Does temperature affect breeding success in cavity nesting birds?
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Nest box provision is used as a method to provide secondary cavity nesters with nesting spaces in areas where natural tree cavities are scarce. Orientation have been identified as a factor affecting the nest box temperature, and microclimate. Nest box microclimate, and especially temperature, have been found to influence nestling development and mortality. This was conducted to see if there was a relationship between temperature and nestling mortality, if there was a difference in heat related mortality between species, and lastly if there was a difference in nest box temperature between different orientation. In this study I had 32 nest boxes that were placed in Midt-Telemark municipality, Southeast-Norway. Blue tits occupied 12, and great tits occupied the rest of boxes. A positive correlation was found between temperature and nestling mortality (r(30) = 0,600, p-value < 0,001). Blue tit nestling mortality in relation to temperature was not statistically significant (r(10) = 0,449, p-value = 0,143), and showing a weaker correlation than great tit nestling mortality in relation to temperature (r(18) = 0,700, p value < 0,001). I found no orientation related difference in temperature for the nest boxes (F-value = 1,37, p-value = 0,273). These results suggest that there is a negative relationship between nestling mortality and high nest box temperatures, and that there may be a difference in heat tolerance for different species. All nests with a higher temperature than 44°C contained at least one dead nestling. Due to a small sample size, one should be cautious when making conclusions, but these finds may give an indication on how high temperatures may affect these species. No orientation related difference in temperature was found, which might suggest that sun exposed or not is more important than orientation itself is when considering temperature. Future research should be carried out to increase knowledge of how and where to hang nest boxes, to maximise the efficiency of nest box provisioning, and to not create potential ecological traps.