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1. Sixteen species of ground-nesting desert birds build ramparts of stones around the entrance to their nests.

2. We tested Orr’s hypothesis (Orr Y. (1970) Condor 72, 476-478) that the rampart of the nest of the Desert Lark Ammomanes deserti, in the Negev desert of Israel, facilitates self-incubation by its ameliorative influence on nest temperatures.

3. We found that the rampart significantly lowered the nest temperature relative to ambient temperature in the heat of the day in 3 of the 5 nests studied.

4. The effects of the rampart on the heating rate of the nests were equivocal, reducing this rate in 2 nests and increasing it in 2 others.

5. Our results indicate that the effect of the rampart is inconsistent with Orr’s hypothesis and that there is considerable variation in the biophysical effects of the rampart, in spite of the considerable selective force expected of high ambient temperatures in the desert in early summer.