Surprising and familiar

The pied butcherbird and the art of composing

pied butcherbird, male. V. Nunn

A clever composer is able to grip the audience with variations, but without presenting music that is a confusing chaos. The pied butcherbird masters that art too, as Eathan Janney and colleagues report.

A piece of music with more variety in it is more pleasing to listen to. But it should not be too surprising: the piece must remain recognizable as a unit. In order to maintain consistency, a composer will repeat parts of the music and take care that themes can be heard several times.

In this respect, the beautiful singing pied butcherbird can compete with a good composer, according to research done by Eathan Janney and colleagues.

The black and white bird, slightly smaller than a magpie, lives in Australia where it is the most accomplished song bird with a very complex song. The bird may sound like a flute, a cornet or organ; hence the name. Males can sing continuously for hours at night. Their song consists of hundreds of clear phrases which take about two and a half second. After each phrase they wait a few seconds before they proceed.

Motifs

Janney wondered if they, just as composers, keep a balance between novelty and repetition. That would be important to prevent habituation in female listeners while at the same time the bird remains identifiable as an individual. He studied the nocturnal solo songs of 17 birds. He divided the phrases of each bird in types and investigated how often and in what order he sang each type. Also, he discerned motifs; a motif is a single tone or a group of a few tones (syllable) that often recurs. Several types of phrases may share a same motif. Finally, for each bird he investigated how he arranged his phrases and motifs. Was there any structure in the temporal patterning?

The singing of the birds is well organized, the analysis shows. Types of phrases and particularly motifs were regularly spaced in time. That regularity arises, as the researchers show, because a performing bird orders the different types of phrases in such a way, that each motif is heard at constant time intervals.

Large repertoire

The birds differ greatly in the amount of variation in their song. Some birds have more types of phrases and more different motifs in their repertoire than others. The more variety, the greater the risk that the song as a whole will be incoherent. But, as it turns out, the birds with the most different phrases and motifs organized their song more strictly. The larger the repertoire is, the stronger the temporal regularity with which the motifs are repeated. The birds seem to actively maintain the balance between variety and regularity – just like a good composer.

Willy van Strien

Photograph: Pied butcherbird male. Vicki Nunn (Wikimedia Commons, Creative Commons CC BY-SA 4.0)

An accomplished performer can be heard on this video of the researchers
Hear another record of the song

Source:
Janney, E., H. Taylor, C. Scharff, D. Rothenberg, L.C. Parra & O. Tchernichovski, 2016. Temporal regularity increases with repertoire complexity in the Australian pied butcherbird’s song. Royal Society Open Science 3: 160357. Doi: 10.1098/rsos.160357

Fly trap

Parachute flower smells like a tasty bee in distress

ceropegia-sandersonii-alzheimer1

Flowers of the African parachute plant are deceivers, as Annemarie Heiduk and colleagues show. The flowers mimic the smell of honeybees that are caught in the jaws of a spider. Their volatiles attract flies that feed on the fluids that such unhappy bees excrete. These flies pollinate the flowers.

Many plants have their flowers pollinated by insects. The insects take up pollen from one flower they visit and leave some of it on the pistil of the next flower, that can then grow seeds. And in return, most plants offer their pollinators nectar as a reward.

Clumps of pollen

But not all plants are honest plants. Some lure their pollinators with false promises of a reward.

A sophisticated deceptive plant is the African parachute plant Ceropegia sandersonii, a climbing herb from southern Africa, as Annemarie Heiduk and colleagues reveal.
Its pollinators are Desmometopa-flies. They visit the flowers and disperse the pollen, but not voluntarily. The flower is a trap where they go into. Downward pointing hairs on the flower wall make it impossible for them to get out. Clumps of pollen (pollinaria) within the flower dislodge and stick to their mouthparts.

Only the next day, when the flower withers, the flies are able to escape, packed with pollen. In the flower that they enter next, they will deposit the pollinaria unwittingly on the right place.

The question arises: how is it that the flies can be tricked time and again? Now, Heiduk answered that question: the flower smells like their food.

Volatiles

The flies, especially the females, need protein and they derive it from honeybees. They can’t overpower a honeybee by themselves, as they are much smaller. But when a spider has caught one, they come and feed on the fluids that leak from the dying bee. They find such a bee as they detect compounds that are released from its mandible glands and sting glands when it tries to defend itself by biting or stabbing. Also, they detect the pheromones that the bee releases to alert conspecifics.

Heiduk analysed the blend of volatiles dispersed by the flowers of the parachute plant, and found that many components are identical to the compounds that are released by bees in agony. This blend of volatiles is unique among flowering plants, and clearly adapted to lure the flies. Upon detection, they approach the flower, expecting to find a helpless bee. They find nothing of the kind, however, but are imprisoned for a time and meanwhile serve the plant. For free.

Willy van Strien

Photograph: Ceropegia sandersonii. Alzheimer1 (via Flickr. Creative Commons BY-NC-SA 2.0)

Nasty video: a honeybee is hold by a spider and licked by Desmometopa-flies

Source:
Heiduk, A., I. Brake, M. von Tschirnhaus, M. Göhl, A. Jürgens, S.D. Johnson, U. Meve & S. Dötterl, 2016. Ceropegia sandersonii mimics attacked honeybees to attract kleptoparasitic bees for pollination. Current Biology, online October 6. Doi: 10.1016/j.cub.2016.07.085