Earlier breeding,lower success: does the spatial scale of climatic conditions matter in a migratory passerine bird?

Following over 20 years of research on the climatic effects on biodiversity we now have strong evidence that climate change affects phenology, fitness, and distribution ranges of different taxa, including birds. Bird phenology likely responds to changes in local weather. It is also affected by climatic year‐to‐year variations on larger scales. Although such scale‐related effects are common in ecology, most studies analyzing the effects of climate change were accomplished using climatic information on a single spatial scale. In this study, we aimed at determining the scale‐dependent sensitivity of breeding phenology and success to climate change in a migratory passerine bird, the barn swallow (Hirundo rustica). For both annual broods, we investigated effects of local weather (local scale) and the North Atlantic Oscillation (NAO, large scale) on the timing of breeding and breeding success. Consistent with previous studies in migratory birds we found that barn swallows in Eastern Germany bred progressively earlier. At the same time, they showed reduced breeding success over time in response to recent climatic changes. Responses to climatic variation were observed on both local and large climatic scales, but they differed with respect to the ecological process considered. Specifically, we found that the timing of breeding was primarily influenced by large‐scale NAO variations and to a lesser extent by local weather on the breeding grounds. Conversely, climatic conditions on the local scale affected breeding success, exclusively. The observed decrease in breeding success over years is likely a consequence of scale‐related mismatches between climatic conditions during different breeding phases. This provides further evidence that a species' response of earlier breeding may not be enough to cope with climate change. Our results emphasize the importance of considering the response of ecological processes along different climatic scales in order to better understand the complexity of climate change effects on biodiversity.     

Are incubation costs in female pied flycatchers expressed in humoral immune responsiveness or breeding success?

Although clutch size variation has been a key target for studies of avian life history theory, most empirical work has only focused on the ability of parents to raise their altricial young. In this study, we test the hypothesis that costs incurred during incubation may be an additional factor constraining clutch size in altricial birds. In the pied flycatcher (Ficedula hypoleuca), we manipulated the incubation effort of the female by enlarging and reducing clutch sizes. To manipulate incubation effort only, the original clutch sizes were restored shortly after hatching. We found that fledging success was lower among broods whose clutches were enlarged during incubation. There was, however, no effect of manipulation on female body condition or on their ability to mount a humoral immune response to diphtheria or tetanus toxoid during the incubation or nestling provisioning period. Instead, we found that the original clutch size was related to the immune response so that females with seven eggs had significantly lower primary antibody responses against tetanus compared to those with six eggs. Our results suggest that incubating females are not willing to jeopardise their own condition and immune function, but instead pay the costs of incubating a larger clutch by lower offspring production. The results support the view that costs of producing and incubating eggs may be substantial and hence that these costs are likely to contribute to shaping the optimal clutch size in altricial birds.     

How much do we know about the breeding biology of bird species in the world?

Knowledge on species’ breeding biology is the building blocks of avian life history theory. A review for the current status of the knowledge at a global scale is needed to highlight the priority for future research. We collected all available information on three critical nesting parameters (clutch size, incubation period and nestling period) for the close to 10 000 bird species in the world and identified taxonomic, geographic and habitat gaps in the distribution of knowledge on avian breeding biology. The results show that only one third of all extant species are well known regarding the three nesting parameters analyzed, while the rest are partly or poorly known. Most data deficient taxonomic groups are tropical forest nesters, particularly from the Amazon basin, southeast Asia, Equatorial Africa and Madagascar – the places that harbor the world's highest bird diversity. These knowledge gaps could be hampering our understanding of avian life histories. Ornithologists are encouraged to pay more efforts to explore the breeding biology of those poorly‐known species.     

