Great tit research news

Text  Margus Ots, Bird of the Year project leader
Photo Arne Ader
Translation Liis
Great tits
 
On the website of the Bird of the Year there will regularly be research news too, at least twice a month.
 
The great tit is one of the most studied bird species in the world; in Estonia too the behaviour, breeding and food of the great tit has been studied for half a century. For researchers the great tit is a very good research subject – they are many and they breed in nest boxes where it is easy to observe them.
 
During the year researcher Marko Mägi at the Bird Ecology department of the University of Tartu will present research reports on various aspects of the life of the great tit. We will in particular report about work and studies by Estonian researchers that may be interesting to a wider audience from some aspect but certainly also results from elsewhere in the world.
 
How much to eat: belly full or not?
 
It is winter, the weather is cold and many of us start feeding birds. All in order to make it easier for birds during the cold period. But have you considered that the the motivation of birds to visit the feeder is not similar for all individuals? Great tits and our other tits are sociable birds and each individual has a specific rank in the flock. The old males are on the highest levels of the power ladder, on the lower however the females and juveniles. The latter must usually wait patiently at the feeding place for their turn until the older birds have had their bellyfuls, and only then they can get to eat.
 
Surely many have noticed that birds of prey lurk around the feeders, catching passerines. Thus the birds need to be on guard all the time in order to flee quickly in case of danger. Precisely the speed of fleeing may turn out to be decisive for life or death. According to the laws of physics the speed of escape depends on the mass.  Each eaten milligram should make the bird slower and easier to catch for the bird of prey. In winter however  it is vital for the small passerines to collect a sufficient reserve of energy during the day which would allow them to survive the cold night. Thus the bird has a dilemma – how much to eat to survive the night but at the same time not become an easily caught prey by eating too much. The answer seems simple – one has to eat optimally, but it is complicated by the social status of the bird.  It can be presumed that the dominant birds will not eat a great amount at one time, and so will not lose escape speed as much as the young birds might. The access of young birds to the food is limited, and they must use the opportunity to collect plenty of reserves at each feeding.
 
Latvian scientist Indrikis Krams studied whether social status affects the feeding strategy of great tits on visiting feeders, and whether the collected energy store has an influence on the escape speed of the bird. For this he caught the same great tits in early morning as well as before sunset at the feeder, tens of times during the winter. The birds were measured and weighed and the speed of the bird’s escape attempt in case of a threat was noted. The results showed that the weight of dominant males increased by 6.2% during the day, that of young females however asmuch as 12,2%. The males fled significantly faster than the females both in the morning and the evening, and the speed of the escape of males did not change on average during the day. The females however fled significantly slower in the evening than in the morning. It shows that the larger fat store of the subdominant individuals, which is decisive for a successful wintering, at the same time increases their risk to end their lives in the claws of a sparrowhawk. The dominant males however may permit themselves to have a less full stomach which in turn allows them to flee faster in case of a threat.
 
Next time when you observe the activities at the feeder you can be able to explain to your friends the factors influencing the feeding of birds.
 
Krams, I. 2002. Mass-dependent take-off ability in wintering great tits (Parus major): comparison of top ranked adult males and subordinate juvenile females. Behavioral Ecology and Sociobiology 51:345–349.
 
The catalogue of greattit scientific studies is here: LINK
 
The research news in the year of the great tit are edited by:
Marko Mägi
 
Looduskalender will let you know when there are new reports to read.


 

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