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Zavalaga C.B.,University of North Carolina at Wilmington | Zavalaga C.B.,Nagoya University | Halls J.N.,University of North Carolina at Wilmington | Mori G.P.,Calle Eduardo del Castillo 2543 Lima | And 2 more authors.
Marine Ecology Progress Series | Year: 2010

GPS loggers and time-depth recorders were used to characterize the foraging behavior of the sexually dimorphic Peruvian booby Sula variegata on 2 islands in northern Peru. We evaluated whether (1) its foraging behavior differed from tropical boobies and temperate gannets (the Peruvian boobies feed in areas of enhanced productivity and high fish density), and (2) females and males exploited different foraging habitats as a consequence of size dimorphism. Birds foraged only during daylight hours, 1 to 3 times a day, in trips of short duration (median = 1.8 h). Overall, 92% of the total foraging time was spent flying. They fed exclusively on anchovetas Engraulis ringens, which were captured in shallow dives (median = 2.5 m, max = 8.8 m) with a dive median rate of 11 dives h- (max = 37 dives h-1). The median foraging range was 25 km (max = 68 km), whereas the median total distance traveled was 69 km (max = 179 km). Foraging site fidelity was high, and the orientation of foraging flights in any given day was similar among birds that departed at the same time. There were no sex-specific differences in 13 of 15 foraging variables; however, females dived slightly deeper and spent a larger proportion of time sitting on the water. We speculate that (1) the foraging behavior of Peruvian boobies contrasts with that of their tropical and temperate relatives as a result of the proximity and predictability of food sources, elevated energetic demands of the brood (up to 4 chicks) and high prey encounter rate in the Peruvian upwelling system, and (2) the lack of spatial segregation between sexes may be related to the attraction of birds to feeding aggregations that are formed in the vicinity of the colonies. Once the foraging patches are localized, females dive deeper because of passive mechanisms associated with a heavier mass. © Inter-Research 2010. Source


De Marchi G.,University of Pavia | Chiozzi G.,Museo Civico di Storia Naturale | Dell'Omo G.,Ornis Italica | Fasola M.,University of Pavia
Ibis | Year: 2015

We used GPS data-loggers, video-recordings and dummy eggs to assess whether foraging needs may force the low incubation attentiveness (<55%) of the Crab Plover Dromas ardeola, a crab-eating wader of the Indian Ocean that nests colonially in burrows. The tidal cycle was the major determinant of the time budget and some foraging trips were more distant from the colony than previously known (up to 26km away and lasting up to 45h). The longest trips were mostly made by off-duty parents, but on-duty parents also frequently left the nest unattended while foraging for 1-7h. However, the time spent at the colony area (47%) and the time spent roosting on the foraging grounds (16%) would have allowed almost continuous incubation, as in other species with shared incubation. Therefore, the low incubation attentiveness is not explained by the need for long foraging trips but is largely dependent on a high intermittent rhythm of incubation with many short recesses (5.8±2.6recesses/h) that were not spent foraging but just outside the burrow or thermoregulating at the seashore. As a result, the eggs were warmed on average only 1.7°C above burrow temperature, slightly more during high tide periods and when burrow temperature was lower between 20:00 and 10:00h, only partly counteracting the temperature fluctuations of the incubation chamber. These results suggest that low incubation attentiveness is due to the favourable thermal conditions provided by safe nesting burrows and by the hot tropical breeding season, a combination that allows simultaneous foraging by parents and the exploitation of distant foraging grounds. Why Crab Plovers engage in many short recesses from incubation still remains to be clarified but the need to thermoregulate at the seashore and to watch for predators may play a role. © 2014 British Ornithologists' Union. Source


Muller M.S.,Nagoya University | Massa B.,University of Palermo | Phillips R.A.,Natural Environment Research Council | Dell'omo G.,Ornis Italica
Current Zoology | Year: 2014

