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PubMed1992

Demography of the Hadza, an increasing and high density population of Savanna foragers.

This is a report on the demography of the Hadza, a population of East African hunter-gatherers. In it, we describe the results of a census, and our estimation of age structure, survivorship, mean age of women at childbearing, number of live children, total population size and density, and rate of change since 1967. We show that relevant measures fit closely the stable population model North 6 chosen by Dyson to represent Hadza demography in the 1960s. We compare aspects of Hadza demography with surrounding non-Hadza and with the !Kung. Among other things, we find that the Hadza have a higher population density, higher fertility, and a faster population growth rate than do the !Kung. These demographic differences are consistent with our expectations, which were based on differences in the costs and benefits of foraging in the two regions. We also show that Hadza demographic parameters display remarkable consistency over the past 20 years. Since neighboring populations have been encroaching on the area used by the Hadza, and Hadza foragers have been subject to interludes of externally imposed settlement, this consistency is surprising. We discuss some of the implications.

Adolescent↗
PubMed2006

Body size among Holocene foragers of the Cape Ecozone, southern Africa.

Temporal and geographic variability in adult body size can be a useful indicator of a population's adaptation. The southern African Cape supported foraging populations exclusively until some pastoralism is seen, ca. 2000 BP. This paper describes and interprets body-size patterns among foragers, as deduced from maximum femoral lengths and femoral head diameters, using 127 individually dated adult skeletons from the western (70) and southern (57) regions of the Cape (64 male, 60 female, 3 sex undetermined). Estimated statures are comparable to historic Khoesan samples, but show lower values and greater variance during the fifth/fourth millennium before the present among both sexes and both biomes. Variation in femoral length does not correlate with diet protein, as reflected in stable isotope (delta(13)C and delta(15)N) values. Positive correlations between femoral head diameter and isotopic indicators suggest greater body mass with more reliance on marine protein. A decline in femoral length begins at around 4000 BP, a time when archaeologists suggest that population growth led to the incorporation of lower-ranked food resources, and to reduced mobility. A clearly identifiable linear recovery, beginning at around 3000 BP, greatly predates the earliest evidence of pastoralism on the Cape. Apparent problems of food sufficiency were addressed and solved, within a hunting and gathering economy.

Africa, Southern↗
PubMed2006

Impairment and recovery on a food foraging task following unilateral vestibular deafferentation in rats.

It has been suggested that the vestibular system may contribute to the development of higher cognitive function, especially spatial learning and memory that uses idiothetic cues (e.g., dead reckoning). However, few studies have been done using behavioral tasks that could potentially separate the animals' ability for dead reckoning from piloting. The food foraging task requires the animal to continuously monitor and integrate self-movement cues and generate an accurate return path. It has been shown that bilateral vestibular-lesioned rats were impaired on this task. The present study used the same task to further examine the contribution of vestibular information to spatial navigation by comparing unilateral and bilateral lesions and by testing the animals at different time points following the lesion. The results demonstrated that animals with unilateral vestibular deafferentation were impaired in performing the task in the dark at 3 months after the lesion, and this impairment disappeared at 6 months after the lesion. This supports the notion that vestibular information contributes to dead reckoning and suggests possible recovery of function over time after the lesion. Animals with bilateral vestibular deafferentation were not able to be tested on the foraging task because they exhibited behavior distinct from the unilateral-lesioned animals, with significant hesitation in leaving their home cage for as long as 6 months after the lesion.

Animals↗
PubMed2005

Influence of body reserves and eye opacity on foraging behaviours of tiger snakes.

Physiological states such as reproductive stage, parasite load, body condition, and environmental conditions, influence behaviours in complex ways. According to the Clark's asset-protection principle (Clark, 1994. Behav Ecol 5:159-170), individuals in good body condition take fewer predation risks than conspecifics in lesser condition. In many ectotherms, foraging, digestion, and moulting require an elevation of the metabolism achieved through intensive basking, thereby increasing the risk of being detected by predators. Using four experimental groups of snakes, we showed that two independent physiological states, (1) the presence of prey in the stomach and (2) eye opacity associated with moulting, increase predator vulnerability. In a parallel experiment, two groups of snakes were maintained on contrasting diets (high food intake vs. low food intake) for 6 months. Apart from sloughing periods, most individuals (89%) accepted their meal irrespective of food treatment. Consequently, well-fed snakes exhibited higher body condition (one third physiological state) relative to less-fed individuals. During sloughing events, however, well-fed individuals often refused (78%) to eat while the less-fed individuals readily accepted (86%) their meal despite eye opacity. Individuals with less body reserves accepted the cumulative risks owing to eye opacity and stomach fullness. By contrast, well-fed snakes remained more "prudent" (i.e., exhibited behaviours that depended on their internal state). Our results show that snakes can adjust their foraging "decision" by combining different physiological informations.

