, Hyperia sp and unidentified gammariids. Seasonal differences in the size of prey taken by Adélie Penguins appear to reflect either local changes in the availability of certain age classes at various times in the breeding season, or are due to year to year changes in food availability and abundance, possibly caused by environmental conditions.

Key words: Pygoscelis adeliae, diet, stomach contents, creche period, South Orkney islands

 

Cruz, J., Kitson, J. & Lyver, P. 1998. Seafood smorgasbord for Sooty Shearwaters Puffinus griseus. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban. Ostrich 69: 370.

We are interested in the long-term population dynamics of Sooty Shearwaters (titi, or Puffinus griseus) in New Zealand. Therefore, we need to know the effects fluctuations in food supplies have on the population and whether they are consistent throughout the bird's range in New Zealand. For this, we have identified food species from regurgitates obtained spontaneously on the Otago mainland and from spew samples obtained on islands where birds are traditionally harvested. Major prey items include arrow squid (Nototodarus sp.), krill (Nyctiphanes australis), amphipods (Hyperiella antarctica) and fish. We are also comparing the diet of chicks on the Titi Islands in 1997 with their diet during the 1998 El Nino-Southern Oscillation event. Identification of food species has given a preliminary indication of where the titi are feeding, both geographically and within the water column, and has also help delineate their prey's distribution. Knowledge of these feeding zones will help us define our future course of satellite telemetry studies in relation to fisheries by-catch.

Key words: diet composition, titi, prey distribution, New Zealand

 

Dietz, V. & Prinzinger, R. 1998. New results on embryonic development of oxygen consumption in altricial and precocial birds. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban. Ostrich 69: 370.

Metabolic rate during development increases exponentially but shows a stagnation phase (plateau) between 75 to 90% of the incubation time. This plateau covers a stable portion of total incubation time which is different in duration and absolute level for altricial and precocial bird species. Our own investigations show that the plateau is shorter in the altricials (12% of the incubation time, 17% in precocials) (Prinzinger, R. and Dietz, V. 1995. Respir. Physiol. 100, 289-294, Prinzinger et. al. 1995. Respir Physiol.100, 283-287). Some authors deny a plateau phase in altricials. Altricial bird species have a shorter compressed incubation time and therefore a relatively short plateau. This shortening could be the reason for overlooking its occurrence. The existence of a plateau is mentioned inter alia in connection to the process of internal pipping with the shift from allantois to lung respiration, an event which is found in both modes of development. Additional new data from not yet investigated altricial and precocial birds help to clear the controversy about the qualitative occurrence of a plateau during embryonic development (current investigations).

Key words: incubation, metabolic rate, plateau

 

Ellis, H.I., Woolfenden, G.E. & Bowman, R. 1998. Field metabolism of Florida Scrub-Jays during breeding. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban. Ostrich 69: 371.

Florida Scrub-Jays Aphelocoma coerulescens are an endangered species living in a fragmented oak scrub woodland. Until now, their energetics were not known. Doubly-labelled water (³HH¹⁸O) was used to measure field metabolism in these birds during their nesting season. During incubation and early brooding, the breeding male and helpers at the nest feed the female and chicks. Toward the end of the second week of brooding, the female begins to forage as well. Two locations were chosen: A natural oak scrub habitat on the Archbold Biological Station in Lake Placid, Florida; and in suburban parts of Lake Placid where fragments of oak scrub habitat remain near homes that have been built in recent years. Scrub-Jays hold territories in both areas, but suburban territories are smaller, perhaps due to the people in the area who put out feeders. Field metabolism was compared between males and females and between the two locations. The metabolic rates (in L CO₂ d^-1) of males were greater than those of females in each location. Elevated female rates, when found, seem associated with having older chicks in the nest. Field metabolism of suburban birds was nearly twice as high as males from the Archbold Station. The implications for conservation of this higher rate among suburban birds is discussed.

Key words: energetics, field metabolism, Aphelocoma coerulescens

 

Galetti, M., Laps, R. & Pizo, M.A. 1998. Frugivory by toucans (Ramphastidae) at two altitudes in the Atlantic forest in Brazil. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban. Ostrich 69: 371.

Toucans Ramphastidae are endemic of the Neotropics. There are few studies of this group in the wild. The diet of four species Ramphastos vitellinus, R. dicolorus, Baillonius bailloni, Selenidera maculirostris was studied at two altitudes (60 and 900 m a.s.l.) in the Brazilian Atlantic forest. The diet of toucans was richer (43 species) in the lowlands than in the highlands (23 species). While the main plants consumed in the highlands were Cecropia glaziovii, Euterpe edulis and Virola oleifera, only E. edulis was important for toucans in the lowlands. The two Ramphastos species occur sympatrically only at peak of fruit availability in the lowlands, suggesting competition. In the lowlands all species were frugivorous, while in the highlands the toucans were more insectivorous. Beak size and body mass were apparently not important characteristics in diet partitioning among the toucans since smaller species can eat the largest fruit eaten by the largest toucan.