Recently-developed capabilities for tracking the movements of individual birds over the course of a year or longer has provided increasing evidence for consistent individual differences in migration schedules and destinations. This raises questions about the relative importance of individual consistency versus flexibility in the evolution of migration strategies, and has implications for the ability of populations to respond to climatic change. Using geolocators, we tracked the migrations of Scopoli’s shearwaters Calonectris diomedea breeding in Linosa (Italy) across three years, and analysed timing and spatial aspects of their movements. Birds showed remarkable variation in their main wintering destination along the western coast of Africa. We found significant individual consistency in the total distance traveled, time spent in transit, and time that individuals spent in the wintering areas. We found extensive sex differences in scheduling, duration, distances and destinations of migratory journeys. We also found sex differences in the degree of individual consistency in aspects of migration behaviour. Despite strong evidence for individual consistency, which indicates that migration journeys from the same bird tended to be more similar than those of different birds, there remained substantial intra-individual variation between years. Indeed, we also found clear annual differences in departure dates, return dates, wintering period, the total distance traveled and return routes from wintering grounds back to the colony. These findings show that this population flexibly shifts migration schedules as well as routes between years in response to direct or indirect effects of heterogeneity in the environment, while maintaining consistent individual migration strategies. © 2014 Current Zoology. Source


Casagrande S.,University of Groningen | Casagrande S.,University of Parma | Costantini D.,University of Glasgow | Dell'Omo G.,Ornis Italica | And 2 more authors.
Behavioral Ecology and Sociobiology | Year: 2012

Despite extensive research, the potential costs that keep secondary sexual traits honest and evolutionary stable remain somewhat elusive. Many carotenoid-based signals are regulated by testosterone (T), which has been suggested to impose a cost to the signaller by suppression of the immune system or an increase in oxidative stress. Results are, however, inconsistent, which may be due to the fact that T can be metabolised to both 5α-dihydrotestosterone (DHT, a potent androgen) and oestradiol (E2, a potent oestrogen). To evaluate for the first time the independent effect of these testosterone metabolites on oxidative status, circulating carotenoids and a carotenoid-dependent sexual signal, we administered DHT and E2 to captive non-breeding adult kestrels Falco tinnunculus of both sexes. E2 increased oxidative damage and downregulated the antioxidant barrier without affecting colouration or circulating carotenoids. In contrast, DHT did not affect oxidative status, but increased skin redness, again without affecting circulating carotenoids. No sex-specific effects were found. These results suggest that the pro-oxidant activity of T could be induced indirectly by its metabolite, E2, whereas the other metabolite, DHT, stimulates signal expression. Finally, the study shows that changes in oxidative damage or antioxidant status of plasma were not correlated with either skin redness or circulating carotenoids. © 2012 Springer-Verlag. Source


Muller M.S.,Nagoya University | Massa B.,University of Palermo | Phillips R.A.,Natural Environment Research Council | Dell'Omo G.,Ornis Italica
Animal Behaviour | Year: 2015

Long-term pair bonds occur in diverse animal taxa, but they are most common in birds, and can last from a few years to a lifetime. In many of these species, after the reproductive season, birds migrate to distant nonbreeding grounds where they remain for several months, and until recently, little was known about whether partners maintain contact during migration. This gap in knowledge was primarily due to past methodological difficulties in tracking long-term, large-scale movements of individuals. However, the development of new animal-borne geolocation devices has enabled researchers to track movements of individuals for a year or more. We tracked the annual migrations of both members of breeding pairs of Scopoli's shearwaters, Calonectris diomedea, breeding on Linosa Island (Italy) and found that although they did not migrate together, they did spend a similar number of days travelling to and from similar terminal nonbreeding areas. Although migration destinations were alike, they were not identical. That partners did not appear to travel or spend time together in the nonbreeding season suggests that similarities were not due to behavioural coordination. We performed additional analyses to uncover alternative, potential proximate mechanisms. First, we found that body mass of breeding adults during the chick-rearing period correlated positively with the decision to migrate further south, so conceivably pair members may migrate to similar areas because of shared reproductive costs; however, partners were not of similar body mass. Distances between nonbreeding areas for individuals that nested closer together were smaller than for individuals that nested far apart. As neighbours tend to be more closely related due to high natal philopatry, this suggests that similarities within pairs in migration behaviour may reflect the influence of shared genes on migration strategy. © 2015 The Association for the Study of Animal Behaviour. Source

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