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Most bird species will defend a territory during the breeding period to assure the availability of resources for their reproductive success. Migratory birds abdicate their territory ownership during the non-breeding period, posing a challenge for the following breeding season. Here we investigated the territorial behavior of male Lined Seedeaters Sporophila lineola, an intra-tropical migrant, during the breeding season (December–May) 2018/2019 in south-eastern Brazil. The Lined Seedeater is a sexually color-dimorphic species that inhabits open areas and feeds on seeds. We followed 18 color-banded individuals, during the period in which they had an active nest. For each individual, we recorded the locations in which they exhibited any potential territorial behavior, with the aid of a handheld GPS. We then estimated the size and shape of the territories using a Kernel Density Estimator. The breeding territories had on average 0.59 ± 0.24 ha, ranging from 0.21 to 0.91 ha in area. Males exhibited agonistic behavior whenever another male intrudes on their territories, especially if in the vicinity of their nests. Our observations indicate that male Lined Seedeaters defend small territories of exclusive use during the breeding season, but forage over a wider home range shared with other conspecifics. Therefore, Lined Seedeaters and other members of Sporophila seem to exhibit home ranges that are much larger than their breeding territories. Empirical studies are needed to understand the influence of territory size and quality on reproductive fitness.

Altricial birds face the challenge of defending their offspring against potential threats in a fixed location: their nest. In species with biparental care, both parents have an equal interest in defending their nest, although the sexes may differ in their investment in anti-predatory behaviours. We conducted a field experiment to investigate sex-asymmetry in anti-predatory behaviours in a breeding population of Lined Seedeaters Sporophila lineola, a small passerine that exhibits sexual dimorphism in adult plumage colour, in south-eastern Brazil. In Lined Seedeaters females are known to be solely responsible for nest building and incubation. Males help to feed the nestlings and are expected to assume the main role in performing anti-predatory behaviours. We presented stuffed models of nest predators (toucans Ramphastidae) and non-predators (pigeons Columbidae) at active nests and measured the number of alarm calls per minute, number of visits during the trial and latency to resume nest visits after the trial. Our results show that birds emitted alarm calls at higher rates when facing a predator than a control stimulus. Moreover, males generally emitted more alarm calls than females, irrespective of the treatment. Both parents did not visit the nest during the predator trials and they took longer to return to the nest after the model had been concealed than during the control trials. Although males seem to take the main role when it comes to responding to intruders (predator and non-predator), further studies, testing a bigger array of predatory stimuli, are needed to better test and understand sex asymmetry in risk-taking behaviours.

Wild birds use social knowledge to avoid being deceived., Many species give deceptive warning calls, enabled by the high risk of ignoring them. In Siberian jays, a territorial, group-living bird, individuals give warning calls toward perched predators and mob them. However, intruding neighbors can emit these warning calls in the absence of predators to access food, but breeders often ignore these calls. Playback field experiments show that breeders flee sooner and return later after warning calls of former group members than those of neighbors or unknown individuals. Thus, breeders respond appropriately only to warning calls of previous cooperation partners. This mechanism facilitates the evolution and maintenance of communication vulnerable to deceptive signaling. This conclusion also applies to human language because of its cooperative nature and thus, its vulnerability to deception.

The social paper wasp Agelaia pallipes is known to eat carrion and scavenge on vertebrates. There are few records of wasps predating vertebrates, including an attack on an adult hummingbird and the predation of bird nestlings. During a project monitoring reproductive behaviour of a neotropical songbird, the Lined Seedeater Sporophila lineola in south-eastern Brazil, we recorded the predation of a four-day-old nestling by a social paper wasp. In the video, the adult female bird attempted to visit the nest prior to the predation. The male could be seen with its crest feathers erect after a wasp left the nest, when the nestling was presumably already dead. When we arrived at the nest to remove the camera, we found the nestling dead, and did not observe the parents in the vicinity. We also registered two other dead nestlings in a different nest with similar wounds. However, the conclusive cause of death of those nestlings is unknown. Nest predation is a major selective pressure in birds, and insects are rarely assumed to play a notable role in this process. Further research is needed to better understand the nature of the relationship between wasps and birds.