Why collect winter stores if you can steal from others

Submitted by Looduskalender EN on Fri, 18.11.2016 - 22:30
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Science news from the year of the great tit edited by Marko Mägi, marko.magi@ut.ee University of Tartu Bird Ecology department
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Some days ago I observed a nuthatch in the park who was carrying something into a branch crevice. I was not the only one observing this, so also did a great tit. When the nuthatch disappeared out of sight the tit grabbed the booty and went off. This happened several times. Is this behaviour the reason why great tits don’t collect winter stores? Is it simpler to keep one’s eyes open, and memorize the hiding places of others, in order to empty them later?

Snatching winter stores from others occurs quite often in nature. The near relations of great tits, the willow, marsh and coat tits gather  stores for rainy days. Moreover scientists have found out in the course of different investigations that many of the hiding places of willow and marsh tits are emptied already within eight hours. Often they are found by chance since a deliberate pilfering presumes a certain cognitive capacity: the behaviour of the victim at collecting the food must be observed, the hiding place remembered, and the right moment found. It is known that  great tits have a very good learning ability, but are they also able to remember the location of food collected by others and use this in their own interest which until now only has been noted for Corvidae birds?

Researchers at the Swedish University of Lund started investigating the problem when they noted great tits eating sunflower seeds away from the feeder only when willow and marsh tits previously had carried the seeds into hiding places. This made the scientists think that great tits can remember the location of stores collected by others.

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Marsh tit / Photo:Uku Paal

To find the answer the great tits were caught and taught to search for food in an aviary in holes drilled in artificial logs. When they had grasped the search process they were allowed to observe from a distance of 2 metres how a marsh tit hid sunflower seeds into the holes. After this the great tits were let into the test room after 1 and after 24 hours, to search for the hidden seeds during five minutes. In the meantime the birds did not see the room. The results were compared to the situation when the bird searched for the food without having seen the behaviour of the marsh tits. As measures of searching success the success on visiting the first ten holes and the number of mistakes before finding the first hidden seed were used.

After one as well as after 24 hours the great tits found seeds significantly more successfully than the controls – of the 10 first visited holes there were 29% and 19% with seeds, ordinarily 5%. After one hour the great tits checked on average 3,9 empty holes before finding the first seed, and after 24 hours 10 holes but this was still significantly fewer than the 24 errors in normal conditions.

This shows that although great tits are not store collectors they are able only by looking to remember the positions of the goods (English  observational learning). It might be thought that since a great part of tit family birds collect food stores the ability is inherited from the tit family’s common evolutionary ancestor. At the same time phylogenetic studies contradict this and show that the common ancestors more probably did not collect winter stores. The hippocampus of great tits (the part of the brain the size of which determines the spatial memory power) is comparatively smaller than in the species that do collect winter stores which however does not prevent great tits to learn from observing others. It is possible that they have a certain capacity to see the space allocentrically (i e from the point of view of another individual) which helps to orientate in the space.

The study of the Swedish researchers is the first that has proved the capacity of great tits to connect the behaviour of another species and food and to remember the location of the hiding place, in order to later snatch from there. This memorizing differs from the collectors of the stores who carefully inspect the hiding place and its surroundings. It is however important to remember that stealing directly after the hiding of the goods does not presume a very great capacity for remembering  information..

Brodin A, Urhan AU, 2014. Interspecific observational memory in a non-caching Parus species, the great tit Parus major. Behavioral Ecology and Sociobiology 68: 649-656 DOI: 10.1007/s00265-013-1679-2