Centro de Zoologfa Aplicada, Universidad Nacional de C6rdoba, Casilla de Correos 122, C6rdoba, Argentina During a long-term study of the biology of the Monk Parakeet (Myiopsitta monachus), we have re- peatedly observed the Spot-winged Falconet (Spiziap- teryx circumcinctus) roosting and breeding in the par- akeet's communal nests. Despite this behavior being quite frequent, at least in our study area, the only previous reference we have found is a brief mention made by Hoy (1980). Our observations were carried out mainly in C6r- doba Province, Argentina at the Estancia San Anto- nio, 8 km east of the town of Arroyito (31ø25'S, 62ø59'W). The area includes mainly cultivated land with interspersed patches of xerophytic woods. Av- erage annual rainfall is around 700 mm. Comple- mentary observations were made in La Rioja Prov- ince near the city of Chamical at the Instituto Nacional de Tecnologla Agropecuaria (INTA) Experimental Station (30ø30'S, 66ø03'W), where xerophytic dry sa- vannah is the predominant vegetation, and annual rainfall is 411 mm. The Spot-winged Falconet uses the Monk Para- keet's nests for roosting in winter and for breeding in summer (November-December). We have ob- served small and medium-sized parakeet nests (of less than 0.80 m in diameter and with up to three holes) occupied by the falconet. (Big nests may reach 1.50 m and have 15 holes.) In most cases, falconets pre- ferred nests with only one entrance hole. Nests with more than three entrance holes were not used, al- though there were many of this size in the area. This may suggest that falconets have a tendency to choose nests with a small population of parakeets, perhaps because these nests are not so vigorously defended by the parakeets. Of a sample of 70 parakeet nests we visited in C6rdoba during the summer of 1982-1983, 15 were occupied by falconets. Falconets flying near always created a state of ex- citement and alarm in the whole population of par- akeets, as described by Straneck and Vasina (1982). When the predator approached the nests, the par- akeets reacted by flying away and giving an alarm call that provoked the escape of other birds that were inside the nests (mainly during the breeding season). Activities returned to normal for the distressed birds in about half an hour. In contrast, the parakeets do not appear to be greatly disturbed when a neighbor- ing colony, as close as 5 m, has been occupied by a falconet, even during the breeding season. The Spot-winged Falconet invades both aban- doned and occupied nests. The parakeets are sup- planted from active nests, and we have not seen fal- conets and parakeets sharing the same communal nests. When entering a parakeet nest, the falconet en- larges the entrance tunnel to a large elliptical hole of about 30 cm wide by 20 cm high in one side. The hole is easy to see from a considerable distance, up to 100 m. The nest chamber is enlarged until it be- comes almost spherical, with a diameter of about 30 cm. We observed two breeding attempts during the summer of 1982-1983 at the C6rdoba study area. Both nests were about 16 m high in eucalyptus trees (Eu- calyptus viminalis) near a house. We checked the nests with an aerial truck crane. One falconet nest was found on 6 November 1982, when it had two eggs. On 13 November a third egg had been laid. On 20 November the final egg had been added. On 27 November the same number was found. On 4 December one egg had disappeared. The eggs were similar to those described by Dean (1971). On 10 December the nest contained a chick covered with white down and two eggs. On 17 December one egg had disappeared. The nestling had its first feath- ers, especially on its wing and head, and was able to walk on its tarsi. It displayed against us by moving to the opposite side of the nest, widely opening its bill, and extending its claws. On 23 December the chick was almost completely feathered and was very aggressive toward us. The remaining egg was still in the nest bowl. On our next visit (8 January 1983) the nest was empty. The bird would have been a maxi- mum of 33 days old, and, judging from the devel- opment attained on the last visit, we assume that it had fledged. No remains or empty shells were found. At the second nest three eggs were found on 23 December 1982. On 8 January 1983 the nest was emp- ty (no eggshells remained). Prey remains found in the first nest indicated that the food of the nestling was mainly insects and birds. Arthropods were generally reduced to small frag- ments, making identification difficult. We recognized one species of grasshopper (Tropinotus) and a cicada (Quesada gigas). Bird remains included feathers of a nestling Guira Cuckoo (Guira guira) and of adult and nestling Monk Parakeets. The use of the large thorny nests of Monk Para- keets by the Spot-winged Falconet is analogous to the nesting niche of the African Pigmy Falcon (Po- lihierax semitorquatus), which uses the communal nests of Sociable Weaver (Philetairus socius). Unlike the Af- rican Pigmy Falcon, however, the Spot-winged Fal- conet preys on it host species. MacLean (1973) pro- posed that the African Pigmy Falcon nesting in weaver colonies provides protection against preda- tots for the weavers. Our observations suggest that the Spot-winged Falconet may not benefit the Monk Parakeet in such a manner. We are grateful to A. G6mez Dur&n and J. C. Vera (INTA) for granting us the use of the fieldwork areas, to N. Arguello and M. Nores for their assistance in the identification of food remains, and to J. Navarro for his help in the field. This work was supported by a grant from the Subsecretaria de Ciencia y Tecno- logla (SUBCYT) of Argentina. LITERATURE CITED DEAN, A. 1971. Notes on Spiziapteryx circumcinctus. Ibis 113: 101-102. HoY, G. 1980. Notas nidobio16gicas del noroeste ar- gentino. II. Physis (Buenos Aires), Secc. C, 39 (96): 63-66. MACLEAN, G.L. 1973. The Sociable Weaver, part 4: predators, parasites and symbionts. Ostrich 44: 241-253. STRANECK, R., & G. VASINA. 1982. Unusual behav- iour of the Spot-winged Falconet (Spiziapteryx circumcinctus). Raptor Res. 16: 25-26. Received 7 July 1983, accepted 21 February 1984.