Analysis of Variance↗
PubMed1998

Experimental evidence for spatial memory in foraging wild capuchin monkeys, Cebus apella.

Obtaining convincing evidence for spatial memory of natural food sources in wild animals is hard because the observer rarely knows as much about the available food as does the animal, and the ability of the animal to detect novel food sources is usually not measured. In this study, I took advantage of the scarcity of natural fruit sources in the subtropical winter to present a wild group of brown capuchin monkeys with a large-scale array of 15 feeding platforms spaced ca 200 m apart. With this array, I could control the location, productivity and renewal schedule of the major fruit sources used by these animals. Combining an independent measurement of their detection field for these platforms with the known locations of the platforms, I calculated the expected patterns of movement among platform sites by the group under various models of 'random' foraging. These expected patterns were compared to the actual spatial movements of the group. The capuchin group moved significantly more often toward closer platforms and in straighter lines than expected by any random search model using their observed detection field of 82 m, although their behaviour did agree with such models for unrealistically large search fields of 225-350 m. I infer that the movements of this study group are likely to be guided by spatial memory. However, straight-line movement and a preference for closer platforms are in general not convincing evidence for spatial memory unless the detection field of the forager for the resources is known. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1998

How mixed-species foraging flocks develop in response to benefits from observational learning.

We created experimental situations where observers (great tit, Parus major and marsh tit, P. palustris) acquired one of five types of experience near conspecific and non-conspecific demonstrators: (1) neither demonstrator was feeding; (2) only the conspecific was feeding; (3) only the non-conspecific was feeding; (4) both were feeding and the observer received a reinforcement (food) near the conspecific; and (5) as (4), but the reinforcement was given near the non-conspecific. After each treatment, we recorded whether the observer approached a caged conspecific or a caged non-conspecific. There was a baseline preference for approaching conspecifics but this could be overcome by learnt associations so that the birds would then approach non-conspecifics. When there was an opportunity to distinguish between successful and unsuccessful foragers (demonstrators), and the successful forager was not conspecific, observers of the dominant species approached the successful subordinate non-conspecifics. Observers of the subordinate species approached the dominant species only if they had received a food reinforcement near them. Observers followed non-conspecific individuals more often at temperatures below than above 0 degreesC and chose a conspecific individual more often above than below 0 degreesC. Copyright 1998 The Association for the Study of Animal Behaviour. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1998

Who follows whom? Shoaling preferences and social learning of foraging information in guppies.

Preferences of fish for different types of shoals may influence the transmission of novel information through them. We investigated the factors influencing the preferences of guppies, Poecilia reticulata, for different shoals in order to shed some light on how information transmission occurs. Adult subjects were given a choice between swimming with two diverging shoals of conspecifics that differed with respect to key characteristics. In six choice experiments, subjects discriminated between shoal partners on the basis of: (1) shoal size, subjects preferring a shoal of 10 to a single fish; (2) size of shoaling fish, small fish preferring small conspecifics rather than an equal number of large fish, while large fish showed no preference; (3) local foraging experience of shoaling fish, shoals containing fish that had previously been repeatedly fed in the experimental tank being preferred to shoals with no such experience; and (4) familiarity of shoaling fish, guppies preferring familiar rather than unfamiliar conspecifics. No discrimination on the basis of colour or hunger was observed. In addition, following a shoal to a food site on just three trials allowed guppies to learn a route, or food site, preference. Guppies were considerably more likely to learn to adopt the behaviour shown by members of a shoal of several demonstrators than an alternative behaviour shown by a single conspecific demonstrator. The relationship between preferences for different shoals and the social transmission of information is discussed in the light of these findings. The results suggest that shoaling preferences may strongly influence the social transmission of novel foraging information or feeding preferences through fish populations, and imply that learned infor-mation may diffuse through fish populations in a nonrandom, or directed, manner. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1998

Flexible foraging strategy of Cory's shearwater, Calonectris diomedea, during the chick-rearing period.

