Tesis de Doctorado (110 pp.) en Ecología defendida el 20 de mayo de 2020 por Marina Trancoso Zaluar <marinaza-luar@hotmail.com. Lugar: Universidad Federal de Río de Janeiro, Postgrado en Ecología, Brasil Director: Mariana M. Vale. Miembros del Tribunal: Helena G. Bergallo, Carlos Eduardo V. Grelle, Henrique B. Rajão, Leornado C. Oliveira.

Callithrix jacchus and C. penicillata are primates endemic to the Caatinga and Cerrado biomes in Brazil, but have become invaders in the south and southeast of the country. Invasive marmosets are a cause for concern due to their potential negative impact on biodiversity, especially on the bird fauna, although there are few studies that directly assess the issue. This thesis seeks to understand the occurrence and impact of invasive marmosets on biodiversity through a bibliographic review and field studies in the Tijuca Forest, in the city of Rio de Janeiro, Brazil. The literature review focused on records and studies of predation and competition of marmosets and native species. In the field study, 18 points were randomly selected in the Tijuca Forest, where environmental variables were measured, and marmoset detections and estimates of bird abundance, diversity, and diversity of vocalizations were done with specialized recorders (Song Meter) and bioacoustic indexes.

In the systematic review a low rate of competition and predation of marmosets over birds was found, both in native and invaded areas. We compiled a list of 19 species of birds preyed by marmosets, composed mainly of common and non-threatened species. The only exception was the great negative impact of egg predation by marmosets on the reproductive success of Formicivora serrana littoralis and Thamnophilus ambiguus, two birds endemic to restinga habitats. The review points to a low impact of marmoset predation on birds in general. The studies, however, are mostly focused on marmosets’ diet and not on the populations of bird prey, which represents a lack of studies on the subject. The field study showed a relationship between detection of marmosets and variables associated with greater forest disturbance (large number of jackfruit trees and a short distance from the edge), corroborating the hypothesis that invasive marmosets occur preferentially in degraded, fragmented and anthropized areas. Our results also show greater abundance, diversity and different vocalizations within the Tijuca Forest and in areas with variables associated with low forest disturbance. Finally, the results show that the detection of marmosets is associated with less diversity and different vocalizations of birds. It is not clear, however, whether this result is due to the impact of marmosets on bird populations, through predation, or through behavioural responses of birds to the presence of marmosets, reducing vocalizations in the context of the ecology of fear.

We conclude that invading marmosets are not a relevant threat to avifauna on a regional scale, especially in disturbed forests and border environments where they are generally found. However, there is evidence of a negative impact of marmosets on avifauna on a local scale, which requires further studies to elucidate the mechanisms through which this impact occurs. Scientific literature often takes it for granted that invasive marmosets negatively interfere with bird life. This study shows that the issue is much more complex than is supposed and important gaps still remain to understand the impacts of invasive marmosets on birds (see more https://doi.org/10.1016/j.pecon.2021.02.007 and https://doi.org/10.1007/s10530-022-02748-z).