Structure of the breeding bird assemblage of a primeval alder swamp in the ?úr National Nature Reserve

The structure of a breeding bird assemblage of a primeval alder swamp in the Šúr National Nature Reserve (the Danube Basin) was studied in the period 1992–1995. A 16 ha forest interior study plot was established for bird censusing. Population abundances were estimated by a combined version of the mapping method from the end of March to the beginning of July. Altogether, 42 breeders were recorded and the mean total density of species total across years was 125.15 ± 12.73 pairs/10 ha (CV = 10.17%). Two species were eudominant (≥ 10%): Sturnus vulgaris and Anas platyrhynchos, and six species were dominant (5% ≤ 10% <): Ficedula albicollis, Fringilla coelebs, Phylloscopus collybita, Parus major, Sylvia atricapilla, Erithacus rubecula. The Shannon diversity index (H′) varied between 3.98–4.10 bites. The evenness index (J′) reached values between 0.79–0.81. Expected species diversity in a random sample of 100 pairs calculated by rarefaction [E (S _{100 pairs})] was 21.35 ± 0.92 species derived as a mean value from the years 1992–1995. The mean rarefaction estimate on the area [E (S _{10 ha})] was 22.75 ± 1.58 species. Bird species richness and diversity were significantly higher in the study plot in comparison to the mean value of European wet alder forests. These results are comparable with the values of structural assemblage parameters of the primeval stands dominated by alder within the Białowieża National Park, Poland.     

Does prior breeding experience improve reproductive success in collared flycatcher females?

In order to assess the importance of breeding experience in shaping age-specific patterns of reproduction an experiment on collared flycatchers (Ficedula albicollis) was performed. Experimental females were restrained from reproduction by destroying their nests after prolonged incubation. Unmanipulated females were used as controls. Only young, first time breeders were considered. A year after manipulation, experimental (inexperienced) and control (experienced) females were compared for a number of breeding traits. They did not differ with respect to laying date, clutch size, number of fledglings and number of local recruits. However, fledglings from broods of inexperienced females were significantly lighter and had shorter tarsi. This suggests that prior experience of feeding young may indeed influence the future reproductive performance in altricial bird species such as the collared flycatcher.     

Quantity or quality? Determinants of maternal reproductive success in tropical pythons (Liasis fuscus)

A female''s reproductive output (size and number of offspring) may say little about her reproductive success; the ''quality'' of her progeny and the time that they are produced may be more important in this respect. We marked and released 1224 hatchling water pythons (Liasis fuscus) from 116 clutches of laboratory-incubated eggs, in a study site in tropical Australia. Clutches varied widely in the number of eggs, mean offspring sizes, the proportion of eggs that hatched, and recapture rates of offspring. Clutch size was not significantly correlated with the number of recaptured hatchlings in either year, nor was mean offspring size related to recapture probability. Instead, offspring recapture rates varied as a function of the time of hatching. Recapture rates were higher for hatchlings released in a year with high prey availability than in a year with few prey. In addition, recapture rates were higher for earlier-hatching clutches in the year with few prey. The other significant effect on recapture rates involved offspring viability: some clutches had a much higher proportion of surviving offspring than did others, and recapture rates were higher from clutches with higher hatching success (i.e. proportion of eggs hatching). Hence, the usual measures of reproductive output (clutch size and offspring size) offer only a poor index of a female''s reproductive success in this system.     

All you can eat: is food supply unlimited in a colonially breeding bird?

Food availability is generally considered to determine breeding site selection and therefore plays an important role in hypotheses explaining the evolution of colony formation. Hypotheses trying to explain why birds join a colony usually assume that food is not limited, whereas those explaining variation in colony size suggest that food is under constraint. In this study, we investigate the composition and amount of food items not eaten by the nestlings and found in nest burrows of colonially nesting European bee‐eaters (Merops apiaster). We aimed to determine whether this unconsumed food is an indicator of unlimited food supply, the result of mistakes during food transfer between parents and chicks or foraging selectivity of chicks. Therefore, we investigated the amount of dropped food for each nest in relation to reproductive performance and parameters reflecting parental quality. Our data suggest that parents carry more food to the nest than chicks can eat and, hence, food is not limited. This assumption is supported by the facts that there is a positive relationship between dropped food found in a nest and the number of fledglings, nestling age, and chick health condition and that the amount of dropped food is independent of colony size. There is variation in the amount of dropped food within colonies, suggesting that parent foraging efficiency may also be an important determinant. Pairs nesting in the center of a colony performed better than those nesting on the edge, which supports the assumption that quality differences between parents are important as well. However, dropped food cannot be used as an indicator of local food availability as (1) within‐colony variation in dropped food is larger than between colony variation and, (2) the average amount of dropped food is not related to colony size.     

