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The fascinating world of migratory birds

Published 12 May 2023 by Rowan Mott

I am new to Bush Heritage, working as an ecologist in Victoria. My previous role involved working on waterbird ecology in the Coorong, which is a Ramsar-listed wetland of international importance in South Australia. It can be home to upwards of 100,000 to 300,000 waterbirds, many of which are migratory shorebirds.

My work aimed to better understand the habitat requirements of the Coorong’s waterbirds and involved tracking the movements of a few key species to figure out which parts of the wetland they were using and some of the habitat features that drove their patterns of habitat selection. We also worked to develop reliable measures that could be used to monitor habitat quality for the Coorong’s shorebirds.

Here are three migratory birds I find particularly interesting. 

Sharp-tailed Sandpiper 

Sharp-tailed Sandpipers migrate from Australia to Siberia and back again each year to breed. They're occasionally recorded on Bush Heritage reserves. They can increase their body mass by more than 50% in the lead up to migration. This increase is mostly because of fat deposits and enlargement of the flight muscles that will be used to fly thousands of kilometres.

To accommodate these changes, the birds will reduce the size of their digestive organs and leg muscles so they don’t have to carry unnecessary weight.

It’s the equivalent of you and I packing only the essentials - maybe just taking carryon luggage for a holiday.

These changes are reversible. Once the birds reach their destination, they'll regain digestive tissues and the excess fat they put on will be burned during travel so they return to a ‘normal’ body mass.

When Sharp-tailed Sandpiper chicks hatch, they're cared for by their parents for the first few weeks of life, but then the adult birds depart on their migration before the chicks. The chicks must finish growing and gaining the necessary fat loads to fuel their migration on their own. They depart several weeks after the adults leave and usually take a different migration route to the adult birds. It's completely down to instinct as to how they know where they're going. 

Blue-winged Parrot 

Another migratory species that's particularly special to me from my time at Bush Heritage is the Blue-winged Parrot. I was lucky enough to find a couple of them on our Bellair Reserve, Dja Dja Wurrung Country, Victoria on my first data collection trip as a Bush Heritage staff member.

Blue-winged Parrots have an interesting migration ecology that's not fully understood. Those that spend the summer in Tassie migrate to the mainland for the winter, but it's a bit unclear what happens with the mainland birds. Do they just have to share their space with the Tassie interlopers, or do they push north as well, with Victorian birds gate-crashing the party of New South Wales and Queensland populations?

Blue-winged Parrots have just been listed Federally as a threatened species, so I think there will be more incentive for researchers to figure this question out soon.

Scarlet Honeyeater

These stunningly beautiful, fire truck-red birds migrate up and down the east coast. At the southern end of their migration, they're regularly being encountered further south and west in recent years than they were historically. This is probably a result of climate change making the climate more favourable to them at sites where it may have once been too cold. I am expecting to find them one summer very soon at our Victorian reserves in the Kara Kara-Wedderburn focal landscape, which are at the extreme west of their current distribution. 

There are lots of migratory birds that visit Bush Heritage reserves. On our Victorian reserves, we witness the arrival of various species during winter migration, including Silvereyes, Striated Pardalotes, Grey Fantails, and occasionally Blue-winged Parrots that have crossed Bass Strait.

Over the summer period, we observe movements of Rainbow Bee-eaters from northern Australia to our southern reserves. Similarly, along the east coast, our reserves become home to migrating honeyeaters such as the Yellow-faced Honeyeater and Scarlet Honeyeater.

Additionally, altitudinal migrants like Flame Robins and Pied Currawongs leave alpine areas during winter, when cold weather and snow make finding food challenging. It's during the winter months that we have a higher likelihood of spotting these species on Bush Heritage reserves.

Migratory birds face greater threats compared to resident species.

Their need for high-quality habitats across different locations and seasons, as well as the requirement for habitat connectivity along migration routes, makes them vulnerable to habitat loss and degradation.

These factors contribute to the acute challenges faced by migratory species.

Furthermore, certain migratory species accumulate substantial energy reserves (i.e., fat) to sustain them during migration. As a result, they're particularly sensitive to changes in food availability prior to migration. Climate change poses a risk if it alters the seasonality of food resources, causing mismatches with the birds' migration schedule and jeopardizing their survival.

Sharp-tailed Sandpiper at Hamelin Reserve, WA. Photo Ben Parkhurst. Sharp-tailed Sandpiper at Hamelin Reserve, WA. Photo Ben Parkhurst.
Blue-winged Parrot. Photo Rowan Mott. Blue-winged Parrot. Photo Rowan Mott.
Scarlet Honeyeater. Photo Bradley Ellis. Scarlet Honeyeater. Photo Bradley Ellis.
Slivereye in Tasmania's Liffey Valley. Photo Wayne Lawler/EcoPix. Slivereye in Tasmania's Liffey Valley. Photo Wayne Lawler/EcoPix.
Grey Fantail at Brogo Reserve, NSW. Photo Joshua Wellington. Grey Fantail at Brogo Reserve, NSW. Photo Joshua Wellington.
Striated Pardalote at Edgbaston Reserve, Qld. Photo Anthony Darlington. Striated Pardalote at Edgbaston Reserve, Qld. Photo Anthony Darlington.
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