Pūkeko (Porphyrio melanotus)

Aileen Sweeny

Ph.D. Student, School of Biological Sciences, The University of Auckland, New Zealand

  Fig. 1.  Banded adult Pūkeko at the study site in Auckland, New Zealand. Photo credit Aileen Sweeney.

Fig. 1. Banded adult Pūkeko at the study site in Auckland, New Zealand. Photo credit Aileen Sweeney.

The Australasian swamp hen is known by its native Maori name “Pūkeko” in New Zealand. This brightly coloured rail (Fig. 1) is found throughout Oceania, having first arrived in Australia around 600,000 years ago (Garcia-R & Trewick, 2015). New Zealand, however, is one of its more recent conquests, with estimates of self-colonisation (from Australia) between 500-1000 years ago (Trewick & Worthy, 2001; Worthy & Holdaway, 1996). Pūkeko are found throughout New Zealand in a range of habitats, however they favour open grass areas near vegetated water systems (Dey & Jamieson, 2013). The endemic and endangered Takahē (Porphyrio hochstetteri) is closely related to the Pūkeko and, interestingly, this flightless bird is believed to have evolved from a previous colonisation of New Zealand by a Porphyrio species ~2.5 million years ago (Garcia-R & Trewick, 2015).

Pūkeko are one of the few native New Zealand species which haven’t experienced significant population declines since the introduction of two major contributors to ecosystem change: agriculture and invasive species. Indeed not only have Pūkeko been unaffected by these changes, they have proliferated in response to them, to the point that they are often regarded as a pest (Dey & Jamieson, 2013). Unlike endemic New Zealand species, Pūkeko evolved in the presence of a variety of terrestrial marsupial predators in Australia and therefore exhibit appropriate anti-predator behaviours (Jamieson, 1994). For this reason, they generally thrive in habitats where introduced predators such as brushtail possum (Trichosurus vulpecula), stoat (Mustela ermine) and rats (Rattus spp.) are present (Bunin & Jamieson, 1995).  

  Fig. 2.  Adult Pūkeko displaying its frontal shield. Photo taken during the banding process. Photo credit Aileen Sweeney.

Fig. 2. Adult Pūkeko displaying its frontal shield. Photo taken during the banding process. Photo credit Aileen Sweeney.

Pūkeko have complex social structures. Generally, they live in polygynandrous groups (both, males and females have multiple mating partners), which defend a shared territory (Craig, 1980). They do, however, show considerable inter-population variability in their mating systems and may also be monogamous, polyandrous or polygynous (Jamieson, 1997, 1999). Both sexes can be highly philopatric, which is unusual in avian species (Craig & Jamieson, 1988). Within these social groups, adults form mixed-sex dominance hierarchies which influence access to reproductive opportunities (Craig, 1980; Jamieson & Craig, 1987) as well as non-sexual resources (Craig, 1977). Males and females are morphologically very similar (low sexual dimorphism) and both sexes have a bright red fleshy frontal shield (figure 1 & figure 2). This ornament acts as a “badge of status” and its color is correlated with dominance (Dey, Dale, & Quinn, 2014; Dey, Quinn, King, Hiscox, & Dale, 2017). It is likely that the color is carotenoid-based, given that carotenoids are common components in red, orange and yellow ornaments in other animals (Goodwin, 1984). Similarly, as it is found for the frontal shields of the closely related moorhen (Gallinula chloropus), it is likely to be testosterone-mediated (Dey et al., 2017; Eens, Van Duyse, Berghman, & Pinxten, 2000).

One of the most intriguing facts about Pūkeko is that they are cooperative breeders, meaning that the entire group contributes to raising chicks regardless of parentage (Craig, 1980). Cooperative breeding is rare in avian species; only 8.9% of non-marine bird species are known to engage in this breeding system (Jetz & Rubenstein, 2011). When there is more than one reproductive male and reproductive female in a Pūkeko group, chicks are always of mixed parentage (Lambert, Millar, Jack, Anderson, & Craig, 1994). Furthermore, if there are multiple breeding females present in a group they all lay in a single nest, a phenomenon known as joint-laying (Craig, 1980; Vehrencamp & Quinn, 2004). Females typically lay 4-6 eggs each, meaning that clutch sizes of up to 18 eggs in a single nest can be observed when multiple females lay together (Dey & Jamieson, 2013) (figure 3). Interestingly, conspecifics in Australia have not been reported to exhibit joint-laying, which suggests that this behaviour has evolved relatively recently in New Zealand populations (Dey & O’Connor, 2010).

