White-crowned Sparrow Males Unruffled by Younger Rivals

March 13, 2012 by  
Filed under News

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.

New Research into Bird Song

August 20, 2010 by  
Filed under Features

While zebra finch females utter single note, low-pitched calls, males have the ability to sing in a variety of frequencies, even producing a whistle that goes beyond a piano keyboard’s high end. Male birds make use of song to attract mates and to protect their territory. It is believed that the varied frequency of songs may be more attractive to females, as well as providing greater and more precise information.

The two variables affecting the pitch of a bird’s song are air pressure and muscle activity. Recent research has revealed that muscle activity plays the larger role in this respect. This study was conducted by Tobias Riede of the National Center for Voice and Speech (under the administration of the University of Utah), as well as Franz Goller, and John H. Fisher. Funding for the research was provided by the National Institutes of Health.

The zebra finch’s vocal organ is called the syrinx, and measures a mere one-eighth of an inch on either side. It was already known, through past studies, that male zebra finches had larger vocal muscles controlling the syrinx than did the females. In this study the cartilage scaffold, which supports the bird’s syrinx, as well as the “labia” (the part that oscillates when air moves through it) in the syrinx, were investigated. This revealed that the male finch’s cartilage scaffold is larger, while the labia are a different shape to that of the female. Riede concluded that this must be so that the labia can be tensioned tightly by the muscles that pull the scaffold, so as to reach the high-frequency notes.

The researchers sought to study whether lung pressure or vocal muscle strength was the more important factor in the control of the male zebra finch’s pitch. They began by recording the sounds of six male finches and six female finches for a period of two weeks. Tubes containing air pressure sensors were implanted into an air sac. Specially designed equipment ensured that the birds could continue to fly and sing freely whilst measurements were taken and their sounds recorded again. The results showed that higher air pressure lead to higher pitch, indicating that lung pressure does affect song frequency.

Following this experiment, the researchers cut the nerves that control the birds’ vocal muscles. They then recorded the birds’ sounds as they sang and flew about. It was noted that the pitch of all birds dropped to approximately the same level and males were unable to produce high frequencies. The fact that they could no longer put sufficient tension on the labia showed that the vocal muscles play a key role in bird song pitch.

Nightingale’s Journey Provides Valuable Migratory Information

July 20, 2010 by  
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While being fairly nondescript in appearance, the nightingale is legendary for its amazing singing ability, which can often be heard at night, as well as in daylight hours. The name nightingale literally means ‘night songstress’ revealing the misconception early writers had that it is the female that produces the complex range of trills, whistles and gurgles, when in fact it is the male. It has long puzzled researchers as to where exactly in Africa these migratory birds spent the northern hemisphere’s winter months. Now thanks to technological advances, it has been possible for scientists in Norfolk to track a single nightingale’s 3,000 mile migratory journey, thereby providing invaluable information that will hopefully assist in halting the decline in numbers of this fascinating bird.

In April 2009, scientists from the British Trust for Ornithology (BTO) captured a male nightingale near Methwold Hythe in Norfolk and fitted it with a geolocator – a tiny device for tracking the bird’s position. This new technology has proven to be vastly superior in providing accurate information as compared to the method of ringing birds which has been used for decades prior to this. The information gathered helps scientist not only to examine threats to the wellbeing of breeding birds in their home territory, but also to evaluate whether migratory destinations of the birds are impacting negatively on their numbers.

Codenamed OAD, the nightingale left its home territory in Norfolk on July 25, 2009, arriving in southern France in mid-August. By September, OAD had arrived in northern Morocco, where it remained for around three weeks. The nightingale continued on to the Western Sahara, where it appeared to stop for a while before continuing to Senegal in November, and from there to Guinea Bissau where it remained until returning to Norfolk in February 2010. Due to the locator failing, the exact route of the return journey is not known, nevertheless it was captured by researchers about 50 yards from the spot where it was initially found in April 2009.

No doubt, the information gleaned from OAD’s epic journey will be of great value to BTO as they continue their work of understanding the pressures faced by birds migrating to Africa.

Bird Breeding

February 9, 2009 by  
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Bird breeding generally begins as the daylight hours of summer increase. Territorial behavior becomes evident with males selecting and defending their territory by means of singing and flight displays. Territories vary in size depending on availability of food and requirements of birds breeding in the area. When a female enters a male’s territory she may be threatened by him as if she were another male. However, she will not fight back or fly away if she is ready to mate, and copulation will take place.

The first eggs are usually laid the day after the breeding pair completes the nest. Eggs may be laid daily or on alternate days, even up to five day intervals depending on the species. For the breeding of birds to be successful, the eggs must be incubated. The parents transmit heat to the eggs by means of brood spots (bare patches on underbelly with many blood vessels). Eggs are turned as often as 12 times an hour and incubation periods vary according to species. When they hatch, some chicks are completely dependent on their parents, these are called altritial. Others are able to run and feed themselves immediately, and these are called precocial.

Many people are interested in finding out about bird species breeding in their area. Studies are conducted and breeding bird atlases are produced which will provide this information. If for example you would like to find out about a British bird’s breeding habits, you would consult a breeding bird atlas for Britain.

The basic concepts discussed above also apply to breeding birds in captivity. For example, when breeding love birds it is important that they receive the correct amount of sunlight so as to stimulate breeding. Breeding love birds can be done in aviaries or individually in bird breeding cages. Bird breeding cages must have enough space for the birds to move around comfortably and continue with normal behaviour. Ensure that breeding pairs are fed properly so that they remain in good condition and that the eggs will not have defects. Once the young hatch, they too require suitable nutrition.

Breeding, whether in captivity or in the wild, is vital for the continuation of bird species and our continued pleasure in these beautiful feathered creatures.

Golden Eagle (Aquila chrysaetos)

February 9, 2009 by  
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The Golden eagle’s scientific name is Aquila chrysaetos and it is part of the Booted or True Eagle family. These beautiful birds can be found throughout the northern hemisphere, living in prairie coulees, mountainous areas and in rugged terrains that create a profuse amount of updrafts.

The golden eagle is about 3 feet or just under a metre, weighing about 15 pounds or 7 kg’s and has a wingspan of about 7 feet or 2 metres. The colour of the eagle is a dark yellowish brown and the bird can live between fifteen and twenty years.

The golden eagle’s territory is in remote areas where it lives a solitary life even through winter. This great hunter, hunts in a large territory that can be up to 162 square miles or 260 square km in size. Due to its expertise in hunting it’s not very often that you will see it eating carrion. The golden eagle eats a wide variety of small animals like the marmots, groundhogs, snakes, pheasants, rabbits, cats, foxes, skunks, grouse, ground squirrel, meadowlarks, crows and tortoises.

The golden eagle will start mating at the age of four years and will stay paired with the same mate for as long as it lives. Occasionally they build their nest in a tree but prefer to nest on cliff faces or in rocky crags, returning every year to the same nest. The female golden eagle will lay between one to three eggs once every year and will do the majority of the 41 to 45 day incubation of the eggs. The male golden eagle’s job is to regularly supply the female with food and together they share the responsibility of looking after and raising the young. When the eaglets are first born they weigh about three ounces and will stay in the nest between nine to eleven weeks before they fledge.

Depending on the territory of the golden eagle, they will either live in their nesting territory throughout the year, or if there is a lack of food in winter, they will migrate a short distance away because of their excellent hunting abilities.

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