Ibis最新文献

Studies in the tropics suggest a regional similarity in survival rates of adult birds; however, this literature often overlooks species in semi-arid tropical environments. Bird survival in seasonally dry environments (e.g. seasonally dry tropical forests (SDTFa)) may be lower than that in more constantly wet areas (e.g. tropical rainforests (TRFs)), especially if the birds are negatively affected by seasonal rainfall or food-limitation. However, survival could be similar across these tropical environments, as the asymmetry between young and adult mortality tends to be high in all tropical areas, and the higher risk of mortality in young animals may favour adult survival (residual reproductive investment) regardless of the local climatic conditions. To fill this knowledge gap, we tested the hypothesis that bird survival is similar between seasonally dry (SDTF) and constantly wet (TRF) Neotropical environments. We estimated the apparent survival of 27 South American bird populations from three SDTF areas and 39 populations from a TRF. Apparent survival was estimated from Cormack–Jolly–Seber (CJS) models fitted using a Bayesian structure and the resulting variation in survival rates between study areas and with body mass was explored using a Bayesian phylogenetic mixed model. Apparent annual survival of passerines did not differ between areas (geometrical mean of survival: SDTF = 0.50, 0.56, 0.64; TRF = 0.58), but body mass was positively associated with survival. The variation in bird survival was partially explained by phylogenetic relationships among species. Our results suggest that bird survival is regionally similar in Neotropical forests, despite the climatic variation. We discuss possible physiological and behavioural mechanisms adopted by birds in SDTFs to attenuate effects of environmental seasonality on survival.

According to the structural-function hypothesis, the eggshell pigment protoporphyrin, deposited at weak spots, can strengthen the shell structure when calcium is lacking in avian species. However, this hypothesis has not been tested in species that produce pigmented eggs of uniform ground colour without spotting patterns. We tested the structural-function hypothesis using 435 eggs produced on seven calcium diets (0.2–4.5%) given to Common Pheasants Phasianus colchicus, a species that produces a large number of eggs on a low-calcium diet with unspotted eggshells composed of a uniform ground colour of mainly protoporphyrin. We found that pheasants on the lowest calcium diet (0.2%), which had thinner eggshells, produced eggs containing more protoporphyrin-based coloration than four of six other diets, suggesting this species employs pigmentation as ground colour to strengthen eggshells when available calcium is low. Our results provide the first, at least partial support for a structural function for eggshell pigments producing ground colour without spotting in a species that is often calcium-limited. This pattern may be more widespread in other ground-nesting taxa that also produce large numbers of eggs with protoporphyrin-based ground colour and are potentially limited by calcium during breeding.

Learned vocal signals of birds provide one of the most comprehensive sources of evidence for culture in animals. Such vocal signals often vary spatially and temporally. Signal variation can be driven by direct factors such as cultural drift and selection or by indirect factors such as changes in the environment, which may affect morphology and therefore acoustic capability. In this study we analysed flight and excitement calls of several call types of the Red Crossbill Loxia curvirostra and other crossbill species. Calls were recorded between 1962 and 2019 across the Palaearctic region. We measured acoustic similarity within flight and excitement calls and modelled the size of the effect attributed to temporal and geographical distance. Geographical distance between different sampling locations explained less call variation compared with temporal distance, and temporal variation within the excitement calls was smaller than in the flight calls. We conclude that calls of most call types of Red, Scottish and Parrot Crossbill are an example of cultural evolution. We suggest that excitement calls are less modifiable because they can serve better in dangerous situations when they are stable in time and space. In addition, we found no clear support for increasing or decreasing flight call similarity of call types while or after being in contact, as found in another study from North America. The reasons for the cultural evolution in calls of Palaearctic crossbills remain unclear.