Procellariiformes are well known for their low rates of food provisioning to their slow-growing chicks. In some species, the patterns of food delivery to chicks have been deduced from changes in their weight, obtained from periodic weighings. However, the behaviour of individual parents cannot be resolved using this method. In this study, we used a periodic weighing protocol with Cory's shearwater chicks on Selvagem Grande island, in the northeast Atlantic. In addition, we used an automatic logging system to examine the attendance of individual parents. In 1997, the chicks were fed infrequently, and were in significantly poorer condition, than in other years and at other colonies. This suggests that the adults were experiencing some difficulties in finding an adequate food supply close to the colony. Under these conditions, individual parents adopted a dual provisioning strategy, making both short and long foraging trips, a previously undescribed behaviour in any northern hemisphere petrel species. Although meals delivered to chicks were larger after long trips than after short trips, the average amount of food provisioned per day spent at sea decreased with increasing trip length, and so chicks did not benefit from longer trips. This finding suggests that long trips can be used to restore the adult's body condition, presumably depleted during short trips as shown previously for some petrels and albatrosses. The adoption of this flexible foraging strategy, which differs from the uniform intervals observed in Cory's shearwaters experiencing situations of 'normal' food abundance, may represent a mechanism through which breeding birds compromise between the needs of their chicks and the maintenance of their own body condition. Copyright 1998 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1999

The effects of demonstrator social status and prior foraging success on social learning in laying hens.

Opportunities for social learning within a group of animals are likely to be influenced by the social dynamics of that group. Some individuals may be more influential demonstrators than others even when there are no differences in their skill level or performance. In this study of domestic hens, Gallus gallus domesticus, differences in demonstrator salience were examined. From 24 separate flocks we selected as demonstrators a dominant cockerel, a dominant hen, a mid-ranking hen or a subordinate hen. Demonstrators were pretrained to perform an operant discrimination task to obtain food. Six observers from each flock individually watched the demonstrator perform the task for four 5-min sessions held on consecutive days. On the fifth day observers were tested individually in the operant chamber. We analysed data from 19 flocks, where there were no quantitative differences in demonstrator performance. Observer hens of relatively high social status performed more correct operant pecks than observer hens of relatively low social status. Demonstrator category also had a significant effect on subsequent observer behaviour. Hens that had observed cockerels performed very few general pecks or operant pecks. Hens that had observed dominant hens performed more operant pecks, but hens that had observed sub-ordinate hens performed more general pecks in the chamber. The results suggested either that there was an interaction between dominance and gender in demonstrator salience or that dominant hens might have been influential because of some factor imperfectly associated with their dominance status. A possible candidate was the foraging ability of the dominant hens. In a second experiment using the same protocol, we manipulated the prior foraging success of dominant hens from four additional flocks but this had no significant effect on their subsequent influence as demonstrators. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1999

The foraging and antipredator behaviour of growth-enhanced transgenic Atlantic salmon.

Growth rate has been established as a key parameter influencing foraging decisions involving the risk of predation. Through genetic manipulation, transgenic salmon bred to contain and transmit a growth hormone transgene are able to achieve growth rates significantly greater than those of unmanipulated salmon. Using such growth-enhanced transgenic Atlantic salmon, we directly tested the hypothesis that relative growth rates should be correlated with willingness to risk exposure to a predator. We used size-matched transgenic and control salmon in two experiments where these fish could either feed in safety, or in the presence of the predator. The first experiment constrained the predator behind a Plexiglas partition (no risk of mortality), the second required the fish to feed in the same compartment as the predator (a finite risk of mortality). During these experiments, transgenic salmon had rates of consumption that were approximately five times that of the control fish and rates of movement approximately double that of controls. Transgenic salmon also spent significantly more time feeding in the presence of the predator, and consumed absolutely more food at that location. When there was a real risk of mortality, control fish almost completely avoided the dangerous location. Transgenic fish continued to feed at this location, but at a reduced level. These data demonstrate that the growth enhancement associated with the transgenic manipulation increases the level of risk these fish are willing to incur while foraging. If the genetic manipulation necessary to increase growth rates is achievable through evolutionary change, these experiments suggest that growth rates of Atlantic salmon may be optimized by the risk of predation. Copyright 1999 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed2000

Can a minority of informed leaders determine the foraging movements of a fish shoal?

