Space for a song
Geoff Sample is a field recordist, natural history author (Harper Collins) and sound artist (BBC radio), with a special interest in birdsong and the cultural history of hearing music in nature.
Fig. 1 The British warblers by Grönvold Henrik, 1907
1. On a walk / singing together
It’s mid-January and a gorgeous winter day, absolutely calm under a big blue sky, though frosty out of the sun. We’re walking down the inland margin of the sand dunes of Druridge Bay in Northumberland, when we become aware of a soft, massed twittering emanating from a few hawthorn bushes ahead of us. As expected, it’s soon revealed to be a group of 30-40 linnets song-basking, their breasts lit up by the low-slung winter sun like candle-lights on a Christmas tree. They sound as one, with no individual voice discernible in the ensemble, though each is respectfully distanced from its neighbours.
I’ve come to think of this as flock song, also sometimes referred to as communal song or corporate song , probably more widely familiar from starlings at a roost - though starlings also gather during the day and sing synchronously. Here I find yet again that I’m troubled by short-comings in the usual (traditional) explanation of why birds sing, the stock answer for what birdsong is all about, sometimes referred to as the dual function hypothesis. It’s based largely on the singing behaviour of male songbirds in temperate habitats: birds sing to defend a territory and attract a mate.
It’s not that I disagree with this dual function theory: I know it’s valid in a deep-seated, evolutionary way, but there’s so much it doesn’t explain. The group singing, just mentioned of linnets and starlings, occurs in a range of families from finches, hirundines (swallows, house martins) and thrushes (redwing, fieldfare) to waders (golden plover, dunlin) and ducks (display with the equivalent of song). While sexuality may subtley infuse much animal social behaviour like this, such examples of flock song seem intuitively to convey little demand for individual territory. And I think it’s the territorial aspect that troubles me more, partly because it corresponds too easily with the particularly human institution of private property, and partly because there are various other modes of singing where the urge for territory also appears to play little part.
My path here follows the concepts and terminology used in research on bird song: the words and phrases used to frame and interpret the data are so often influential in an overview of a subject area in nature. It’s important since bird song is often considered to provide an analogue for comparison with human communication and has wider implications in the interpretation of animal social behaviour. 
2. Territorial aggression
Furthermore some bird species are far more territorial than others: finches are a good example of this. While chaffinches are strongly territorial in their breeding, in other finches like goldfinch, siskin, redpoll and linnet (which used to be referred to as cardueline finches) such behaviour is less pronounced. And it’s worth noting that while chaffinch males sing fairly short stereotyped songs (rigid patterns), male song in these other species is looser and more meandering. Bullfinch males hardly show any territorial behaviour at all; and while some might argue they don’t really have a song, they certainly do sing, usually very softly, and have an exceptional ability to learn a tune.
A bullfinch trained to sing German folk tunes.
Desmond Nethersole-Thompson, a keen observer of bird behaviour, has this to say about crossbills (another finch species): ‘A desire for aloneness, rather than orthodox territorialism, motivates many fierce fights, but the division between these two impulses is narrow … Increasing desire for isolation and a continuous defence of the hen, rather than of territory, inspires the fighting’ [when flocks break up].  While largely a matter of emphasis, I find the idea of personal space, with space for the song giving space for the self, more fitting than a cry for real estate.
The antagonism and competitive confrontations of territorial behaviour also change over time: so while individual males may behave aggressively towards each other when establishing territories at the beginning of the breeding season, this tends to decline between established neighbours as breeding proceeds. Researchers have begun referring to this as the ‘dear enemy’ effect.  I think this roughly equates with the aphorism ‘better the enemy you know’. But notice use of the term ‘enemy’: the later context might just as well be framed as singing to maintain the status quo between neighbours. And in many cases (including skylarks) the males of territorial species gather into more or less coherent flocks outside the breeding season.
There is also a variety of quiet song that gets lumped together as ‘subsong’, and not just from younger birds; this is far more ubiquitous than we are generally aware, simply because it is so quiet and easily missed.  It’s probably most widely noticed from blackbirds and robins in gardens and parks outside of the breeding season, in autumn and winter: I’m not sure what bird song paradigm this kind of singing fits.
While recognition of territorial behaviour in birds goes back a long way (Aristotle mentions eagles’ need for space), Birkhead suggests in his history of ornithological science  that the study of bird behaviour (encompassing such territoriality) is fairly recent and was not initially accepted as proper ornithology by the ‘professionals’ of the time. Following Edmund Selous’ lead in observational field studies, it was Eliot Howard who proposed the central role of territoriality in a bird’s breeding behaviour with the publication of Territory in Bird Life in 1920.  Howard was born to a propertied family in the West Midlands, owners of their own business, one of the largest steelworks in the UK, of which he became a director: much of the fieldwork for his first book The British Warblers (1907-14) was pursued on his own estate by the side of the river Severn and this fed into his work on territory.