Spatial distribution of communal nests in a colonial breeding bird: benefits without costs?

Abstract The spatial organization of individuals, or groups of individuals, within a population can provide valuable information about social organization and population dynamics. We analysed the spatial distribution of nests of the sociable weaver (Philetairus socius) on two farms in the Kalahari. Sociable weavers build large communal nests on big savannah trees, forming a pattern of trees with and without nests. We used two spatial statistics, Ripley's K and the pair correlation function, to describe characteristics of the point patterns over a range of distances. (i) At distances of 200 and 300 m, communal nests were clustered. (ii) At distances greater than 1000 m, communal nests were regularly distributed. These findings are independent of the spatial distribution of trees. Furthermore, we used Moran's I to analyse spatial autocorrelation of nest sizes. We expected negative autocorrelation because of competition between nests. But on both farms there was no significant autocorrelation of nest sizes for any distance class. The regular distribution observed at larger distances may indicate competition and/or territoriality among different nests, but the lack of spatial autocorrelation between nest sizes suggests that these interactions may happen between nest clusters rather than between single nests. This was confirmed by significant clustering of nests on small scales. We thus suggest, that colonies of P. socius consist of several nests on adjacent trees forming a cluster of subcolonies. The question why sociable weavers establish subcolonies instead of adding more chambers to the natal nest, could not simply be answered by limitation of nesting space. We suggest a strategy to avoid costs due to increasing colony size.     

Why do some adult birds skip breeding? A hormonal investigation in a long-lived bird

Skipping reproduction is often observed in long-lived organisms, but proximate mechanisms remain poorly understood. Since young and/or very old snow petrels (Pagodroma nivea) commonly skip breeding, we tested whether they are physiologically able to breed during the pre-laying stage. To do so, we measured the ability of known-age (11-45 years old) petrels to release luteinizing hormone (LH, a crucial driver for breeding), by injecting exogenous gonadotropin-releasing hormone (GnRH). Although young petrels exhibited low baseline LH levels, they were able to elevate LH levels after a GnRH challenge. Moreover, young and very old petrels showed a stronger decrease in LH levels after the 10 min post-GnRH injection compared with middle-aged petrels. Birds that skipped breeding were as able as breeders to release LH after a GnRH challenge, indicating that they had functional pituitaries. However, the decision to skip reproduction was linked to a strong LH decrease after the 10 min post-GnRH injection. Our result suggests that the youngest and the oldest petrels fail to maintain elevated baseline LH levels, thereby do not initiate reproductive activities. Skipping reproduction in long-lived birds probably results from age-related changes in the dynamics of the hypothalamic-pituitary-gonadal (HPG) axis function.     

Does conspicuous colouration of Magpies Pica pica influence aggressive behaviour in nesting Great Reed Warblers Acrocephalus arundinaceus?

Capsule: Using dummy experiments at nests of Great Reed Warblers Acrocephalus arundinaceus, we found no evidence to support the hypothesis that the contrasting black and white plumage colouration in Magpies Pica pica has evolved to reduce mobbing defensive attacks by potential prey species. We suggest instead that it might have evolved in the context of sexual selection or as a signal for flock formation.     

Urbanization mechanisms in bird species: population systems transformations or adaptations at the individual level?

