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.