Performance in tests of various cognitive abilities has often been compared, both
within and between species. In intraspecific comparisons, habitat effects on cognition
has been a popular topic, frequently with an underlying assumption that urban animals
should perform better than their rural conspecifics. In this study, we tested problem-solving
ability in great tits Parus major , in a string-pulling and a plug-opening test. Our
aim was to compare performance between urban and rural great tits, and to compare
their performance with previously published problem solving studies. Our great tits
perfomed better in string-pulling than their conspecifics in previous studies (solving
success: 54%), and better than their close relative, the mountain chickadee Poecile
gambeli , in the plug-opening test (solving success: 70%). Solving latency became
shorter over four repeated sessions, indicating learning abilities, and showed among-individual
correlation between the two tests. However, the solving ability did not differ between
habitat types in either test. Somewhat unexpectedly, we found marked differences between
study years even though we tried to keep conditions identical. These were probably
due to small changes to the experimental protocol between years, for example the unavoidable
changes of observers and changes in the size and material of test devices. This has
an important implication: if small changes in an otherwise identical set-up can have
strong effects, meaningful comparisons of cognitive performance between different
labs must be extremely hard. In a wider perspective this highlights the replicability
problem often present in animal behaviour studies.
