Report of an extra-pair copulation in the Rufous Hornero, Furnarius rufus (Aves: Furnariidae)

In the last decade, studies in bird breeding biology have shown that infidelity is prevalent in socially monogamous species. Here, we describe an extra-pair copulation (EPC) event in the Rufous Hornero (Furnarius rufus), a socially monogamous bird with year-round territoriality and low levels of extra-pair paternity. Before the EPC, a within-pair copulation (WPC) occurred inside the pair’s territory. The WPC occurred on the ground and between a banded male (ca. 6 years-old) and an unbanded female. Ten minutes later this breeding pair invaded a neighboring territory, presumably to forage. The territorial male was chased back to its territory by an unbanded male neighbor after being detected. The male neighbor was paired with an unbanded female that did not participate in the aggressive interaction. When flying back to its territory the male neighbor copulated with the territorial female on the ground (ie. EPC). The territorial male flew, vocalized, and perched above the male neighbor, interrupting the EPC. The aggressive interaction then ceased as each pair resumed foraging in their respective territories. These observations suggest that Rufous Horneros can use EPC to obtain immediate benefits (food access in a neighbor’s territory). Moreover, WPC may be detected by neighbors and physical mate guarding and/or frequent WPC may be necessary to prevent EPC in the Rufous Hornero.

First Description of Reproductive Behavior and Alternative Reproductive Strategy in the Deep-sea Fish, Careproctus pellucidus.

The reproductive biology of deep-sea fishes is largely unknown because of the difficulty of behavioral observations in this environment. In this study, the reproductive behavior of the deep-sea snailfish, Careproctus pellucidus, which lives at depths > 200 m, was observed in an aquarium. To the best of our knowledge, this is the first report to observe and describe the reproductive behavior of deep-sea fish under free-living conditions. Fishes were collected at a depth of approximately 300 m (36°70′ N; 141°00′ E) on July and August 2018 and kept for observation until March 2019. We observed that almost all spawnings took place between one male and one female. Males defended a spawning substrate against other males and exhibited body-wiggling behavior for both courtship and aggressive display. Females visited the male’s territory and spawned a demersal adhesive egg mass on the substrate. The territorial male then sought the spawned eggs using filamentous rays in the lower pectoral-fin lobe and released sperm when he located the eggs. Males remained near the spawning substrate after spawning but did not perform any parental care. Notably, sneaking behavior by a non-territorial male was observed in one case; this is the first report of this alternative reproductive strategy (or tactic) in a deep-sea fish. Our study reveals the unique reproductive biology of the deep-sea fish, C. pellucidus, which does not depend on visual information and uses other sensory modalities.

Spatial asymmetry of the paternity success in nests of a fish with alternative reproductive tactics

Guard-sneaker tactics are widespread among fish, where territorial males defend a nest and provide parental care while sneakers try to steal fertilizations. Territorials and sneakers adopt diverse pre- and post-mating strategies, adjusting their ejaculate investment and/or behavioural responses to the presence of competitors. The relative distance of competitors from the spawning female plays a major role in influencing male mating strategies and the resulting paternity share. However, territorial male quality and sneaking intensity do not fully account for the variability in the relative siring success occurring among species. An often neglected factor potentially affecting sneakers proximity to females is the nest structure. We conducted a field experiment using the black goby, whose nests show two openings of different size. We found that territorial males defend more and sneaking pressure is higher at the front, larger access of the nest than at the back, smaller one. Moreover, microsatellite paternity analysis shows that territorials sire more offspring at the back of their nest. Such a predictable spatial distribution of the paternity share suggests that nest structure might work as an indirect cue of male relative siring success, potentially influencing the territorial male investment in parental care and/or the female egg deposition strategy.

