Within brood trade-offs in reproductive effort: An experimental study on the common tern: Sterna hirundo

• Main Author: Heaney, Victoria Frances
• Format: Thesis
• Language: English
• Published: 1997
• Subjects: QL Zoology; Common tern; Sterna hirundo
• Online Access: http://theses.gla.ac.uk/71774/; https://theses.gla.ac.uk/71774/1/10391415.pdf; https://eleanor.lib.gla.ac.uk/record=b1711762

The optimal allocation of effort during reproduction is a key component of life history theory, with trade-offs predicted to operate both within and between reproductive attempts. Experimental work in this field has largely concentrated on the latter. The need to partition investment between the different phases of the current reproductive event, and how this varies between individuals, has received little empirical investigation. The primary aims of this project were to investigate the capacity of birds to adjust their reproductive effort in response to increasing demand, and to investigate within brood trade-offs between the different phases of the reproductive attempt. To do this the project involved experimental manipulation of effort (within the natural range) at the stages of egg production, incubation and chick rearing. Only those pairs that were given a free chick (incurring chick rearing costs only) were able to rear a significantly larger brood than unmanipulated controls. When parents incurred the full costs (egg production, incubation and chick rearing) of producing additional young to their intended clutch size, their capacity to rear an enlarged brood was negated. A within clutch trade-off was identified between producing and rearing extra young, with experimental parents subsequently showing reduced chick provisioning, growth and survival. In an experiment to increase the costs of incubation alone, which have often been considered relatively trivial, study birds showed a significantly depressed performance in the later stage of chick rearing. Again a within clutch trade-off in reproductive effort was identified with second hatched chicks in experimental nests growing at a significantly lower rate and Hedging at a significantly lighter mass than those in control broods. The effects of experimental manipulation on aspects of the dynamics of parental foraging suggested that an increase in reproductive demand may affect strategy, but the relationship was not clear. An increase in the costs of egg ...