Strategies of mass change in breeding birds

Birds experience strikingly different patterns of mass change during breeding. In some species with uniparental incubation, the incubating parents (mostly females) lose mass and attain their lowest point when the chicks hatch (Incubatory mass loss strategy = IML). In species with shared incubation, or with intense incubation feeding, the incubating parents maintain or increase in body mass without reducing attentiveness levels (Incubatory mass constancy = IMC). In other species, uniparental incubation with IMC is associated with reduced levels of attentiveness. The mobilization of fat stores or its preservation are involved in the two strategies. IML leads to mass increases after hatching of the young, while the opposite is true for IMC. The non-incubating sex in uniparental species does not experience significant mass changes during breeding. Fasting endurance, predation risk and mode of development are proposed as the main selective factors determining strategy. Latitude, climate, diet and food availability interact with the main factors. From a revision of the literature we can deduce that IML is mainly found among large birds with precocial development, while IMC is typical of smaller species with altricial development. Proportional mass losses are positively correlated with body mass in IML-species, as well as in precocial species, where body mass explains more than 70% of the variation in proportional mass change. Incubation periods increase with body mass in uniparental IMC-species, but not in IML-species. IML is thus associated to fast embryonic growth in large species. Successful raising of highly-dependent young in altricial and semialtricial species apparently depends on one of the parents retaining reserves until hatching. Subsequent mass losses may be necessary to maintain the brooding parent through a period when nestlings require heat, insulation and food. Patterns of mass change are not mere consequences of reproductive stress but the outcome of adaptive compromises between different selective factors and constitute an important aspect of the breeding biology and life history of birds.     

Explaining variation in maternal care in a cooperatively breeding mammal

Because of the necessity of lactation, mammalian mothers must perform at least a minimum amount of infant care. In cooperatively breeding species, other group members aid in all other aspects of infant care. However, some mothers continue to carry and nurse their infants more than others. The golden lion tamarin, Leontopithecus rosalia, is a small, communally breeding primate in the family Callitrichidae. We studied hormonal, individual, historical and social factors hypothesized to contribute to variation in levels of maternal care. We used neonatal weight as a measure of prenatal care, and carrying and nursing as measures of postnatal care. Greater neonatal weight was associated with smaller litter size, lower prepartum levels of oestrogen conjugates, and higher prepartum cortisol levels. Higher rates of carrying during weeks 2 and 3 were associated with higher maternal weight, larger litter size and smaller numbers of helpers per infant. Higher rates of nursing in weeks 2 and 3 were predicted by smaller group size and provisioning of the mother. The most important factors affecting postnatal maternal care were maternal weight, group size, litter size and provisioning status of the mother. Thus, females that display higher levels of maternal care do so either because they have to (they have fewer helpers) or because they can (they are in better condition).     

Foraging patterns of breeding birds in eucalypt forest and woodland of southeastern Australia

The foraging ecology of eucalypt forest and woodland birds was studied on three 10 ha plots in southeastern Australia. Quantitative data were obtained for 41 species of which 31 were insectivorous, eight were nectar-feeders, and two were parrots that fed primarily on eucalypt seeds. Birds-of-prey, large omnivores and frugivores were uncommon. Insectivorous birds differed in foraging behaviour, the substrates on which they found prey, and foraging height. Nectar- feeders exploited a variety of carbohydrates including nectar, honeydew, lerp, manna and sap. Nectarivorous birds were separated by foraging behaviour, substrate, height and by the extent to which they used the different types of carbohydrates. Carbohydrates were also an important food resource for some insectivores. By understanding how birds exploit food resources within forest and woodland environments, the features of the environment which need to be conserved or manipulated to manage forest avifaunas can be identified. For example, in addition to the substrates such as foliage and bark, usually associated with the foraging of forest birds, carbohydrates and loose bark were identified as important resources for birds in eucalypt forests and woodlands. The broad importance of these two resources to the avifauna had not been previously appreciated, yet both may be sensitive to environmental changes associated with logging and other forest management practices which alter the composition or age-class structure of forests.     

Monitoring and managing genetic variation in group breeding populations without individual pedigrees

The genetic management of captive populations to conserve genetic variation is currently based on analyses of individual pedigrees to infer inbreeding and kinship coefficients and values of individuals as breeders. Such analyses require that individual pedigrees are known and individual pairing (mating) can be controlled. Many species in captivity, however, breed in groups due to various reasons, such as space constraints and fertility considerations for species living naturally in social groups, and thus have no pedigrees available for the traditional genetic analyses and management. In the absence of individual pedigree, such group breeding populations can still be genetically monitored, evaluated and managed by suitable population genetics models using population level information (such as census data). This article presents a simple genetic model of group breeding populations to demonstrate how to estimate the genetic variation maintained within and among populations and to optimise management based on these estimates. A numerical example is provided to illustrate the use of the proposed model. Some issues relevant to group breeding, such as the development and robustness evaluation of the population genetics model appropriate for a particular species under specific management and recording systems and the genetic monitoring with markers, are also briefly discussed.     

