Mountain birds on higher alert

The mountain chickadee stashes away food, when it's plentiful, for later consumption.

Birds living high in the mountains are better problem solvers and have more reliable memories than ones living lower down, according to research just published, writes Richard Collins.

Chickadees are the North America equivalents of the tits in Irish gardens. The mountain chickadee, a little grey and white acrobat, resembles our coal tit. It’s found from the Yukon to Mexico up to altitudes of 2,500m. A voracious eater, one found dead in Arizona, had 275 tiny caterpillars in its stomach. The nest is made in a hole behind the hard bark of a pine tree. It’s a particularly safe location; the female can afford to spend longer incubating than her cousin, the black-capped chickadee, which excavates a hole in softer wood.

Dovid Kozlovsky, and a team at the University of Nevada, caught 24 mountain chickadees in a Californian forest. Twelve of them were trapped at an altitude of 1,800m. The others came from 600m higher up. All were just a few months old, none having lived through a winter. The captives were taken to an aviary where their problem-solving skills were tested.

Glass test-tubes, with juicy wax-worms inside them, were plugged with cotton wool and placed in the birds’ cages. A marked difference in the responses of the two groups soon became evident. Birds from higher up on the mountain figured out how to remove the plug, and get at the food, much more quickly than ones from the lower level. Males and females performed equally well.

Like Irish blue and coal tits, chickadees stash away food, when it’s plentiful, for later consumption. But birds, like ourselves, have ‘senior moments’; they may fail to remember where food caches are. Timothy Roth and colleagues, studying black-capped chickadees, found that those in austere Alaskan environments had better memories than ones resident in more laid-back Kansas. The Alaskans made fewer mistakes when relocating caches and their memories lasted longer. There was a physical basis for this finding; examination of dead ones showed that the better performers had larger hippocampi with more neurons in them.

‘Hippo’ and ‘campus’ come from the Greek, meaning ‘horse’ and ‘sea-monster’. These structures, resembling seahorses, are found beneath the cerebral cortex, the brain’s outer layer. They play a key role in several activities. Memory and spatial awareness depend on them. When damaged at the onset of Alzheimer’s disease, the victim’s ability to recall recent events deteriorates.

But why are birds from on high better problem-solvers and why do they need superior memories? The mountain environment, the researchers argue, is particularly challenging. Winters last longer at high altitudes, snow cover is more extensive and weather conditions fluctuate wildly. The range of plants and animals is limited and food is harder to find. To succeed in such harsh conditions, a bird must have its wits about it. Constantly encountering new problems, the more gifted individuals tend to survive at the expense of more ‘intellectually challenged’ ones. Being able to remember where food has been stored could mean the difference between life and death. Natural selection, therefore, favours the evolution of large hippocampi.

Roth found that the Alaskan black-capped chickadees were more willing to explore novel objects placed in their environment. Surely, mountain chickadees would be more adventurous the higher up they lived? When Kozlovski’s team tested for this, however, they were in for a surprise.

The captive tits were offered food in feeders which looked very different from the ones they were used to. Irrespective of the altitude from which they came, all of the birds were ‘neophobic’. Even when wax-worms, the chickadees’ favourite food, were placed in the vicinity of a feeder, none would approach the unfamiliar object. This, the researchers claim, shows that problem-solving skills and a willingness to experiment with new things don’t always go hand in hand. It’s an odd finding!

  • Dovid Kozlovsky. Problem solving ability and response to novelty in mountain chickadees from different elevations. Behavioural Ecology and Sociobiology. 2015.

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