  Fig. 3.  Pūkeko nest containing 17 eggs. Note the varying patterns on the eggs. Photo credit Aileen Sweeney.

Fig. 3. Pūkeko nest containing 17 eggs. Note the varying patterns on the eggs. Photo credit Aileen Sweeney.

Joint-laying is a puzzling behaviour as it can lead to intragroup conflict due to the fact that hatching success decreases with increasing total clutch size (Dey, O’Connor, & Quinn, 2014; Quinn, Haselmayer, Dey, & Jamieson, 2012). However, no such conflict appears present in Pūkeko despite the fact that dominant females experience a reproductive cost when a subordinate breeding female is present (Dey, O’Connor, Balshine, & Quinn, 2014; Quinn et al., 2012). There are two possible reasons for this: first, there is an apparent lack of egg recognition in individuals, despite the fact that eggs have distinctive colouring/patterning that is unique to each female (making it relatively easy for researchers to identify separate clutches within a single nest) (Craig, 1974; Quinn et al., 2012). If females are unable to distinguish between eggs then the risk of accidentally ejecting or destroying their own egg is high. Secondly, males have been shown to decrease their incubation investment, occasionally to the point of complete nest abandonment, in response to female-female competition, and so it can be assumed that the threat of this may influence females to tolerate co-breeders (Dey, O’Connor, Balshine, et al., 2014). It is interesting to note that territory size, and therefore quality, is correlated with the number of males present in a group (Craig & Jamieson, 1990). A breeding female benefits from having access to a higher quality territory, which therefore means having more than one breeding males present. However, breeding males benefit from having more than one breeding female present as it increases their potential reproductive output. As such, this may also explain the presence of joint-laying in Pūkeko (Vehrencamp & Quinn, 2004).

Having previously worked with primates, I enjoy referring to Pūkeko as feathered baboons; they are noisy, aggressive, territorial, and have social ranks within their groups. Due to their complex and variable social structure, Pūkeko are excellent models for examining cognition and social learning in the wild. Cognition can be defined as “the acquisition, processing, storage and use of information”, and cognitive abilities allow animals to adjust their behaviour in response to new situations (Shettleworth, 2010). Traditionally, it has been studied almost exclusively in the lab, however studying cognition in the field has become more common in recent years, providing numerous benefits including reduced stress, ecologically relevant settings and a wider array of species (Pritchard, Hurly, Tello-Ramos, & Healy, 2016). There have been fascinating results emerging from recent cognition studies on wild bird populations (for examples please refer to: Cauchard, Angers, et al., 2017; Cauchard, Doucet, Boogert, Angers, & Doligez, 2017; Preiszner et al., 2017), and therefore there is huge potential for further research in this field. My research interests encompass establishing any potential relationships between cognitive ability, dominance, testosterone and ornamentation. The project is still in its early stages (designing and trialling experiments, as well as banding/PIT tagging individual birds), but I have no doubt that the coming years will uncover new insights into these rails, and indeed - hopefully - into animal cognition in general.

About the Author

Aileen Sweeney is a Ph.D. student in the School of Biological Sciences at The University of Auckland in New Zealand. She is co-supervised by Dr Kristal Cain and Dr Gregory Holwell. Hailing from Ireland, she spent time researching Vervet monkey (Chlorocebus pygerythrus) and Kinda baboon (Papio kindae) behaviour in South Africa and Zambia before emigrating to New Zealand. Her Ph.D. is focused on Pukeko behaviour, specifically their cognition and social learning in relation to dominance, testosterone and ornamentation.



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