Numerous bird species exhibit striking white patches on their plumages that have been reported as signals of individual quality in the context of sexual selection. Whereas differences in white plumage traits between individuals have been well studied, phenotypic variation and the factors affecting their consistency within the individual have received less attention. Here, we studied the consistency in the size of the white wing patch and its components of variation in a Spanish population of European Stonechats Saxicola rubicola rubicola monitored over 6 years (2007–2012). The wing patch was larger in males than in females for all age-classes, and first-year individuals exhibited smaller wing patches than older birds, particularly males. This trait also varied within the plumage-year at both population and individual level, with slight changes from the moulting period to the breeding season and a sharp decrease afterwards. In addition, patch size varied both between and within individuals across years. The daily mean temperature experienced in the month immediately prior to the moult (i.e. May) had a positive effect on male wing patch size. In females, however, no variable was found to explain wing patch variation satisfactorily. Despite being a dynamic trait throughout the moults, baseline and adjusted repeatabilities indicated a moderately high consistency for white wing patch size in both sexes. Therefore, the white wing patch in Stonechats is a dynamic trait that changes throughout individuals' lives, but is also a consistent trait at the individual level. These results indicate that this depigmented patch could convey information about both the long-term quality and the current state of individuals, harmonizing the existence of intra-individual changes in the size of sexual traits with its potential role as a genetic quality indicator.

Breeding habitat loss and depletion of genetic diversity can have critically negative impacts on species, and especially so for habitat specialists. The Aquatic Warbler Acrocephalus paludicola is a threatened European songbird that breeds in fens, which have been lost and fragmented over centuries. We used microsatellite loci to perform a spatial and longitudinal comparison, comparing samples collected recently (contemporary) with those obtained about two decades earlier (historical) from c. 25% of the breeding range (Biebrza and Polesie) of the Aquatic Warbler. With these data we explored changes in genetic diversity, expansions and reductions of population size, population structure, and gene flow. Allelic richness, expected heterozygosity, the number of effective and private alleles, and effective population size (N_E ≈ 200) were low and comparable across time and space. We detected a genetic bottleneck in contemporary Biebrza, and a less certain bottleneck in both historical and contemporary Polesie. Across space, Biebrza and Polesie were not genetically differentiated in either period. All the historical samples clustered together, but in the contemporary samples a small part of Polesie clustered separately (F_ST = 0.011). Across time, Biebrza and Polesie showed low but significant differentiation (F_ST = 0.026–0.064), and historical and contemporary groups clustered apart. A principal coordinate analysis on genetic distance detected three groups, which spanned sampling locations. In the temporal comparison, the contemporary group and contemporary Biebrza had elevated mean within-group pairwise relatedness. We did not recover signals for sex-biased dispersal, asymmetric gene flow or isolation-by-distance using the molecular data. Our results suggest that the studied populations show: (1) impoverished genetic diversity, (2) a change in allele frequencies over the two decades studied and (3) high gene flow between distant breeding sites, implying high resilience to habitat fragmentation that should facilitate the success of recolonising restored habitat patches by Aquatic Warblers.

Protected areas are essential conservation tools for mitigating the rapid decline of biodiversity. However, climate change represents one of the main challenges to their long-term effectiveness, as it induces rapid changes in the geographical distribution of many species. We used ecological niche modelling to predict the impacts of climate change on the distribution of five endemic owls in the Atlantic Forest and evaluated the effectiveness of the protected areas network for their conservation. The results indicate that the protected areas network is currently effective in terms of representativeness for most species; however, there will be a decline for all species in the coming decades because of climate change. We found that the ecoregions in the northern part of the Atlantic Forest will experience a higher loss of species, whereas those ecoregions in the southern part will be important stable climatic refuges in the future. Therefore, we emphasize the need to complement the network of protected areas to increase their representativeness in the distribution of species that will be affected by climate change, reducing species loss and increasing connectivity between suitable areas. We hope the results presented herein will serve as a basis for decision-makers to re-evaluate and improve current conservation policies and decisions in order to address the challenges posed by climate change and secure the survival of these species.

