Robert Heinsohn

Declining body size: a third universal response to warming?

A recently documented correlate of anthropogenic climate change involves reductions in body size, the nature and scale of the pattern leading to suggestions of a third universal response to climate warming. Because body size affects thermoregulation and energetics, changing body size has implications for resilience in the face of climate change. A review of recent studies shows heterogeneity in the magnitude and direction of size responses, exposing a need for large-scale phylogenetically controlled comparative analyses of temporal size change. Integrative analyses of museum data combined with new theoretical models of size-dependent thermoregulatory and metabolic responses will increase both understanding of the underlying mechanisms and physiological consequences of size shifts and, therefore, the ability to predict the sensitivities of species to climate change.

Animal personality: what are behavioural ecologists measuring?

The discovery that an individual may be constrained, and even behave sub‐optimally, because of its personality type has fundamental implications for understanding individual‐ to group‐level processes. Despite recent interest in the study of animal personalities within behavioural ecology, the field is fraught with conceptual and methodological difficulties inherent in any young discipline. We review the current agreement of definitions and methods used in personality studies across taxa and systems, and find that current methods risk misclassifying traits. Fortunately, these problems have been faced before by other similar fields during their infancy, affording important opportunities to learn from past mistakes. We review the tools that were developed to overcome similar methodological problems in psychology. These tools emphasise the importance of attempting to measure animal personality traits using multiple tests and the care that needs to be taken when interpreting correlations between personality traits or their tests. Accordingly, we suggest an integrative theoretical framework that incorporates these tools to facilitate a robust and unified approach in the study of animal personality.

The cost of helping

Cooperative breeding in mammals, birds and fish has provided evolutionary biologists with a rich framework for studying the causes and consequences of group-based reproduction. Helping behaviour is especially enigmatic because it often entails an individual sacrificing personal reproduction while assisting others in their breeding attempts. The decision to help others to reproduce is affected by immediate and future costs analogous to those of direct reproduction, but these components of the equation have usually been neglected. Recent research suggests that the type of benefit sought could determine the extent of help given.

Helping is costly to young birds in cooperatively breeding white-winged choughs

Cooperative breeding among birds is at its most extreme in white-winged choughs (Corcorax melanorhamphos). Choughs have never been observed to breed successfully without helpers, and reproductive success increases linearly across all group sizes (maximum = 16). Further, helpers contribute to every aspect of reproduction, including nest building and incubation. Here we show that the contribution of young helpers (one year old and less) to incubation depends on the group in which they live. In small groups (3-5 birds), young helpers contribute as much to incubation as older birds, but in large groups they contribute little. In large groups, help increases sharply with age. Old birds contribute equally, regardless of group size. Although choughs generally do not lose body mass over incubation, young helpers lose mass in proportion to the amount of incubation they perform, independent of any effect of group size. This provides evidence that helpers in cooperatively breeding birds suffer costs from providing help additional to the costs incurred from remaining philopatric. It also demonstrates that the needs of the group influence whether young birds provide help.

Online Localization of Radio-Tagged Wildlife with an Autonomous Aerial Robot System

The application of autonomous robots to efficiently locate small wildlife species has the potential to provide significant ecological insights not previously possible using traditional landbased survey techniques, and a basis for improved conservation policy and management. We present an approach for autonomously localizing radio-tagged wildlife using a small aerial robot. We present a novel two-point phased array antenna system that yields unambiguous bearing measurements and an associated uncertainty measure. Our estimation and informationbased planning algorithms incorporate this bearing uncertainty to choose observation points that improve confidence in the location estimate. These algorithms run online in real time and we report experimental results that show successful autonomous localization of stationary radio tags and live radio-tagged birds.

Experimental manipulation of brood reduction and parental care in cooperatively breeding white-winged choughs

1. White-winged choughs, Corcorax melanorhamphos (Vieillot), are obligate cooperative breeders. Only very large groups routinely fledge all their brood of three to four chicks, while small groups usually lose young during the nestling period. Hatching asynchrony generates a weight hierarchy within the brood, and small, late-hatched chicks are most susceptible to mortality. 2. In order to examine the effects of food availability on parental care and brood reduction, we provided supplementary food to groups during late incubation and the nestling phase. 3. Food supplementation increased the rate of food delivery to the nest by both breeders and helpers, leading to increased chick survival and fledging, and reduced variance in chick size at fledging. Helpers with supplemental food appeared more responsive to the need of chicks, increasing food delivery rates as the chicks grew older, and as brood size increased. 4. Control groups fed larger chicks preferentially, while supplemented groups favoured small chicks. This suggests that choughs deliberately manipulate the survival of individual young to maximize the fledging of healthy chicks, consistent with Lacks hypothesis for hatching asynchrony. 5. These data support the hypothesis that choughs must breed in groups because they cannot provide enough food to nestlings without help. Hatching asynchrony and behavioural control over brood reduction allow choughs to maximize offspring production according to group size and food availability.