There is no information on whether the daily foraging movements of fish shoals are the result of chance, the collective will of all shoalmates, or the leadership of a few individuals. This study tested the latter possibility. Shoals of 12 golden shiners, Notemigonus crysoleucas, were trained to expect food around midday in one of the brightly lit corners of their tank. They displayed daily food-anticipatory activity by leaving the shady area of their tank and spending more and more time in the food corner up to the normal time of feeding. Past this normal time they remained in the shade, even on test days when no food was delivered. Most of these experienced individuals were then replaced by naïve ones. The resulting ratio of experienced:naïve fish could be 5:7, 3:9 or 1:11. On their own, naïve individuals would normally spend the whole day in the shade, but in all tests the experienced individual(s) were able to entrain these more numerous naïve fish out of the shade and into the brightly lit food corner at the right time of day. Entrainment was stronger in the 5:7 than in the 1:11 experiment. The test shoals never split up and were always led by the same fish, presumably the experienced individuals. These results indicate that in a strongly gregarious species, such as the golden shiner, a minority of informed individuals can lead a shoal to food, either through social facilitation of foraging movements or by eliciting following behaviour. Copyright 2000 The Association for the Study of Animal Behaviour.

Journal Article↗
PubMed1999

Influence of production and bioassay methods on infectivity of two ambush foragers (Nematoda: steinernematidae)

The influence of production and bioassay methods on infectivity of two ambush foragers, Steinernema carpocapsae and Steinernema scapterisci, was evaluated. Both species were mass-produced in vitro in liquid culture and in vivo using live insects: S. carpocapsae in last instar wax moth Galleria mellonella larvae and S. scapterisci in adult house crickets Acheta domesticus. Infectivity was assessed at 28 degreesC against last-instar G. mellonella larvae using a filter-paper bioassay and a newly developed "sand-well" bioassay. The infectivity of S. carpocapsae was not influenced by the method of production or bioassay, whereas the infectivity of S. scapterisci was influenced by both factors. Both in vivo and in vitro produced S. carpocapsae caused >60% larval mortality at one nematode per larva (1:1) in the filter-paper bioassay, but S. scapterisci elicited less than 10% mortality. At 50 nematodes per larva, in vitro S. scapterisci caused 41.7% mean larval mortality in the filter-paper bioassay, whereas in vivo S. scapterisci elicited only 28.5% mortality. The replacement of filter paper with a 2.5-mm-deep layer of sand (termed sand well) resulted in 2.5-fold increase in infectivity of S. scapterisci. In the new sand-well procedure, 15 S. scapterisci per larva (15:1) caused an overall mean larval mortality of 47.5% and the pattern of mortality showed a normal distribution. The infectivity of S. carpocapsae was not different in the 1:1 filter paper or 1:1 sand-well bioassay. These results demonstrate that nematode infectivity could be strongly influenced by both the production and bioassay methods, and there are no universal assays even when nematodes have similar foraging strategies. Copyright 1999 Academic Press.

Journal Article↗
PubMed1999

Exploration of optimal giving-up time in uncertain environment: a sit-and-wait forager

I address variability of giving-up time of a sit-and-wait forager in a stochastic environment. Behavioral variability is considered as an essential unavoidable feature of animals. In a stochastic environment, this unavoidable behavioral variability will increase. Thus, the existence of some behavioral variation would be considered to be a constraint. I analyse the expected long-term reward rate for a model of patch exploitation by a sit-and-wait forager as a function of giving-up time (GUT) given environmental stochasticity and a base behavioral variability. While the animal is learning about the environment, a mixed strategy is favored and thus, more variability is added to behavior. I claim that it is important to study not only the final optimal strategy but also the strategy used during the exploration process. Copyright 1999 Academic Press.

Journal Article↗
PubMed2000

Optimal trajectories for the short-distance foraging flights of swans.