My understanding is that until the second half of the 20th century independent means were generally necessary for the study of ornithology, as indeed with so much of academic education and scientific enquiry. Either that or one needed a wealthy patron.
The palaeontologist and essayist Stephen Jay Gould has argued that science never quite achieves the objectivity it strives for, but is always influenced by the social context and prejudices of the time, ‘yet stumbling in its erratic path towards a better understanding of nature’.  Certainly, the idea of territory as exclusive property harmonised neatly with the cultural outlook of Howard’s contemporary naturalists and continues to appeal.
3. And anthropomorphism
In many ways song is an ideal territorial signal; the sound needs physical space to exist, to resonate in, and is significant for as far as it can be heard. It might be said to own the space: and certainly territorial males respond strongly to another male singing too close to them, or their mate. But even the most territorial of male song is a displacement of the urges driven by competition and lust into a less combative and less potentially damaging activity than fighting, which may be a real indicator of territorial aggression. To a large extent, song has evolved as a successful aspect of territorial behaviour because it helps avoid the damaging consequences of physical confrontation: in this respect, it might be considered a medium of negotiation and exchange.
A certain amount of anthropomorphism seems inherent in describing the behaviour of other species - all our conceptualisation is determined by our human minds and expressed through our human language. But we need to be self-aware of this to the next level and consider how much this projects onto bird behaviour human traits, whose framing may be highly culturally biased.
In recent decades other analytical frameworks have been emerging in the study of bird song.  One exciting area is the idea of social networking, which puts more emphasis on listening and communication - (though again we find ourselves following contemporary preoccupations!).  Considering the operation of bird song as social network communication is an important shift in its scope, taking account of listeners’ reactions, eaves-dropping, broadcasting and meme sharing, rather than merely the layout of one-to-one competition in the case of males, and one-to-one attraction in the case of females.
‘Eaves-dropping’ has also emerged as a significant concept here, again emphasising the role of listening in the communicatory process; whether there is an immediate reaction in the listener, or it contributes in a small way to some future decision, listening, including eaves-dropping, is an important part of the flow of activity in the network. In our social media, friends and followers are all an important part of the picture, contributing in small ways to the flow of communication, by liking something or not, commenting or not, or just lurking, taking it all in for future reference.
While maybe the role of territory in bird song has been overstated, the social behaviour of birds remains a fascinating field to map against our own, with all the benefits and dangers of anthropomorphism. In line with the idea of communication networks, I do wonder if something like ‘social status’ may be a more useful concept than ‘territory’ in gaining a wider understanding of the currency of bird song.  Quality of song buys status. Through their song, each of those linnets singing in the hawthorns on Druridge Bay becomes truly part of the flock.
 Armstrong, E. (1963). A Study of Bird Song. Oxford University Press.
 Catchpole, C.K. & Slater, P.J.B. (1995). Birdsong - biological themes and variations. Cambridge University Press. p94.
 Bolhuis, J.J. & Everaert, M. eds. (2013). Birdsong, Speech and Language - exploring the evolution of mind and brain. M.I.T.
 Nethersole-Thompson, D. (1975). Pine Crossbills. T & A D Poyser
 e.g. Briefer, E., Rybak, F. & Aubin T. (2008). When to be a dear enemy: flexible acoustic relationships of neighbouring skylarks, Alauda arvensis. Animal Behaviour 76: 4 pp 1319-1325
 Dabelsteen, T., McGregor, P.K., Lampe, H.M., Langmore, N.E. & Holland, J. (1998). Quiet song in song birds: an overlooked phenomenon. Bioacoustics 9, 89-105.
 Birkhead, T. (2008). The Wisdom of Birds. Bloomsbury.
 Howard’s works retain a kind of charisma and his original warblers volumes, with colour and photogravure plates by Henrik Grönvold, are now valued collectors’ items. The full text and illustrations to Territory in Bird Life can be accessed here.
 e.g. in Piltdown Revisited. Gould, S.J. (1980) The Panda's Thumb. Norton.
 Burt, J.M. & Vehrencamp S.L. Dawn chorus as an interactive communication network. In: McGregor, P.K., editor. (2005). Animal communication networks. New York: Cambridge University Press. p. 321–343
 Fitzsimmons, L.P., Foote, J.R., Ratcliffe, L.M., & Mennill, D.J. (2008). Eavesdropping and communication networks are revealed through playback and an acoustic location system. Behav. Ecol. 2008 19: 824-829.
 Bird species that perform at leks are particularly interesting in this respect. Groups of anything up to 30 male black grouse gather daily at traditional sites to perform in competitive displays: individual males tend to pair up to size up against each other in sound, posture and moves, in a kind of ritualised mock combat (that occasionally, and only occasionally, breaks out into a real fight). After the lek the birds head off to feed sometimes individually, sometimes associating with each other; but the performance is over and all antagonism is dissipated. The objective at the lek is to hold a place in the central area, since when the females visit they tend to mate with the male at the centre. The central stance has become a kind of symbolic breeding territory.