Trans-shell infection by pathogenic micro-organisms reduces the shelf life of non-incubated bird's eggs: a constraint on the onset of incubation?

Many birds initiate incubation before clutch completion, which results in asynchronous hatching. The ensuing within-brood size disparity often places later-hatched nestlings at a developmental disadvantage, but the functional significance of the timing of the onset of incubation is poorly understood. Early incubation may serve to maintain the viability of early-laid eggs, which declines over time owing to the putative effects of ambient temperature. An unexplored risk to egg viability is trans-shell infection by micro-organisms. We experimentally investigated the rate and magnitude of microbial trans-shell infection of the egg, and the relative effects of ambient temperature and micro-organisms on hatching success. We show that infection of egg contents is prevalent and occurs within the time required to lay a clutch. The probability of infection depends on the climatic conditions, the exposure period and the phylogenetic composition of the eggshell microbiota. We also demonstrate that microbial infection and ambient temperature act independently to reduce egg viability considerably. Our results suggest that these two factors could affect the onset of avian incubation in a wide range of environments.

Emerging Issues in Population Viability Analysis

Population viability analysis ( PVA) has become a commonly used tool in endangered species management. There is no single process that constitutes PVA, but all approaches have in common an assessment of a population's risk of extinction (or quasi extinction) or its projected population growth either under current conditions or expected from proposed management. As model sophistication increases, and software programs that facilitate PVA without the need for modeling expertise become more available, there is greater potential for the misuse of models and increased confusion over interpreting their results. Consequently, we discuss the practical use and limitations of PVA in conservation planning, and we discuss some emerging issues of PVA. We review extant issues that have become prominent in PVA, including spatially explicit modeling, sensitivity analysis, incorporating genetics into PVA, PVA in plants, and PVA software packages, but our coverage of emerging issues is not comprehensive. We conclude that PVA is a powerful tool in conservation biology for comparing alternative research plans and relative extinction risks among species, but we suggest caution in its use: (1) because PVA is a model, its validity depends on the appropriateness of the model's structure and data quality; (2) results should be presented with appropriate assessment of confidence; (3) model construction and results should be subject to external review, and (4) model structure, input, and results should be treated as hypotheses to be tested. We also suggest (5) restricting the definition of PVA to development of a formal quantitative model, (6) focusing more research on determining how pervasive density-dependence feedback is across species, and (7) not using PVA to determine minimum population size or (8) the specific probability of reaching extinction. The most appropriate use of PVA may be for comparing the relative effects of potential management actions on population growth or persistence.

Assessing parental effort in a Neotropical parrot: a comparison of methods

Various behavioural or body condition indices are frequently used to measure avian parental effort. To determine which of the indices provide meaningful short-term assessments of parental effort, we used four of them concurrently on breeding green-rumped parrotlets, Forpus passerinus, and then compared the results with field metabolic rate (FMR) measurements obtained using the doubly labelled water (DLW) technique. Nest provisioning rate correlated significantly with FMR among both males and females, while proportion of time away from the nest was correlated with FMR in females but not in males. Adult mass change during the breeding cycle and feeding latency were both unrelated to FMR. Our results suggest researchers should be cautious in assuming that any indirect method of quantifying parental effort is reliable for a particular species. We also tested whether the relatively invasive DLW protocol causes potentially confounding changes in study animals' subsequent behaviour. Paired observations before and after DLW injection showed no measurable changes in parrotlet nest attendance patterns or nest provisioning rate. Copyright 1999 The Association for the Study of Animal Behaviour.

Social constraints on the onset of incubation in a neotropical parrot: a nestbox addition experiment

We examined whether the early onset of incubation serves to protect eggs from the dangers imposed by conspecifics in the green-rumped parrotlet, Forpus passerinus, a small neotropical parrot that lays a large clutch and begins incubation on the first egg. Nestboxes with eggs were installed and their fate was followed for 72 h to determine whether egg destruction and nest site take-overs occurred as predicted by the Egg Protection and Limited Breeding Opportunities Hypotheses, or whether additional eggs appeared in the boxes as predicted by the Brood Parasitism Hypothesis. Eggs were destroyed at 40.6% of 69 experimental boxes but at only 4.5% of control nests occupied by laying pairs. No eggs were laid in the experimental boxes. Egg destruction at experimental nests occurred during daylight hours and all mortality was caused by green-rumped parrotlets. Over 75% of the nests were destroyed by male-female pairs prospecting for nest sites, and the remainder were destroyed by male-male pairs. Lone males never destroyed eggs, although they frequently visited experimental boxes. Two of three failures at control nests were the result of nocturnal predators, and the other nest was apparently destroyed by parrotlets. There was no significant difference between experimental and control boxes in the frequency of visitations by lone males, male-female pairs and male-male pairs. Although experimental boxes that parrotlets visited were discovered quickly after placement, parrotlets were usually slow to enter them (X=5.8 h after discovery, range 0.3-23.5 h). Control nests were rarely left unattended: females spent nearly 75% of their time in the box, and pairs were typically absent for short intervals (median=7.5 min). Control females responded to intruding parrotlets by remaining in the box 94% of the time when alone, whereas males actively displaced and chased intruding parrotlets 66% of the time. Parrotlets that visited control nests approached the box significantly less often than those visiting experimental boxes. To ensure the survival of eggs, parrotlet parents must begin incubating eggs or guarding nests soon after laying to minimize destruction of clutches, loss of nest sites, a decline in the viability of their eggs and the time that all nestlings are exposed to predators. Copyright 1998 The Association for the Study of Animal Behaviour.