Right to Quiet Society Noiseletter
Winter 2013, page 2

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The early bird gets the worm

Embryonic Learning of Vocal Passwords in Superb Fairy-Wrens Reveals Intruder Cuckoo Nestlings

Highlights: Female superb fairy-wrens call to their eggs during late incubation; The call has a signature element later present in the nestling begging calls; Call similarity between mother and nestling calls is learned during the egg stage; Males and females detect foreign nestlings that do not emit the signature element.

Summary

How do parents recognize their offspring when the cost of making a recognition error is high. Avian brood parasite-host systems have been used to address this question because of the high cost of parasitism to host fitness. We discovered that superb fairy-wren (Malurus cyaneus) females call to their eggs, and upon hatching, nestlings produce

begging calls with key elements from their mothers incubation call. Cross-fostering experiments showed highest similarity between foster mother and nestling calls, intermediate similarity with genetic mothers, and least similarity with parasitic Horsfield's bronze cuckoo (Chalcites basalis) nestlings. Playback experiments showed that adults respond to the begging calls of offspring hatched in their own nest and respond less to calls of other wren or cuckoo nestlings. We conclude that wrens use a parent-specific password learned embryonically to shape call similarity with their own young and thereby detect foreign cuckoo nestlings.

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Grasshoppers Alter Their Courtship Song Around Traffic Noise

By Brett Smith for redOrbit.com - Your Universe Online

Males looking to find a mate are always trying to stand out, from peacocks' colourful plumage to the slightly fictitious profiles on Match.com. According to a newly published report in the journal Functional Ecology, scientists at the University of Bielefeld in Germany have found that male grasshoppers also try to stand out by altering their mating song when surrounded by a noisy urban environment. "We found that grasshoppers from noisy habitats boost the volume of the lower-frequency part of their song, which makes sense since road noise can mask signals in this part of the frequency spectrum," said study co-author Ulrike Lampe, from the university's Department of Evolutionary Biology.

While the effects of artificial noise on animal communication have been studied in the past, previous research has focussed on vertebrates alone. "Bow-winged grasshoppers are a good model organism to study sexual selection because females can respond to male courtship songs with their own low-frequency acoustic signal, if they are attracted to a male song," Lampe said. The bow-winged grasshopper (Chorthippus biguttulus) is a widespread species across Central Europe, with adults establishing their presence between July and September in the region's grasslands. The average grasshopper is about 0.6 inches long and they can vary in colour from green to red or purple.

Lampe and her colleagues caught 188 male bow-winged grasshoppers, half of which were taken from quiet locations and the other half from beside busy roads. The team then studied the two groups' courtship songs in the laboratory after exposing them to a female grasshopper.

The grasshoppers produced their song by running a toothed file on their hind legs along their front wings, causing them to vibrate. The typical song consists of two short phrases, two or three seconds long that increase in amplitude towards the end. The insect begins the phrase with slower ticking sounds that gradually increase in speed and amplitude, becoming a buzzing sound towards the end of the phrase.

After analysing almost 1,000 recordings of their grasshoppers, the German research team found that grasshoppers that had lived beside noisy roads produced different songs than their more rural counterparts. The grasshoppers from noisy environments had boosted the levels of their songs in the 6 to 9 kHZ range that coincides with low-frequency road noise that could disrupt their songs. "Increased noise levels could affect grasshopper courtship in several ways," Lampe said. "It could prevent females from hearing male courtship songs properly, prevent females from recognizing males of their own species, or impair females' ability to estimate how attractive a male is from his song."

In their report, the scientists said that future studies could work to determine if the difference in songs is due to "a more permanent mechanism for signal adjustment" or a change in behaviour, "which was found in different bird species adjusting to high background noise levels." Those more permanent mechanisms include determining if the grasshoppers begin to adapt to noise during their larval stage and if genetic differences play a role in the adaptation.

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A concept worth pondering and implementing

With regards to creating quiet neighbourhoods, I still think the best would be to talk one's town or city into zoning at least one section of their community for "quiet living". After the stunning increase in popularity through good citizenship, "me too"-towns would start popping up everywhere. - C. Daniels



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Entire contents 2013 Right to Quiet Society. Cartoon, 1996, Right to Quiet Society


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