The present research deals with urbanization of wild bird and mammal species. Forms and mechanisms of population steadiness in the urban landscape have been examined. The urbanization process turned out to be a directed change of the population system forming de novo in the urbolandscape leading to a sustainable organization peculiar for the particular environment. The population organization of different types in urbolandscape is found to provide its stability under conditions of directed and fast changes accompanied with instability and heterogenous structure of habitats. It is shown that the same type of population organization meets the corresponding demands among different species settling in the urban environment. Its features are "openness" and "flowage" of the groups, far order of settlement levels and other units of population system, constant movements of the individuals between the groups as a respond to the signals of urboenvironment significant changes. The "urban" variant of the population system organization turns out to be opposite to that of the same species in the non-urban habitats. After formation of the urban types by the species and successful developing of the town, the urban population becomes separated from the maternal local population and begins to exist independently in the urban landscape. The variety of adaptation aberrations in ecology, behavior, and mode of life of urban birds is the population system stability function in the urban landscape and is not a results of individual selection. It is shown that the urbanization process of the species goes firstly on the population level being the system structure transformation developed by the species towards the most stable state in the town (city) territory. Only after the appearance of stable urban population, the urban individuals show the rapid growth of different changes in ecology, behavior, mode of life that was traditionally described by naturalists as species adaptation to the city conditions. The key features of urban population stability/instability are described. Their application to closely related species allows us to distinguish potential urbanists from instable and vulnerable species that could be soon pushed out of the city. The application of corresponding criteria to the urban populations of such species constituting one guild allows us to predict if their developing in the given town would be successful or unsuccessful. The latter is very important since close species are, as a rule, ecologically indistinguishable in the urbanized landscapes. So one can not predict successful/unsuccessful urbanization taking into account the differences in the range of habitats, breeding success, and other external features.     

Are European starlings breeding in the Azores archipelago genetically distinct from birds breeding in mainland Europe?

The European starling (Sturnus vulgaris) has recently been found to eat eggs of the endangered roseate tern (Sterna dougallii) in the Azores. Azorean starlings are considered an endemic subspecies (S. vulgaris granti), so we investigated how much genetic divergence has accumulated between the Azores and other European populations in order to assess whether lethal control measures might be possible, as previous experiments have found that taste aversion is not likely to be successful. For this purpose, we sequenced a region of the protein-coding mitochondrial gene ND2 for samples from six different populations. Of the 1,026 base pairs sequenced, 19 (1.7%) were variable and formed 15 different haplotypes. The Azores had high and significant genetic differentiation from all the other populations studied. Haplotype diversity was high in the mainland populations studied, ranging from 0.767 to 0.900, but there was no variation among the Azores samples, which were collected from a geographically broad region. Given the lack of genetic variability in the Azores birds and their abundance throughout the archipelago, lethal control on a local basis and as part of an integrated control plan can be seen as a reasonable measure to protect tern colonies.     

Age-specific reproductive success in a long-lived bird: do older parents resist stress better?

In many vertebrates, reproductive performance increases with advancing age but mechanisms involved in such a pattern remain poorly studied. One potential mechanism may be the hormonal stress response, which shifts energy investment away from reproduction and redirects it towards survival. In birds, this stress response is achieved through a release of corticosterone and is also accompanied by a decrease in circulating prolactin, a hormone involved widely in regulating parental cares. It has been predicted that, when the value of the current reproduction is high relative to the value of future reproduction and survival, as it is expected to be in older adults, the stress response should be attenuated to ensure that reproduction is not inhibited. We tested this hypothesis by measuring the corticosterone and prolactin responses of known-age (8-36 years old) incubating snow petrels (Pagadroma nivea) to a standardized capture/handling stress protocol. We also investigated whether an attenuation of the stress responses will correlate with a lower occurrence of egg neglect, a frequently observed behaviour in snow petrels. The probability of successfully fledging a chick increased from 6 years to 12 years before stabilizing after 12 years of age. Corticosterone response to stress was unaffected by age. Prolactin response to stress, however, was influenced clearly by age: in both sexes older breeders had higher stress-induced prolactin levels than younger ones. This was due to an increasing attenuation of the prolactin response to stress with advancing age in females, and in males this was due to a probably higher intrinsic capacity of older males to secrete prolactin. Moreover, higher stress-induced prolactin levels were correlated with a lower probability of neglecting the egg. In young breeders, the combination of a robust corticosterone increase with a lower ability to maintain prolactin secretion during acute stress is probably one of the functional causes of their lower incubation commitment. We suggest that the ability to maintain a threshold level of prolactin during a stressful situation may be an important physiological mechanism involved in the improvement of reproductive performance with advancing age in long-lived birds.     

