Hörak, P. & Ots, I. 1998. Immunological ecology of the Great Tit Parus major. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban. Ostrich 69: 232.

The basic tenet of life-history theory is that reproduction incurs costs in terms of trade-offs between future survival and fecundity of individuals. Immunological methods have especially promising applications in the study of these trade-offs because both reproduction and immune responses are energetically costly, and therefore, reproduction is predicted to lead to an individual’s lowered ability to defend itself against diseases. Hence, the decreased resistance against parasites and infectious diseases may appear to be the potential mechanism linking reproductive effort to reproductive costs. Testing of this hypothesis requires detection of changes in an individual’s state of health caused by reproductive effort, and examination whether these changes have any fitness consequences. We will describe the application of immunological methodology for assessment of the physiological condition of Great Tits, and present the results of experiments, testing whether (1) Increased reproductive effort leads to immune suppression and (2) Immune suppression is associated with lowered future performance.

Key words: immunological ecology, reproductive effort, reproductive costs, Parus major

Moreno, J., De León, A., Fargallo, J.A. & Moreno, E. 1998. Breeding time, health state and immune response in the Chinstrap Penguin Pygoscelis antarctica. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban. Ostrich 69: 232 - 233.

Little is known about the proximate causes of individual variation in the attainment of breeding condition in birds. Health status and immunocompetence have been proposed as important factors. We studied individual variation in serological variables indicating health status (blood sedimentation rate, haematocrit, 'buffy coat' layer, proportions of different types of leucocytes) in two groups of breeding Chinstrap Penguins Pygoscelis antarctica with breeding dates nine days apart. We sampled these individuals shortly after hatching of their young and at the end of the chick-raising period. A group of failed breeders was also sampled. Birds of both sexes were included. We also measured the T-cell-mediated immunoresponse as indicated by hypersensitivity responses to an intradermal injection of Phytohemagglutinin in early and late breeders. Late breeders had poorer health (more leucocytes, especially heterophils and lymphocytes) and a lower immune response than early breeders, independently of sex. Failed breeders were more similar to late than to early breeders. Early breeders suffered a decline in health status throughout the chick-raising period. The impact of pathogens on variation in life-history traits in avian populations is important also in extreme Antarctic environments.

Key words: Antarctic, individual variation, pathogens, chick-raising period

Nager, R.G., Monaghan, P. & Houston, D.C. 1998. The price of eggs: Trade-offs between egg production and chick rearing in gulls. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban. Ostrich 69: 233.

Clutch size is a key life history parameter, and constraints operating at the time of egg production will therefore play an important role in determining life history patterns. It has generally been assumed that egg production is a relatively inexpensive phase of the reproductive cycle, and that factors shaping the evolution of clutch size operate primarily during the chick-rearing phase. However, experimental investigations of egg production capacity are few, and the consequences of increased egg production on subsequent adult performance and on offspring quality have not been separated. In this paper we report the results of experimental manipulations of the number of eggs produced by Lesser Black-backed Gulls Larus fuscus. Birds were made to lay more eggs than their usual clutch size and, by cross fostering, the within brood consequences for parents and chicks were independently investigated. We show that increased egg production influences both offspring quality (egg size, egg composition, hatchling condition and chick survival) and the capacity of parents to rear a normal brood.

Key words: clutch, Lesser Black-backed Gull, reproductive costs, egg quality, breeding success, Larus fuscus

Burtt Jr., E.H., Fink, D.F., Ichida, J.M. & Lauffer, D.P. 1998. Effect of bacterial degradation on differently coloured feathers. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban. Ostrich 69: 234.

Could bacteria in the plumage affect avian colours, colour patterns, or moult cycles? We have isolated two feather-degrading bacteria from the plumage of North American birds: Bacillus licheniformis from 8% of 1583 birds sampled and Streptomyces sp. from 50% of 1616 birds sampled. Feathers are the carbon source for both bacterial species. B. licheniformis is most active from 35 °C to 50 °C, whereas Streptomyces sp. is most active from 25 °C to 40 °C, but breaks up feathers more slowly than B. licheniformis. Long before a feather is damaged macroscopically, the bacteria reduce its flexibility and it becomes brittle. The presence of melanins (eumelanin or phaeomelanin) and carotenes increase a feather's resistance to bacterial degradation and to its subsequent loss of flexibility. The mechanisms by which melanins and carotenes inhibit bacterial action are unknown, however, resistance to bacterial degradation could be important to the evolution of colours and colour patterns. For example, Gloger's Rule, which states that the intensity of melanic colour increases in hot, humid climates and decreases in cold, dry climates may in part reflect the need to protect the plumage from bacterial degradation in habitats that favour bacterial growth.

Key words: feathers, bacteria, colouration, melanin, carotene

Lundberg, A. & Hemborg, C. 1998. Cost of reproduction and moult: An example from the Pied Flycatcher, Ficedula hypoleuca. In: Adams, N.J. & Slotow, R.H. (eds) Proc. 22 Int. Ornithol. Congr., Durban. Ostrich 69: 234.

Moult in birds is a process with an increased rate of energy expenditure, which may explain why this process is separated from other energetically costly processes, e.g. reproduction. In this study we investigated the importance of separating moult from the breeding activities. We induced a moult-breeding overlap by removing the two innermost primaries on both wings, which imitates the natural moult found among late breeding individuals in this Pied Flycatcher Ficedula hypoleuca population. Experimentally induced moult-breeding overlap reduced both adult and nestling body conditions at the time of fledging of the young. The fledging success, however, in terms of number of recruits to the subsequent year of manipulation was significantly lower for the manipulated group. The total survival rate of adults and recruits to the subsequent year of the experiment was significantly reduced when a moult-breeding overlap was induced. Thus, our results suggest that there is a trade-off, either physiological or ecological, between reproduction and moult. In passerine birds, this trade-off should be of great importance for many behavioural decisions during reproduction, e.g. timing of breeding and reproductive effort versus time and energy needed for the post-breeding moult.

Key words: trade-off, moult, reproduction, success, breeding