Element patterns in albatrosses and petrels: Influence of trophic position, foraging range, and prey type

We investigated the concentrations of 22 essential and non-essential elements among a community of Procellariiformes (and their prey) to identify the extent to which trophic position and foraging range governed element accumulation. Stable isotope analysis (SIA) was used to characterise trophic (δ¹⁵N) and spatial patterns (δ¹³C) among species. Few consistent patterns were observed in element distributions among species and diet appeared to be highly influential in some instances. Arsenic levels in seabird red blood cells correlated with δ¹⁵N and δ¹³C, demonstrating the importance of trophic position and foraging range for arsenic distribution. Arsenic concentrations in prey varied significantly across taxa, and in the strength of association with δ¹⁵N values (trophic level). In most instances, element patterns in Procellariiformes showed the clearest separation among species, indicating that a combination of prey selection and other complex species-specific characteristics (e.g. moult patterns) were generally more important determining factors than trophic level per se.     

Does optimal foraging theory explain why suburban Florida scrub-jays (Aphelocoma coerulescens) feed their young human-provided food?

Optimal foraging theory assumes that a forager can adequately assess the quality of its prey and predicts that parents feed their young low-quality foods only when suffering unpredicted reductions in their ability to provision. Wildland Florida scrub-jays feed their young exclusively arthropods, but suburban parents include human-provided foods in the nestling diet, with possible costs in terms of reduced growth and survival. We tested experimentally whether parents feed human-provided foods, given the apparent costs, because: 1) they do not discriminate between food types, 2) they switch to low-quality, abundant foods when natural food availability in the environment is low, or 3) they switch when the time needed to obtain natural food is high. Parents discriminated between natural and human-provided foods by showing a preference for natural foods when rearing young. When the handling time of natural foods was increased experimentally, parents in the suburban and wildland habitats switched to human-provided foods. Supplementation with natural foods increased preference for this food in both habitats. Suburban parents chose more natural foods than wildland parents, suggesting that they have a greater preference for natural foods. Regardless of preferences demonstrated at feeders, parents in both the suburbs and wildlands delivered mostly natural foods to nestlings, independent of natural food availability. Nonetheless, natural foods are likely to be scarcer in the environment than in our experimental tests. Because natural food availability is lower in the suburbs than in the wildland habitat, parents in the suburbs may be forced to switch to human-provided foods when feeding nestlings.     

The influence of prey distribution on the foraging strategy of the lizard Oligosoma grande (Reptilia: Scincidae)

The grand skink, Oligosoma grande, is a diurnal rock-dwelling lizard from the tussock grasslands of Central Otago, New Zealand, whose diet includes a variety of arthropods and fruit. We conducted a field experiment to examine the influence of prey distribution on foraging behavior and spacing patterns. On sites where prey distribution was unaltered (control sites), males and females differed in diet and foraging behavior. Most male feeding attempts were directed at large strong-flying insects, and males used a saltatory search pattern that involved relatively infrequent moves of long duration. Females spent more effort catching small weak-flying insects and visiting fruiting plants. Their search behavior involved frequent moves of short duration. The placement of meat-bait on experimental sites led to a redistribution of large flies without influencing other prey types. Experimental females switched foraging strategy by adopting a search pattern of relatively infrequent moves of long duration, increasing the frequency of attempts to capture large prey, and reducing the importance of fruit in their diet. The experimental manipulation appeared to influence space use. On control sites, both sexes had comparably sized home ranges. On experimental sites, male home ranges were significantly larger than female home ranges. Received: 3 November 1997 / Accepted after revision: 13 December 1998     

The meat-scrap hypothesis: small quantities of meat may promote cooperative hunting in wild chimpanzees (<Emphasis Type="Italic">Pan troglodytes</Emphasis>)

A common explanation for hunting in groups is that doing so yields a greater per capita caloric benefit than hunting solitarily. This is logical for social carnivores, which rely exclusively on meat for energy, but arguably not for omnivores, which obtain calories from either plant or animal matter. The common chimpanzee, Pan troglodytes, is one of the few true omnivores that regularly hunts in groups. Studies to date have yielded conflicting data regarding the payoffs of group hunting in chimpanzees. Here, we interpret chimpanzee hunting patterns using a new approach. In contrast to the classical assumption that hunting with others maximizes per capita caloric intake, we propose that group hunting is favored because it maximizes an individual’s likelihood of obtaining important micronutrients that may be found in small quantities of meat. We describe a mathematical model demonstrating that group hunting may evolve when individuals can obtain micronutrients more frequently by hunting in groups than by hunting solitarily, provided that group size is below a certain threshold. Twenty five years of data from Gombe National Park, Tanzania are consistent with this prediction. We propose that our ‘meat-scrap’ hypothesis is a unifying approach that may explain group hunting by chimpanzees and other social omnivores.     

