Blue tits individually decide: "Should I stay or should I go?"

A new study reveals that energy resources, shelter and the environment are not the only factors involved in blue tits’ decisions to migrate or remain resident, their individual personalities also play a role.

Previous research has shown that in certain regions blue tits are partially migratory; some of the population migrates each year while others remain resident, and individuals decide what they will do with each coming year. It is throught that the proportion of birds which choose to migrate do so depending on environmental conditions. However, the factors that govern migratory decisions in individual birds were not well known.

Researchers from Liverpool John Moores University (LJMU), University of Oslo, and Lund University, Sweden, captured 24 migrating female blue tits (Cyanistes caeruleus) at the Southern tip of Sweden throughout the month-long migratory season to investigate if blue tits that migrated early in the season displayed different behaviour to those that migrated late.

They assessed individuals’ age and size, and measured how long they took to explore an unfamiliar environment and to start feeding, as measures of personality traits such as boldness and adaptability.

The study, published in PLOS ONE, reveals that throughout the migratory season, lean and large individuals were more exploratory and quicker to feed than smaller birds or those with larger fat reserves, indicating that foraging may be mostly driven by energy requirements. However, exploratory behaviour also varied over the migratory season. Blue tits that migrated later, particularly juveniles, were more exploratory than birds migrating earlier. As late-migrating birds are under increased time pressure to find shelter and food, the relative need to obtain such environmental information may also determine blue tit behaviour.

Whilst the study only examined a small sample of blue tits in a single region, it suggests that energy requirements and the need to obtain environmental information may be important in determining their behaviour during migration. However, there was also some indication that the personality of a bird – how well it can deal with unfamiliar situations – affected the decision when to leave and how to behave en route.

LJMU’s Dr Claudia Mettke-Hofmann, Reader in Animal Behaviour, commented: "The flexibility in behaviour of young migratory blue tits is in stark contrast to the more stereotyped behaviour of long-distance migrants and may help partial migrants dealing with environmental change. An exciting finding of the study was that at least to some extent decisions when to migrate are affected by the personality of a bird."

Lead author Dr Anna Nilsson, of the University of Oslo, added: "Our study presents one of the first results showing a smooth transition from more to less migratory personality characteristics as the migratory season progressed which influenced decisions when to migrate and while on migration."

The paper entitled ‘Energy reserves, information need and a pinch of personality determine decision-making en route in a partially migratory blue tit’ appeared in PLOS ONE. http://dx.doi.org/10.1371/journal.pone.0163213

Image credits: G. Hofmann