1,721,237 research outputs found
Intra-seasonal changes in distribution and habitat associations of a multi-brooded bird species: implications for conservation planning
No full textIntra-seasonal changes of the ecological needs and the distribution patterns of multi-brooded bird species are a poorly studied but potentially important topic in avian conservation planning. In this study of a passerine species of conservation concern, the woodlark Lullula arborea, we highlight the conservation implications of spatial shifts of breeding territories and changes of habitat requirements during the course of the breeding season. We described the factors affecting the distribution and habitat selection of this species in the Trebbia river valley (northern Apennines, Italy), where we mapped woodlark territories during the average time of first and second clutches. A strong shift of territories towards higher altitudes with the progression of the season was observed. The habitat models predicting woodlark occurrence varied between the early and the late period. Specifically, fodder cover positively predicted occurrence early in the season, whereas late in the season occurrence was positively influenced by shrub cover, length of woodland edge, alfalfa cover and rocky areas. Accordingly, territories that were occupied throughout the entire season had greater fodder, shrub and rocky cover compared with those that were occupied only early in the season, suggesting that these variables were important in determining territory quality for woodlarks. Therefore, changing ecological needs of multi-brooded bird species during the breeding season have to be taken into account for defining appropriate conservation strategies. This was demonstrated by showing that the habitat variables predicting woodlark occurrence early in the season poorly predicted occurrence late in the season and vice versa. In conclusion, this study provides the first detailed assessment of habitat factors affecting the occurrence of breeding woodlarks in an important portion of the species' range, and represents the first explicit attempt to model seasonally changing ecological requirements of bird species for conservation purposes. Our findings suggest that complex data and flexible habitat management strategies are required to account for temporal changes in habitat suitability in multi-brooded bird species
Water rail Rallus aquaticus breeding density and habitat preferences in Northern Italy
No full textThe Water Rail Rallus aquaticus is an elusive and poorly studied species, despite its widespread distribution in Eurasian wetlands. We carried out a survey of the species' macrohabitat preferences during the breeding season at a natural wetland site in northern Italy, by comparing habitat features of territory plots (determined by accurate territory mapping) and plots located at random within the wetland area. Overall, 20 territorial pairs inhabited the study area (21.6 ha) during the 2002 breeding season, leading to a breeding density of 0.93 territories/ha. Compared to random plots, territory plots were characterised by a higher Phragmites, Typha and water cover. Thus, at the single-site level, the Water Rail showed a marked association with the presence of wet reeds, while avoiding the drier habitats, which replace Phragmites reeds in wetland ecological successions. In conclusion, our study strengthens previous findings and further highlights that the management of wet reeds should be a priority in wetland conservation planning
Tail length correlates with fat stores in pre-migratory roosting Barn Swallows Hirundo rustica
No full textElongated outer tail streamers in Barn Swallows may play a functional role during the feeding activity, by enhancing manoeuvrability. Here we focus on the relationship between tail length and fat stores in adult male and female Barn Swallows captured during the post-breeding and pre-migratory periods. Fat score was higher among long-tailed males, but no such relationship was evident among females. However, the effect of tail on fat stores did not differ between the sexes. Hence, the relationship between fat and tail may be related both to naturally and sexually selected aspects of tail length, that is considered to be a sexually selected character and indicator of individual quality in males. Our results suggest that long-tailed males, due to their higher quality, may be able to raise their fat stores more than other individuals during the pre-migratory fattening period, and, at the same time, that long-tailed individuals of both sexes may be able to store food faster, according to the aeroelastic properties of outer tail streamers
Head ornaments in owls: what are their functions?
No full textWe studied head ornamentation in owls by focussing on the hypothesis that it may serve both intra- and interspecific communication. We carried out pairwise comparisons of morphological, ecological and behavioural traits on a subset of closely related species with contrasting head ornamentation patterns. We found that the degree of head ornamentation was associated with habitat and activity rhythm, highly ornamented species (e.g., most of the genus Bubo) living preferentially in open habitats and being active by day, but not with body size. Although our results do not exclude the possibility that head ornaments may represent a warning mechanism to startle predators and mobbers, they nevertheless suggest that such signals have evolved for visual communication with conspecifics, being more expressed in species that may use them more effectively without incurring the risk of predation or disturbance
The niche variation hypothesis and the evolution of colour polymorphism in birds: A comparative study of owls, nightjars and raptors
No full textWe studied the evolution of colour polymorphism in diurnal raptors, owls and nightjars, the avian taxa in which this trait is most widespread, in relation to species ecological niche width and diet. Two main mechanisms have been put forward to explain the maintenance of polymorphism, namely apostatic selection and disruptive selection. The niche variation hypothesis states that species with broader ecological niches should be more variable compared with those with narrow niches because of the action of disruptive selection; the apostatic selection hypothesis conversely suggests that intraspecific colour variation should be promoted in predators by prey forming an avoidance image for the more common colour morph. Our aim was to determine if colour polymorphism occurrence was associated with broad ecological niches as predicted by the niche variation hypothesis, or with predation on intelligent and sharp-sighted prey as predicted by the avoidance image hypothesis. Pairwise comparisons were made between pairs of closely related species differing in variables expected to influence the occurrence of polymorphism. We found that polymorphic species of all three groups showed wider and more continuous distribution ranges, frequented many different habitats, both open and closed, and lived in seasonally alternating dry/wet climates. Polymorphic species were more migratory compared with monomorphic ones, and they showed an activity pattern covering both day and night. Conversely, colour polymorphism was not higher in species preying on birds and mammals. All these findings support the hypothesis that colour polymorphism evolved in bird species with wider niche breadth and not in species preying on intelligent prey. Therefore, we propose that disruptive selection may be the main mechanism maintaining colour polymorphism in these bird groups by favouring different morphs in different environmental conditions
