Friday, 4 August 2017

Banded Stilts and Red-necked Avocets

Banded Stilts (Cladorhynchus leucocephalus) and Red-necked Avocets (Recurvirostra novaehollandiae) are both Australian endemic shorebirds which share habitat preferences. However their very different bill shapes and feeding styles show they each exploit different foods, though they no doubt overlap to some extent. They are both nomadic and are often found together.

Both species turn up on wetlands of the Gippsland Lakes, finding refuge here when conditions inland are dry – but they do not breed here.

The wetlands at both Hollands Landing and Jones Bay are good places to find both species when they are present on the Gippsland Lakes. Recently we found an estimated 300 Banded Stilts and 700 Red-necked Avocets on Victoria Lagoon at Hollands Landing.

In the past I have recorded a flock of Banded Stilts on Jones Bay of 650 birds, counted on computer from a series of photos taken of the birds resting together along a shoreline - they are intensely gregarious birds.

The largest flock of Red-necked Avocets I have recorded exceeded 1,300 birds.  This was also on Jones Bay. They also are gregarious though more so when resting/roosting and not so much when feeding.

Please click on photos to enlarge.

A section of Victoria Lagoon at Hollands Landing. The water is shallow and most of it can be waded by Stilts and Avocets at this level.
The view as I approached a mixed flock of Banded Stilts and Red-necked Avocets on Victoria Lagoon. The structure in the middle of the photo is a duck shooting hide - the birds are strung out in a line in the water behind the hide.

Following a dry year so far in 2017, Victoria Lagoon is drying out rapidly and in the process large areas of shallow water and wet muddy/sandy shoreline are being exposed. The lagoon is roughly 2km by 2km and varies over time from fresh to hypersaline. At present, there are good food resources available as evidenced by the presence of large numbers of ducks (teal est. 300+), Red-necked Stints (est.400), Red-capped Plovers (est.100) and the Stilt and Avocet numbers quoted above.

The foods available include crustaceans, worms, molluscs and insects.

This photo shows two small species of long dead beach washed molluscs – live ones no doubt form part of the diet of at least some of waterbirds on this lagoon.

Obtaining photos of the birds on Victoria Lagoon is limited by the distance the birds permit approach, their FID (Flight Initiation Distance) varies with their mood, as sometimes they appear relaxed and at other times, nervous and flighty. At best the birds have a minimum FID beyond which you cannot approach with the Banded Stilts FID generally greater than the Red-necked Avocets from my experience. There is no cover around the lagoon shoreline and the wet margins are muddy, though wallowing into the mud is not required as by this point the FID has usually been exceeded. A long lens is required to obtain reasonably close shots of the birds under these conditions.

On both occasions when I recently observed the Stilts and Avocets, the Avocets were mostly resting in tight, though strung out flocks, which included a few Stilts, while most of the Banded Stilts were actively feeding together in lines.

One of several groups of Red-necked Avocets resting on Victoria Lagoon.
A closer view of mostly Avocets resting – if you look closely you will see some Banded Stilts.
Some of the Banded Stilts feeding – they tended to feed close together in a line.

The following selection of photos were taken from two visits – unfortunately it was overcast on both occasions.

Avocets making their way past me along the shoreline with out-of-focus Banded Stilts in the background.
Focus reversed with Banded Stilts in focus in the background.

Not only is the Red-necked Avocet’s bill an amazing shape but it is incredibly thin and hardly seems capable of the hard work required to trawl for food without sustaining damage. In the following photo the middle bird with its head down has its bill slightly open – take a close look at just how thin the two bill segments are – and yet they use the bill partially open in a side to side sweeping motion to capture food!

This Avocet has a dirty face from foraging. Apparently the female bill is more steeply upturned, otherwise the sexes are similar.
In this photo the following bird has a more steeply upturned bill and therefore is likely to be a female with a male in front.
Some of the birds had flushed, flown a lap and then returned to the bulk of the resting birds that had stayed put.

It is interesting to observe flocking birds and what causes them to flush. Sometimes the cause is obvious, such as a raptor appearing or my approach, however at other times it seems like a false alarm with no obvious cause. I guess for vulnerable birds it is safer to err on the side of caution. That said a flock will sometimes flush leaving a few birds behind alone and on their own looking decidedly vulnerable without the protection of numbers. Are these outliers brave and not easily spooked or simply foolhardy? Or are they just not smart enough - or perhaps they are down on energy, not well, and simply do not have the reserves to fly with the others?

A section of a flock of Avocets that had flushed and then returned to the group. The small birds are Red-necked Stints. The black wing tips and shoulder bars against the brilliant white plumage make Avocets in flight a stunningly beautify sight.
Shorebirds often do wing and leg stretches when they are uncomfortable and getting ready to fly – a sign they are likely to flush.
Sure enough this group is taking off.
Banded Stilts in flight.
Another group of mostly Banded Stilts in flight.

A cropped section of another shot of the above group.
Ditto above.

I was surprised to find when editing the photos that one of the Banded Stilts had a red flag on its right leg.   

Cropping some of the other photos revealed a fuzzy but possibly good enough image to show the letters CKY.

Joris from the Australian Wader Study Group advised the following in a preliminary email response to my report on the flagged bird:

I cannot get you information immediately as there seems to be a scribe error in the banding database. However, looks to be part of a big catch in Western Port Bay in January 2015. Will let you know the details as soon as possible.

After a couple of sessions at Victoria Lagoon it was a real bonus to find among a bunch of photos a leg flag and report this as it helps build a picture of the movements of this highly nomadic and erratic bird, both in term of movement and lifestyle, especially their breeding requirements.

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