Quantifying resource partitioning between co-occurring species can provide insight into processes facilitating coexistence by closely related species, a fundamental question in ecology. We tested whether the habitat requirements of two closely related Neotropical forest eagles, the Crested Eagle Morphnus guianensis and Harpy Eagle Harpia harpyja, differ at fine and coarse resolutions across their shared geographical range. Using landcover and topographical covariates, we quantified potential resource overlap first using higher resolution (30 arc-s, ~ 1-km² data) generalized linear models (GLMs), and secondly using coarser-grain (2.5 arc-min, ~ 4.5-km² data) environmental ordination to capture the potential effect of scale on habitat overlap. The distribution of both eagles was largely explained by canopy tree species richness and canopy structural complexity, with peak suitability of 60–80% evergreen forest cover. Both eagles were negatively associated with mosaic forest and cultivated areas. From the GLMs, habitat overlap was >93% in geographical space but was reduced to 73% when considering environmental space, a proxy for resource overlap. From ordination (principal component analysis), resource overlap was 67% in environmental space, with randomization tests supporting equivalent environmental space for both eagles. Our results suggest that at the continental scale, Crested and Harpy Eagles share identical environmental space when quantified at fine and broad scales, with little difference in distribution and habitat use. At the continental scale used here, both eagles can coexist, presumably with sufficient habitat heterogeneity for coexistence when they occur in close proximity. Therefore, further research is required at the local level to capture fully where coexistence at the local scale is facilitated more by fine-scale habitat selection, or difference in diet between two species with indistinguishable habitat use.

The deciduous tree-herbivorous caterpillar-insectivorous bird food chain is a well-studied system for investigating the impacts of climate change across trophic levels. To date, across Europe, most attention has focused on the impacts of increasing spring temperature on changes to phenology in Oak-dominated (Quercus spp.) woodlands. Paridae species and Pied Flycatcher Ficedula hypoleuca are the most studied secondary consumers, all of which demonstrate an advancement in reproductive phenology with increases in spring temperature. Shifts in climate and phenology may also impact on reproductive investment in clutch size, and the effects of climate on phenology and clutch size may vary depending on woodland composition. To date, the effects of among-habitat variation in phenology and reproductive investment have received little attention. Insectivorous birds inhabiting woodlands that differ in tree composition may differ in the timing of breeding, due to local tree leafing phenology acting as a cue for egg-laying date and/or clutch size. Moreover, for most insectivorous birds, woodland composition within a territory is likely to be the main determinant of food availability for both adults and chicks. Consequently, if warming springs affect the temporal patterns of food availability differently across different woodland compositions, this may affect the optimal average local phenology for nesting birds. Here, using data from 34 long-term (mean 15 years) nest monitoring sites across the UK, we investigate the effect of woodland tree composition and temperature on Blue Tit Cyanistes caeruleus first egg date (FED) and clutch size. We supplemented the nest monitoring data by quantifying woodland composition, at a site level, through modified point counts. We predict that birds breeding in woodlands with greater proportions of late-leafing species, such as Oak and Ash Fraxinus excelsior, will breed later than those breeding in woodlands with greater proportions of early-leafing species, such as Birch Betula spp. and Beech Fagus sylvatica. We found no evidence for differences in Blue Tit FED or clutch size in relation to the proportion of any of the tree species investigated, after controlling for temperature and latitude (FED: −3.4 and 2.2, clutch size: −0.4 and − 0.2 eggs for one-unit increase in temperature and latitude, respectively). In recent decades and across all sites, clutch size has decreased as spring temperatures have increased, a strategy which could allow birds flexibly to adjust their breeding phenology such that nestling demand coincides with peak food availability. The lack of an effect of woodland composition on Blue Tit phenology suggests Blue Tits do not fine-tune their reproductive phenology to the local tree composition. Whether this lack of evidence for phenological divergence is due to an absence of divergent selection on breeding phenology and clutch size or to gene flow is not clear.