Gladalski, M., Banbura, M., Kalinski, A., Markowski, M., Skwarska, J., Wawrzyniak, J., Zielinski, P. and Banbura, J. 2016. Effects of extreme thermal conditions on plasticity in breeding phenology and double-broodedness of Great Tits and Blue Tits in central Poland in 2013 and 2014. International Journal of Biometeorology 60: 1795-1800.
Noting the "the impact of climate changes on populations of birds has recently been under extensive study," as their contribution to this growing body of research Gladalski et al. (2016) set out to investigate the response of Great Tits (Parus major) and Blue Tits (Cyanistes caeruleus) to an extreme variation in spring temperature that occurred in central Poland between 2013 and 2014; the spring of 2013 was the coldest in 40 years, whereas the spring of 2014 was the warmest in 40 years.
In accomplishing their objective, Gladalski et al. gathered data from two different habitats (an urban parkland and a deciduous forest) in Lódź (central Poland), which locations and data collection were part of an ongoing long-term study into the "breeding biology of hole-nesting birds occupying nestboxes." By comparing their observations from the two spring temperature extremes, the authors hoped to observe the effects of extreme thermal conditions on the plasticity of breeding phenology and double broodedness of both bird species.
In describing their findings, Gladalski et al. report that (1) "extremely low spring temperatures in 2013 (coldest spring in 40 years) resulted in birds laying [eggs] unusually late," and that (2) this phenomenon "was followed in 2014 by the earliest breeding season on record (warmest spring in 40 years)." Additionally, they found that (3) "the breeding date of Great Tits and Blue Tits turned out to be a flexible trait," that (4) "populations of both tit species may tune their egg-laying dates to diverse weather conditions by about 3 weeks," while (5) in some cases they have both early and late clutches. And in light of these findings they go on to conclude that (6) "such a buffer of plasticity may be sufficient for Blue Tits and Great Tits to adjust the timing of breeding to the upcoming climate changes."Posted 3 April 2017