Key words: toucans, Atlantic forest, seed dispersal, diet, fruit size

 

M. Gauthier-Clerc, J.P. Gendner, Y. Le Maho & Y. Handrich

CEPE/CNRS, 23 rue Becquerel, F-67087 Strasbourg cedex. France, e-mail michel.gauthier-clerc@c-strasbourg.fr

Gauthier-Clerc, M., Gendner, J.P., Le Maho, Y. & Handrich, Y. 1998. Trip durations at sea and body mass of King Penguins as indicators of food availability. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban. Ostrich 69: 371.

Breeding King Penguins Aptenodytes patagonicus of the Crozet Archipelago rely on fish patches at the Polar Front, 350 km or more south of their colonies. Thus, each mate alternates long foraging trips and long periods of fasting ashore. Using an automatic set-up for identification and weighing over a period of four years at Possession Island, we investigated the individual variations in the duration of foraging trips and the body condition during incubation and brooding periods of king penguins. About five thousand data were obtained. Duration of foraging trips decreased with advancement of breeding, but, at the same breeding stage, duration was longer with a later laying date. At certain times, whatever was the breeding stage of the birds, a dramatic increase in their trip duration occurred. This was interpreted as a response to a drop in marine food availability. This period was variable from year to year and appeared to be related to the position of major frontal zones. Variation in body mass indicated that energetic strategies of birds depended upon food availability: When marine resources are poor, adults allocate energy to themselves by building larger fuel reserves. This accords with the idea that the King Penguin, a long-lived sea bird, adopts a strategy to increase chances of survival rather than breeding success.

                           Key words: sea birds, bioindicator, nutritional state, marine resource, Aptenodytes patagonicus

Gavrilov, V.M. 1998. The cost of high level of the basal metabolic rate in Passeriformes. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban. Ostrich 69: 372.

A high level of basal metabolic rate (BMR) in Passeriformes is connected not just with net profits because its maintenance requires a definite cost. The correlation between evaporative and non-evaporative heat loss at different ambient temperatures (T_A) shows this cost. The dependence of evaporative water loss (EWL) from the body mass at different T_A (0° C, lower, T_lc, and upper, T_uc, critical) varies in the same way as the correlation between evaporative and non-evaporative heat loss. In Passeriformes, EWL is about 25 to 40% higher than in non-passerines (especially at high T_A), which is in good agreement with the ratio of their BMR levels. At 0° C and T_{l c}, the lines describing the effects of evaporative and non-evaporative heat losses on body mass do not intersect in the range of real sizes, but at T_uc, the lines of regressions for evaporative and non-evaporative heat losses intersect at a body mass of about 25 g in Passeriformes. These facts show that relatively larger passerine birds at high ambient temperatures find it more difficult to maintain their heat balance and they have to use additional water evaporation. Thus, a large expenditure of evaporative water reflects the cost of the advantages of BMR increase, and results in a higher energetic capability.

Key words: energetics, basal metabolism, passerines, critical temperature, evaporative cooling

 

Gavrilov V.V. 1998. Energetics of reproduction and development in some northern shore birds and passerine birds. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban. Ostrich 69: 372.

Energetics of reproduction in 18 species of shorebirds and in 10 species of passerine birds were studied in natural northern environments in May-August at the Lower Kolyma district of Yakutia and Novaya Zemlya. The daily energy of parental investment in males during the pre-nesting period depends on the type of territorial distribution and decreases in a series: (1) Males that have territories, which they defended from other males. (2) Males that are semi-territorial type (the individual areas exist but are not defended). (3) Males3. that are not have territorial. (4) Males that have leks. During incubation the daily energy of parental investment in males having territorial distribution is the same as during the pre-nesting period. The daily energy of parental investment in other incubating birds is lower and does not depend on bird gender. During the brood-raising period, the daily energy of parental investment is the same in all shore birds caring for chicks and lower in passerines. Birds spend from 18 to 40% of their daily energy budget on productive activity, depending on the period of the reproduction cycle. The daily energy of parental investment is maximal in females during the pre-nesting period.

