Text University of Tartu bird ecology researcher Marko Mägi and coordinator of the Year of Great Tit Margus Ots,
The great tit that has been staying overnight in the nest box has gathered many viewers via the webcam. Lately it has arrived in the nest box in the evenings between 16.00-17.00 and left by 8.00 at the latest in the mornings. Thus it sleeps more than 15 out of 24 hours during the dark period. How much energy does the tit use during the long winter nights and how much weight does it lose?
The camera image is transmitted by OÜ Teetormaja: www.tt.ee
Direct stream camera: LINK
Results of investigations by Estonian scientists have shown that great tits spending the night in nestboxes have weighed on average 21 grams and in comparatively mild nights (down to -5 degrees) have lost on average 2,2 grams of their body mass – this equals 10,5% body mass loss per night (Mägi & Lepik 2014). In Latvia the weight loss of great tits has been recorded in very cold nights (down to -43 degrees). In such nights a part of the birds freeze to death. The birds that had died in the cold had lost nearly 24% of their body mass, the survivors however about 13% (Krams et al. 2013).
In the case of blue tits, hypothermia has been noted: in severe winters: they are able to reduce their body temperature during sleep by up to 5 degrees below normal in order to reduce the energy consumption (Nord et al. 2009).
Krams, I., Cirule, D., Vrublevska, J., Nord, A., Rantala, M., Krama, T. 2013. Nocturnal loss of body reserves reveals high survival risk for subordinate great tits wintering at extremely low ambient temperatures. Oecologia 172 (2): 339-346. DOI 10.1007/s00442-012-2505-7.
Mägi, M., Lepik, A. 2014. Talvituvate rasvatihaste (Parus major) kehakaalu ööpäevased erinevused. Hirundo 27 (1): 9-20.
Nord, A., Nilsson, J., Sandell, M., Nilsson, J.-Å. 2009. Patterns and dynamics of rest-phase hypothermia in wild and captive blue tits during winter. Journal of Comparative Physiology B 179 (6): 737-745. DOI 10.1007/s00360-009-0357-1.
(Estonian article posted 25.11.2016)