Balancing moult data by subsampling non-moulting birds prior to regression analysis
- Authors: Bonnevie, Bo T
- Date: 2010
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/448057 , vital:74694 , https://doi.org/10.2989/00306525.2010.517941
- Description: During the analysis of moult records from the SAFRING database it was found that for some datasets the records were not evenly distributed temporally and the proportion of moulting to non-moulting birds was not what would be expected from random sampling. In an attempt to balance these data, the records of non-moulting birds were subsampled with different sample sizes prior to moult regression analysis, and the resulting moult estimates were then compared. The results suggest that subsampling non-moulting birds such that they occur in the expected proportion to actively moulting birds, based on the duration of moult, provides the best estimates of moult.
- Full Text:
- Date Issued: 2010
- Authors: Bonnevie, Bo T
- Date: 2010
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/448057 , vital:74694 , https://doi.org/10.2989/00306525.2010.517941
- Description: During the analysis of moult records from the SAFRING database it was found that for some datasets the records were not evenly distributed temporally and the proportion of moulting to non-moulting birds was not what would be expected from random sampling. In an attempt to balance these data, the records of non-moulting birds were subsampled with different sample sizes prior to moult regression analysis, and the resulting moult estimates were then compared. The results suggest that subsampling non-moulting birds such that they occur in the expected proportion to actively moulting birds, based on the duration of moult, provides the best estimates of moult.
- Full Text:
- Date Issued: 2010
Regional patterns in moult and sexual dimorphism of adult Southern Red Bishops Euplectes orix in southern Africa
- Craig, Adrian J F K, Bonnevie, Bo T, Oschadleus, Hans-Dieter
- Authors: Craig, Adrian J F K , Bonnevie, Bo T , Oschadleus, Hans-Dieter
- Date: 2010
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/449503 , vital:74826 , https://doi.org/10.2989/00306525.2010.488357
- Description: Using the SAFRING database and the Underhill-Zucchini model of primary moult, we analysed the timing of wing moult in Southern Red Bishops Euplectes orix in relation to sex and geographical region. Birds from the winter rainfall region in the south-western sector of the Western Cape start the annual moult more than two months before any other population, but there were no significant differences in starting date within the summer rainfall region. There were striking differences in the estimates of moult duration (62–114 d), which did not follow a consistent pattern in relation to sex or geography; annual variation within a region may be an additional factor. Throughout southern Africa, both sexes showed a trend for longer-winged birds to take more time to complete their moult. We suggest that sex, geographical area and possible annual environmental variations may all influence the timing of moult in local populations. In this sexually dimorphic species, males are consistently longer-winged and heavier than females.
- Full Text:
- Date Issued: 2010
- Authors: Craig, Adrian J F K , Bonnevie, Bo T , Oschadleus, Hans-Dieter
- Date: 2010
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/449503 , vital:74826 , https://doi.org/10.2989/00306525.2010.488357
- Description: Using the SAFRING database and the Underhill-Zucchini model of primary moult, we analysed the timing of wing moult in Southern Red Bishops Euplectes orix in relation to sex and geographical region. Birds from the winter rainfall region in the south-western sector of the Western Cape start the annual moult more than two months before any other population, but there were no significant differences in starting date within the summer rainfall region. There were striking differences in the estimates of moult duration (62–114 d), which did not follow a consistent pattern in relation to sex or geography; annual variation within a region may be an additional factor. Throughout southern Africa, both sexes showed a trend for longer-winged birds to take more time to complete their moult. We suggest that sex, geographical area and possible annual environmental variations may all influence the timing of moult in local populations. In this sexually dimorphic species, males are consistently longer-winged and heavier than females.
- Full Text:
- Date Issued: 2010
Relative feather mass indices: are feather masses needed to estimate the percentage of new feather mass grown for moult regression models?
- Authors: Bonnevie, Bo T
- Date: 2010
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/448313 , vital:74721 , https://doi.org/10.2989/00306525.2010.455820
- Description: During the moult of primary wing feathers in birds it is likely that new feather material is being produced at an approximately constant rate if the energetic requirements of the birds are met. In moult regression analyses it is, therefore, desirable to transform moult measurements into a variable based on the amount of new feather material produced because of its linear properties. This can be achieved if the mass of each primary feather is known, and used as a weighting factor in a moult index. These primary feather masses would have to be known for every species being analysed. As an alternative, it is here tested if feather mass indices may be sufficient replacements for species-specific feather masses. Thirty-five species of birds with known primary feather masses were divided into four wing-shape groups, and a feather mass index was built for each group. Within each group, comparisons were made between estimates of moult parameters using the moult index with those using the known primary feather masses. Within groups there were no significant differences between any of the moult estimates.
- Full Text:
- Date Issued: 2010
- Authors: Bonnevie, Bo T
- Date: 2010
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/448313 , vital:74721 , https://doi.org/10.2989/00306525.2010.455820
- Description: During the moult of primary wing feathers in birds it is likely that new feather material is being produced at an approximately constant rate if the energetic requirements of the birds are met. In moult regression analyses it is, therefore, desirable to transform moult measurements into a variable based on the amount of new feather material produced because of its linear properties. This can be achieved if the mass of each primary feather is known, and used as a weighting factor in a moult index. These primary feather masses would have to be known for every species being analysed. As an alternative, it is here tested if feather mass indices may be sufficient replacements for species-specific feather masses. Thirty-five species of birds with known primary feather masses were divided into four wing-shape groups, and a feather mass index was built for each group. Within each group, comparisons were made between estimates of moult parameters using the moult index with those using the known primary feather masses. Within groups there were no significant differences between any of the moult estimates.
- Full Text:
- Date Issued: 2010
Timing of primary wing moult in sexually dimorphic passerines from the Western Cape, South Africa
- Bonnevie, Bo T, Oschadleus, Hans-Dieter
- Authors: Bonnevie, Bo T , Oschadleus, Hans-Dieter
- Date: 2010
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/448355 , vital:74724 , https://doi.org/10.2989/00306525.2010.455821
- Description: SAFRING ringing data was used to investigate the differences in the timing and duration of primary wing moult between males and females of sexually dimorphic passerines from the Western Cape, South Africa. In the sunbirds, weavers and canaries that were considered, the males generally started moult before the females, whereas this was not so for other species. In the species where males started moult before the females, the standard deviation of the start of moult was generally smaller in the males and the males generally took longer to moult. These differences in the patterns of moult are discussed in the context of differences in parental care between males and females of each species and within their taxonomic groups.
- Full Text:
- Date Issued: 2010
- Authors: Bonnevie, Bo T , Oschadleus, Hans-Dieter
- Date: 2010
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/448355 , vital:74724 , https://doi.org/10.2989/00306525.2010.455821
- Description: SAFRING ringing data was used to investigate the differences in the timing and duration of primary wing moult between males and females of sexually dimorphic passerines from the Western Cape, South Africa. In the sunbirds, weavers and canaries that were considered, the males generally started moult before the females, whereas this was not so for other species. In the species where males started moult before the females, the standard deviation of the start of moult was generally smaller in the males and the males generally took longer to moult. These differences in the patterns of moult are discussed in the context of differences in parental care between males and females of each species and within their taxonomic groups.
- Full Text:
- Date Issued: 2010
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