12 Cotinga 32 Eared Pygmy Tyrant Myiornis auricularis is one of the smallest passerines in the world 4 . It inhabits the forest interior and borders of Atlantic Forest, from south-east Brazil to south-east Paraguay and north-east Argentina 4 . Very little is known about its breeding biology other than the period of reproduction 1,4 , and the description of nests 3,4 . Here we report observations made at ive nests found in south-east Brazil. We especially studied the incubating, brooding and food-provisioning behaviour of parents. Observations were made at Parque Estadual Intervales (24°16’S 48°25’W; c.650–800 m), a reserve of 490 km 2 in the state of São Paulo. The vegetation is a mosaic ranging from early second growth near settlements to old-growth vegetation (sensu Clark 2 ). Climate is generally wet, with frequent rain or fog. Mean annual precipitation is c.1,500 mm, with a dry-cold season in April–August (winter), and a wet-hot season in September–March. Mean annual temperature is 17.6°C. Nests were found opportunistically along the margins of dirt roads when adult birds were observed carrying nest material or food to nestlings. The behaviour of the adults attending three of the nests was observed from concealed positions 5–10 m from the nests, to record incubation, brooding and food provisioning. Because the sexes are alike, we did not distinguish males from females. In total we made 19.8 hours of observations. In one nest the eggs were measured with callipers and weighed using a spring scale. Following the departure of the nestlings, two of the nests were measured. The nest is a pensile, domed structure with a side entrance (closed / ovoid / pensile sensu Simon & Pacheco 8 ) made of dried leaves attached to branches of shrubs and fern fronds no more than 1 m above the ground (Fig. 1). The total length, diameter, and the height and width of the nest entrance were, respectively, 12.0, 6.5, 2.7, and 2.5 cm for one nest, and 13.0, 5.0, 3.0, and 2.8 cm for the other. Nest 1 was found in October 1990 with three eggs and observed in the morning of 24 October during a single seven-hour observation period seven days before hatching. An adult stayed in the nest for 65.4% of this period, with each incubation period lasting on average 27.2 ± 7.0 minutes (range 18–41 minutes, n=10). Incubation sessions were interspersed by off-bouts lasting 14.4 ± 6.8 minutes (range 10–31 minutes, n=10). In no instance did Observations on the breeding biology of Eared Pygmy Tyrant Myiornis auricularis Marco Aurélio Pizo, Marcos Rodrigues and Caio Graco Machado Received 16 March 2009; final revision accepted 23 November 2009 Cotinga 32 (2010): OL 12–14 published online 16 March 2010 A partir da observação de cinco ninhos encontrados na Mata Atlântica do sudeste do Brasil, apresentamos aqui informações acerca da incubação e do cuidado parental no miudinho Myiornis auricularis, um dos menores passeriformes do mundo. Ambos os pais alimentam os ilhotes, mas apenas as fêmeas parecem ser responsáveis pela incubação dos ovos. Em comparação com outros tiranídeos, tanto a constância de incubação quanto a taxa de alimentação dos ilhotes são mais elevadas no miudinho, o que pode ser relexo da relação em geral negativa entre massa corporal e taxa metabólica observada em animais. Figure 1. A nest of Eared Pygmy Tyrant Myiornis auricularis attached to a fern frond in Parque Estadual Intervales, São Paulo, Brazil (Marco Aurélio Pizo) Cotinga32-100216.indd 12 2/16/2010 10:57:37 PM