The influence of social-grouping on territorial defense behavior in the black-crested titmouse (Baeolophus atricristatus)

Status signals have evolved for individuals to avoid energetic and physical costs of resource defense. These signals reflect an individual’s competitive ability and therefore influence competitors’ decisions on how to invest in a fight. We hypothesized that the response of receivers to status signals will depend on the social context. During territorial defense, group members may provide support to a territory owner by participating in defense. We investigated whether the presence of juveniles—who group together with territorial males—alters the territorial male’s attack decisions and level of aggression in the black-crested titmouse (Baeolophus atricristatus). Crest-length in this species functions as status signal. We simultaneously presented two taxidermic male models in a territory: one with an unmanipulated crest and one with a modified shortened crest. Models were presented to males that had resident juveniles cohabiting on their territory, and to males without juveniles. During intrusions, juveniles actively defended against the simulated intruders by approaching and sometimes attacking. The presence of juveniles affected how territorial males responded to the status signals of the intruders: when juveniles were present, males were more likely to first attack the model with the unmanipulated crest (i.e., longer, and more threatening), compared to males residing without juveniles. This suggests that juvenile support alters the risk-taking decision of the territorial male. To our knowledge, this is the first indication that behavioral responses to a status signal depends on the presence of supportive group members. Significance statement Status signals can indicate relative quality of animals and can therefore be used to evaluate a competitor when deciding whether or not to fight over resources. The black-crested titmouse has been shown to use its crest length as a status signal during fights over food. In our study, we assessed if this status signal is also used in territorial defense, by conducting an experiment where we presented two taxidermic male models with different crest sizes to a territorial male. We also investigated whether juvenile presence influenced which model was attacked. In trials where juveniles were present, territorial males attacked the longer crested model significantly more often than in trials where territorial males were alone. This suggests that the presence of juveniles, which help the male defend the territory, allows the male to attack the more aggressive-appearing intruder.

Male song sparrows modulate their aggressive signaling in response to plumage signals: experiments with 3-D printed models

Competitive interactions among conspecifics are often resolved by assessing signals that honestly indicate individual fighting ability or dominance. In territorial species, signals of competitive ability are thought to function primarily during the early stages of territory establishment, but recent evidence suggests that these signals continue to influence interactions with floaters and neighbors well after territory establishment. Here, we examine the influence of the extent of chest spotting displayed by an intruding male on the response of territorial male song sparrows. We exposed males to 3-D printed models with large or small spotting area coupled with conspecific playback and recorded their behavior. We also assessed the response of a subset of males to both the 3-D printed models and a traditional, taxidermic mount to ensure the 3-D models were a realistic stimulus. We found no differences in the number of attacks or proximity to the model due to spotting area. However, territorial males produced more soft songs and tended to sing fewer loud songs, both of which predict attack in our population, in response to the model with less chest spotting. One possibility is that males with less chest spotting elicit a stronger response because they are seen as a greater threat. Based on our previous findings in this system, we think it is more likely that models with less chest spotting are perceived as subordinate and therefore easier to defeat, leading to a stronger response by territory holders. We found males were equally likely to attack 3-D printed models and a taxidermic mount but signaled more aggressively during trials with the taxidermic mount than the 3-D printed models. This suggests that birds recognized the 3-D models as meaningful stimuli but that the use of 3-D printed models should be validated through comparison to a traditional taxidermic mount when possible.

Dung-pile use by guanacos in eastern Patagonia

Previous studies on guanacos have reported that only territorial males create and maintain dung-piles. The aim of this analysis was to compare dung-pile use by territorial males with the use by females and young in family groups, and by bachelor males. Although territorial males showed the highest dung-pile use, all individuals dropped feces on piles frequently, in contrast to what was previously observed within other guanaco populations. Besides stressing the behavioral plasticity of guanacos, these results suggest an additional adaptive function of localized-defecation other than demarcating territory ownership by the territorial male.

Effect of territory intruders on the perceived quality of territorial males in an endangered pupfish, Cyprinodon bovinus

Social eavesdropping can guide mate choice and the assessment of competitor quality. In the endangered Leon Springs pupfish (Cyprinodon bovinus), males establish breeding territories that they defend from conspecifics and heterospecific egg predators. Females enter the breeding area to assess males and spawn in their territories. It was hypothesized that male and femaleC. bovinuseavesdrop on social interactions within male territories to evaluate each territorial male’s ability to exclude intruders and attract potential mates. Using a repeated design, a bottle containing either a femaleC. bovinus, a non-territorial maleC. bovinus, a swarm ofG. nobilis, or water was placed at the centre of a male’s territory. Territorial males received more spawns and females spawned more frequently per visit when a female stimulus was present. These results suggest that females eavesdrop to inform their mating decisions, but this may be limited to the assessment of extra-pair females within territories.