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1.5.3 Intra-seasonal variation of body mass and metabolic performance

As for the inter-seasonal analyses, we found no year effect on average body mass in wintering Black-capped chickadees. However, body mass varied over time within winter (month: F6,212 “ 8.3, p < 0.0001) increasing by 4.0% between October and December (Tukey: p <0.01) and remained constant until August (figurę 1.2, Tukey: p = 0.07). Mass also differed between sexes (F2.218= 146.8, p < 0.0001) with males being on average 11.5% heavier than females (males: 12.00 ± 0.05 g; females: 10.76 ± 0.06 g, undetermined 11.18 ± 0.07 g, Tukey: p < 0.0001) and, as these birds are fattening up on a daily basis (Lehikoinen, 1987; Mandin & Yćzina, 2012), body mass was positively affected by time of capture (F|_t225 = 57.1, p < 0.0001).

Figurę 1.2 Intra-seasonal changes in body mass. Data are least sąuarc means of body mass controlling for year, month, time of capture, sex with bird ID as random parameter. Different letters represent significant difference between months.