Rock climbing and raven Corvus corax occurrence depress breeding success of cliff-nesting peregrines Falco peregrinus
No full textAims: To assess the significance of rock climbing-induced disturbance and Raven Corvus corax occurrence on the breeding output of a cliff-nesting Peregrine Falco peregrinus population. Location: Northern Italy- southern Switzerland. Methods: Breeding success, productivity and fledgling rate of 29 Peregrine pairs were analysed in relation to the occurrence of rock climbing activities and Ravens at nesting cliffs. Results: Breeding success and productivity were lower for pairs coexisting alternatively with Ravens or climbers, compared to undisturbed pairs. In addition, pairs settled at cliffs simultaneously occupied by Ravens and frequented by climbers did not fledge any young, suggesting that Raven predation on Peregrine eggs/chicks may be predisposed by human disturbance. Conclusion: It is proposed that rock climbing should be regulated or banned in the proximity of Peregrine nests, in particular at sites hosting Ravens
Phenological response to climate change and population trends of migratory birds
No full textThe recent increase in temperatures across the Northern Hemisphere is causing marked changes
in the phenology of plants and animals, which shows a trend towards earlier start of spring
events, such as flowering and leaf emergence, or earlier onset of breeding activities. Migratory
birds make no exception, and there are several studies documenting advances in timing of spring
migration in recent decades. However, not all species have advanced their migration timing, and
this may have lead to a mismatch between timing of reproduction of these species and the peak
seasonal availability of their main food sources. In fact, organism belonging to different trophic
levels, such as e.g. insectivorous birds and their invertebrate prey, may have different abilities to
show a phenological response to rapid climate change, and prey could advance phenology more
than predators. Importantly, mismatched species could suffer from reduced reproductive output,
leading to population declines. We have reviewed the long-term changes in timing of spring
migration among European bird species in the period 1960-2006, and - besides confirming a
general pattern of advance of migration dates - found that such changes varied significantly among
species, different populations of the same species consistently showing an advance, whereas
populations of other species did not change or even delayed their phenology. We then analysed
whether the phenological response to climate change, as assessed by long-term trend in spring migration timing, predicted population trends, assuming that species that did not advance timing of
migration could be more mismatched compared to their food sources, and thus be characterized
by declining populations. Indeed, we found that species that did not advance timing of spring
migration suffered stronger population declines in the period 1990-2000 compared to species which
advanced their timing of spring migration, whose populations were instead stable or increasing.
Therefore, failure to adjust timing of spring migration to climate change may increase the chances
of extinction of migratory bird species in the near future
Analysis of sex sequences by means of generalized linear mixed models
No full textAdaptive strategies of sex allocation functioning to increase fitness, including strategic allocation of sex in relation to birth order and sex composition of the progeny, have frequently been explored, but the development of a statistical framework for these analyses has lagged behind. In this paper, we contribute to filling this gap by devising a method for analyzing sex sequences based on a proper parameterization of generalized linear mixed models (GLMMs). The method is highly flexible and can be easily extended to investigate sequences of traits or events or other longitudinal data. As a worked example, we focus on the analysis of sex sequences of offspring produced by females in a single reproductive event and develop a method that allows analyzing simultaneously sequences of different length (e.g., clutches of different size) and sequences with missing data, as may frequently happen in "real-world" data sets. Different patterns of allocation among traits or events along the sequence were investigated, and a real data base of sex sequences of eclectus parrots (Eclectus roratus) fledglings produced by different females was analyzed. A tutorial for running the analyses with the R or the SAS software is provided in the Electronic Supplementary Material
Replacement of body feathers is associated with low pre-migratory energy stores in a long-distance migratory bird, the barn swallow (Hirundo rustica)
No full textMoult and pre-migratory fuelling are energy-demanding processes in birds, usually showing a limited degree of temporal overlap. The barn swallow Hirundo rustica, a strictly aerial insectivorous, long-distance passerine migrant (15-20 g), accumulates conspicuous energy stores (up to 30-40% of lean body mass) before embarking on the autumn migratory flight between western European breeding areas and African sub-Saharan winter quarters. During the pre-migratory fattening period (September October), both adult and juvenile birds replace body (contour) feathers. The seasonal overlap between moult and energy storing was studied in barn swallows in Italy. Data from 23 000 birds, measured during eight study seasons, were analysed to investigate whether the simultaneous replacement of body feathers and fuelling was associated with reduced energy stores. Among all age and sex-classes, non-moulting individuals showed a relatively greater level of energy stores compared to moulting birds. This was particularly evident during the last phase of the pre-migratory fuelling period, when birds were building up energy stores at maximum rate. The proportion of moulting birds was greater among adults as compared to juveniles, and adult males moulted faster/earlier than females. The frequency of individuals with growing feathers among the innermost primary feathers was greater among birds replacing body feathers. The presence of moulting wing feathers in adult birds only marginally affected energy stores, as compared to the replacement of body feathers. Hence, our data show a negative association between replacement of contour feathers and energy stores in a long-distance migratory bird, suggesting that a physiological trade-off between these two energy-demanding processes may occur, and that a late moult may ultimately have a negative effect on the successful termination of the migratory journey
- …
