MagazineR944

The male European starling iswell known for its diverse rangeof song phrases, some of whichhave sometimes beenrecognizably poached from thoseof other species and even fromanthropogenic sources: it is notentirely unusual to hear the oddtelephone ringtone or car alarmamongst their complex songs.There’s evidence that the widerange of the bird’s song phrasesprovide an indication of a male’soverall quality and is the subjectof sexual selection amongstfemales. It is thought this isbecause the development of theneural pathways of songproduction and learning developearly in life and may be sensitiveto developmental stresses.

Experiments have shown thatnutritional stress duringdevelopment can lead to areduced song range in adultmales. But could other factorsalso contribute to the adult males’final repertoire? Out of thebreeding season, starlings mostlyforage in groups in which a socialhierarchy develops involvingaggressive encounters betweenindividuals. From other studies itis known that such encounters

can lead to raised levels of stresshormones. But the relationshipbetween stress hormones anddevelopmental stress is not clear,so a team of researchers haveexamined a group of captivestarlings for evidence of a linkbetween, nutrition, social andhormonal status and songrepertoire.

K.A. Spencer, K.L. Buchanan,A.R. Goldsmith and C.K.Catchpole of the Universities ofCardiff, Bristol and RoyalHolloway, University of London,report in the Proceedings B of theRoyal Society of London(published online) work with agroup of captive birds. Forty-eight juvenile starlings were heldin four groups of twelve animals.Two groups were held under anunpredictable food supply, withthe other two provided withunlimited food. In each group thedominance hierarchy wasdetermined and the effect ofnutritional stress and social rankon song complexity investigated.

When they examined theresults, they found that birdsunder nutritional stress producedsmaller song repertoires thanthose with unlimited access to

food. However, they also foundthat males of more dominant rankproduced larger repertoires thanthose of lower rank in all thecages. Social status was notrelated to individual weight,testosterone levels or stresshormone levels. And birds undernutritional stress maintained abody mass no lower than controls.

The results suggest that birdsof lower social rank may incur acost potentially due to limitedaccess to food or reduced abilityto practice their song.

The authors warn that becausethe birds were captive,aggressive encounters may havebeen heightened but their resultssuggest that female’s keennesson the range of her potentialmate’s song may not only give anhonest indication of his nutritionalhistory but that of his past socialstatus too.

‘This study is, to ourknowledge, the first to show theeffects of developmental stresson repertoire size in a bird with asexually selected song structure.It has also uncovered a possiblelink between social status duringdevelopment and song quality,’the authors say. Males, therefore,may be singing for more than justtheir supper with their complexsongs.

Low down on the singing

On the line: The diversity of a male starling’s wide song repertoire appears to be a signal of his nutritional stress and socialstatus during development which may form the basis of a sexually selected trait amongst potential female mates. Starlingsgather in large groups outside the breeding season, shown here. (Photograph: Oxford Scientific Films.)