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Foraging Conditions (foraging + condition)
Selected AbstractsPostfledging habitat selection of juvenile middle spotted woodpeckers: a multi-scale approachECOGRAPHY, Issue 4 2009Carlos Ciudad Despite its relevance for the persistence of populations, the ecological mechanisms underlying habitat use decisions of juvenile birds are poorly understood. We examined postfledging habitat selection of radio-tracked juvenile middle spotted woodpeckers Dendrocopos medius at multiple hierarchically-nested spatial scales in NW Spain. At the landscape and home range scales, old oak forest was the most used and selected habitat, young oak forests and pine plantations were avoided, and riverside forests were used as available. At a lower scale, birds selected larger diameter trees for foraging. Home ranges had higher densities of large deciduous trees (mainly oaks Quercus spp., but also poplars Populus spp. and willows Salix spp. >22,cm and >33,cm DBH) selected for foraging by juveniles than non-used areas. These results suggest that foraging conditions may drive, at least partly, habitat use decisions by juvenile birds. We also discuss the potential influence of intraspecific competition, the search for a future breeding territory in the early postfledging period and predation avoidance on habitat use decisions by juvenile birds. Contrary to previous studies on migrant forest birds, postfledging juvenile woodpeckers selected the same habitat as for the breeding adults (i.e. old oak forest), indicating that migrant and resident specialist avian species may require different conservation actions. Conservation strategies of woodpecker populations should consider the protection of old oak forests with high densities of large trees to provide suitable habitat to breeding adults and postfledging juveniles. The habitat improvement for this indicator and umbrella species would also favour other organisms that depend on characteristics of old-growth oak forests. [source] Prey availability influences habitat tolerance: an explanation for the rarity of peregrine falcons in the tropicsECOGRAPHY, Issue 3 2001Andrew R. Jenkins The density and productivity of peregrine falconFalco peregrinus populations correlate positively with distance from the Equator, while habitat specificity increases with proximity to the Equator. Low peregrine densities in the tropics may he a result of competition with similar conveners (e.g. the lanner falcon F. biarmicus in Africa), which replace them in many areas. Alternatively, tropical peregrines may he limited by resource deficiencies that do not affect their close relatives. Data from peregrine and lanner populations in South Africa support the resource deficiency hypothesis, and there is no evidence to suggest direct competition between the two species. In areas where prey are not spatially or temporally concentrated, or otherwise particularly vulnerable to attack, morphological and behavioural specializations of peregrines probably restrict them to optimal foraging conditions. The relative dynamics of.Arctic and temperate vs tropical prey populations is suggested as an important factor determining peregrine distribution globally. Populations of other widespread hut particularly specialized avian predators (e.g. osprey Pandion haliaetus) may he similarly controlled. Food limitation (in terms of a dearth of particularly vulnerable prey) in the tropics has resulted in specialization and rarity in peregrines and generalization and relative abundance in similar congeners. [source] Prey availability influences habitat tolerance: an explanation for the rarity of peregrine falcons in the tropicsECOGRAPHY, Issue 3 2001Article first published online: 30 JUN 200 The density and productivity of peregrine falcon Falco peregrinus populations correlate positively with distance from the Equator, while habitat specificity increases with proximity to the Equator. Low peregrine densities in the tropics may be a result of competition with similar congeners (e.g. the lanner falcon F. biarmicus in Africa), which replace them in many areas. Alternatively, tropical peregrines may be limited by resource deficiencies that do not affect their close relatives. Data from peregrine and lanner populations in South Africa support the resource deficiency hypothesis, and there is no evidence to suggest direct competition between the two species. In areas where prey are not spatially or temporally concentrated, or otherwise particularly vulnerable to attack, morphological and behavioural specializations of peregrines probably restrict them to optimal foraging conditions. The relative dynamics of Arctic and temperate vs tropical prey populations is suggested as an important factor determining peregrine distribution globally. Populations of other widespread but particularly specialized avian predators (e.g. osprey Pandion haliaetus) may be similarly controlled. Food limitation (in terms of a dearth of particularly vulnerable prey) in the tropics has resulted in specialization and rarity in peregrines and generalization and relative abundance in similar congeners. [source] Colony productivity and foundress behaviour of a native wasp versus an invasive social waspECOLOGICAL ENTOMOLOGY, Issue 6 2003Tracy R. Armstrong Abstract., 1.,Colony productivity, prey utilisation, and foundress behaviour of a North American native wasp (Polistes fuscatus) versus an European invasive wasp (Polistes dominulus) were investigated in a controlled field experiment with optimal versus natural foraging conditions. Colonies with the optimal prey foraging conditions were provided with prey ad libitum within an enclosed area. The other colonies foraged in the adjacent field,woodland but had the same nest conditions as the other treatment. 