Key words: shore birds, passerine birds, energetics, reproduction, territorial distribution, daily energy budget

1School of Biological Sciences, Flinders University, GPO Box 2100, Adelaide, 5001, South Australia, Australia, e-mail bikjs@cc.flinders.edu.au; ²Department of Zoology, University of Adelaide, Adelaide, 5005, South Australia, Australia

Jurisevic, M.A., Sanderson, K.J. & Baudinette, R.V. 1998. Energetics of avian vocalisations. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Conger.. Durban, University of Natal. Ostrich 69: 372

Rates of oxygen consumption were measured during begging behaviour in nestlings of seven species, and distress calling behaviour in adults of eight species of Australian birds. A transparent mask coupled to an openflow respirometry system was used and calling was elicited by the presentation of food or by the perceived threat of a predator. Distress calling significantly increased oxygen consumption above the measured resting levels in only two species of birds, with a factorial increase greater than two. Begging behaviour in juvenile birds caused a significant increase in metabolic rate in most cases, with a factorial increase in oxygen consumption over fourfold in some individuals.

Key words: energetics, vocalisations, metabolic rate, oxygen consumption

The Johnstone Centre, Charles Stuart University, PO Box 789, Albury, NSW 2640, Australia, e-mail nklomp@csu.edu.au

Klomp, N.I. & Schultz, M.A. 1998. The remarkable foraging behaviour of Short-tailed Shearwaters breeding in eastern Australia. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban. Ostrich 69: 373.

The chick provisioning behaviour of the Short-tailed Shearwater Puffinus tenuirostris breeding in southern NSW was examined during 1995 to 1997. Individual parents mixed a long foraging trip (14.6 ± 2.2 days) with 1-3 short foraging trips (mode: 1 day) gaining body mass on long trips and losing weight on short trips. The size of meals fed to the chicks was significantly greater after a long trip (160 ± 22 g) than after a short trip (140 ± 30 g). Adults embarking on long foraging trips were satellite-tracked in 1997. They flew directly south from Montague Island to forage in the Southern Ocean, around sub-antarctic islands and along the ice-shelf of Antarctica, travelling up to 15,000 km per trip, and flying at speeds up to 88 km/h. Adults on short foraging trips were never more than 500 km from the colony. Short foraging trips increase the overall chick feeding frequency. The variable number of short trips and the relationship with adult body condition are consistent with life-history theory: adults did not sacrifice their own body condition to increase food delivered to their chicks. This dual foraging strategy of Short-tailed shearwaters results in a stochastic variability of food delivery to individual chicks. This variability may have led to the evolution of an over-feeding strategy by parents, leading to the nestling obesity typical for this and other petrels.

Key words: Puffinus tenuirostris, chick provisioning, long-distance foraging, satellite tracking, mixed foraging strategy

1Department of Zoology and Marine Biology, University of Dar es Salaam, P.O. Box 35064, Dar es Salaam, Tanzania, e-mail zmb@udsm.ac.tz; ²Institut für Vogelforschung "Vogelwarte Helgoland", An der, Vogelwarte 21, 26386 Wilhelmshaven, Germany, e-mail t-bairlein@rz-fs-2.rz.fh-wilhelmshaven.de

Mlingwa, C. & Bairlein, F. 1998. Nutritional ecology of African bulbuls (Pycnonotidae). In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban. Ostrich 69: 374.

Omnivory is common among African bulbuls, however the dietary proportion and the nutritional role of vegetal and animal matter are poorly understood. We analysed the gut contents of four bulbul species, Andropadus importunus, A. virens, Chlorocichla flaviventris and Pycnonotus barbatus, collected from mist-net bird samples in the wild in Tanzania between June 1994 and May 1995. Dietary items were categorised and the relative proportion of vegetal and animal components estimated. On average, the proportion of fruits was higher (78 to 82% by volume) than that of insects (18 to 22% by volume) except for P. barbatus which had 53% and 47% by volume of fruit and insect diets respectively. Feeding experiments were later carried out in Germany on P. barbatus taken from Tanzania. Captive birds showed spontaneous preferences for fruits. Others fed on diets differing only in the concentrations of protein, lipid and non-structural carbohydrates, respectively, exhibited higher energy intake and stable or slight increase in body mass on low protein-sugar rich compared to high protein-low sugar diets. The results indicate greater dependence on fruits by these bulbuls than previously thought, a situation related to low nutritional protein requirements. This study was supported by the Deutsche Akademische Austauschdienst.