The use of body mass loss to estimate metabolic rate in birds

During starvation, energy production occurs at the expense of body reserve utilisation which results in body mass loss. Knowing the role of the fuels involved in this body mass loss, along with their energy density, can allow an energy equivalent of mass loss to be calculated. Therefore, it is possible to determine daily energy expenditure (DEE) if two body mass loss measurements at an interval of a few days are obtained. The technique can be cheap, minimally stressful for the animals involved, and the data relatively simple to gather. Here we review the use of body mass loss to estimate DEE in birds through critiquing the strengths and weaknesses of the technique, and detail the methodology and considerations that must be adhered to for accurate measures of DEE to be obtained. Owing to the biology of the species, the use of the technique has been used predominantly in Antarctic seabirds, particularly penguins and albatrosses. We demonstrate how reliable the technique can be in predicting DEE in a non-Antarctic species, common eiders (Somateria mollissima), the female of which undergoes a fasting period during incubation. We conclude that using daily body mass loss to estimate DEE can be a useful and effective approach provided that (1) the substrate being consumed during mass loss is known, (2) the kinetics of body mass loss are understood for the species in question and (3) only species that enter a full phase II of a fast (where substrate catabolism reaches a steady state) and are not feeding for a period of time are appropriate for this method.     

Processes generating macroevolutionary patterns of morphological variation in birds: a simulation study

Multivariate patterns of morphological variation in birds are analysed. In general, there are strong allometric patterns among characters such that most of the variation is confined to a major “size” axis. To analyse the possible evolutionary processes behind this pattern I employed a computer simulation of cladogenesis and anagenesis based on a genetic and a random walk model (drift). All runs started with one species and speciation occurred to generate 100 species. Three levels of correlations were allowed. The results from the simulations were compared with the pattern of variation in finches (Fringillidae). The simulations showed two things. First, the univariate drift model was inappropriate in terms of the level of variation; the observed level was lower than expected by drift. Univariate drift was also unable to create tight correlations among characters as observed in several taxa. Second, to create the pattern observed, either relatively strong genetic correlations (r_g ≈ 0.5), or alternatively strong correlated selection, was needed. This suggests that morphological change in birds in general consists of changes in growth such that species become larger or smaller than their ancestors but retain their ancestral shape. The results stress the importance of stabilising selection in shaping the macroevolutionary patterns of morphological variation in birds.     

Colonial breeding and speciation in birds

Summary It was recently suggested that bird species which breed colonially might be under stronger sexual selection, have faster rates of evolution and might therefore speciate more rapidly than bird species which do not. If true, then colonial taxa should contain more species than non-colonial taxa, other things being equal. When similarity through common descent is accounted for, there is little evidence for an association between the number of species in a clade and whether it is colonial or not.     

Patterns of seasonal and yearly mass variation in West African tropical savannah birds

Birds in the northern hemisphere usually increase mass reserves in response to seasonal low temperatures and shorter day length that increase foraging unpredictability and so starvation risk. In the lowland tropics, relatively low temperatures and short day lengths are absent and so the risk of starvation may be reduced, leading to much smaller seasonal effects on mass. Nevertheless, other factors such as high temperatures and water and food availability may vary greatly between tropical wet and dry seasons, leading to variable starvation risk and seasonal mass effects. Using data collected from 47 species of birds caught over a 10‐year period in a tropical savannah region in West Africa we tested for seasonal variation in mass in response to a predictable, strongly seasonal tropical climate. Many species (91%) showed seasonal variation in mass, and this was often in a clear annual pattern that was constant across the years. Many species (89%) varied their mass in response to seasonally predictable rainfall. Annual variation in mass was also important (45% of species). Relatively few species (13%) had a seasonal pattern of mass variation that varied between years. Feeding guild or migratory status was not found to affect seasonal or annual mass variation. Seasonal mass change was on average 8.1% across the 21 species with a very large sample size and was comparable with both northern and southern temperate species. Our study showed that biologically significant consistent seasonal mass variation is common in tropical savannah bird species, and this is most likely in response to changing resource availability brought about by seasonal rainfall and the interrupted foraging response due to the constraints of breeding.     