Optimal flight theory relates body measurements (wing span, body cross-section, body mass) and aerodynamic variables (air density, drag, profile and induced power ratios) to the most energy-efficient velocity for long distance migration. For short-range (2-10 km) foraging flights the theory is expanded to include non-negligible costs for take-off and energy savings/losses for climbing to altitude (drag decreases with air density and therefore with altitude). The theory predicts clear differences between Tundra and Trumpeter swans. Generally speaking, for flights between 2 and 10 km Trumpeter swans can be expected to fly approximately 5-10 m lower in altitude and 1-2 ms(-1)more slowly than Tundra swans. Moreover, the total energy required for these foraging flights is approximately 150% larger for a Trumpeter than a Tundra swan (80 vs. 120 kJ of direct mechanical energy for a 5 km flight), suggesting that Trumpeter swans may be less inclined to take-off than Tundra swans. These factors indicate that even Trumpeters native to the area (as opposed to recently translocated) would be more vulnerable to hunting than native Tundra swans. The expanded theory is compared to observations made in Utah's Bear River Migratory Bird Refuge.

Animals↗
PubMed2002

A lifetime perspective on foraging and mortality.

Food intake carries many potential risks which may impair an animal's reproductive success not only in the current breeding cycle, but also for the rest of its lifetime. We examine the lifetime trade-off between the costs and benefits of food intake by presenting a simple animal foraging model, where each unit of food eaten carries with it a risk of mortality. We show that the optimal food intake rate over an animal's lifetime, for both semelparous and iteroparous animals, is not maximal. Instead, animals are required to strike a balance between the immediate reproductive benefits of gathering food and the future reproductive costs incurred by the food's mortality risk. This balance depends upon the lifespan of the animal as well as the nature of the risk. Different mortality risks are compared and it is shown that a mortality risk per unit time spent foraging is not, in general, equivalent to a mortality risk per unit of food consumed. The results suggest that a mortality risk per unit of food consumed, such as that presented by the presence of a toxin or of a parasite in the diet, has important consequences for feeding behaviour and is a possible factor involved in food intake regulation.

Animals↗
PubMed1980

Foraging strategies of Drosophila melanogaster: a chromosomal analysis.

Two larval foraging strategies in Drosophila melanogaster were identified, "rover" and "sitter." "Rovers" traverse a large area while feeding whereas "sitters" cover a small area. The difference between "rovers" and "sitters" was analyzed genetically by chromosomal substitutions between isogenic stocks. Differences in larval locomotor behavior ("crawling behavior") can be attributed to the second chromosome, the "rover" strategy being dominant over the "sitter" strategy. Differences in feeding rate ("shoveling behavior") are affected additively by both the second and third chromosomes. Natural populations of Drosophila larvae were sampled three times over a 2-month period; "rovers" and "sitters" were at constant frequencies in these populations. The two foraging strategies are discussed in the light of resource utilization in environments where food is distributed continuously or discontinuously.

Animals↗
PubMed1989

Analysis of six foraging behaviors as toxicity indicators, using juvenile smallmouth bass exposed to low environmental pH.

Six foraging behaviors were evaluated for use in toxicity bioassays with fishes. Response time and strike frequency were used to measure fish activity, average and longest fixation distance, to measure visual acuity, while prey capture frequency and strike success were used to measure fish coordination and agility. In this study, the feeding behaviors were used to evaluate the effects of chronic exposure to acidic water on juvenile smallmouth bass (Micropterus dolomieui). Feeding responses to two types of live prey, tubificids and Daphnia magna, were recorded for bass exposed to pH 4.7 and 4.2. Fish held at the lower pH level had significantly lower fixation distances, prey capture success and capture frequencies with both prey types, indicating that high levels of acidity may impair visual acuity, coordination, and agility. The foraging behaviors evaluated herein appear to be useful in toxicity testing because they are easily quantified and indicate changes that may affect growth and survival in long-term exposures.

Animals↗
PubMed1977

Selenium in pollen gathered by bees foraging on fly ash-grown plants.

Pollen collected from the rear legs of honey bees found foraging on asters voluntarily growing on a fly ash dump in Endwell, New York, was found to contain a high concentration of selenium. Pollen from bees foraging on asters growing on field soil contained no detectable selenium.

Animals↗