1,721,133 research outputs found
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
Fear is the mother of invention: anuran embryos exposed to predator cues alter life-history traits, post-hatching behaviour and neuronal activity patterns
No full textNeurophysiological modifications associated to phenotypic plasticity inresponse to predators are largely unexplored, and there is a gap of
knowledge on how the information encoded in predator cues is processed by prey sensory systems. To explore these issues, we
exposed Rana dalmatina embryos to dragonfly chemical cues (kairomones) up to hatching. At different times after hatching (up to
40 days), we recorded morphology and anti-predator behaviour of tadpoles from control and kairomone-treated embryo groups as well as
their neural olfactory responses, by recording the activity of their mitral neurons before and after exposure to a kairomone solution. Treated
embryos hatched later and hatchlings were smaller than control siblings. In addition, the tadpoles from the treated group showed a
stronger anti-predator response than controls at 10 days (but not at 30 days) post-hatching, though the intensity of the contextual response
to the kairomone stimulus did not differ between the two groups. Baseline neuronal activity at 30 days post-hatching, as assessed by the
frequency of spontaneous excitatory postsynaptic events and by the firing rate of mitral cells, was higher among tadpoles from the treated
versus the control embryo groups. At the same time, neuronal activity showed a stronger increase among tadpoles from the treated versus
control groups after a local kairomone perfusion. Hence, a different contextual plasticity between treatments at the neuronal level was not
mirrored by the anti-predator behavioural response. In conclusion, our experiments demonstrate ontogenetic plasticity in tadpole neuronal
activity after embryonic exposure to predator cues, corroborating the evidence that early-life experience can contribute to shaping the
phenotype at later life stages
Patterns of migratory connectivity in the European-African migratory system as inferred by ring recovery analysis of the EURING database
No full textUnderstanding how individuals redistribute after migration assists in the conservation and
management of mobile species, yet the eco-evolutionary drivers of migratory connectivity
remain unclear. Taking advantage of an exceptionally large (~150,000 individuals, 83 species)
and more-than-a-century long dataset of bird ringing encounters, we investigated determinants
of avian migratory connectivity on both short- and long-distance migrants. Most species
exhibited significant connectivity likely due to the large intraspecific variability in migration
strategies, which often led to the identification of distinct migratory populations. Migratory
connectivity was strongly predicted by geography, especially migration distance, but it was
evolutionary labile and weakly influenced by biological traits due to flexibility in migratory
behaviour. By unravelling determinants of migratory connectivity we improve knowledge about
the resilience of migrants to ecological perturbations. Also, our population-level analysis
provides a critical tool to inform transboundary conservation and management strategies by
explicitly considering the large intraspecific variability of avian migration
Geographic patterns in reproductive parameters among Nearctic herons (Ardeidae)
No full textAvian clutch size has been reported to show a poleward increase, a pattern that is well supported in landbirds but less so in waterbirds. We analyzed geographic variation in clutch and brood size among seven species of Nearctic herons and egrets (Ardeidae) over a latitudinal range spanning from 25 degrees to 52 degrees N. We included in the analysis data from 71 published references that reported information on both clutch and brood size. We found a strong and coherent latitudinal increase in clutch size in all species, but no unequivocal latitudinal variation in brood size. This resulted in a decreased index of productivity (brood size:clutch size ratio, excluding nest failures) with increasing latitude. In addition, we detected habitat-related variation in clutch size, which was, on average, smaller in salt-water than in freshwater habitats. The latitudinal decrease of the productivity index, which was not associated with latitudinal variation in nest-failure rates at either the clutch or brood stage, contrasts with previously proposed explanations for gradients in clutch size, which invoke latitudinal differences in seasonal variation of food abundance or nest-predation intensity. We suggest that factors other than those proposed in the case of landbirds may explain the latitudinal variation in clutch size in herons. In any case, our results suggest that herons may pay higher reproductive costs to obtain similar benefits when breeding at higher latitudes
Eagle Owl Bubo bubo and power line interactions in the Italian Alps
No full textWe reviewed the importance of power lines as a cause of mortality for Eagle Owl in the Italian Alps. Power lines were the most important cause of unnatural mortality for this species, accounting for over 50% of recorded casualties. The number of reported dead owls tended to be higher in September-October, suggesting an influence on juvenile dispersal. Furthermore, the significance of power lines as a cause of mortality increased over time, being lower in the 1960-1980 period than in 1981-1999. Electrocution, which usually takes place at medium-voltage (15-30 kV) electricity poles, accounted for the vast majority of casualties. We suggest some protective measures that may be put into practice in the proximity of Eagle Owl breeding territories
Identifying drivers of avian migratory connectivity in the European-African migration system
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