White-crowned Sparrow Males Unruffled by Younger Rivals

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In the territorial world of nature, it’s not uncommon for older males to give way to the younger generation, albeit with a fight. Researchers have recently discovered that this is not necessarily the case with mature white-crowned sparrow males. In fact older males don’t even bother to get involved in any altercation, verbal or physical, and this is seen as evidence that they don’t view younger males as a threat.

In the study, which was carried out by Angelika Poesel and Douglas Nelson of the Ohio State University and funded by the National Science Foundation, it was noted that the older male would, however, become agitated and aggressive upon hearing a rival bird of the same age in his territory. It appears that the males of this species assess the fighting ability of their opponents based on age, and younger males simply don’t scare them.

The study observed a migratory population of white-crowned sparrows nesting in Bandon, Oregon, from 2008 to 2011. While plumage is an important indicator of maturity, the results of the study reveal that some birds use each other’s songs to determine age and threat level. As is the case with many bird species, male white-crowned sparrows use their songs to establish nesting territory and court a potential mate. Should a male sing in another’s territory, he can expect to be attacked and driven off if perceived to be a threat. With this particular bird species, second-year males do have plumage differences, but they also sing two or more versions of their species unique song before they choose one, and abandon the rest. This multiple version singing indicates to more mature males that the bird singing in his territory is a second-year male, and not a threat worth getting ruffled feathers about.

The research was carried out by playing various songs through loudspeakers within the established territories of mature males, and careful observation of the birds’ behavior. It was noted that second-year males that have established territory, did not tolerate other second-year males invading their space. It is thought that female birds are naturally more attracted to mature birds than to younger ones, and the older birds know this. Also, younger birds are disinclined to push their luck with a mature male which is likely to be stronger and more experienced.

Lead author of the study, Angelika Poesel, is curator of the Borrer Laboratory of Bioacoustics. Douglas Nelson is associate professor of evolution, ecology and organismal biology, and director of the University’s Borrer Laboratory.

Rose-breasted Grosbeak (Pheucticus ludovicianus)

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The Rose-breasted grosbeak or as it is scientifically called, Pheucticus ludovicianus, is about 7.25 inches long and has a large, cone shaped, pale colored bill. The female grosbeak looks similar to the female-plumaged Black-headed grosbeak but has an orange-brown breast with streaks only on the side of its body. The Grosbeak lives near open woodlands that are near to water. It also likes thick brush or small trees, large trees, marsh borders, gardens, parks and overgrown pastures.

The adult male Rose-breasted Grosbeak has a rose red, triangular shape patch on its white breast. The upper parts of its body and head are all black and the under parts are white. The wings have white patches and are lined with rose red. His black tail feathers are speckled with white spots. In winter and autumn the male becomes browner and dull in colour. The juvenile bird has a similar coloring to the male’s winter and autumn colour.

The adult female Grosbeak has black and white stripes on its crown above its eyes. The under parts of the bird are white with extensive streaking, whereas the upper parts are a dark grey. Where the male has a rose red lining the female has a more yellow to yellowish-orange wing lining. The juvenile has an orangey-brown breast and the juvenile female has similar coloring to the adult female.

The Grosbeak mating system is monogamous and so the male and female will pair off and have between three to five pale green, blue eggs. During the courtship the male will fly after the female while singing to her; he will then crouch down and spread and droop his wings; spread his tail, withdraw his head with his nape against his back; once in position he will start singing and waving his head and body in an erratic dance.

The cup-shaped nest is made up of loose twigs, rough plant material and then lined with thin twigs, hair and rootlets. The nest is normally 5-15 feet above the ground and is built by the female with help from the male Rose-breasted Grosbeak. The incubation of the eggs takes up to two weeks and will be looked after by both the male and female bird. The development of the chicks is altricial, which means that they are immobile and eyes closed. Once the young hatch it takes just less than two weeks before they will leave the nest.