Thermal conditions for successful breeding in Great Tits (Parus major L.) : II. Thermal properties of nests and nesthoxes and their implications for the range of temperature tolerance of Great Tit broods.

A model is described in which the thermal properties of nests and nestboxes are integrated with allometric equations describing the metabolic properties of Great Tit broods. These allometric equations were presented and discussed in the preceding paper.The effect of changing certain dimensions of the nest and the nestbox and the size of the brood is discussed in relation to the over-all conductance of the whole system and the influence of these factors on the range of temperature tolerance of Great Tit broods. It seems likely that the over-all conductance of the nest and nestbox system, and consequently the rate of heat loss of the brood, are roughly proportional to the 2/3 power of the brood weight. This is explained by the fact that the value of the over-all conductance is mainly determined by the heat transport due to radiation and convection from the upper surface of the brood. The fact that Great Tits build their nests mainly of moss is discussed in relation to special properties of this nest material by which the upper limit of the range of temperature tolerance can rise under conditions of heat stress.