Incubation temperatures and sex ratios in Australian brush-turkey (Alectura lathami) mounds

Abstract Megapodes are exceptional among birds because they use external heat sources for incubating their eggs. In Australian brush-turkeys (Alectura lathami), this source is the heat produced by microbial decomposition in mounds of leaf litter. A recent laboratory study showed that artificial incubation of eggs at different temperatures affects the sex ratio of brush-turkey hatchlings. Here, this phenomenon is confirmed for eggs incubated in natural incubation mounds. Eggs from which females hatched were found at significantly higher incubation temperatures in the mounds (mean 33.7°C) than those from which males hatched (mean 32.9°C). Also, sex ratios of chicks from individual mounds were significantly correlated with mean incubation temperatures in those mounds. Furthermore, incubation temperatures differed significantly between incubation mounds during the same month of the year. Within some mounds, incubation temperatures differed up to 9°C between eggs, in others this difference was only up to 1°C. These latter results show that males differ in their ability to maintain stable incubation temperatures. While the effect of incubation temperatures on sex ratio is a novel discovery for any bird, it was previously suggested that incubation temperatures in megapodes also affect embryo mortality and chick survival. These combined effects of incubation temperature, and the limited ability of males to provide optimal temperatures, seem to provide answers to the question why so few birds have adopted this unusual mode of reproduction – a question asked by many behavioural ecologists and evolutionary biologists.8 page(s

Juvenile dispersal and habitat selectivity in the megapode Alectura lathami (Australian Brush-turkey)

Dispersal and habitat selectivity of young precocial birds is usually determined by parents, as these lead their chicks after hatching. Megapode chicks receive no parental care and little is known about factors determining their dispersal and habitat selectivity. Here, we present such results for the Australian brush-turkey (Alectura lathami). Chicks were radio-tracked in two small remnant rainforest patches (Mary Cairncross Rainforest Park and Aplin Forest) from their second day of life and for up to 30 days. At Mary Cairncross Rainforest Park, the median dispersal distance was significantly affected by age, as it decreased from approximately 100 m on each of the first five days to around 50 m per day thereafter. At Aplin Forest, age had no significant effect on dispersal. The difference between the two sites can be explained by incorporating habitat selectivity. Chicks preferred to stay in thickets and avoided the more open rainforest, as evident from time selectivity indices calculated for both habitats. At Aplin Forest, 31% of the area was covered by thickets, such as lantana (Lantana camara) and raspberry (Rubus ssp.), whereas at Mary Cairncross Rainforest Park this proportion was only 6%. Management plans for endangered megapodes should consider the role of thickets in the chicks' dispersal behaviour, and thus in population spread, recolonisation and gene flow.6 page(s

Ontogeny of social behaviour in the megapode Alectura lathami (Australian Brush-turkey)

Megapodes meet conspecifics at an unpredictable age, and it is unknown how their social behavior develops under such conditions. The authors induced encounters between 2-day-old socially naive hatchlings and up to 49-day-old chicks of the Australian brush-turkey (Alectura lathami) in a large outdoor aviary. All social behavior patterns found in older chicks were present in hatchlings and did not change in form or the frequency in which they occurred thereafter; the frequency of calling was the only feature that changed significantly with age. Chicks stayed only 0.3–2.0 m (medians) apart and synchronized their feeding activity from the age of 20 days. These results indicate that megapode chicks show social behavior without social experience and that this requires no postnatal learning.8 page(s

Social responses without early experience: Australian brush-turkey chicks use specific visual cues to aggregate with conspecifics

Almost all birds depend upon early experience with adults and siblings to learn recognition cues. Megapodes, such as the Australian brush-turkey (Alectura lathami), have evolved a very different life history. Eggs are incubated in mounds of decaying organic material. Chicks hatch asynchronously and receive no parental care, so imprinting cannot occur. Nevertheless, chicks subsequently form groups with similar-aged conspecifics. We explored the perceptual basis of this aggregation response, focussing on likely visual cues, such as pecking movements and body colour. Experiments were conducted under naturalistic conditions in a large aviary, using realistic robot models and colour filters. The robots successfully evoked a range of social responses resembling those of a live companion. Aggregation depended upon both behaviour and morphology. Simultaneous choice tests revealed that brush-turkey chicks preferred a pecking robot over either a static model or a scanning robot, suggesting that responsiveness depends upon particular movement patterns. In addition, chicks were sensitive to changes in appearance but only those that affected radiance at short wavelengths. The mechanism underlying social aggregation after hatching hence involves relatively specific cues. This perceptual bias seems to be largely experience independent and may exploit attributes to which potential predators are insensitive.10 page(s

Egg size predicts motor performance and postnatal weight gain of Australia Brush-turkey (Alectura lathami) hatchlings

Birds usually influence offspring survival through the amount of parental care they provide. Megapodes have evolved a different life history. Eggs are incubated by external heat sources, and chicks dig themselves out of their underground nest and live independently of their parents. Egg size is one of the few means by which females can influence chick survival. We found that in the Australian Brush-turkey, Alectura lathami Gray, 1831, eggs and hatchlings varied considerably in size, with a ratio of 1.62 between the largest and the smallest egg. Egg size was positively correlated with hatchling body mass and tarsus length. It also significantly predicted the chicks' motor performance: chicks from larger eggs dug their way out of their underground nest faster and were more active when kept in a resting box and monitored by motion detection software. The main advantage of reaching the surface more quickly is likely that such chicks will have more time to find suitable food, refuge, and a tree for roosting at night while still feeding on their internal yolk reserves. Egg size also interacted significantly with body mass during the first 10 months of life. A size advantage at hatching thus seems to have an immediate effect on motor performance and a longer term effect on the ability to gain mass.8 page(s

Call recognition in chicks of the Australian brush-turkey (Alectura lathami)

Most birds rely on imprinting and experience with conspecifics to learn species-specific recognition cues. Australian brush-turkeys (Alectura lathami) do not imprint and form no bonds with parents. They hatch asynchronously, disperse widely and meet juvenile conspecifics at an unpredictable age. Nevertheless, in captivity, hatchlings respond to other chicks. A recent study, which involved the use of robotic models, found that chicks prefer to approach robots that emit specific visual cues. Here, we evaluated their response to acoustic cues, which usually play an important role in avian social cognition. However, in simultaneous choice tests, neither 2-day-old nor 9-day-old chicks preferred the choice arm with playback of either chick or adult conspecific calls over the arm containing a silent loudspeaker. Chicks of both age classes, however, scanned their surroundings more during chick playback, and the response was thus consistent in younger and older chicks. We also presented the chicks with robotic models, either with or without playback of chick calls. They did not approach the calling robot more than they did the silent robot, indicating that the combination of visual and acoustic cues does not evoke a stronger response. These results will allow further comparison with species that face similar cognitive demands in the wild, such as brood parasites. Such a comparative approach, which is the focus of cognitive ecology, will enable us to further analyse the evolution and adaptive value of species recognition abilities.8 page(s