Holly and Ivy

I was reading about 'optimal foraging theory' - an idea in behavioural ecology that aspects of animal behaviour can be explained by the fact that, within a particular ecosystem, animals are trying to obtain as much food energy as possible for the expenditure of the least possible effort. If the animal exists in different environments, it may behave differently. The theory has been used to model the behaviour of honeybees (of course), starlings and fish. The book did not mention pigeons, but this one came along at the appropriate moment to ask the question

Human behaviourists have tried to apply the same ideas to early human societies, suggeeting that the societies that existed in different places were determined by the most 'efficient' organisation necessary to exploit their environment for food. Native Americans on the coasts of Canada, Washington and Oregon relied primarily on fish. People in California used much less fish and collected acorns and pine nuts. The northern people were warlike, profligate, slave-owners in a highly stratified society. The Californians were almost a parody of the Calvinist mind-set that some European settlers brought with them: hard-working, aquisitive, living in a much more equal society, dismissive of slavery as immoral, disinclined to conflict

It's an interesting idea. The authors of my book are unconvinced. I think their arguments boil down 'people are complicated'. Who am I to say? 

The rowan berries are long gone. I'm surprised the holly are still there - usually they are eaten before now. Although it has been wet, it has been mostly warm - I expect the birds are still finding insects. Often we bring in ivy berries as Xmas decoration. 'What eats ivy berries?', I wondered. Also the birds, apparently, but not until February when they have ripened and softened, and the holly and hawthorn are all gone. Optimal foraging