Biggest number of heat producing bees are in the centre of cluster
the oxygen consumption of winter clusters increases as the ambient temperature decreases.
The increase is moderate between approximately +10°C and -5°C and is steep below approximately -5°C to -10°C.
In swarm clusters, the steep increase has already started at +10°C
Oxygen consumption also increases with decreasing cluster size
the frequency and intensity of endothermic heat production have to be assumed to increase with decreasing ambient temperature and cluster size.
On the other hand, we suggest that at higher ambient temperatures large (swarm) clusters that have come to rest (e.g. at night) may be able to largely reduce endothermy