A DNA test to sex most birds.

The authors draw together and develop previous timing models for a broad range of conditioning phenomena to reveal their common conceptual foundations: First, conditioning depends on the learning of the temporal intervals between events and the reciprocals of these intervals, the rates of event occurrence. Second, remembered intervals and rates translate into observed behavior through decision processes whose structure is adapted to noise in the decision variables. The noise and the uncertainties consequent on it have both subjective and objective origins. A third feature of these models is their timescale invariance, which the authors argue is a very important property evident in the available experimental data. This conceptual framework is similar to the psychophysical conceptual framework in which contemporary models of sensory processing are rooted. The authors contrast it with the associative conceptual framework.

Time, rate, and conditioning.

Introduction Walter D Koenig and Janis L Dickinson 1 Evolutionary origins J David Ligon and D Brent Burt 2 Delayed dispersal Jan Ekman, Janis L Dickinson, Ben J Hatchwell and Michael Griesser 3 Fitness consequences of helping Janis L Dickinson and Ben J Hatchwell 4 Parental care, load-lightening and costs Robert G Heinsohn 5 Matings systems and sexual conflict Andrew Cockburn 6 Sex-ratio manipulation Jan Komdeur 7 Physiological ecology Morne Du Plessis 8 Endocrinology Steven J Schoech, S James Reynolds and Raoul K Boughton 9 Incest and incest avoidance Walter D Koenig and Joseph Haydock 10 Reproductive skew Robert D Magrath, Rufus A Johnstone and Robert G Heinsohn 11 Joint-laying systems Sandra L Vehrencamp and James S Quinn 12 Conservation biology Jeffrey R Walters, Caren B Cooper, Susan J Daniels, Gilberto Pasinelli and Karen Schiegg 13 Mammalian contrasts and comparisons Andrew F Russell Summary Steven J Pruett-Jones Names of bird and mammal species mentioned in the text References Index

Ecology and evolution of cooperative breeding in birds

Several comparative research programs have focused on the cognitive, life history and ecological traits that account for variation in brain size. We review one of these programs, a program that uses the reported frequency of behavioral innovation as an operational measure of cognition. In both birds and primates, innovation rate is positively correlated with the relative size of association areas in the brain, the hyperstriatum ventrale and neostriatum in birds and the isocortex and striatum in primates. Innovation rate is also positively correlated with the taxonomic distribution of tool use, as well as interspecific differences in learning. Some features of cognition have thus evolved in a remarkably similar way in primates and at least six phyletically-independent avian lineages. In birds, innovation rate is associated with the ability of species to deal with seasonal changes in the environment and to establish themselves in new regions, and it also appears to be related to the rate at which lineages diversify. Innovation rate provides a useful tool to quantify inter-taxon differences in cognition and to test classic hypotheses regarding the evolution of the brain.

/pdf/brains-innovations-and-evolution-in-birds-and-primates-6nkg6zf79d.pdf

Brains, innovations and evolution in birds and primates.

SYNOPSIS This paper concerns the response of foraging animals to variability in rate of gain, or risk. Both the empirical and theoretical literatures relevant to this issue are reviewed. The methodology and results from fifty-nine studies in which animals are required to choose between foraging options differing in the variances in the rate of gain available are tabulated. We found that when risk is generated by variability in the amount of reward, animals are most frequently risk-averse and sometimes indifferent to risk, although in some studies preference depends on energy budget. In contrast, when variability is in delay to reward, animals are universally risk-prone. A range of functional, descriptive and mechanistic accounts for these findings is described, none of which alone is capable of accommodating all aspects of the data. Risk-sensitive foraging theory provides the only currently available explanation for why energy budget should affect preference. An information-processing model that incorporates Weber's law provides the only general explanation for why animals should be risk-averse with variability in amount and risk-prone with delay. A theory based on the mechanisms of associative learning explains quantitative aspects of risk-proneness for delay; specifically why the delay between choice and reward should have a stronger impact on preference than delays between the reward and subsequent choice. It also explains why animals should appear to commit the "fallacy of the average," maximising the expected ratio of amount of reward over delay to reward when computing rates rather than the ratio of expected amount over expected delay. We conclude that only a fusion of functional and mechanistic thinking will lead to progress in the understanding of animal decision making.

/pdf/risky-theories-the-effects-of-variance-on-foraging-decisions-53qwhohgta.pdf

Risky Theories—The Effects of Variance on Foraging Decisions

To test the hypothesis that selection for spatial abilities which require birds to locate and to return accurately to host nests has produced an enlarged hippocampus in brood parasites, three species of cowbird were compared. In shiny cowbirds, females search for host nests without the assistance of the male; in screaming cowbirds, males and females inspect hosts' nests together; in bay-winged cowbirds, neither sex searches because this species is not a brood parasite. As predicted, the two parasitic species had a relatively larger hippocampus than the non-parasitic species. There were no sex differences in relative hippocampus size in screaming or bay-winged cowbirds, but female shiny cowbirds had a larger hippocampus than the male.