Daily patterns of body mass gain in four species of small wintering birds

Theoretically, the trajectories describing the daily accumulation of body reserves are expected to differ between bird species in relation to whether or not they hoard food. To carry reserves on the body may be costly and hoarding species can be expected to hoard food early in the day when light and retrieve it in the afternoon, with a concomitant rapid increase in body mass. Also, the increased food predictability resulting from being able to consume hoarded food late in the day should lead to a relatively faster gain in body reserves in the afternoon in hoarding species compared to non-hoarders. Non-hoarders may have to hedge against possible afternoon losses of foraging opportunities by accumulating more reserves early in the day.
In this study the daily patterns of body mass gain in four small bird species resident during winter in Scandinavia are described. Individually known birds were trained to come to a permanent feeder and their body masses were recorded every hour throughout the day with a remote-controlled balance. The hoarding willow tit Parus montanus , marsh tit P. palustris and European nuthatch Sitta europaea all displayed the most rapid gain in body mass in the early hours of the day. After the initial burst in the morning, reserves were accumulated at a roughly constant rate for the remainder of the day. In contrast, the non-hoarding great tit P. major apparently gained body reserves at a more even rate. The daily pattern of body mass gain found in the hoarding species differs from prevailing theoretical predictions, whereas the pattern in the non-hoarding great tit is in a better agreement with theory, from which this pattern has been predicted repeatedly.     

Sex ratio variation in birds

Significant variation in the sex ratio at hatching is unusual in birds. In contrast, sex differences in juvenile mortality have been found in a variety of species, especially when food is scarce- In some cases, these differences may be a consequence of reduced viability of males when food is scarce but, in others, the available evidence suggests that parental manipulation is involved.     

Diffusion of individual birds in starling flocks

Flocking is a paradigmatic example of collective animal behaviour, where global order emerges out of self-organization. Each individual has a tendency to align its flight direction with those of neighbours, and such a simple form of interaction produces a state of collective motion of the group. When compared with other cases of collective ordering, a crucial feature of animal groups is that the interaction network is not fixed in time, as each individual moves and continuously changes its neighbours. The possibility to exchange neighbours strongly enhances the stability of global ordering and the way information is propagated through the group. Here, we assess the relevance of this mechanism in large flocks of starlings (Sturnus vulgaris). We find that birds move faster than Brownian walkers both with respect to the centre of mass of the flock, and with respect to each other. Moreover, this behaviour is strongly anisotropic with respect to the direction of motion of the flock. We also measure the amount of neighbours reshuffling and find that neighbours change in time exclusively as a consequence of the random fluctuations in the individual motion, so that no specific mechanism to keep one''s neighbours seems to be enforced. On the contrary, our findings suggest that a more complex dynamical process occurs at the border of the flock.     

Intraspecific variation in movement patterns: modeling individual behaviour in a large marine predator

In large marine predators, foraging entails movement. Quantitative models reveal how behaviours can mediate individual movement, such that deviations from a random pattern may reveal specific search tactics or behaviour. Using locations for 52 grey seals fitted with satellite-linked recorders on Sable Island; we modeled movement as a correlated random walk (CRW) for individual animals, at two temporal scales. Mean move length, turning angle, and net squared displacement (R²_n: the rate of change in area over time) at successive moves over 3 to 10 months were calculated. The distribution of move lengths of individual animals was compared to a Lévy distribution to determine if grey seals use a Lévy flight search tactic. Grey seals exhibited three types of movement as determined by CRW model fit: directed movers – animals displaying directed long distance travel that were significantly underpredicted by the CRW (23% of animals); residents – animals remaining in the area surrounding Sable Island that were overpredicted by the model (29% of animals); and correlated random walkers – those (48% of animals) in which movement was predicted by the CRW model. Kernel home range size differed significantly among all three movement types, as did travel speed, mean move length, mean R²_n and total distance traveled. Sex and season of deployment were significant predictors of movement type, with directed movers more likely to be male and residents more likely to be female. Only 30% of grey seals fit a Lévy distribution, which suggests that food patches used by the majority of seals are not randomly distributed. Intraspecific variation in movement behaviour is an important characteristic in grey seal foraging ecology, underscoring the need to account for such variability in developing models of habitat use and predation.     