Virulence or Niche Factors: What's in a Name?

The increasing interest in the human microbiota raises some interesting questions about the terminology we use to describe some of the structures and strategies employed by commensal and pathogenic microbes to compete in these complex biological ecosystems. For example, all microbes arriving in the alimentary tract face the task of surviving passage through the stomach, coping with bile, interacting with the immune system, competing with the established microbiota, and obtaining sufficient nutrients to gain a foothold in this hostile environment. It is not surprising then that many gastrointestinal microbes (both pathogens and commensals) use similar strategies to overcome the challenges associated with this particular biological niche. Given that many of these structures and strategies were discovered and characterized in pathogens and because they often play important roles in establishing and maintaining an infection, they have often been characterized as virulence factors. It would be misleading to describe the same strategies and structures found in harmless commensals as “virulence factors,” since they represent a sine qua non for life in the gastrointestinal tract. It may be time to reconsider and refer to them as “niche factors,” both in terms of providing scientific accuracy but also in light of the growing interest in using gut microbes as probiotics, where the distinction between virulence factors and niche factors is likely to be very important from a regulatory perspective.     

Wetlands policy of the Dutch government: failure or success?

An overview is presented of Dutch wetlands and the perspectives and threats to which they are exposed. The general environmental problems of The Netherlands are reflected in the problems with the preservation of wetlands: deterioriation of water quality is one of the main problems, directly followed by the desiccation of former wet areas. Also splitting up of larger coherent areas into smaller fragments due to infrastructural works does not favour long time existence of complete (eco)systems. The policy of the Dutch government and its different ministries towards the protection of wetlands will be described. The policy to protect the Wadden Sea and which is based on concepts of wise use and sustainability will be presented as an example of Dutch integral environmental policy for wetlands particularly. Our conclusion is that wetlands policy is tardy but successful.     

Vibratory courtship in a web-building spider: signalling quality or stimulating the female?

Courtship behaviour in spiders in the form of premating vibrations by males may function (1) as a male identity signal used for species recognition, (2) in suppression of female aggressiveness, (3) to stimulate female mating behaviour, or (4) as a quality signal used in female choice. We investigated the function of web vibration by male Stegodyphus lineatus in a series of experiments. Regardless of vibratory performance, all males mated successfully with virgin females but only 56.4% of males mated with nonvirgin females. Vibratory performance did not influence male mating success, but heavier males had a higher probability of mating with mated females. Males vibrated less often and produced fewer vibrations when introduced on the web of a mated female. Males that vibrated webs of virgin females mated faster than nonvibrating males, but there was no effect of vibration rate or body mass. There was no effect of male vibratory effort or vibration rate on female reproductive success measured as time to egg laying, clutch size, number of hatched young, number of dispersed young and offspring body mass after a single mating. Males vibrated on abandoned virgin female webs but the response decreased with increasing duration of female absence, suggesting that females produce a web-borne pheromone, which elicits male vibrating behaviour. Mated females were less receptive and not stimulated by male vibrating behaviour. We conclude that male premating vibrations in S. lineatus do not function as a male quality signal selected via female choice. Rather, the primary function of this behaviour may be to stimulate a receptive female to mate. Copyright 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.