“Under Nature, the slightest differences of structure or constitution may well turn the nicely balanced scale

in the struggle for life, and so be preserved.”

(Charles Darwin, 1959, The Origin of Species,

Chapter IV, “Natural Selection; or the Survival of the Fittest,” p.90)

Coinciding with the 200^th anniversary of the birth of Charles Darwin on February 12^th, 2009, a Special Issue of Behavioural Processes (Elsevier) entitled "Comparative Cognition in Context” honors the scientific contributions of Sara J. Shettleworth. Edited by Karen Hollis, the Special Issue features 16 papers – original research articles as well as insightful theoretical reviews – by leading researchers worldwide in the field of comparative cognition, the study of how animals perceive, learn about and understand their physical and social worlds. Aptly illustrating the theme that Shettleworth, well-known author of Cognition, Evolution, and Behavior (Oxford University Press), details in her contribution to the Special Issue, the remaining papers document not only the rapidly expanding dimensions of comparative cognition – an expansion to new study species, new techniques and newly discovered abilities – but also the breadth and depth of the field’s multidisciplinary analyses.

· Several species of food-storing birds use memory to return to those storage sites, either hours, days, or, in some species, weeks later. Sherry, a pioneer in the study of spatial memory in food storing birds, and co-author Hoshooley show how both the birds’ behaviour and their brains change with the seasons. Gibson and Kamil, another pioneer in the study of birds’ spatial memory, use Tinbergen’s four questions about behaviour – namely cause, development, function and evolution – to outline specific questions that remain to be addressed. Healy, Bacon, Haggis, Harris, and Kelley focus on the relationship between food hoarding behaviour, spatial cognition and hippocampal structure, and review the conflicting evidence for sex differences in spatial cognition.
· Cheng, Narenda, Sommer and Wehner describe how a Central Australian desert ant, which forages during the hottest part of the day in the summer months, is able to navigate expertly, in diverse ways, under these incredibly hostile desert conditions.
· Ratcliffe reports the results of a comparative analysis of leaf-nosed bats, an ecologically diverse family that includes predatory, omnivorous, frugivorous and nectivorous species, demonstrating an extraordinarily close relationship exists between their foraging behaviour, diet selection and their brain size.
· Guillette, Hollis and Markarian report the first evidence that antlions, a larval insect, can learn to anticipate prey blundering into their traps, and can use this information to prepare efficiently for meals that, in nature, may be days or weeks apart.
· Several papers address questions about how animals make efficient choices when foraging for food. Freidin, Aw and Kacelnik show how animals’ ecology shapes its choice behaviour; Stephens and Dunlap find clear evidence that challenges the generality of current models of choice behaviour. Houston wrestles with the inconsistencies between observed and expected performance in foraging behaviour, arguing that the laboratory environment may not capture critical details of the environment in which behavioural “rules of thumb” evolved, and providing new theoretical insights.
· Humber, Brodbeck and Warkentin report findings of the first study of memory in pine siskins, nomadic birds that remember precisely where they have found especially good sources of food.
· That animals learn the geometric features of their environments is the subject of several papers in this Special Issue. Miller, co-author with Shettleworth of an already-influential associative model of geometry learning, shows how animals of several different species, including humans, switch from using specific cues when navigating their worlds to relying on the geometrical features of that world. Sutton reviews the literature on animals’ use of geometric information and suggests a rethinking of how we characterize that information.
· Concerning future-oriented thinking in animals, Raby and Clayton develop a new theoretical approach to multiple forms of future-oriented thinking, delineating what, exactly, animals know about the future and whether they can plan ahead, while Paxton and Hampton tease apart the precise locus of monkey’s inability to anticipate a future need that is different from the one they currently experience.
· Reid explores why domestic dogs outsmart chimpanzees when it comes to understanding human social cues.
· Crystal explores the neurobiological bases of memory, showing that non-human animals likely have a memory system very much like the system impaired in human Alzheimer's disease, providing enormous potential for understanding the neurobiological bases of human memory disorders.

All around the world, Charles Darwin’s 200^th birthday and the 150^th anniversary of his publication of On the Origin of Species are being celebrated in 2009. Two of the leading research publications, Nature and Science, devote special coverage to Darwin and his scientific contributions at:

http://www.nature.com/news/specials/darwin/index.html

http://www.sciencemag.org/darwin/

Contents of the Special Issue: Comparative cognition in context

Perspective

S.J. Shettleworth (Canada)

The evolution of comparative cognition: Is the snark still a boojum?

Research reports

E. Freidin, J. Aw and A. Kacelnik (UK)

Sequential and simultaneous choices: Testing the diet selection and sequential choice models

L.M. Guillette, K.L. Hollis and A. Markarian (USA)

Learning in a sedentary insect predator: Antlions (Neuroptera: Myrmeleontidae) anticipate a long wait

J.M. Humber, D.R. Brodbeck and I.G. Warkentin (Canada)

Use of spatial and colour cues by foraging pine siskins (Carduelis pinus): A field study

R. Paxton and R.R. Hampton (USA)

Tests of planning and the Bischof-Köhler hypothesis in rhesus monkeys (Macaca mulatta)

J.M. Ratcliffe (Denmark)

Neuroecology and diet selection in Phyllostomid bats

D.W. Stephens and A.S. Dunlap (USA)

Why do animals make better choices in patch-leaving problems?

Theoretical reviews

K. Cheng, A. Narendra, S. Sommer and R. Wehner (Australia, Switzerland)

Traveling in clutter: Navigation in the Central Australian desert ant Melophorus bagoti

J.D. Crystal (USA)

Elements of episodic-like memory in animal models

B. Gibson and A. Kamil (USA)

The synthetic approach to the study of spatial memory: Have we properly addressed Tinbergen's "four questions"?

S.D. Healy, I.E. Bacon, O. Haggis, A.P. Harris and L.A. Kelley (UK)

Explanations for variation in cognitive ability: Behavioural ecology meets comparative cognition

A.I. Houston (UK)

Flying in the face of nature

N. Miller (Canada)

Modeling the effects of enclosure size on geometry learning

C.R. Raby and N.S. Clayton (UK)

Prospective cognition in animals

P.J. Reid (USA)

Adapting to the human world: Dogs' responsiveness to our social cues

D.F. Sherry and J.S. Hoshooley (Canada)

The seasonal hippocampus of food-storing birds

J.E. Sutton (Canada)

What is geometric information and how do animals use it?