Nest site selection in a hot desert: trade-off between microclimate and predation risk?

Nest placement affects the risk of predation on both eggs and incubating parents and determinesthe microclimate for incubation, two functions that may be in conflict, especially in hot deserts.We studied the rolesof microclimate and nest predation on nest site selection by Hoopoe Larks (Alaemon alaudipes) in the ArabianDesert. Hoopoe Larks build nests in three microsites: on the gravel plain away from vegetation, at the base ofbushes, or above ground in bushes. Early in the breeding season, 70% of nests were placed on the ground, butas the season progressed, nests in small bushes represented 77% of total nests; nest cover increased from 5% to21%. Daily survival rate of natural nests was 0.82. Predation on eggs did not differ among nest sites, either fornatural nests or in an experiment with artificial nests. Measurements of operative and egg temperatures showed thatartificial nests on the gravel plain experience higher temperatures than those under and in bushes. Nest attendancetotaled 77% of daytime in nests under bushes and 81% in nests in or on top of bushes, with the larger shareof attendance contributed by females. However, during midday, when evaporative water requirements—estimatedfrom temperature profiles at artificial nests—were 10–15-fold higher than during early morning, males and femalesshared incubation duties almost equally. We hypothesize that Hoopoe Larks favor exposed nest sites to reducepredation risk to themselves as incubating parents, but as the season progresses, they select nest sites with morecover at the base of or within bushes because the thermal environment forces them to do so.