Microclimate of tree cavities during winter nights—implications for roost site selection in birds

Abstract

We examined the relationships between cavity temperature, ambient temperature outside the cavity and structural characteristics of 70 cavities measured for 1 night to determine if cavity roosting birds may potentially select warmer tree cavities for wintertime roosting. The mean temperature increment of the cavity (=cavity-ambient temperature) varied from -2.4 to 4.9 degrees C and increased with higher day-to-night fluctuations in the ambient temperature, smaller cavity entrance and better health status of the cavity tree. Cavities in healthy trees were warmer than those in dead trees, but this difference disappeared with rising mean ambient temperatures. This interaction between the effects of tree health status and mean ambient temperature, as well as the effect of day-to-night fluctuations in the ambient temperature, were supported by the analysis of repeated measurements of temperature taken on 12 consecutive nights in five cavities. The variability in cavity microclimates makes the selection of warmer roost sites possible, and the predictors of microclimate may provide indirect cues to prospecting birds.

Selection of winter roosts in the Great Tit Parus major: influence of microclimate

“…Cavities with a smaller entrance diameter, located in living wood and with better insulation from the outdoor microclimate can be warmer (McComb and Nobble 1981;Pinowski et al 2006;Paclík and Weidinger 2007). The same features can also produce a cooler microclimate on hot days (Vonhof and Barclay 1997;Kerth et al 2001).…”

“…The roost-site occupancy and the success in energy saving are potentially influenced by the dimensions of the cavity and entrance orientation (Kempenaers and Dhondt 1991;Pinowski et al 2006;Paclík and Weidinger 2007), safety conditions against predators (Mazgajski 2002), presence of competing cavity dwelling species (Kempenaers and Dhondt 1991), social status of the bird (Báldi and Csörg} o 1994;Dingemanse and Goede 2003), parasite load of the roost (Christe et al 1994) and roost microclimatic characteristics (McComb and Nobble 1981;Walsberg 1986). Forest habitats offer a variable spectrum of treeroosts with these features.…”

“…In natural conditions, tree cavities have various microclimatic characteristics (see Paclík and Weidinger 2007). Cavities with a smaller entrance diameter, located in living wood and with better insulation from the outdoor microclimate can be warmer (McComb and Nobble 1981;Pinowski et al 2006;Paclík and Weidinger 2007).…”

Why do Corsican Blue Tits Cyanistes caeruleus ogliastrae not use nest boxes for roosting?

“…Costs of cavity roosting are related to increased nocturnal predation risk in the cavity, and to the presence of ectoparasites. Occupied cavities are warmer than the ambient environment, and the energetic benefits to the bird increase with decreasing outside temperatures (Kendeigh 1961;McCafferty et al 2001;Paclik and Weidinger 2007). Sleeping in a cavity during cold nights also reduces overnight weight loss (Dhondt and Eyckerman 1979).…”

Bird and beetle assemblages in relict beech forests of central Italy: a multi-taxa approach to assess the importance of dead wood in biodiversity conservation

“…Our results show the importance of standing dead trees belonging to the fourth class decay and dead trees on the ground of second class decay for holenesting birds. Cavities in living trees are more durable, have more solid walls, and provide better thermoregulation than cavities in snags (Wiebe 2001, Paclík andWeidinger 2007). Heartwood decay facilitates digging activity of woodpeckers and provides nest sites for secondary cavity nesters (tits, nuthatches, treecreepers and hoopoes).…”