2.,When given prey ad libitum, both wasp species captured similar amounts of prey and the conversion to total offspring biomass was similar. But P. dominulus colonies produced 2.5 times the number of workers as P. fuscatus colonies, reflecting the smaller size of P. dominulus wasps. 3.,Foundresses of P. dominulus were observed more often building or repairing the nest, thereby contributing to the production of colonies with twice as many cells as colonies of P. fuscatus. Foundresses of P. dominulus showed more acts of aggression toward workers than did P. fuscatus foundresses, which was not a function of adult density on the nest. 4.,At the end of the experiment, P. dominulus colonies with optimal prey foraging conditions still had a high level of egg-laying and peaked in the number of pupae then, whereas egg-laying and the number of pupae per colony of the other treatments began to decline 2,3 weeks earlier. These results indicate that P. dominulus is more opportunistic than P. fuscatus, which may account in part for P. dominulus's success as an introduced species in North America. [source] Individual dispersal among colonies of Little Egrets Egretta garzettaIBIS, Issue 2 2002Mauro Fasola Colonial waterbirds are unusual in that competition for nest-sites or mates may occur at a scale of a few metres, whereas thousands of birds may overlap in their foraging range at a larger scale. Dispersal has been evaluated for only a few such species, and its adaptive significance remains unclear. We studied Little Egret dispersal among all the colonies within the Camargue, southern France. The overall probability of dispersal between successive years was 0.45. The probability of dispersal was unaffected by a bird's age, or by any density-dependent effect of colony size. Juveniles dispersed at distances that would be expected if colony selection were random, while adults tended to remain within 10 km of their previous colony. We found no obvious environmental ,trigger' for an individual to disperse. Although our evidence is inconclusive, the short dispersal distances of adults are not consistent with foraging conditions as the primary trigger for dispersal. Little Egrets generally forage within 8 km of their colony, so birds dispersing less than 10 km would gain little advantage in response to unfavourable foraging conditions. Our data, with 75% of dispersing birds coming from decreasing colonies and 72% joining increasing colonies, suggest that individual dispersal depended on colony dynamics as a whole, i.e. (1) a social component of dispersal at the individual level, or (2) a simultaneous colony response to unfavourable environmental conditions or (3) both. Further investigation at a higher social level may be necessary to understand dispersal of this colonial nesting species. [source] Functional response of juvenile pink and chum salmon: effects of consumer size and two types of zooplankton preyJOURNAL OF FISH BIOLOGY, Issue 2 2007J. H. Moss Feeding rate experiments were conducted for pink salmon Oncorhynchus gorbuscha fry [mean fork length (LF) 39 mm], juveniles (103,104 mm LF) and juvenile chum salmon Oncorhynchus keta (106,107 mm LF). Fishes were presented with small copepod (Tisbi sp.) or larger mysid shrimp (Mysidopsis bahia) prey at varying densities ranging from 1 to 235 prey l,1 in feeding rate experiments conducted at water temperatures ranging from 10·5 to 12·0° C under high light levels and low turbidity conditions. Juvenile pink and chum salmon demonstrated a type II functional response to mysid and copepod prey. Mysid prey was readily selected by both species whereas the smaller bodied copepod prey was not. When offered copepods, pink salmon fry fed at a higher maximum consumption rate (2·5 copepods min,1) than larger juvenile pink salmon (0·4 copepods min,1), whereas larger juvenile chum salmon exhibited the highest feeding rate (3·8 copepods min,1). When feeding on mysids, the maximum feeding rate for larger juvenile pink (12·3 mysids min,1) and chum (11·5 mysids min,1) salmon were similar in magnitude, and higher than feeding rates on copepods. Functional response models parameterized for specific sizes of juvenile salmon and zooplankton prey provide an important tool for linking feeding rates to ambient foraging conditions in marine environments, and can enable mechanistic predictions for how feeding and growth should respond to spatial-temporal variability in biological and physical conditions during early marine life stages. [source] | ||||||||||