How we know our birds are coming home

While the haunting cries of Eastern Curlews clearly signal the beginning of the northward migration of our migratory shorebirds, their return to Roebuck Bay is signalled by a different species of shorebird in a much more muted fashion. Instead of looking for lines of hopping and flapping birds on the mud, like we do at the start of the year, we’re scanning wetlands, the sewage works and the bay for a small, independent, tail-bopper called a Common Sandpiper.

But why is the return of shorebirds so different to their departure and why are we so interested in the Common Sandpiper?

There are still heaps of shorebirds in the bay during the dry season. Photo: Larry O’Brien

When the shorebirds leave Roebuck Bay between March and May to fly to the northern hemisphere to breed, they leave in flocks of (usually) nicely organised V-formations with lots of calling and jumping beforehand and usually in the mid to late afternoon. When the shorebirds return to the fattening grounds of the Roebuck Bay mudflats, they return in dribs and drabs between August and November, at all times of day. This makes sense as it is similar to how a marathon starts with everyone leaving at the same time but the finishing line is a different story. Some of the shorebirds that arrive back in the bay after their arduous 20,000 km journey look scrawny and exhausted after burning all their energy. Add to this the fact that the bay wasn’t empty after northward migration anyway – there are always around 20,000 shorebirds in Roebuck Bay mostly due to the young birds that don’t migrate until their second or third year. While this number increases to around 100,000 during the wet season once all the shorebirds have returned, this is a gradual change that can be hard to pick, especially at the start. So we need a clear signal that birds that actually left on migration have in fact returned to the bay.

Common Sandpipers are found in a range of habitats in the Broome region. Photo: Ric Else

Cue the Common Sandpiper. Common Sandpipers are small brown and white sandpipers found on rocky shores and along muddy banks of saline and freshwater wetlands, both inland and on the coast. In the Broome region, you can see them in the bay, at the Broome South Wastewater Treatment Plant (‘sewage works’), and amongst the mangroves and muddy banks of Little Crab Creek, as well as at various wetlands and lakes. They mostly eat small molluscs and aquatic and terrestrial insects. Their piping call and bobbing walking style are pretty distinctive. You often only see one or two together as they tend not to join large flocks of other feeding and roosting waders. Our population of Common Sandpipers mostly breeds in the Russian far-east.

What makes Common Sandpipers so important for the return migration is that they completely disappear from Roebuck Bay during the dry season (even the juveniles make the journey to Russia in their first year) so when we see them in the Broome region, we know that these are birds that have returned from Russia. They are also one of the first species to return, arriving in late July/early August. It is for these two reasons, their complete disappearance after migration and being one of the first to return, that Common Sandpipers are our clearest signal that our Roebuck Bay shorebirds have started to return.

This Common Sandpiper has just caught a meal. Photo: Adrian Boyle

As the end of July loomed, we waited for the appearance of Common Sandpipers with excited anticipation, knowing it signalled a change of season and the start of a guessing game of which species would next appear and where. This year, the first returned Common Sandpipers were spotted at the sewage works on the 26th of July (Nigel Jackett). One was seen at Lake Eda a day later and in the first week of August they were seen on the mudflats during a Mangrove Tour. It was surprising to discover how familiar and welcoming their piping call sounded once I heard it in the bay again. By this time, two other species, that had also completely disappeared from the region during the breeding season, were seen at a couple of the lakes. These were Wood Sandpipers and a Long-toed Stint which both tend to be found in freshwater or brackish wetlands rather than coastal mudflats. Wood Sandpipers breed throughout northern Europe and Asia while Long-toed Stints are thought to breed in Siberia. The next clear returnees were three Pacific Golden Plovers that were spotted in the bay at Quarry Beach on the 9th of August. They were a thrilling addition to that night’s Bird Log after having not seen any in the bay during the dry season. Pacific Golden Plovers breed on the Arctic tundra of western Alaska between June and July where their impressive gold and black breeding plumage camouflages them well.

Sharp-tailed Sandpipers on the banks of Little Crab Creek, still with a reddish tinge to their feathers. Photo: Larry O’Brien

Often, returned birds still have nice remnants of their breeding plumage. The recent increase in the number of Sharp-tailed Sandpipers in the bay may be due in part to the mostly freshwater wetland-inhabiting species moving from drying inland wetlands rather than returning from migration. However, ten Sharp-tailed Sandpipers with very nice orange-red plumage along the banks of Little Crab Creek on the 14th of August was suggestive of breeding birds that had returned from northern Siberia. Along a similar tone, a week earlier, 20 Curlew Sandpipers in their brick-red breeding plumage had been seeing arriving at Quarry Beach from the west. Curlew Sandpipers are a Critically Endangered shorebird with a long drooping bill that breeds in northern Siberia.

You can see the contrast in breeding plumage versus non-breeding plumage in these three Curlew Sandpipers in the mid-ground (Red-necked Stints are in front and the pink legs of Pied Stilts behind). Photo: Larry O’Brien

Sometimes, shorebirds don’t quite make it to the bay before they need to stop to refuel. A Great Knot was seen flying into the sewage works and drinking heavily on the 6th of August (Adrian Boyle) and a non-breeding adult Greater Sand Plover was seen at Taylor’s Lagoon and then flying south-east (towards the bay) on the 11th of August. Both of these species are predominantly seen in the bay, and Great Knots and Greater Sand Plovers are coastal birds in general. Their appearance at these ponds and wetlands and their behaviour there were uncharacteristic and suggestive of being returned individuals from a long migration journey. Speaking of birds appearing at unusual places, in recent weeks, Brolgas have been seen in the bay on numerous occasions and a Magpie Goose has consistently been seen at the sewage works. We tend to see Brolgas on the plains and around freshwater wetlands and Magpie Geese around freshwater wetlands.

It’s hard to see, but that large dark bird in the centre of the photo is a Magpie Goose making itself at home amongst the Plumed Whistling Ducks at the Broome sewage works. Photo: Mattea Taylor

It is very exciting to see our bay filling up with shorebirds but also to think that these birds have just completed their 20,000 km round trip, having traversed hemispheres and continents. Soon, we may see some very young-looking shorebirds – ones that hatched just a few months ago and have managed to eat enough and grow strong enough to successfully complete their first solo flight (unguided no less!) from the breeding grounds in the northern hemisphere to Roebuck Bay. This is where they will stay, feeding on the bay’s rich mudflats for the next couple of years before attempting their first northward migration. Except, of course, for a couple of species like the Common Sandpiper.

- Mattea