Extreme bias in sex allocation in Eclectus parrots

We investigated extraordinary patterns of sex allocation in captive eclectus parrots (Eclectus roratus). These birds are extremely unusual as they show reverse sexual dichromatism, they are the only cooperatively breeding parrot, and they are one of the few birds with nestlings that are easily sexed. They lay two eggs per clutch, but often only fledge one young, and the sex ratio of 209 fledglings did not differ significantly from parity. However, when two young are fledged together they are very likely to be of the same sex, and some females produce long unbroken runs of one sex (the maximum was 20 males) before switching to the other sex. Monte–Carlo simulations show that these runs of same–sex clutches defy expectation if we assume that the sex of chicks within each clutch is independent of the previous clutch. We use further simulations to show that the sex bias must occur at fertilization (i.e. the primary sex ratio), although the female may make further adjustments via infanticide. Control over sex allocation in eclectus parrots is one of the most extreme reported from birds.

Visual mimicry of host nestlings by cuckoos

Coevolution between antagonistic species has produced instances of exquisite mimicry. Among brood-parasitic cuckoos, host defences have driven the evolution of mimetic eggs, but the evolutionary arms race was believed to be constrained from progressing to the chick stage, with cuckoo nestlings generally looking unlike host young. However, recent studies on bronze-cuckoos have confounded theoretical expectations by demonstrating cuckoo nestling rejection by hosts. Coevolutionary theory predicts reciprocal selection for visual mimicry of host young by cuckoos, although this has not been demonstrated previously. Here we show that, in the eyes of hosts, nestlings of three bronze-cuckoo species are striking visual mimics of the young of their morphologically diverse hosts, providing the first evidence that coevolution can select for visual mimicry of hosts in cuckoo chicks. Bronze-cuckoos resemble their own hosts more closely than other host species, but the accuracy of mimicry varies according to the diversity of hosts they exploit.

Cooperative enhancement of reproductive success in white-winged choughs

SummaryWhite-winged choughs are a cooperatively breeding species which provide parental care to their young over an entire year. I traced the reproductive success of groups of white-winged choughs from the start of one breeding season to the next over 3 years. I examined the effect of helper number on timing of breeding, the success of each effort, the number of efforts made in a season, and the final reproductive success at the end of each year. Timing of commencement of breeding varied between years but was not related to group size. Early broods were not more successful than late broods. Nest building (July–September) commenced earlier in years which had high rainfall in July; choughs rely on rainfall for supplies of mud for nest construction. Most nest failures occurred gradually and were attributed to starvation of nestlings, although some sudden failures were attributed to predation. Large groups have more young by the beginning of the following season; this is due to higher fledging success and a greater likelihood of having second broods. Disappearance of young after fledging and during the transition to independence was not dependent on group size. Only groups of seven and above produce more than one young on average over the entire year; choughs provide one of the most marked cases for helpers enhancing the reproductive success of breeders. Large groups are virtually guaranteed of reproductive success over the whole year and grow more quickly than small groups. These results highlight the need to consider the effect of helpers over the entire period of reproduction and care of young, rather than just at fledging.

Social constraint and an absence of sex‐biased dispersal drive fine‐scale genetic structure in white‐winged choughs

This study used eight polymorphic microsatellite loci to examine the relative effects of social organization and dispersal on fine‐scale genetic structure in an obligately cooperative breeding bird, the white‐winged chough (Corcorax melanorhamphos). Using both individual‐level and population‐level analyses, it was found that the majority of chough groups consisted of close relatives and there was significant differentiation among groups (FST = 0.124). However, spatial autocorrelation analysis revealed strong spatial genetic structure among groups up to 2 km apart, indicating above average relatedness among neighbours. Multiple analyses showed a unique lack of sex‐biased dispersal. As such, choughs may offer a model species for the study of the evolution of sex‐biased dispersal in cooperatively breeding birds. These findings suggest that genetic structure in white‐winged choughs reflects the interplay between social barriers to dispersal resulting in large family groups that can remain stable over long periods of times, and short dispersal distances which lead to above average relatedness among neighbouring groups.