255 research outputs found
Innate Sex Differences in the Timing of Spring Migration in a Songbird
In migrating animals protandry is the phenomenon whereby males of a species arrive at the breeding grounds earlier than females. In the present study we investigated the proximate causes of protandry in a migratory songbird, the northern wheatear Oenanthe oenanthe. Previous experiments with caged birds revealed that males and females show differentiated photoperiod-induced migratory habits. However, it remained open whether protandry would still occur without photoperiodic cues. In this study we kept captive first-year birds under constant photoperiod and environmental conditions in a âcommon gardenâ experiment. Male northern wheatears started their spring migratory activity earlier than females, even in the absence of environmental cues. This indicates that protandry in the northern wheatear has an endogenous basis with an innate earlier spring departure of males than females
Combining survey and remotely sensed environmental data to estimate the habitat associations, abundance and distribution of breeding thin-billed prions Pachyptila belcheri and Wilsonâs storm-petrels Oceanites oceanicus on a South Atlantic tussac island
Small petrels are the most abundant seabirds in the Southern Ocean. However, because they breed in burrows on remote and
often densely vegetated islands, their colony sizes and conservation status remain poorly known. To estimate the abundance
of these species on Bird Island in the Falkland archipelago, we systematically surveyed their breeding burrow density and
occupancy across this near-pristine tussac (Poa flabellata)-covered island. By modelling burrow density as functions of
topography and Sentinel 2 satellite-derived Normalised Difference Vegetation Index data, we inferred habitat associations and
predicted burrow abundance of the commonest speciesâThin-billed Prions (Pachyptila belcheri) and Wilsonâs Storm-petrels
(Oceanites oceanicus). We estimate that there are 631,000 Thin-billed Prion burrows on the island (95% CI 496,000â904,000
burrows). Assuming that burrow occupancy lies between 12 and 97%, this equates to around 76,000â612,000 breeding pairs,
making Bird Island the second or third largest P. belcheri colony in the world, holding approximately 3â27% of the speciesâ
breeding population. We estimate that 8200â9800 (95% CI 5,200â18,300 pairs) pairs of Wilsonâs Storm-petrels also
breed on the island. Notably, the latter burrowed predominantly under and within tussac pedestals, whereas they are usually
assumed to breed in rock cavities. Thin-billed Prions are declining in the Kerguelen archipelago, but their population trends
in the Falklands are unknown. Given the wide confidence intervals around our own and other population estimates for these
cryptic species, we recommend that their populations should be monitored regularly, at multiple sites.Fundação para a CiĂȘncia e Tecnologia - FCTinfo:eu-repo/semantics/publishedVersio
Extreme events are more likely to affect the breeding success of lesser kestrels than average climate change
Climate change is predicted to severely impact interactions between prey, predators and habitats. In
Southern Europe, within the Mediterranean climate, herbaceous vegetation achieves its maximum
growth in middle spring followed by a three-month dry summer, limiting prey availability for
insectivorous birds. Lesser kestrels (Falco naumanni) breed in a time-window that matches the
nestling-rearing period with the peak abundance of grasshoppers and forecasted climate change may
impact reproductive success through changes in prey availability and abundance. We used Normalised
Difference Vegetation Index (NDVI) as a surrogate of habitat quality and prey availability to investigate
the impacts of forecasted climate change and extreme climatic events on lesser kestrel breeding
performance. First, using 14 years of data from 15 colonies in Southwestern Iberia, we linked fledging
success and climatic variables with NDVI, and secondly, based on these relationships and according
to climatic scenarios for 2050 and 2070, forecasted NDVI and fledging success. Finally, we evaluated
how fledging success was influenced by drought events since 2004. Despite predicting a decrease in
vegetation greenness in lesser kestrel foraging areas during spring, we found no impacts of predicted
gradual rise in temperature and decline in precipitation on their fledging success. Notwithstanding, we
found a decrease of 12% in offspring survival associated with drought events, suggesting that a higher
frequency of droughts might, in the future, jeopardize the recent recovery of the European population.
