Development and behaviour of hatchlings of the Australian Brush-turkey Alectura lathami
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Megapode (Family Megapodiidae) hatchlings are the most precocial of all avian species. Upon emergence from the incubation site, they receive no parental care and must survive on their own. Due to their advanced stage of development at hatching, megapodes have been described as ‘superprecocial’, occupying one extreme of the altricial-precocial spectrum. Such abilities have given rise to questions regarding the innate skills of megapode hatchlings. However, there have been very few comprehensive studies conducted on the hatchlings, which are difficult to observe in the wild because of their cryptic colouring and their immediate dispersal from the incubation site. I studied the eggs and hatchlings of the Australian Brush-turkey, Alectura lathami, in southern Queensland, in order to provide a greater understanding of the development, behaviour and morphological changes over the first 200 days of life. Eggs for this study were excavated from mounds located in Brisbane suburban areas and artificially incubated at Griffith University. The eggs were weighed and measured regularly, as well as candled using a hand-held torch. Hatchlings were kept in aviaries and measurements were taken at regular intervals. There was a significant trend for egg weights to progressively decrease between the 1993-94 and 1997-98 breeding seasons, which may have been due to either unfavourable environmental conditions or the natural variation between different laying females. The mean mortality rate of hatchlings in this study was between two and four times those recorded in previous studies. This may have been due to a combination of the higher tendency of suburban mounds to fail and the unnatural stresses caused by excavation and transportation. A useful outcome from the candling measurements was a reliable method for ageing Brush-turkey embryos based on the changes in appearance of the chorioallantoic membrane. A regression graph was constructed to enable the prediction of the hatch date of embryos. The graph was tested in the 1997-98 breeding season and the date of hatching predicted by the regression consistently underestimated the actual hatch date by a mean of three days. Brush-turkey hatchlings lost weight immediately after hatching, a trend previously observed in other megapode species. The growth rate of Brush-turkey hatchlings during the first 25 days was similar to or greater than Malleefowl, Leipoa ocellata, and Maleo, Macrocephalon maleo, hatchlings of the same age, but significantly slower than Domestic Chickens, Gallus gallus. The megapode is viewed as a ‘specialised’ galliform, having extended the phasianid incubation period and producing superprecocial hatchlings that have developed in the egg for a further four weeks. Previous descriptions of megapode moult have been made using limited numbers of museum specimens. A detailed schedule of wing, tail and body moult was constructed using measurements of live individuals. Megapodes hatched in juvenile plumage and had more advanced primary and secondary feathers than newly hatched Domestic Chickens. Wing moult proceeded in a periodic stepwise manner. A ‘gap’ was observed between the primary and secondary feather sets, in which a feather emerged when the hatchling was several days old. A possible function of this ‘gap’ could be as a carpal remex to assist in vertical flight or the feather may simply be a late-emerging secondary feather. The stage of head and body moult could be used to age juveniles up to 200 days. The first detailed descriptions of hatchling postures and behaviours were compiled from observations in captivity. Hatchling foraging behaviour resembled that of adults and was observed from the second or third day after hatching. The movement of live food appeared to be an important food recognition cue and may provide a learning experience to develop efficient foraging abilities. Similarly, drinking was a learned behaviour, brought about by pecking at objects floating on the water surface. Daily activities were synchronised between hatchlings, particularly foraging and resting periods. There was no evidence from this study of the antisocial tendencies of hatchlings. In fact, younger individuals were seen perching in relatively close proximity to one another. Staged pair-wise encounters indicated the existence of a dominance hierarchy in a group of hatchlings. The hierarchy was based upon a combination of the sex and age of the chick, with the largest and oldest male and female hatchlings at the top and the much younger hatchling at the bottom. This most likely represents the situation in the wild when individual hatchlings randomly encounter each other. Domestic Chickens are known to imprint on moving objects and it may be expected that megapode hatchlings, having descended from a galliform ancestor, would also possessthat ability. Standard imprinting procedures were used to investigate the following response and preference for familiar over novel stimuli. Control experiments using Domestic Chickens also served as a statistical comparison. The Domestic Chickens showed significant following responses and preferences for the stimulus object, whereas the Brush-turkey hatchlings did not follow or show any preference for the stimulus object. These results indicate Brush-turkey hatchlings do not possess the ability to imprint upon a moving object in the same way as a Domestic Chicken. Experiments using video images and actual stimuli were conducted to examine the visual predator recognition abilities of the Brush-turkey hatchling and any associated responses. There were no significant differences between the behaviours observed before and after the presentation of the stimuli, whether it was predator or non-predator, moving or non-moving. The hatchlings did not respond with any escape or avoidance behaviours, instead maintaining normal activities, such as feeding, scratching or resting. This suggests that Brush-turkey hatchlings do not have an innate mechanism to respond to the visual presence or movement of a potential predator.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Australian School of Environmental Studies