Groups Of Finches Research Articles

Foraging rate versus sociality in the starling Sturnus vulgaris.

It is well established that social conditions often modify foraging behaviour, but the theoretical interpretation of the changes produced is not straightforward. Changes may be due to alterations of the foraging currency (the mathematical expression that behaviour maximizes) and/or of the available resources. An example of the latter is when both solitary and social foragers maximize rates of gain over time, but competition alters the behaviour required to achieve this, as assumed by ideal free distribution models. Here we examine this problem using captive starlings Sturnus vulgaris. Subjects had access to two depleting patches that replenished whenever the alternative patch was visited. The theoretical rate-maximizing policy was the same across all treatments, and consisted of alternating between patches following a pattern that could be predicted using the marginal value theorem (MVT). There were three treatments that differed in the contents of an aviary adjacent to one of the two patches (called the 'social' patch). In the control treatment, the aviary was empty, in the social condition it contained a group of starlings, and in a non-specific stimulus control it contained a group of zebra finches. In the control condition both patches were used equally and behaviour was well predicted by the MVT. In the social condition, starlings foraged more slowly in the social than in the solitary patch. Further, foraging in the solitary patch was faster and in the social patch slower in the social condition than in the control condition. Although these changes are incompatible with overall rate maximization (gain rate decreased by about 24% by self-imposed changes), if the self-generated gain functions were used the MVT was a good predictor of patch exploitation under all conditions. We discuss the complexities of nesting optimal foraging models in more comprehensive theoretical accounts of behaviour integrating functional and mechanistic perspectives.

THE MITOCHONDRIAL AND NUCLEAR GENETIC HOMOGENEITY OF THE PHENOTYPICALLY DIVERSE DARWIN'S GROUND FINCHES.

The most extensively studied group of Darwin's finches is the genus Geospiza, the ground finches, and yet little is known about the evolutionary history and genetic relationships of these birds. Studies using either allozyme or morphological data have been unable to resolve relationships between the six species and numerous populations of ground finches. In this paper we report the results of a study using mitochondrial control region and nuclear internal transcribed spacer (ITS) 1 sequence data. The differentiation of the ground finch species based on morphological data is not reflected in either mitochondrial or nuclear DNA sequence phylogenies. Furthermore, there is little concordance between the mitochondrial haplotypes and ITS alleles found within individuals. We suggest that the absence of species-specific lineages can be attributed to ongoing hybridization involving all six species of Geospiza. There are no long term selective pressures against hybridization within this genus, and therefore a genetically homogenous genus may be maintained indefinitely. Hybridization has apparently played a role in the adaptive radiation of Darwin's finches.

Molecular Phylogenetics of Finches and Sparrows: Consequences of Character State Removal in CytochromebSequences

The complete mitochondrial cytochromebgenes of 53 genera of oscine passerine birds representing the major groups of finches and some allies were compared. Phylogenetic trees resulting from three levels of character partition removal (no data removed, transitions at third positions of codons removed, and all transitions removed [transversion parsimony]) were generally concordant, and all supported several basic statements regarding relationships of finches and finch-like birds, including: (1) larks (Alaudidae) show no close relationship to any finch group; (2)Peucedramus(olive warbler) is phylogenetically far removed from true wood warblers; (3) a clade consisting of fringillids, passerids, motacillids, and emberizids is supported, and this clade is characterized by evolution of a vestigial 10th wing primary; and (4) Hawaiian honeycreepers are derived from within the cardueline finches. Excluding transition substitutions at third positions of codons resulted in phylogenetic trees similar to, but with greater bootstrap nodal support than, trees derived using either all data (equally weighted) or transversion parsimony. Relative to the shortest trees obtained using all data, the topologies obtained after elimination of third-position transitions showed only slight increases in realized treelength and homoplasy. These increases were negligable compared to increases in overall nodal support; therefore, this partition removal scheme may enhance recovery of deep phylogenetic signal in protein-coding DNA datasets.

Let's keep the APGAR score in perspective

The complete mitochondrial cytochromebgenes of 53 genera of oscine passerine birds representing the major groups of finches and some allies were compared. Phylogenetic trees resulting from three levels of character partition removal (no data removed, transitions at third positions of codons removed, and all transitions removed [transversion parsimony]) were generally concordant, and all supported several basic statements regarding relationships of finches and finch-like birds, including: (1) larks (Alaudidae) show no close relationship to any finch group; (2)Peucedramus(olive warbler) is phylogenetically far removed from true wood warblers; (3) a clade consisting of fringillids, passerids, motacillids, and emberizids is supported, and this clade is characterized by evolution of a vestigial 10th wing primary; and (4) Hawaiian honeycreepers are derived from within the cardueline finches. Excluding transition substitutions at third positions of codons resulted in phylogenetic trees similar to, but with greater bootstrap nodal support than, trees derived using either all data (equally weighted) or transversion parsimony. Relative to the shortest trees obtained using all data, the topologies obtained after elimination of third-position transitions showed only slight increases in realized treelength and homoplasy. These increases were negligable compared to increases in overall nodal support; therefore, this partition removal scheme may enhance recovery of deep phylogenetic signal in protein-coding DNA datasets.