Key words: fruits, frugivory, diet, feeding, insects, protein requirements, Tanzania

1Universidade do Vale do Paraíba, Säo José dos Campos, Säo Paulo, Brazil; ²Universidade Federal de Juiz de Fora, Juiz de Fora, Minas Gerais, Brazil, ³Universidade Federal de Viçosa, Viçosa, Minas Gerais, Brazil

Monteiro, A.R., Ribeiro, A.L., Granzinolli, M.A.M. & Silveira, J.M.B. 1998. Analyses of pellets of White-tailed Hawk Buteo albicaudatus in the southeast region of Brazil. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban. Ostrich 69: 374.

In Brazil there are few studies about raptors despite the great number of falconiformes and the literature is very scarce. Since the raptors are in the top of the food chain, many studies are necessary to know and to protect these birds against the environmental pollutants. In 1996 sixty three pellets of White-tailed Hawk were collected on the nest and on the ground near the nest in the Viçosa Region (20° 45' S and 42° 7' W) and in the Juiz de Fora Region (21° 42' S and 43° 20' W). The pellets were fumigated and stored in plastic tubes. Later they were weighed and measured. The pellets were separated into their component parts under water and then stored in 70% alcohol. Pellets ranged from 132 mm to 513 mm in length. Body fragments and appendages of arthropods (> 90%) and rodent skins were identified. Some fragments of insects heads could not be identified. The results give some idea of the food preferences of White-tailed Hawk in Southeast Region of Brazil. This research was sponsored by CNPq-Brazil.

Key words: pellets, diet, nutrition, Accipitridae, Falconiformes

University of North Carolina, Chapel Hill, NC, 27599-3280, USA, e-mail jabowers@execpc.com

Mueller, H.C. 1998. Age and sex differences in fat of migrating Sharp-shinned Hawks Accipiter striatus. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban. Ostrich 69: 375.

It has been hypothesised that in raptors, males are more efficient foragers than females. We might thus expect males to be fatter than females during fall migration. The capture of prey improves with experience and adults would be expected to be fatter than juveniles in fall. More than 5000 Sharp-shinned Hawks were trapped at Cedar Grove, Wisconsin, during fall migration. Deposits of fat in the axilla were visually estimated and placed into 12 classes. Mean fat of males more than two years old was significantly greater than that of all other age and sex classes, that of juvenile females greater than all but that of older males, and that of juvenile males greater than that of females greater than one year old. Very few males less than two years old breed. Breeding is a stress for a male, when he provides most or all of the food for a female and young. Females are 1.7 times larger than males and have less prey readily available to them, and young females are stressed as they learn to capture prey efficiently. My alternative hypothesis is that high fat levels of older males and young females are an overcompensation for recent food stress.

Key words: hawks, migration, fat, differences, age

Smithsonian Institution, Washington, D.C., USA, e-mail SchreiberE@aol.com

Schreiber, E.A. 1998. Lack of energy constraint in time-energy budgets of Red-tailed Tropicbirds Phaethon rubricauda. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban. Ostrich 69: 376.

Life history characteristics of tropical seabirds are often referred to as extreme: small clutch size, slow growth, deferred maturity, and long life span. It is hypothesised that small clutch and slow growth of young are adaptations to energy limitation on adults which cannot supply food at a faster rate. Having found no data to support this hypothesis in tropical pelecaniformes, I investigated time-energy budgets of tropicbirds and tested their ability to increase food delivery to the nest through a series of experiments. Radio transmitters recorded adults' presence at the nest and watch activity recorders recorded amount of time spent on the water when away from the nest. Experimental manipulations included increasing brood size and other tests of adaptability. When away from the nest, adults with chicks spent 54 to 70% of their time on the water not searching for food, indicating spare time. Adults immediately increased food delivery to the nest (successfully raising all the young) when brood size was increased. The presence of spare time in daily time-energy budgets and the ability of adults to adapt activity budgets to demand at the nest indicate that adults are not strictly energy limited and that their life history adaptations are not necessarily linked to energy constraints.

Key words: energy budget, time budget, Red-tailed Tropicbird, life history characteristics

1Department of Biology, University of Natal, Durban 4041, South Africa, ²Department of Zoology, University of Durban-Westville, Private Bag X54001, Durban, 4000, South Africa, ³Birdlife South Africa, 29 Winston Avenue, Robindale, 2194, South Africa

Soobramoney, S., Baker, C.M. & Berruti, A. 1998. The diet of the Red-billed Quelea Quelea quelea. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban. Ostrich 69: 376.

