Abstract

Several methods have been used to determine the thermal properties of nests and in the last few years small
iButton® temperature loggers have been used to determine an insulatory value. A recent study on Common
Bullfinch (Pyrrhula pyrrhula) nests used a different method, namely infrared (IR) thermography, to study nest
wall insulation because pushing temperature loggers into the nest wall materials would have destroyed their
structural integrity and probably adversely affected the insulatory value. Here, we compared the insulatory
values of Common Linnet (Carduelis cannabina) nests determined using temperature loggers (to record
cooling rates in ºC 20 s–1) with the temperature differences (ΔT in ºC) across the nest wall as measured with
IR thermography when the inside of the nest was heated under a steady state. Insulatory values were more
variable than ΔT but there was no correlation between these two proxy measures of insulation. Despite being
within the same family, Common Linnets build nests with very different materials from Common Bullfinches
but ΔT values measured using IR thermography suggested that the nest wall of Common Linnet nests offered
better insulation than the walls of Bullfinch nests. Our results suggest that comparative studies need to use the
same methodologies but more research is needed to better understand the limitations of different methods in
determining nest wall insulation.