Competition and group size in Thomas’s langurs (Presbytis thomasi): the folivore paradox revisited

Among primates, group size is highly variable. The standard ecological model assumes that better predation avoidance as group size increases favours living in larger groups, whereas increased travel costs and reduced net food intake due to within-group competition for resources set the upper limit. Folivorous primates, however, tend to defy this generalisation in that some live in small groups despite low costs of feeding competition. To resolve this ’folivore paradox’, it has been suggested that folivore group size is limited by social factors such as male harassment or infanticide, or that females can disperse more easily and thus maintain group size near optimum levels. In this paper, we examine the effects of group size on home range size, day-journey length, activity budget and diet in wild Thomas’s langurs (Presbytis thomasi), which live in one-male multi-female groups with a limited life cycle. We examined only data from the stable middle tenure phase when factors such as the strength of the breeding male or the way in which groups were formed did not influence ranging and activities. During this phase, group size affected day-journey length and home range size, and had a minor effect on diet, but did not influence time spent feeding or resting, allogrooming or birth rates. Hence the upper limit to group size during the middle tenure phase in Thomas’s langurs is not set by feeding competition. The folivore paradox is not due to frequent female dispersal in Thomas’s langurs. The timing of female dispersal is not as expected if it serves to keep group sizes near the ecological optimum, and groups seem to be below this optimum. Instead, female reproductive success is presumably maximised in small to mid-sized groups because larger groups show a clear trend to experience higher risk of take-over, often accompanied by infanticide. Because females can redistribute themselves among nearby groups when groups reorganise each time a new male starts up a new group, females can keep the group small. Thus, a social factor, risk of infanticide, seems to provide the selective advantage to small group size in Thomas’s langurs. Received: 29 July 1999 / Revised: 17 November 1999 / Accepted: 15 October 2000     

Biodiversity, food consumption and ecological niche dimension: a study case of the riverine populations from the Rio Negro, Amazonia, Brazil

In this study we perform an ecological analysis of the resources use in the diet of the ribeirinho populations of the Barcelos municipality, Rio Negro, Amazonas, Brazil. Data on food composition, seasonality, and origin took place during three field trips between 1999 and 2000. Data were gathered based on structured interviews and observations from a total of 320 meals of 114 randomly selected families and 164 fishing trips. The staple food of the studied populations is based on fish and manioc, although the food niche amplitude can vary according to the factors such as the access to imported food items, resources seasonality, and socio-economic conditions. The migration to urban centers along with the changes in subsistence activities (reduction of small-scale agriculture and specialization in commercial fishing) may result in changes in the food habits of ribeirinho populations from Rio Negro.

The effects of tertiary treated municipal wastewater on fish communities of a small river tributary in Southern Ontario, Canada

Fish community changes associated with a tertiary treated municipal wastewater effluent outfall in the Speed River, Ontario, Canada, were evaluated at nine sites over two seasons (2008) using standardized electrofishing. Habitat evaluations were conducted to ensure that the riffle sites selected were physically similar. The fish community was dominated by several species of darters that differed in their response to the effluent outfall. There was a significant decrease in Greenside Darter (Etheostoma blennioides) but an increase in Rainbow Darter (E. caeruleum) abundance directly downstream of the outfall. Stable isotope signatures (δ¹³C and δ¹⁵N), which indicate shifts in energy utilization and flow, increased in Rainbow Darter downstream, but showed no change in Greenside Darter. Rainbow Darter may be exploiting a food source that is not as available at upstream sites giving them a competitive advantage over the Greenside Darter immediately downstream of the outfall.     

Organochlorine residue levels in livers of birds of prey from Spain: inter-species comparison in relation with diet and migratory patterns

Livers from 130 specimens corresponding to 18 species of raptors from Spain were analysed for persistent organochlorine (OC) residues. In all species, p,p'-DDE was the most abundant individual OC compound detected, with geometric means ranging from 61 to 40,086 ng/g ww. The geometric mean for summation operator PCB ranged from 225 to 9184 ng/g ww. Migration to Africa, south of Sahara, where p,p'-DDT is still in use, was not associated with higher liver concentrations of its metabolite, p,p'-DDE. The presence of birds in the diet of the species was an important species-specific factor determining the mean liver concentrations of p,p'-DDE and summation operator PCB. The effect of the diet on OC concentrations in liver is explained by the lower metabolising capacity of OC compounds in birds, especially for p,p'-DDE.     

Pb,Cd, Zn and cu intakes of Taiwanese subjects ‐ a duplicate portion study

Thirty diet samples from three different social groups were collected both in summer and in winter seasons using duplicate portion technique with three collection days. Toxic element concentrations, including Pb, Cd, as well as some essential elements were determined by atomic absorption spectrometry (AAS). The average dietary intakes of Taiwanese were estimated as follows (means ± S.D., n = 30): Mg, 175 ± 77 mg/day; Zn, 9.5 ± 11.4 mg/day; Mn, 2.8 ± 1.3 mg/day; Cu, 1.6±1.7mg/day; Ni, 0.13 ± 0.14 mg/day; Cd, 58 ± 62 μg/day, and Pb, 31 ±26 μg/day. The obtained elemental concentrations were scattered due to different dietary habits and cooking methods. In addition, a strong correlation arose between the trace element concentrations in agricultural products and in the diet of regional areas of Taiwan. Analysis results indicated that average intakes are consistently below current US Recommended Daily Allowances (RDAs) for Mg and Zn, within the recommended safe and adequate RDA for Mn, and below the FAO/WHO Provisional Tolerable Daily Intakes (PTDIs) for Pb. The average daily intakes of Cd by regional area of Taiwan markedly exceeded those of other countries and the PTI value during the summer.     

Frequent summer nuptial flights of ants provide a primary food source for bats

In many ant species, nuptial flight tends to be short in time and assumed to be synchronous across a large area. Here, we report that, in the upper Jordan Valley, northern Israel, massive nuptial flights of Carpenter ants (Camponotus sp.) occur frequently throughout the summer, and their alates form up to 90% of the diet of the greater mouse-tailed bat (Rhinopoma microphyllum) during this period. This fat and protein-rich diet enables female bats to lactate during summer, and the large amount of fat that both sexes accumulate may serve as an energy source for their following winter hibernation and posthibernation mating in early spring (March–April). We suggest that the annual movement of these bats to the Mediterranean region of Israel may have evolved in order to enable them to exploit the extremely nutritious forms of ant alates when the bats’ energetic demands are highest.