Microclimate, CO2and CH4concentration on Blue tits (Cyanistes caeruleus) nests: effects of brood size, nestling age and on ectoparasites

ABSTRACT The presence of nestlings and other nest dwelling living beings in nests built in cavities could alter the composition of gases inside the cavity. In addition, this different concentration of gases could be used by some parasites as a cue to localize their hosts. Here, we explored the temporal variation in the concentration and isotopic signature of carbon dioxide (CO 2 ) and methane (CH 4 ) inside nest boxes of blue tits Cyanistes caeruleus during the nestling period (days 3, 8, 13, 20 and 21 post-hatching). Concentration of gases and isotopic signature were significantly different inside of nests than outside (forest) during the nestling period. CO 2 concentration was higher inside nest while CH 4 was lower than in forest air. The differences in the concentration of CO 2 between nest boxes and forest were higher on days 8th and 20th of nestling age than in other ages while the CH 4 was lower on day 20th of nestling age than in other ages. Moreover, CO 2 variation was positive and significantly related with brood size and negative and significantly with hatching date. The difference of CO 2 between inside of nests and forest on 8th day of nestling age were negative and significantly related to flea larvae abundance as measured at the end of the nestling period. A significant positive relationship was found between the difference of CH 4 between nests and forest and the final abundance of flea larvae for the same nestling age. In addition, flea larvae abundance was positive and significantly related with the relative humidity in nests at 8 days of nestling age. Moreover, blowfly pupae abundance was negative and significantly related with the difference of temperature in nests at 3 day of nestling age. The condition of blue tit females was negative and significantly related with the abundance of blowfly pupae.