3.3 | Factors influenced body condition change in winter
The temperature, humidity, ground arthropod biomass, and snowfall event variables exhibited differing effects on three different time scales (Figure. 4A-4C). For temperature, the maximum daily temperature (Tmax) and daily temperature range (Tran) displayed a positive effect on the capture day (Figure. 4A). However, the effect of temperature partially reversed in the seven days preceding the capture day (Figure. 4C). The mean maximum temperature (MTmax) had a negative relationship with the fat score residual, contrasting with the positive effect of mean temperature range (MTran). Meanwhile, all factors related to humidity had an accordant negative influence on the fat score residual in three models, including minimum humidity (Hmin) on the capture day, mean minimum humidity (Mhmin), and mean maximum humidity (Mhmax) three and seven days before the capture day.
Biomass had a significant negative influence on capture day and three days before capture day (Figure. 4A-4B), indicating that birds stored more fat when the availability of food decreased. In our research region, a snowfall event – lasting no more than three days each time – happened twice throughout the winter study period. Snowfall was found to have a significant negative effect on the capture day (Figure. 4A).
The sex of the birds showed little influence on body condition change in the optimal model. Meanwhile, capture status displayed a positive effect on the fat score residual in all models (Figure. 4A-4C), indicating that a capture event might facilitate long-term weight gain and fat storage.