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20 Cards in this Set
- Front
- Back
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Bowerbirds
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Family Ptilonorhynchidae
Artists of the bird world |
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General features
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* No pair bonding
* Male- maintains a bower or court to display to female, dispersed throughout habitat. * Not nests, only 4 courting * Females check a number of males and mate with one or two * Females do all nesting and chick rearing on their own |
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Males attract females
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*Well const bower
*Colorful decorations (natural and man made) inside bower * Singing and dancing * some 'paint' bower |
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Spp in SE QLD
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Regents Bowerbird
Satin bowerbird Green catbird |
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Green and spotted catbirds
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(Ailuroedus crassirostrisand A. melanotis)
• Don’t build bowers • Long-term socially monogamous pairs that defend territories • Minimal courtship behaviour • Loud cat/baby like call |
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Sexual selection
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• = a form of selection that occurs when individuals differ
in their reproductive success due to either –Genes coding for traits that increase their ability to compete for mates with others of their sex (intrasexual selection), or –genes coding for traits that increase their ability to attract mates of the opposite sex (intersexual selection ** BOTH in bowerbirds females choose males and males compete with each other be destroying e/o bowers |
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Why are female bowerbirds so
choosy about which male they mate with? |
• Direct benefits of mate choice –female bowerbirds don’t get any; males don’t provide them with a territory or food or help with parental care
• Indirect benefits of mate choice -‘Good genes model’ suggests that males’ characteristics and/or displays provide information to females about the quality of their genes • Females that mate with the best males may –get genes for their offspring that improve the survival of the offspring and/or –get genes for their sons that will cause the sons themselves to become attractive males and get lots of matings |
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Bowerbirds are model species for investigation of multiple signals in mate attraction
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• In some species one sex (usually the male) uses multiple signals to attract the other sex
• Eg., bowerbirds build and decorate bowers, perform visual and auditory displays, and paint their bowers (possible chemical signal) • Such multiple signals show that processes of mate choice can be very complex • Why do some animals communicate with multiple signals? 2 HYPOTHESES |
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Multiple messages hypothesis
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the different signals are providing different information to the receiver (e.g., providing different information about the quality of the male)
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Redundant signals hypothesis
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the different signals convey the same information but the redundancy increases the chance that the female will really get the message
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Satin bowerbirds: intensive research on patterns of female mate choice
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• by Dr. Gerry Borgia and his group at Wallaby Creek in northern NSW
• by my group at the Bunya Mountains |
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First study of the factors affecting mating success of male satin bowerbirds
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• Study done at Wallaby Creek in NSW by Borgia
• Video cameras placed at each bower and triggered by infra-red beams • Bower characteristics and types of decorations were recorded daily • Bowers were considered high quality if were symmetrical, had thin straight sticks, sticks were packed closely and walls were thick |
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Strong skew among males in male mating success, thus strong sexual selection
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see graph
Some types of decorations significantly correlated with male mating success ie) yellow leaves, blue feathers and snail shells |
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How do females check out males?
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• Females appear to closely inspect about 3-4 males in a
breeding season but usually mate with 1 or maybe 2 • They may check out some bowers/males at a distance and reject them without a closer look • Females inspect some bowers more closely early in mating season before they begin nest-building • Longer visits to same bowers later in the season after nest building begins; some of these end in matings |
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Our study at the Bunya Mountains
(Robson and Goldizen) |
• Do males use different signals for different purposes (multiple messages?)
• How do males attract females to their bowers for closer inspection? • Which male signals make females decide to mate with them once the females have inspected the males and their bowers closely? • Are these two goals accomplished with different signals? |
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Factors that predicted the number of females that VISITED a male
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• Bigger males got more visits
• Males that did more “solitary displays”got more visits • Males with more natural white and blue decorations got more visits |
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Factors that predicted the numbers of COPULATIONS that males achieved
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• Factored out female visitation rate
• Bigger males got more matings • But painting rate was the strongest predictor of male mating success |
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What is painting in bowerbirds?
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• Males chew up plant material, mix it with saliva, and paint it on inside walls of their bower
• On average over 1⁄4of inside walls of bowers is covered with dried paint • Females visiting a bower often nibble at the paint on the walls • Evidence suggests that paint has to be fresh to act as a signal and that the signal may be a chemical one |
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Age-related changes in female
satin bowerbirds’ mate choice patterns |
• Males’ displays were experimentally manipulated by
adding extra blue decorations to some bowers • Males were selected randomly to be either control or experimental males –half were experimentals(given extra blue things), half were controls • Looked at mate choice decisions of females of different ages • 1 and 2 year old females were much more likely to mate with experimental than control males, whereas 3+ year old females weren’t • Suggests that younger females base their mate choice decisions largely on males’ decorations, whereas older females judge males differently, perhaps on their displays |
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Male-male competition formatings in satin bowerbirds (intra-sexual selection)
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• Males steal each others’ decorations
• Males that steal a lot are also stolen from a lot • Hard to distinguish whether stealing is driven by benefit to male of gaining decorations (inter-sexual selection) or by benefit of reducing the competitiveness of other males (intra-sexual selection) • Males also damage other males’ bowers (definitely intra- sexual selection) |
