I LOVE Crested Terns. Their sleek, clean black, white and silver plumage, teamed up with bright yellow bills makes for a beautiful sight, especially when they’re in a tight roost. Their courtship antics are fascinating and highly engaging, including: wing drooping and circumambulation; offering captured fish and; aerial duetting. These are unforgettable sights for anyone lucky enough to enjoy hanging about around our beautiful coastlines.

Crested Terns are gorgeous on the wing, with powerful flight and brilliant soaring ability: true masters of flight. When they dive on their prey in the water, their wings-back plunges are eye-rivetting. Five races of Crested Tern are found across the Indo-Pacific region. The race we have in Australia are Thalasseus bergii cristata and, numbering up to 500,000 birds, it is the most numerous.

A dapper pair prepare for display at Boat Harbour. © 2009 Ricki Coughlan

Banded terns on Sydney headlands

MERRIES REEF at Boat Harbour always has at least a few Crested Terns roosting among various cormorant species, Silver Gulls, Kelp Gulls and a variety of migratory shorebirds. In almost three years of weekly surveys I have only observed three or four Crested Terns wearing numbered aluminium leg bands – one of them an anodised orange band.

On last Wednesday’s high tide count I recorded a roost of 827 Crested Terns on the reef. Of these, 22 birds had numbered aluminium leg bands, one had an orange anodised leg band and another with a green anodised leg band. Clearly, something unusual is going on!

Visitors from Victoria

I contacted Clive Minton, who handles the record keeping of banded shorebirds (which includes gulls and terns) in this part of the East Asian-Australasian Flyway and was informed that the terns with the coloured bands were banded as chicks on Mud Island, Victoria, around 743 kilometres from Sydney, but considerably further if we accept that these birds have flown along the coast. The bird with the orange band was banded in 1995 and the tern with the green band was banded in 1998. I think that under the circumstances, we can also accept that the remainder of the terns with plain aluminium bands were also banded in Victoria.

A Crested Tern on Boat Harbour with orange anodised leg band. © 2009 Ricki Coughlan.

Last Saturday at Long Reef we counted 40 Crested Terns among a roost of cormorants and Silver Gulls. Three of these birds also had leg bands. We have recorded Caspian Terns on the reef which were wearing leg bands, but never any Crested Terns with leg bands.

A Crested Tern on Boat Harbour with green leg band. © 2009 Ricki Coughlan.

Breeding? Fishing? Both? or . . . something unknown?

So what is happening? There is little doubt that we are experiencing an influx of Crested Terns from Victoria and given the large numbers of these birds in breeding plumage and courting at present might mean that these birds have come north to breed.

Another event currently taking place just off the coast may also have a bearing on the arrival of these terns. For the second year running, a large mass of warm water has extended southward from Queensland and is currently extending just south of Sydney, around a kilometer off the coast. This southern movement of the warmer water will effect the patterns of movements of large numbers of fish: species which prefer colder water will be forced further out to sea and closer to the coast. There would be a southward movement of fish which prefer warmer water. They’ll be tracking the warmer current. It may well be that these terns are taking advantage of this shift in the dynamics of ocean currents and are simply following the patterns of movement among those fish species upon which they prey.

According to Clive Minton, these birds have been breeding further north, probably on islands and sandbars off the coast of Queensland. What we are currently seeing on our rocky headlands are birds which are now making their way south towards Victoria again. It may be that, unlike most years when it is not present, the extant body of warm water off the coast is providing them with a food resource of such excellence that the terns are not in any hurry to return to Victoria. These birds were banded with a different colour each year as part of a study aimed at determining the age at which Crested Terns commenced breeding.

Report flagged and banded birds

WHATEVER THE REASON your birds are about, it’s a good reminder to keep your eyes out for leg bands or leg flags on birds, because the more data we have, the more questions we can ask, ultimately leading to more answers and more conservation opportunities. Remember to report your sightings to mintons@ozemail.com.au or visit the Australasian Wader Studies Group sightings page.

Until next time . . . happy birding!

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Birding, Cool sightings by Ricki