Wild hummingbirds require a consistent view of landmarks to pinpoint a goal location

Funding: This work was supported by the University of St Andrews, the University of Lethbridge and the Natural Sciences and Engineering Council of Canada.One outcome of the extensive work on the ways that birds and insects use visual landmarks to return to a rewarded location is that they use landmarks differently. But this conclusion may have been reached because the almost exclusive training and testing of birds in small laboratory environments may prevent birds from using the view-matching strategies seen in insects. To test how birds use landmarks in an open-field environment, we trained free-living hummingbirds to search for a reward near two experimental landmarks. When the angular size and panoramic position of the landmarks were kept consistent, the hummingbirds searched in the direction of the flower and matched either the retinal angle of the landmarks or the absolute distance of the flower during training, even when the actual size and distance between landmarks changed. These data are more similar to data from view-matching ants solving a similar problem than they are to data from birds trained to use landmarks in the laboratory. This suggests that hummingbirds may also use a remembered view to relocate a rewarded site. Regardless of whether hummingbirds use a remembered view for navigation or just to recognize landmarks, data on landmark use collected from birds tested in the laboratory may not fully reflect how birds return to locations in the wild.PostprintPeer reviewe

Wild rufous hummingbirds use local landmarks to return to rewarded locations

Animals may remember an important location with reference to one or more visual landmarks. In the laboratory, birds and mammals often preferentially use landmarks near a goal (“local landmarks”) to return to that location at a later date. Although we know very little about how animals in the wild use landmarks to remember locations, mammals in the wild appear to prefer to use distant landmarks to return to rewarded locations. To examine what cues wild birds use when returning to a goal, we trained free-living hummingbirds to search for a reward at a location that was specified by three nearby visual landmarks. Following training we expanded the landmark array to test the extent that the birds relied on the local landmarks to return to the reward. During the test the hummingbirds’ search was best explained by the birds having used the experimental landmarks to remember the reward location. How the birds used the landmarks was not clear and seemed to change over the course of each test. These wild hummingbirds, then, can learn locations in reference to nearby visual landmarks

Metabolic state alters economic decision making under risk in humans

Background: Animals' attitudes to risk are profoundly influenced by metabolic state (hunger and baseline energy stores). Specifically, animals often express a preference for risky (more variable) food sources when below a metabolic reference point (hungry), and safe (less variable) food sources when sated. Circulating hormones report the status of energy reserves and acute nutrient intake to widespread targets in the central nervous system that regulate feeding behaviour, including brain regions strongly implicated in risk and reward based decision-making in humans. Despite this, physiological influences per se have not been considered previously to influence economic decisions in humans. We hypothesised that baseline metabolic reserves and alterations in metabolic state would systematically modulate decision-making and financial risk-taking in humans. Methodology/Principal Findings: We used a controlled feeding manipulation and assayed decision-making preferences across different metabolic states following a meal. To elicit risk-preference, we presented a sequence of 200 paired lotteries, subjects' task being to select their preferred option from each pair. We also measured prandial suppression of circulating acyl-ghrelin (a centrally-acting orexigenic hormone signalling acute nutrient intake), and circulating leptin levels (providing an assay of energy reserves). We show both immediate and delayed effects on risky decision-making following a meal, and that these changes correlate with an individual's baseline leptin and changes in acyl-ghrelin levels respectively. Conclusions/Significance: We show that human risk preferences are exquisitely sensitive to current metabolic state, in a direction consistent with ecological models of feeding behaviour but not predicted by normative economic theory. These substantive effects of state changes on economic decisions perhaps reflect shared evolutionarily conserved neurobiological mechanisms. We suggest that this sensitivity in human risk-preference to current metabolic state has significant implications for both real-world economic transactions and for aberrant decision-making in eating disorders and obesity

Flower Bats (Glossophaga soricina) and Fruit Bats (Carollia perspicillata) Rely on Spatial Cues over Shapes and Scents When Relocating Food

Natural selection can shape specific cognitive abilities and the extent to which a given species relies on various cues when learning associations between stimuli and rewards. Because the flower bat Glossophaga soricina feeds primarily on nectar, and the locations of nectar-producing flowers remain constant, G. soricina might be predisposed to learn to associate food with locations. Indeed, G. soricina has been observed to rely far more heavily on spatial cues than on shape cues when relocating food, and to learn poorly when shape alone provides a reliable cue to the presence of food.Here we determined whether G. soricina would learn to use scent cues as indicators of the presence of food when such cues were also available. Nectar-producing plants fed upon by G. soricina often produce distinct, intense odors. We therefore expected G. soricina to relocate food sources using scent cues, particularly the flower-produced compound, dimethyl disulfide, which is attractive even to G. soricina with no previous experience of it. We also compared the learning of associations between cues and food sources by G. soricina with that of a related fruit-eating bat, Carollia perspicillata. We found that (1) G. soricina did not learn to associate scent cues, including dimethyl disulfide, with feeding sites when the previously rewarded spatial cues were also available, and (2) both the fruit-eating C. perspicillata and the flower-feeding G. soricina were significantly more reliant on spatial cues than associated sensory cues for relocating food.These findings, taken together with past results, provide evidence of a powerful, experience-independent predilection of both species to rely on spatial cues when attempting to relocate food