Here, we show that extreme events, such as droughts, can have more significant impacts on species
than gradual climatic changes, especially in regions like the Mediterranean Basin, a biodiversity and
climate change hotspotinfo:eu-repo/semantics/publishedVersio
Predicting the distribution of a threatened albatross: The importance of competition, fisheries and annual variability
The ability to predict the distribution of threatened marine predators is essential to inform spatially explicit seascape management. We tracked 99 individual black-browed albatrosses Thalassarche melanophris
from two Falkland Islandsâ colonies in 2 years. We modeled the observed distribution of foraging activity taking environmental variables, fisheries activity (derived from vessel monitoring system data), accessibility to feeding grounds and intra-specific competition into account. The resulting models had sufficient generality to make reasonable predictions for different years and colonies, which allows temporal
and spatial variation to be incorporated into the decision making process by managers for regions and seasons where available information is incomplete. We also illustrated that long-ranging birds from
colonies separated by as little as 75 km can show important spatial segregation at sea, invalidating direct or uncorrected extrapolation from one colony to neighboring ones. Fisheries had limited influence on
albatross distribution, despite the well known scavenging behavior of these birds. The models developed here have potentially wide application to the identification of sensitive geographical areas where special
management practices (such as fisheries closures) could be implemented, and would predict how these areas are likely to move with annual and seasonal changes in nvironmental conditions
Cork oak vulnerability to fire: the role of bark harvesting, tree characteristics and abiotic factors
Forest ecosystems where periodical tree bark harvesting is a major economic activity may be particularly vulnerable to
disturbances such as fire, since debarking usually reduces tree vigour and protection against external agents. In this paper
we asked how cork oak Quercus suber trees respond after wildfires and, in particular, how bark harvesting affects post-fire
tree survival and resprouting. We gathered data from 22 wildfires (4585 trees) that occurred in three southern European
countries (Portugal, Spain and France), covering a wide range of conditions characteristic of Q. suber ecosystems. Post-fire
tree responses (tree mortality, stem mortality and crown resprouting) were examined in relation to management and
ecological factors using generalized linear mixed-effects models. Results showed that bark thickness and bark harvesting are
major factors affecting resistance of Q. suber to fire. Fire vulnerability was higher for trees with thin bark (young or recently
debarked individuals) and decreased with increasing bark thickness until cork was 3â4 cm thick. This bark thickness
corresponds to the moment when exploited trees are debarked again, meaning that exploited trees are vulnerable to fire
during a longer period. Exploited trees were also more likely to be top-killed than unexploited trees, even for the same bark
thickness. Additionally, vulnerability to fire increased with burn severity and with tree diameter, and was higher in trees
burned in early summer or located in drier south-facing aspects. We provided tree response models useful to help
estimating the impact of fire and to support management decisions. The results suggested that an appropriate
management of surface fuels and changes in the bark harvesting regime (e.g. debarking coexisting trees in different years or
increasing the harvesting cycle) would decrease vulnerability to fire and contribute to the conservation of cork oak
ecosystemsinfo:eu-repo/semantics/publishedVersio
Sex Promotes Spatial and Dietary Segregation in a Migratory Shorebird during the Non-Breeding Season
Several expressions of sexual segregation have been described in animals, especially in those exhibiting conspicuous dimorphism. Outside the breeding season, segregation has been mostly attributed to size or age-mediated dominance or to trophic niche divergence. Regardless of the recognized implications for population dynamics, the ecological causes and consequences of sexual segregation are still poorly understood. We investigate the foraging habits of a shorebird showing reversed sexual dimorphism, the black-tailed godwit Limosa limosa, during the winter season, and found extensive segregation between sexes in spatial distribution, microhabitat use and dietary composition. Males and females exhibited high site-fidelity but differed in their distributions at estuary-scale. Male godwits (shorter-billed) foraged more frequently in exposed mudflats than in patches with higher water levels, and consumed more bivalves and gastropods and fewer polychaetes than females. Females tended to be more frequently involved and to win more aggressive interactions than males. However, the number of aggressions recorded was low, suggesting that sexual dominance plays a lesser role in segregation, although its importance cannot be ruled out. Dimorphism in the feeding apparatus has been used to explain sex differences in foraging ecology and behaviour of many avian species, but few studies confirmed that morphologic characteristics drive individual differences within each sex. We found a relationship between resource use and bill size when pooling data from males and females. However, this relationship did not hold for either sex separately, suggesting that differences in foraging habits of godwits are primarily a function of sex, rather than bill size. Hence, the exact mechanisms through which this segregation operates are still unknown. The recorded differences in spatial distribution and resource use might expose male and female to distinct threats, thus affecting population dynamics through differential mortality. Therefore, population models and effective conservation strategies should increasingly take sex-specific requirements into consideration
Are acoustical parameters of begging call elements of thin-billed prions related to chick condition?
