Paul Tatner

Hatching asynchrony, sibling competition and siblicide in nestling birds: Studies of swiftlets and bee-eaters

Abstract The consequence of hatching asynchrony for fledging success and sibling competition in white-bellied swiftlets, Collocalia esculenta, and blue-throated bee-eaters, Merops viridis, was studied by observation and manipulation of nest contents at breeding colonies in Malaysia. A greater synchrony of hatching tended to increase fledging success amongst swiftlets, a result consistent with most other similar manipulative studies to date. Sibling competition in blue-throated bee-eaters invariably led to nest fatalities, which were induced by sibling attacks with an apparently unique, but developmentally temporary, hook at the tip of the upper mandible. Measurements of energy expenditure using the doubly labelled water technique showed that synchrony also reduced the energy cost of nestling competition in bee-eaters, thereby providing a possible mechanism for improved growth and survival of synchronous broods. No universal adaptive function for hatching asynchrony was identified, so it is proposed that a primary function is to encourage distribution of food amongst the brood in a way that permits resource tracking, but can also allow brood reduction under extreme adversity (i.e. a sustained food ‘crash’, parental death or desertion).

Factors influencing the distribution of Magpies Pica pica in an urban environment

Urban Magpie distribution was compared against various habitat characteristics, and found to correlate best with numbers and variety of trees available. Urban tree planting is thought to have aided colonisation, though the Magpies unspecialised diet and relative freedom from persecution must also have been important factors.Urban Magpie distribution was compared against various habitat characteristics, and found to correlate best with numbers and variety of trees available. Urban tree planting is thought to have aided colonisation, though the Magpies unspecialised diet and relative freedom from persecution must also have been important factors.

A model of the natural abundance of oxygen-18 and deuterium in the body water of animals*

Concurrent variability of the stable isotopes oxygen-18 and deuterium in an animals body water is described using an input/output material balance model at equilibrium. Components of isotope flux are given as a product of the rate of material flux, its isotopic ratio ( R value), and an appropriate fractionation factor. The model includes a facility for varying the respiratory substrate so that the influence of the respiratory quotient (RQ) may be investigated. A range of isotope concentrations in the body water are predicted at a given RQ. The range decreased as the RQ increased for both oxygen-18 and deuterium, producing two sets of results, each in the form of a triangle. Physiological data collected in an isotopic tracer study of wild robins were employed in simulations, to investigate the effect of realistic variations in the basic parameters. Simulations provided close agreement with measured isotopic abundance in robins, from low winter to high summer values. They suggested that the principal causes of variation in oxygen-18 and deuterium in an animals body water are changes in the isotopic content of the water intake, and variability in the respiratory substrate. Variable fractionation factors, which arise as a result of a shift in the level of activity, may also exert an influence.