ANIMAL BEHAVIOUR, 1998, 56, 207–217 Article No. ar980766 The possible function of stone ramparts at the nest entrance of the blackstart NOAM LEADER & YORAM YOM-TOV Department of Zoology, Tel-Aviv University (Received 30 May 1997; initial acceptance 6 August 1997; final acceptance 3 December 1997; MS. number: 5556) ABSTRACT Blackstarts, Cercomela melanura, Turdidae, construct a rampart of stones at the entrance to their nests. These ramparts may reach remarkable proportions, containing hundreds of flat rocks. We investigated several hypotheses regarding the function of stone ramparts, by monitoring individually marked blackstarts at the En-Gedi Nature Reserve, Israel. Stones were collected solely by females, who carried them in their beaks, while flying to the nest, at a rate of up to one stone per min, after pair formation had occurred. The number and total weight of stones as well as rampart height showed a highly positive correlation with the size of the nest cavity opening. The rampart decreased the size of the cavity entrance to some nests by as much as 67%, which suggests an antipredator barrier function. Survival rates of eggs and chicks were extremely low and the major cause of reproductive failure was predation. Successful nests tended to be located higher off the ground than predated nests, and often contained fewer stones. Furthermore, larger females in terms of wing and tail length nested in cavities higher off the ground and built smaller ramparts containing lighter stones. An artificial nest predation experiment did not reveal a difference in predation rates between nests with and without stone ramparts. Spiny mice, Acomys sp., were the main egg predators. However, in 37% of nests with ramparts that were predated, the perpetrator flattened the rampart, suggesting that they may serve as a barricade, forcing the predator to invest time in clearing the stones in order to gain access to the nest, and perhaps allowing the nesting female sufficient time to escape. We propose, therefore, that owing to such high nest predation rates, females nesting close to the ground build stone ramparts as an ‘early warning’ mechanism to prevent themselves from being trapped inside nest cavities and predated.  1998 The Association for the Study of Animal Behaviour At least 29 species of ground-nesting, mostly desert- dwelling, passerine birds are known to build a rampart of small stones at the entrance to their nests. These species belong to four families: Turdidae, Alaudidae, Fringillidae and Troglodytidae (Cramp & Simmons 1988; Afik et al. 1991; Roberts 1993; Merola 1995). The scope of building activity in these species ranges from the construction of a small, encircling wall of pebbles around the rim of the nest, a shallow depression or scrape on the ground, lined with vegetation, usually in the shelter of a tussock or small rock (Alaudidae), to the accumulation of hundreds of small, flat rocks, whose total weight may exceed 1 kg, as in species of the genus Oenanthe (Turdidae), which typically nest deep in rock crevices, under boulders and rock piles (Cramp & Simmons 1988). In these latter species, the rocks are piled up in front of the nest, to form a flat mosaic, three or four layers deep and 10–40 cm wide, extending outward from the nest tunnel for as much as 1 m (Fischman 1977; Cramp & Simmons 1988; Palfrey 1988). The bird carries stones in the beak while flying to the nest in intense carrying bouts during the first stage of nest building (Fischman 1977; Palfrey 1988; Moreno et al. 1994). Stone carrying appears to be a costly activity in terms of time and energy. Several functional explanations for the maintenance of this behaviour have been suggested, yet relatively little research has been conducted to test them. Until recently, most of the information accumulated on rampart building behaviour was based on observations alone. The rampart has been suggested to function: (1) as a support for the nest, preventing it from sliding off a sloping surface and thus allowing the birds to use higher nests which are potentially less accessible to ground predators (Richardson 1965); (2) as protection from wind, rain or dust storms (Ferguson-Lees 1960), by anchoring the nest structure to the substrate and possibly stabiliz- ing the soil in the vicinity (Afik et al. 1991); (3) as Correspondence: N. Leader, Department of Zoology, Faculty of Life Sciences, Tel-Aviv University, Tel-Aviv 69978, Israel (email: leader@ccsg.tau.ac.il). 0003–3472/98/070207+11 $30.00/0  1998 The Association for the Study of Animal Behaviour 207