Chicks of burrowing petrels use begging calls to advertise their hunger levels when parents arrived at the nest. In a previous study, adult thin-billed prions Pachyptila belcheri responded to higher begging call rates of their single chick by regurgitating larger meals. We tested whether acoustic parameters of begging call elements may also be involved in signalling. To describe variation in begging, we determined begging session parameters, namely the duration, number of calls and the mean and maximum rate of calling. We then digitised calls and carried out a semi-automatic extraction of six acoustic parameters of call elements, including mean and maximum acoustic frequency, the length of call elements and the location of the maximum frequency and amplitude within calls. Chicks showed strong individual differences in all parameters. While the session parameters were correlated with body condition and with the meal size the chick received, none of the acoustic parameters were related to body condition and provisioning. A cross-fostering experiment showed the same pattern, as only session parameters changed related to an experimentally altered body condition, while acoustical cues appear to play no role in signalling hunger levels. We suggest that this may be explained by the absence of sibling competition in these birds. As parents do not need to decide which chick to feed, immediate information on condition at the time of adult arrival may not be required
Insights into the migration of the European Roller from ring recoveries
AbstractDespite recent advances in avian tracking technology, archival devices still present several limitations. Traditional ring recoveries provide a complementary method for studying migratory movements, particularly for cohorts of birds with a low return rate to the breeding site. Here we provide the first international analysis of ring recovery data in the European Roller Coracias garrulus, a long-distance migrant of conservation concern. Our data comprise 58 records of Rollers ringed during the breeding season and recovered during the non-breeding season. Most records come from Eastern Europe, half are of juveniles and over three quarters are of dead birds. Thus, ring recoveries provide migration data for cohorts of Rollersâjuveniles and unsuccessful migrantsâfor which no information currently exists, complementing recent tracking studies. Qualitatively, our results are consistent with direct tracking studies, illustrating a broad-front migration across the Mediterranean Basin in autumn and the use of the Arabian Peninsula by Rollers from eastern populations in spring. Autumn movements were, on average, in a more southerly direction for juveniles than adults, which were more easterly. Juvenile autumn recovery direction also appeared to be more variable than in adults, though this difference was not statistically significant. This is consistent with juveniles following a naĂŻve vector-based orientation program, and perhaps explains the âmoderateâ migratory connectivity previously described for the Roller. In the first (qualitative) analysis of Roller non-breeding season mortality, we highlight the high prevalence of shooting. The recovery age ratio was juvenile-biased in autumn but adult-biased in spring. Although not statistically significant, this difference points towards a higher non-breeding season mortality of juveniles than adults. Our study demonstrates the complementarity of ring recoveries to direct tracking, providing an insight into the migration of juvenile Rollers and non-breeding season mortality
Seasonal variations in the diet and foraging behaviour of dunlins Calidris alpina in a South European estuary: improved feeding conditions for northward migrants
During the annual cycle, migratory waders may face strikingly different feeding conditions as they move between breeding areas and wintering grounds. Thus, it is of crucial importance that they rapidly adjust their behaviour and diet to benefit from peaks of prey abundance, in particular during migration, when they need to accumulate energy at a fast pace. In this study, we compared foraging behaviour and diet of wintering and northward migrating dunlins in the Tagus estuary, Portugal, by video-recording foraging birds and analysing their droppings. We also estimated energy intake rates and analysed variations in prey availability, including those that were active at the sediment surface. Wintering and northward migrating dunlins showed clearly different foraging behaviour and diet. In winter, birds predominantly adopted a tactile foraging technique (probing), mainly used to search for small buried bivalves, with some visual surface pecking to collect gastropods and crop bivalve siphons. Contrastingly, in spring dunlins generally used a visual foraging strategy, mostly to consume worms, but also bivalve siphons and shrimps. From winter to spring, we found a marked increase both in the biomass of invertebrate prey in the sediment and in the surface activity of worms and siphons. The combination of these two factors, together with the availability of shrimps in spring, most likely explains the changes in the diet and foraging behaviour of dunlins. Northward migrating birds took advantage from the improved feeding conditions in spring, achieving 65% higher energy intake rates as compared with wintering birds. Building on these results and on known daily activity budgets for this species, our results suggest that Tagus estuary provides high-quality feeding conditions for birds during their stopovers, enabling high fattening rates. These findings show that this large wetland plays a key role as a stopover site for migratory waders within the East Atlantic Flyway.This study was supported by Fundação para a CiĂȘncia e a Tecnologia (http://alfa.fct.mctes.pt/) through Project PTDC/MAR/119920/2010 and grants to RCM (SFRH/BD/44871/2008), TC (SFRH/BPD/46967/2008) and CDS (SFRH/BPD/64786/2009). JPG was under a research contract within project âSustainable Use of Marine Resources - MARESâ (CENTRO-07-ST24-FEDER-002033), co-financed by âMais Centroâ Regional Operational Programme (Centro Region) and European Regional Development Fund (ERDF). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.publishe
Senescence and Sexual Selection in a Pelagic Copepod
The ecology of senescence in marine zooplankton is not well known. Here we demonstrate senescence effects in the marine copepod Oithona davisae and show how sex and sexual selection accelerate the rate of ageing in the males. We show that adult mortality increases and male mating capacity and female fertility decrease with age and that the deterioration in reproductive performance is faster for males. Males have a limited mating capacity because they can fertilize < 2 females dayâ1 and their reproductive life span is 10 days on average. High female encounter rates in nature (>10 dayâ1), a rapid age-dependent decline in female fertility, and a high mortality cost of mating in males are conducive to the development of male choosiness. In our experiments males in fact show a preference for mating with young females that are 3 times more fertile than 30-day old females. We argue that this may lead to severe male-male competition for young virgin females and a trade-off that favours investment in mate finding over maintenance. In nature, mate finding leads to a further elevated mortality of males, because these swim rapidly in their search for attractive partners, further relaxing fitness benefits of maintenance investments. We show that females have a short reproductive period compared to their average longevity but virgin females stay fertile for most of their life. We interpret this as an adaptation to a shortage of males, because a long life increases the chance of fertilization and/or of finding a high quality partner. The very long post reproductive life that many females experience is thus a secondary effect of such an adaptation
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