Explaining large-scale patterns of vertebrate diversity

The major clades of vertebrates differ dramatically in their current species richness, from 2 to more than 32 000 species each, but the causes of this variation remain poorly understood. For example, a previous study noted that vertebrate clades differ in their diversification rates, but did not explain why they differ. Using a time-calibrated phylogeny and phylogenetic comparative methods, I show that most variation in diversification rates among 12 major vertebrate clades has a simple ecological explanation: predominantly terrestrial clades (i.e. birds, mammals, and lizards and snakes) have higher net diversification rates than predominantly aquatic clades (i.e. amphibians, crocodilians, turtles and all fish clades). These differences in diversification rates are then strongly related to patterns of species richness. Habitat may be more important than other potential explanations for richness patterns in vertebrates (such as climate and metabolic rates) and may also help explain patterns of species richness in many other groups of organisms.     

Evolutionary routes to non-kin cooperative breeding in birds

Cooperatively breeding animals live in social groups in which some individuals help to raise the offspring of others, often at the expense of their own reproduction. Kin selection—when individuals increase their inclusive fitness by aiding genetic relatives—is a powerful explanation for the evolution of cooperative breeding, particularly because most groups consist of family members. However, recent molecular studies have revealed that many cooperative groups also contain unrelated immigrants, and the processes responsible for the formation and maintenance of non-kin coalitions are receiving increasing attention. Here, I provide the first systematic review of group structure for all 213 species of cooperatively breeding birds for which data are available. Although the majority of species (55%) nest in nuclear family groups, cooperative breeding by unrelated individuals is more common than previously recognized: 30% nest in mixed groups of relatives and non-relatives, and 15% nest primarily with non-relatives. Obligate cooperative breeders are far more likely to breed with non-kin than are facultative cooperators, indicating that when constraints on independent breeding are sufficiently severe, the direct benefits of group membership can substitute for potential kin-selected benefits. I review three patterns of dispersal that give rise to social groups with low genetic relatedness, and I discuss the selective pressures that favour the formation of such groups. Although kin selection has undoubtedly been crucial to the origin of most avian social systems, direct benefits have subsequently come to play a predominant role in some societies, allowing cooperation to persist despite low genetic relatedness.     

MHC variation in birds and reptiles

The major histocompatibility complex (MHC) has been studied in a multitude of mammals by now, but much less is known about its organisation and variation in other vertebrate species. The mammalian MHC is organised as a single gene cluster, but recent studies on birds suggest that this paradigm of MHC organisation has to be supplemented. The domestic chicken thus possesses two separate gene clusters which both contain MHC class I and class II B genes, and we have shown that the ring‐necked pheasant Phasianus colchicus also has two unlinked clusters of class II B genes. We are studying the effect of the MHC on mate choice, survival and reproductive success in natural populations of birds and reptiles. For this reason, we are developing DNA techniques to determine the animals' MHC genotype. The amplification of the hypervariable exon 3 of the class I gene from songbirds and reptiles has provided us with species specific probes that can be used in Southern blot analysis. The first results indicate very extensive variation in all studied species, that is starlings Sturnus vulgaris, great reed warblers Acrocephalus arundinaceus and water pythons Liasis fuscus. The restriction fragment length polymorphism (RFLP) analysis also suggests that the number of MHC genes is significantly larger in these species than in pheasants and domestic chickens. This revised version was published online in July 2006 with corrections to the Cover Date.     

Life history buffering in Antarctic mammals and birds against changing patterns of climate and environmental variation

The consequences of warming for Antarctic long‐lived organisms depend on their ability to survive changing patterns of climate and environmental variation. Among birds and mammals of different Antarctic regions, including emperor penguins, snow petrels, southern fulmars, Antarctic fur seals and Weddell seals, we found strong support for selection of life history traits that reduce interannual variation in fitness. These species maximize fitness by keeping a low interannual variance in the survival of adults and in their propensity to breed annually, which are the vital rates that influence most the variability in population growth rate (λ). All these species have been able to buffer these rates against the effects of recent climate‐driven habitat changes except for Antarctic fur seals, in the Southwest Atlantic. In this region of the Southern Ocean, the rapid increase in ecosystem fluctuation, associated with increasing climate variability observed since 1990, has limited and rendered less predictable the main fur seal food supply, Antarctic krill. This has increased the fitness costs of breeding for females, causing significant short‐term changes in population structure through mortality and low breeding output. Changes occur now with a frequency higher than the mean female fur seal generation time, and therefore are likely to limit their adaptive response. Fur seals are more likely to rely on phenotypic plasticity to cope with short‐term changes in order to maximize individual fitness. With more frequent extreme climatic events driving more frequent ecosystem fluctuation, the repercussions for life histories in many Antarctic birds and mammals are likely to increase, particularly at regional scales. In species with less flexible life histories that are more constrained by fluctuation in their critical habitats, like sea‐ice, this may cause demographic changes, population compensation and changes in distribution, as already observed in penguin species living in the Antarctic Peninsula and adjacent islands.