J. Stuart Bradley

The role of intrinsic factors for the recruitment process in long-lived birds

Recruitment to the breeding population is one of the most important and complex steps in the life history of long-lived animals, with great consequences for their reproductive career. Longitudinal data on individuals has provided new information on recruitment to the natal colony. We approach recruitment from the individual level, and address intrinsic factors affecting the probability of recruitment. Key steps to recruitment to the natal colony are fledging, subadult survival, the return to the natal area, the decision to breed there, and the ability to do so. Determinants characterising the state of an individual before recruitment can have a genetic basis (such as sex, mass) or can originate from the individual’s experience (e.g. degree of parental care, number of siblings and rearing conditions affecting mass and age at fledging—or length of the subadult period). Recruitment depends also on age, experience and body condition, increasing with the number of prospecting years spent at the colony. Threshold levels in body mass and arrival in due time are preconditions to successful first breeding. The improvement of body condition with age may be mainly due to an increase in foraging efficiency, increasing the resources which can be allocated to reproduction beyond those needed for self-maintenance. Prospecting and attendance leads to the acquisition of skills favouring recruitment, concerned with establishing a territory, mating, courtship and chick feeding. It is suggested that the individual optimal age of recruitment is produced by balancing the risk of premature breeding, with the consequent reduction in survival, against the advantage of presumed increased breeding opportunities with the concomitant increase in lifetime reproductive success.

What makes a journal international? A case study using conservation biology journals

The qualitative label ‘international journal’ is used widely, including in national research quality assessments. We determined the practicability of analysing internationality quantitatively using 39 conservation biology journals, providing a single numeric index (IIJ) based on 10 variables covering the countries represented in the journals’ editorial boards, authors and authors citing the journals’ papers. A numerical taxonomic analysis refined the interpretation, revealing six categories of journals reflecting distinct international emphases not apparent from simple inspection of the IIJs alone. Categories correlated significantly with journals’ citation impact (measured by the Hirsch index), with their rankings under the Australian Commonwealth’s ‘Excellence in Research for Australia’ and with some countries of publication, but not with listing by ISI Web of Science. The assessments do not reflect on quality, but may aid editors planning distinctive journal profiles, or authors seeking appropriate outlets.

Should we use the mean citations per paper to summarise a journal’s impact or to rank journals in the same field?

The mean citations per paper is used increasingly as a simple metric for indicating the impact of a journal or comparing journal rankings. While convenient, we suggest that it has limitations given the highly skewed distributions of citations per paper in a wide range of journals.

Does intraspecific variation in the energy value of a prey species to its predators matter in studies of ecological energetics? A case study using insectivorous vertebrates

This study tested the assumption that variation in the energy value of different instars of a hemimetabolous insect makes no ecologically significant difference to rates of energy gain by its vertebrate predators and found it to be supported. Three mammal species, four bird species and a lizard species were used as predators and one grasshopper species as prey. Although instars of both male and female grasshoppers differed significantly in energy values, the energy returns to their predators based on these exact values were qualitatively similar to those produced when a commonly-used constant energy value of 23 J/mg dry weight was substituted. Regressions of specific energy returns on those based on the 23 J/mg constant were highly significant, so energy returns based on the constant were good predictors of those based on specific energy values. Although significant intraspecific variations in energy values occur in Acrida conica and probably in other hemimetabolous insects as well, the 23 J/mg dry weight constant appears adequate for most predation studies.