The effect of group size on vigilance and feeding rate in spice finches (Lonchura punctulata)

We investigated group-size effects on individual vigilance levels and feeding rates in captive groups of spice finches (Lonchura punctulata). The "many-eyes" hypothesis predicts a reduction in vigilance levels in larger groups that can cause higher feeding rates if the time thus saved is used for foraging. We adopted a within-subject procedure whereby in each of six replicates we observed one adult male searching for food in groups varying in size from one to five. As predicted, vigilance levels decreased with group size up to four birds but increased in groups of five. Birds also collected seeds more quickly in larger groups, reflecting (i) a decrease in vigilance levels in larger groups, (ii) a decrease in handling time, and (iii) an increase in search speed. Nearest neighbour distances were smaller in larger groups, a potential confounding factor in the analysis of vigilance time. Although the results are partly consistent with the many-eyes hypothesis, we suggest that the arrow of causation from vigilance to feeding time could be reversed: the increase in feeding rates in larger groups, with a concomitant decrease in vigilance levels, would be caused by increased competition.

Population variation and hybridization: Comparison of finches from two archipelagos

Some populations of Darwin's Finches (Emberizinae) are exceptionally variable in body size and beak traits as a result of introgressive hybridization. A study of museum specimens of honeycreeper-finches (Carduelinae) from the Hawaiian islands was undertaken to see if the same phenomenon was manifested by a different phyletic group of finches in a different archipelago. Five hundred and twenty-four specimens of the seven species with finch-like bills were measured and their coefficients of variation were compared with those of the ground finch group (six species) of Darwin's Finches. Coefficients were smaller in the Hawaiian finches. Sympatric and, hence, potentially hybridizing species on the island of Hawaii were not consistently more variable than the allopatric species on other islands in the archipelago. The one species with both sympatric and allopatric populations did not show greater variation in the sympatric population. There is little evidence from these comparisons of hybridization occurring in the last 100 years. The difference between the two finch faunas can be explained in terms of two factors. Finches have been present for a longer time in the Hawaiian archipelago than in the Galapagos archipelago and have had more time to not only diversify but to evolve pre- and post-zygotic isolating mechanisms. In the generally less seasonal and floristically richer Hawaiian islands they have evolved greater dietary specializations. Beak traits adapted to specialist feeding may have been under stronger stabilizing selection and hybrids (if formed) may have been at a strong disadvantage in the absence of an ecological niche intermediate between the niches of the two parental species. Results of published electrophoretic studies of genetic variation suggest that the early phase of differentiation, involving occasional introgressive hybridization, may last for up to 5 million years.

Chromosomal evolution within the family Estrildidae (Aves) III. The Estrildae (waxbill finches)

The C- and G-banded karyotypes of five species of waxbill finches belonging to the Estrildidae were examined. Extensive chromosomal variation including inversions and fissions was found to differentiate the species, showing the waxbills to be the most chromosomally diverse group of estrildid finches. None of the variation, however, matched that recorded in related species of Pytilia (Christidis, 1983). By comparing the G-banded karyotypes of species belonging to all three estrildid lineages it was possible to reconstruct the presumed ancestral karyotype for the Estrildidae as a whole. This was found to approximate the karyotype of the Australian peophilid species, Poephila guttata most closely. From it chromosomal relationships within the three estrildid lineages, Poephilae, Lonchurae, Estrildae, can be determined.

The Morphological Identification of Domesticated Zebra Finches, Poephila-Guttata (Passeriformes, Estrilidae), in Australia

The zebra finch, Poephila guttata, is a native Australian grassfinch which is used extensively in laboratories of many countries, including Australia. We have compared the morphology of groups of zebra finches from various origins: (1) wild-caught from a population at Bunbartha in northern Victoria; (2) their first-generation offspring which were bred in captivity; (3) fawn colour morphs; (4) white colour morphs; (5) a private collection which included a variety of colour morphs. Birds in groups 3,4 and 5 were considered to be the distant offspring of wild-caught zebra finches. The length of the wing, the head and the tarsus, the width and the depth of the bill, and the weight were measured. All characters, except the width of the bill, differed significantly among the groups. Analyses of variance indicated that head length, tarsus length and bill depth differed significantly between group 1 and groups 3, 4 and 5, but were not significantly different between groups 1 and 2 nor among groups 3,4 and 5. The wild-caught birds and their immediate offspring were larger than those of the colour-morph groups. Discriminant analysis showed that wing length, tarsus length and bill depth were important in classifying individuals into groups. Differences between groups were attributed to the effects of domestication upon birds in aviaries.

The influence of differences in social experience on the development of species recognition in zebra finch males

Zebra finch males were first raised by zebra finch parents and then placed in a group of Bengalese finches between the ages of 30 and 60 days. A higher number of aggressive as well as non-aggressive initiatives by Bengalese finches towards young zebra finch males during this period was correlated with a more Bengalese-finch-directed sexual preference when these males were given a choice between a zebra finch and a Bengalese finch female as adults. Experiments in which a zebra finch male was exposed to Bengalese finches behind a wire screen or to Bengalese finch models gave corresponding results. The study shows that, in contrast to earlier findings, zebra finch males raised by their parents for 31 days can still develop a preference for Bengalese finches. Short term changes in preference are discussed. The results indicate that the behaviour shown by stimulus birds in studies on ‘sexual imprinting’ is important for the development of sexual preferences.

“String-pulling” in birds. (2) differences related to age in greenfinches, chaffinches and canaries

Groups of finches were tested in the “string-pulling” situation. Success in this situation varied according to the species, age and experience of the birds tested, and was related to the length of time spent responding to the string and/or bait. The results raise a number of questions which are discussed in a preliminary manner. They suggest (i) that internal inhibition in Pavlov's sense is unstable in young birds and (ii) that the process of development from the unstable type of inhibition found in younger birds to the more stable type found in older birds may depend on experience as well as age.