Breeding biology of the tropical mockingbird Mimus gilvus (Aves: Mimidae) in northeastern Brazil

In the present study, we describe characteristics of the reproductive biology of the tropical mockingbird (Mimus gilvus), estimate nest success using the Mayfield method and identify the main factors that influence its nest success in an area of restinga vegetation. For this, 45 active nests were monitored during the breeding season of 2010–11, 2011–2012 and 2014–2015 with systematic visits to the study area. The reproductive period ranges from August to March. Nests were found with two, three and six eggs, clutch sizes of two eggs were more frequent, the mean number of eggs per nest was 2 ± 0.51 (n = 20 nests). The mean of the incubation period was approximately 13 ± 1.9 days (n = 11 nests). The mean duration of the nestling period was approximately 11 ± 1.6 days (n = 9 nests). The apparent nest success was 37.8% and the nest success estimated by the Mayfield method was 26.6%. Predation was the main cause of failure of nests in the study area (75% of the nests failure). The average rainfall for each month negatively influenced the number of M. gilvus eggs that hatched. In addition, the number of hatched between the rainy season and dry season was different. The number of nests failure was lower in bushes (n = 11) than in cacti (n = 17), which may explain the greatest number of nests found in bushes. Survival rates in the nestling period were lower than in the incubation period. The tropical mockingbird appears to avoid the rainy season in the study area during reproduction, instead concentrating most of the nests during the period of lower rainfall (dry season).