The granivorous Red-billed Quelea Quelea quelea (Ploceidae), occur in flocks of millions, and are considered to be responsible for substantial grain crop losses throughout Africa. Little is known of the actual diet of wild quelea, and in order to minimise crop damage, an understanding of its feeding biology is essential. Adult birds were collected throughout the year from the Northern and North West provinces, South Africa during control operations. The crop and stomach contents were removed and sorted under a dissecting microscope. The average amount of food consumed by males and females showed significant seasonal variation, with males consuming more food than females. Further analysis of the gut contents revealed that only wild grass seed (Eragrostis, Digitaria, Chloris, Cenchrus, Setaria, Echinochloa, Urochloa, Brachiaria, Aristida, Panicum, Paspalum, Loudetia, and wild Sorgum) and insects (Orders Coleoptera and Isoptera) were consumed. No commercial crop seeds were found. The seasonal availability of grass seeds determined their appearance in the gut of the quelea, and factors such the size, morphology and accessibility of the seeds were instrumental in determining their occurrence. Commercial crop seeds are only eaten when natural food resources are unavailable.

Key words: diet, Red-billed Quelea, Quelea quelea, Africa, pest

University of Stirling, UK, e-mail irs3@stir.ac.uk

Stevenson, I.R. & Bryant, D.M. 1998. Energetic constraints, egg laying and clutch size in Great Tits. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban. Ostrich 69: 377.

Trade-offs between components of reproductive investment operate at all stages of the breeding cycle. These trade-offs are not static, but vary with environmental conditions. As they change, so does the nature and timing of the constraints controlling reproductive output. To predict reproductive investment, therefore, costs and constraints at all stages of reproduction must be understood. In birds, most work has concentrated on incubation and rearing, but egg formation and laying have received less attention. Here, we examine the constraints imposed on clutch size by energetic costs during the laying in Great Tits. Early in the breeding season human disturbance often leads to suspension of laying, but using a novel version of the doubly labelled water technique, we obtained energetic measurements from free-living birds, with no requirement for handling or disruption. The influence of two environmental factors on energetic costs was investigated using controlled experimental manipulations in which level and quality of food supply was increased and nighttime thermoregulatory costs reduced. Our results demonstrate that egg laying is not 'cost-free' and that the energetic demands are as important as those incurred during incubation. Environmental variability early in the breeding season may act through laying costs to influence clutch size variation between years.

Key words: reproductive costs, trade-offs, fecundity, energetic constraints, Parus major

1National Institute of Water and Atmosphere, Christchurch, New Zealand, e-mail albatros@cebc.cnrs.fr; ²CEBC, CNRS, Villiers-en-Bois, France

Waugh, S.M. & Weimerskirch, H. 1998. Foraging of Black-browed Albatrosses at two sites. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Conger. Durban, University of Natal. Ostrich 69: 377.

The foraging behaviour of Black-browed Albatrosses Diomedea melanophrys was studied at Sub-Antarctic Kerguelen and Campbell Islands. Provisioning rates of chicks were measured and adult birds were tracked by satellite, revealing contrasting behaviours related to the local marine environment of the breeding sites. At Kerguelen Island, birds feeding chicks foraged close to the islands. Campbell Island birds had a mixed strategy, foraging on shelf areas close to the breeding sites but also at the polar frontal zone up to 2000 km away. Both species feed on similar prey-types. The strategy exhibited by the birds from the two sites was similar. Particular areas were exploited heavily, but proximity of these favoured areas to the nest sites may explain some differences between the population’s life-history traits.

Key words: foraging, Black-browed Albatross, Diomedea melanophrys

Av. Guardia Chalaca 1333, Callao, Peru, e-mail locales@datos.limaperu.net

Zavalaga, C.B. & Paredes, R. 1998. Why do Humboldt Penguins feed on sea shells? In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr. Durban, University of Natal. Ostrich 69: 377.

Penguins feed on crustaceans, fish or squid. Besides these prey, mollusc shells have also been found as part of their diet, but the role of these items has not been investigated. We found a dead female Humboldt Penguin Spheniscus humboldti with one complete egg low in the oviduct. Her stomach contained only pieces of mollusc shells. We hypothesise that these birds may use shells as a source of calcium for eggshell formation. Between 1992 and 1996 many Humboldt penguins died after being caught in nets near Punta San Juan, Peru. The carcasses were dissected, sexed and their stomachs removed for analysis. Our results revealed that: (1) Mollusc shells were present in 5.7 % of the stomachs. (2) Only females fed on shells (22 out of 165 females). (3) The intake of shells was not independent of egg formation (P < 0.01). (4) The diameter of the largest follicle on females which consumed shells was significantly larger (P < 0.05) than the others. (5) Females collected dead molluscs from the shore. The intake of shells in addition to their normal food may be associated with the high demand for calcium for eggshell formation and the behaviour of females, which starve for several days in the nest during the egg laying period.

Key words: eggshell, Spheniscus humboldti, mollusc shells, calcium intake