Timing of breeding as a determinant of nest success of the vulnerable Chestnut Seedeater(Sporophila cinnamomea)in grasslands of southern South America

The breeding traits of Sporophila seedeaters have been relatively well studied in recent years;nevertheless,a group of ten species in the genus,known as southern capuchinos,remain understudied.That is the case with Chestnut Seedeater(Sporophila cinnamomea),a species vulnerable to extinction,which breeds in the grasslands of southeast South America and,after reproduction,migrates towards the Cerrado region in central Brazil.Here,we investigated breeding ecology and calculated average clutch size,productivity,the sex ratio of nestlings,and estimated nest success.Then we tested(1)whether there is a relationship between the number of active nests and environmental variables,(2)whether the nestling sex ratio deviates from the 1:1 ratio,(3)whether clutch size varies between breeding seasons,and(4)whether the nest success is related to starting date,nest age,plant support,nest height from the ground,and clutch size.During two breeding seasons(October-March 2018-2020),we monitored 98 nests.We generated survival models with five interacting covariates to assess the survival of the nests.We recorded the entire breeding period for Chestnut Seedeater,which was estimated to be 4.6 months,similar to other migratory seedeaters.Clutch size did not differ between breeding seasons.The sex ratio of nestlings was not significantly different from the 1:1 ratio.Nest success was 31%,and predation was the leading cause of unsuccessful nests(83%).The daily survival rate was 0.95±0.01.The main predictor of nest survival was the covariate starting date.These findings,added to other aspects of the species’natural history described here,may help illuminate the ecology and behavior of Chestnut Seedeater and other southern endangered capuchinos,and grassland-dependent species of South America.

Drivers of nest survival rate in a southern Tunisian population of Laughing Doves(Spilopelia senegalensis)

Background:Investigating the ecological factors and processes shaping nest survival is of great importance for assessing the breeding success of bird populations and understanding their spatio-temporal dynamics.Here,this question is addressed for the Laughing Dove(Spilopelia senegalensis),an expanding Afro-tropical bird in the Tunisian oasis habitat.Methods:This study took place in Kettana oasis,in south-eastern Tunisia.Natural Laughing Dove nests were searched for and monitored by means of regular visits,from the discovery date until the end of the breeding attempt(i.e.fledging or failure).Data were then used to investigate the relevance of laying date,nest age(days after clutch initiation),nest height and vegetation structure in the close nest tree environment as predictors of daily nest survival rate,using logistic-exposure models that accounted for heterogeneity in monitoring period among the studied nests.Models including different combinations of covariates were ranked according to their AICc scores,and the modelaveraging technique was used for the assessment of the effects of covariates on daily nest survival rate.Results:Vegetation structure in the close nest tree environment and nest age provided important predictors of daily nest survival rate,whereas neither nest height nor laying date showed significant effects.Daily nest survival rate was negatively associated with the presence of date palm trees in the close nest tree environment,but it was positively related to nest age.Daily nest survival rate was higher during the post-hatching stage than during the pre-hatching stage.Conclusions:Nests placed on fruit trees close to clumps of palm trees suffered higher predation risks compared to those placed on fruit trees situated far from palm trees.This is probably because palm tree clumps provided refuges for nest predators,notably the Black Rat(Rattus rattus)which has been reported to be the main nest predator in the oasis habitat.The predatory activity of this rodent seemed more directed against eggs than nestlings,which may explain the observed increase in daily survival rate with nest age.