Abstract
Same-sex pair bonds have been documented in several animal species and they are widespread in birds. However, little is known about the evolutionary origin and the adaptive value of such behaviour. The aim of this study was to investigate the parental behaviour of four zoo female greater flamingos involved in two breeding pairs, housed in a flock at Parco Natura Viva, Italy. Further, the behaviour of the study females was compared with that of male and female flamingos in heterosexual pairs described in a previous published work on this same flock. For each pair, the behaviour of both birds during the incubation period was recorded and twenty 10-minute sessions were run within the incubation period. A continuous focal animal sampling method was used to collect data on location (on the nest or not on the nest) and the parental care behaviour (e.g.: agonistic behaviours toward disturbing conspecifics, egg-care, nest-building, self-comfort behaviour, sleeping) of the two pairs. Data of the current study females were compared with those of females and males involved in heterosexual pairs of this same flock. Results showed that within each pair the egg-layer female stayed away from the nest more than the other female. In addition, the female that did not lay an egg was more involved in agonistic behaviour compared to other females, particularly when in specific locations. In heterosexual pairs, male flamingos were more involved in the incubation and in nest protection. Moreover, no significant differences in the time spent on the nest and away from the nest between the heterosexual male and the non-layer females of same-sex pairs were found. The same findings were reported when comparing heterosexual females and the egg-layer females of the same-sex pairs. Therefore, our findings suggest that in greater flamingos the behaviour of the female–female pairs seems to be equivalent to that of male-female bonds. Such research provides more insight into flamingo social behaviour, and their reproductive cycle, and provides information on why pair bonds may form and how these affect the wider breeding behaviour of the flock.
Highlights
Despite the variety and widespread presence of same-sex sexual behaviour in animals, little is known about the evolutionary origin and, at least in some cases, the adaptive value of such behaviour (Bailey & Zuk, 2009)
The current study focused on the parental behaviour of two female–female pairs of zoo greater flamingos (Phoenicopterus roseus)
Our findings suggest that during the incubation period female flamingos involved in same-sex pairs displayed behavioural patterns similar to those of males and females involved in different-sex pairs (King, 1994; Shannon, 2000; Brown & King, 2005; Sandri et al, 2017b)
Summary
Despite the variety and widespread presence of same-sex sexual behaviour in animals, little is known about the evolutionary origin and, at least in some cases, the adaptive value of such behaviour (Bailey & Zuk, 2009). Explanations for same-sex sexual behaviour rely on both proximate mechanisms, such as genetic, neurological, hormonal and social foundations of same-sex interactions and the adaptive significance of this phenomenon (Bailey & Zuk, 2009). In socially monogamous species, such as the Laysan albatross (Phoebastria immutabilis), female–female pairings share parenting responsibilities, incubating the eggs and rearing the chicks, faring better than unpaired females (Bailey & Zuk, 2009). No differences in the fledgling mass growth between different pairs were found, suggesting that same-sex behaviour could be a better alternative to postponed breeding or raising chicks alone (Jankowiak et al, 2018)
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