Territorial

Songbirds are usually most vocal in early Spring. Lengthening daylight hours bring the additional solar power that powers the growth of new plant growth and insect abundance which birds convert into song and making babies. Often the loudest and most reliably heard avian vocalisations heard during these months of seasonal abundance is the territorial call.

If I asked you to think about the call of a familiar songbird, chances are that the call you will think of will be its territorial call. Territorial calls are what we think of as a bird’s ‘song’, although it might not always sound particularly musical to our simian ears (have a listen to the Paradise Riflebird below to get my drift).

I might be getting a tad whimsical here, but I like to think of territorial calls as the birdsong-equivalence of property title, a certificate of health, a pub brawl challenge and a Tinder account all wrapped into one. Let me unpack that:

A male superb blue wren standing prominently on the highest tip of a shrub will issue his delightful territorial trill (song) to proclaim to other neighbouring males that he’s the total boss of a defendable kingdom – so don’t mess with him! The same call also advertises the ‘market value’ of his territory in terms of the food and nesting resources it offers, as well as hinting at his own physical vitality. Prospecting females note all this and vote with their genetic choice.

His property claim needs to be sufficiently large enough and resource-rich to keep him in tiptop health whilst he sings his heart out each day and defends against neighbouring rivals. It also needs to supply the energy required for an egg-laying partner and to raise a clutch of hungry young.

Thus, territorial song is part braggardo, part sexual prowess and partly a representation of how much solar energy production his territory is able to offer a growing family (i.e. location, location, location).

Exceptions to the Rule

Although most songbirds nest in Spring, there are various exceptions. The further west a bird lives from the Great Dividing Range, the greater the influence of rainfall is on the timing and frequency of their nesting cycle. No rain generally means no nesting, or poor breeding outcomes for these birds. Plentiful rain signals plentiful food supplies, and this triggers off a mass bird-bonking-fest. Thus, territorial song will more closely map to good rainfall than a particular calendar month.

But even on the east coast of Australia, there’s a bunch of birds who reliably nest through the Autumn and Winter months. Forest owls and lyrebirds are good examples. That’s why I am able to lay in bed on chilly nights throughout May and listen to the resplendent territorial songs of superb lyrebirds and the haunting bomb-falling screech of sooty owls (*who I’m yet to record).

Over-wintering Territorial Calls

I ought to briefly mention here also that over the last few years I’ve come to appreciate that some Spring-breeding songbirds employ a particular type of territorial song in late Autumn. For a while this phenomenon completely baffled me. Why bother defining and defending a territory outside of the breeding season when food is fast-becoming scarce?

The answer (I think) is that these are resident songbirds who are establishing over-overwintering territories for themselves and their partner (and possibly in some cases their recent nestlings). Winters in the south-eastern Australia are still cold enough to dramatically reduce insect and vertebrate prey abundance, so in order to survive the cool months some forest birds will lay claim to a winter territory which holds enough food to get them through to early July when the insects wake up.

These overwintering-territorial calls are unique enough that I will eventually create a new voice category for them.