Comparative aspects of the thermal biology of African and Australian parrots.
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Date
2006
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Abstract
Deserticolous birds inhabit an environment characterised by high ambient temperatures and low
rainfall that has low primary productivity. The combination of these factors may lead to the
evolution of adaptations that minimise food and water requirements. One physiological
adaptation that has been found in many deserticolous birds is the reduction of basal metabolic
rate (BMR).
I measured metabolic rate in the laboratory using four species of African lovebirds
(Agapornis) , and four species of Australian grass parakeets (one Neopsephotus and three
Neophema), all similar in body mass. Tests for differences between groups were carried out
using both conventional and phylogenetically independent methods. The BMRs of the lovebird
and grass parakeet species were not statistically correlated with habitat type. These results
confirm the findings of previous studies on the effect of desert conditions on the BMR of parrots.
I also found no significant differences in BMR between the species assemblages from different
continents. The lack of significant differences in BMR between deserticolous and nondeserticolous
parrots supports the idea that birds are "ex-adapted" to living in desert
environments. I suggest that the results may have been affected by phenotypic plasticity in BMR,
as recent evidence has shown that the scaling exponent of BMR differs between captive-raised
and wild-caught birds.
To elucidate the effect of origin (captive-raised vs. wild-caught) on the BMR of birds
used in this study a large scale analysis of bird BMR data was undertaken. BMR and body mass
data for 242 species of birds were obtained from the literature, this study, and unpublished data
from various sources. A phylogeny was constructed using molecular and morphological
phylogenies from the literature, and analysed using conventional and phylogenetically
independent methods. The conventional analysis found significant differences in the scaling
exponents of BMR of captive-raised and wild-caught birds. However the phylogenetically
independent method showed non-significant differences between these two groups. Conventional
analysis of differences between parrots and all other birds yielded significant differences
between these two groups, with parrots having significantly higher BMRs than other birds.
Again the phylogenetically independent analysis found non-significant differences between these
VII
two groups. A test of homogeneity of variance between these two groups found significant
differences between the variances ofthe two groups, probably due to disparity in sample size and
range of body sizes. The conventional and phylogenetically independent tests for differences
between captive-raised and wild-caught parrots yielded non-significant results, suggesting that
the parrots are not subject to the phenotypic adjustments postulated for all other birds.
The lack of significant differences between captive-raised and wild-caught parrots
suggests that the analyses of differing habitat type for African and Australian parrots is indeed
valid.
Description
Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2006.
Keywords
Parrots., Thermobiology., Desert ecology., Birds--Arid regions., Parrots--Ecology., Parrots--Physiology., Parrots--Africa., Parrots--Australia., Lovebirds--Africa., Neophema--Australia., Birds--Physiology., Captive wild birds., Basal metabolism., Theses--Zoology.