A Multi-Objective Decision Framework for Lifecycle Investment

In this paper we propose a multi-objective decision framework for lifecycle investment choice. Instead of optimizing individual strategies with respect to a single-valued objective, we suggest evaluation of classes of strategies in terms of the quality of the tradeoffs that they provide. The proposed framework takes inspiration from psychological theories which, on the one hand, assert that humans analyze risky choice situations in terms of several competing factors, and, on the other hand, recognize that attribute overload is detrimental to decision making. In particular, we use SP/A (security-potential/aspiration) theory as developed by Lopes and co-authors. The proposed approach is illustrated in a simple lifecycle model. As decision factors, we consider (a) the contribution paid, (b) the ambition level (targeted level of retirement income), and (c) the guarantee level (a level of retirement income that will be achieved with high probability). In terms of the tradeoffs generated between these indices, we compare a class of traditional lifecycle strategies, defined in terms of a glide path, with a class of so called collar strategies

Thermal diffusion factors and intermolecular potentials for noble gas-SF sub 6 systems

Experimental thermal diffusion factors for equimolar mixtures of He-, Ne-, Ar-, Kr-, and Xe-SF{sub 6} have been measured in the temperature range from 225 to 500 K. The data were obtained in a 20-tube trennschaukel, or swing separator.'' The systems containing the four lighter noble gases all exhibited a normal'' thermal diffusion factor, {alpha}{sub T}, that is concentration of the heavy species, SF{sub 6}, in the cold region of the apparatus and increase of {alpha}{sub T} with temperature. Xe-SF{sub 6}, the system with the smallest mass difference, exhibited abnormal'' behavior. The spherically symmetric Pack potentials were used to calculate the thermal diffusion factor with reasonable success. Recently published dipole-dipole dispersion coefficients were used to construct intermolecular potentials of the Hartree-Fock-Dispersion functional form with individually damped attractive terms. The potentials, when tested against the available transport and thermodynamic data, improved the fit to experiment in almost all cases. 35 refs., 7 figs., 2 tabs

Rufous hummingbirds' memory for flower location

We used an open-field analogue of the eight-arm radial maze to investigate the role of memory during foraging by rufous hummingbirds, Selasphorus rufus. In experiment 1 we attempted to determine whether birds were able to differentiate between flowers of the same type that they had emptied, flowers they had seen but not visited and new flowers. They were tested with three trial types, all of which involved birds visiting four rewarded flowers in the first phase of a trial. In 'free' trials, the bird was allowed to choose four from eight flowers. In 'forced' trials there were only four flowers available in phase 1 and in 'mixed' trials the bird could choose four from six available flowers. In all trial types eight flowers (including all those in the same locations as in phase 1) were presented to the bird on its return in phase 2. The four rewarded flowers were those not visited in phase 1. In free and mixed trials, birds were better than chance at avoiding the flowers they had emptied in phase 1. In mixed trials, birds were more likely to visit the new flowers that were unique to phase 2. In experiment 2 we tested whether flower height was a floral feature remembered by birds. Birds were given forced and free trials in which the flowers in the radial maze were presented at two heights. As performance in both trial types was better than chance we suggest that hummingbirds use flower height to remember the locations of flowers. (C) 2001 The Association for the Study of Animal Behaviour.</p

Rufous hummingbirds' memory for flower location

We used an open-field analogue of the eight-arm radial maze to investigate the role of memory during foraging by rufous hummingbirds, Selasphorus rufus. In experiment 1 we attempted to determine whether birds were able to differentiate between flowers of the same type that they had emptied, flowers they had seen but not visited and new flowers. They were tested with three trial types, all of which involved birds visiting four rewarded flowers in the first phase of a trial. In 'free' trials, the bird was allowed to choose four from eight flowers. In 'forced' trials there were only four flowers available in phase 1 and in 'mixed' trials the bird could choose four from six available flowers. In all trial types eight flowers (including all those in the same locations as in phase 1) were presented to the bird on its return in phase 2. The four rewarded flowers were those not visited in phase 1. In free and mixed trials, birds were better than chance at avoiding the flowers they had emptied in phase 1. In mixed trials, birds were more likely to visit the new flowers that were unique to phase 2. In experiment 2 we tested whether flower height was a floral feature remembered by birds. Birds were given forced and free trials in which the flowers in the radial maze were presented at two heights. As performance in both trial types was better than chance we suggest that hummingbirds use flower height to remember the locations of flowers. (C) 2001 The Association for the Study of Animal Behaviour.</p