Species and sex differences in hippocampus size in parasitic and non-parasitic cowbirds.

https://users.ox.ac.uk/~kgroup/publications/pdf/clayton_etal_1997_BehavProc_cowbirds.pdf

Seasonal changes of hippocampus volume in parasitic cowbirds

Starlings' preferences for constant versus variable food sources were studied in the laboratory. The constant alternative gave a fixed amount of food after a fixed delay. The variable alternative offered either a varying amount of food after a fixed delay (treatment A) or a fixed amount of food after a variable delay (treatment B). In both treatments the ratio of amount of food over trial length (the sum of intertrial interval plus delay and handling times) of the constant alternative equaled the average of the two ratios of the variable alternative. The variable ratios were 30% higher and 30% smaller than the fixed ratio. In free-choice trials (both options available in each trial), the subjects were risk-averse or indifferent in treatment A and indifferent or riskprone in treatment B. In no-choice trials (only one source available per trial), the latency to respond was longer in the variable than in the constant source in treatment A and the opposite in treatment B. The greater preference for variability in time than for variability in reward amount is not consistent with either maximizing the ratio of expected energy over expected time or the expected ratio of energy over time for individual trials. There was a negative correlation between individual intake rate and degree of risk proneness for both kinds of variability. We present a model of choice based on an information-processing theory for temporal memory that accounts for the different effects of variability in delay and in amount but cannot explain the effects of intake rate. [Behav Ecol 1991;2:301-308] Juan C. Reboreda Sub-department of Animal Behaviour, University of Cambridge, Madingley, Cambridge, UK

Risk sensitivity in starlings: variability in food amount and food delay

Egg mimicry by obligate avian brood parasites and host rejection of non-mimetic eggs are well-known textbook examples of host–parasite coevolution. By contrast, reciprocal adaptations and counteradaptations beyond the egg stage in brood parasites and their hosts have received less attention. The screaming cowbird (Molothrus rufoaxillaris) is a specialist obligate brood parasite whose fledglings look identical to those of its primary host, the baywing (Agelaioides badius). Such a resemblance has been proposed as an adaptation in response to host discrimination against odd-looking young, but evidence supporting this idea is scarce. Here, we examined this hypothesis by comparing the survival rates of young screaming cowbirds and non-mimetic shiny cowbirds (Molothrus bonariensis) cross-fostered to baywing nests and quantifying the similarity in plumage colour and begging calls between host and cowbird fledglings. Shiny cowbirds suffered higher post-fledging mortality rates (83%) than screaming cowbirds (0%) owing to host rejection. Visual modelling revealed that screaming cowbirds, but not shiny cowbirds, were indistinguishable from host young in plumage colour. Similarly, screaming cowbirds matched baywings' begging calls more closely than shiny cowbirds. Our results strongly support the occurrence of host fledgling mimicry in screaming cowbirds and suggest a role of visual and vocal cues in fledgling discrimination by baywings.

https://royalsocietypublishing.org/doi/pdf/10.1098/rspb.2012.0612

Host–parasite coevolution beyond the nestling stage? Mimicry of host fledglings by the specialist screaming cowbird

We studied the effect of group size on the proportion of time that greater rheas, Rhea americana, allocated to vigilance and feeding during the non-breeding season. We tested whether: (1) the proportion of time that one bird allocates to vigilance (individual vigilance) decreases with group size, and (2) the proportion of time that at least one bird of the group is vigilant (collective vigilance) increases with group size. We analyzed video-recordings of birds that were foraging alone or in groups from two to 12 birds. The proportion of time allocated to individual vigilance decreased and the proportion of time spent feeding increased with group size. In both cases the main significant difference was between birds foraging alone and in groups. Collective vigilance did not vary with group size and it was lower than expected if vigilance bouts were random or sequential. Our results indicate that rheas foraging in large groups would not receive the benefit of an increase in collective vigilance, although they could still benefit from a reduction of predation risk by the dilution effect.

Juan C. Reboreda

Papers

Species and sex differences in hippocampus size in parasitic and non-parasitic cowbirds.

Seasonal changes of hippocampus volume in parasitic cowbirds

Risk sensitivity in starlings: variability in food amount and food delay

Host–parasite coevolution beyond the nestling stage? Mimicry of host fledglings by the specialist screaming cowbird

Effect of Group Size on Individual and Collective Vigilance in Greater Rheas