Great Knots really are great.
Although we are enormous fans of absolutely all shorebirds, one for which we have a special stickybeak soft spot is the Great Knot. This is a species that we came to know and love during our time in northwest Australia, where it is one of the most numerous wader species and forms spectacular flocks on the region’s mudflats during the austral summer.
While most of the world’s Great Knots spend their non-breeding season in Australia, the species breeds in rocky mountain tundra in north east Siberia (although not Kamchatka), completing a round trip of 20,000km or so each year on migration between these areas. Once they finish breeding and set off on their journey south, the mudflats of Kamchatka’s west coast, on the Sea of Okhotsk, are a major stop-over and refuelling site for many Great Knots. Vast sections of this area are still pretty much unexplored by wader watchers, but it was immediately clear that our study site on the Khairusovo Estuary was one of the Okhotsk’s top Great Knot spots…
When we arrived at the estuary on 13th July, an estimated 17,000 Great Knots were already present. These birds, part of the first wave of southbound migrants, were presumably those whose breeding attempts had failed early, and perhaps a few females who had already finished their nesting duties for the year – the females do not stick around long once their eggs hatch, and they soon head south leaving their mate to look after the chicks. It was fantastic to see the throngs of Great Knots in their bright breeding plumage, although by now they had been wearing these feathers for four months or more and were showing distinct signs of wear. The all-important flight feathers still had to carry their owners a further 9,000km to Australia, but would be moulted and replaced soon after arrival there.
Whoa – what the ?!? This leucistic Great Knot certainly stood out from the crowd. We actually saw one just like this on 80-Mile Beach in Australia in 2013 – maybe it’s the same bird!
To be on the mudflats, among the busily feeding Great Knots is a very special shorebird experience. Flocks of thousands move as one, marching across the mud in a dense army of birds, all intently probing the ground for invertebrates, their quiet but excited contact calls combining into a chuckling cacophony. Frequently, at the first hint of danger – usually an overflying raptor, skua or gull – the mass of birds lifts into the air in a single motion, swirling and sweeping evasively through the sky until the all-clear is sensed, and then descending back to mud to resume feeding. Although always alert to danger, the knots are not unduly worried by people and quietly working wader watchers can soon find themselves literally surrounded by furiously foraging birds – at least until the next pesky skua flies by and flushes everything!
Charadriiforme chubbiness chart, taken from Wiersma and Piersma (1994), in which the authors memorably compare knot body shapes to the portrait styles of different Flemish painters.
As well as showing us what countries and locations these birds had been banded and seen in previously, being able to recognise the same individual birds day after day gives and insight into how long they spend at this stopover site, and how their physical condition changes during their stay. The birds are there to feed, feed and feed as much as possible, piling on enough fat to fuel their flight to the furthest end of the flyway. The weight gain can be rapid, and birds can become visibly fatter in just a few days. Although a little subjective, it is possible to visually gauge the rotundity of a knot, scoring a particular bird’s portliness on a 1 to 5 scale – category 1 birds being skinny and category 5 birds positively bulging at the seams. A healthy knot usually resides in category 2 until it is preparing to migrate, when it begins piling on the pounds, building up vital energy stores and reaching category 4 or 5. Most of the birds we were watching at Khairusovo scored 2 or 3 on the scale, but as time went on more 4s and the occasional 5 were recorded. An interesting observation was that birds in similar shape often foraged together – we would frequently study a flock of mostly 2s, and then move onto a different flock in which most of the birds were 3s. Perhaps birds that arrived together remained together throughout their stay, so such a group of knots would have all been present and feeding for the same time period and had consequently comparable corpulence.
Great Knots on a weight-gain program. The one on the right looks lovely and tubby and almost ready for departure – just how Rubens would have painted it.
So what are all those knots guzzling in the mud? Even in slo-mo video it is hard to tell what is in the bird’s sticky beak before it gulps it down and out of sight. Well, usually, the prey is small bivalves, of which a great abundance is present just below the Khairusovo estuary’s muddy surface.
We certainly know Great Knots as bivalve specialists, since these molluscs comprise more than 60% of their diet at stopover sites and more than 90% in their Australian non-breeding grounds (see Zhang et al. 2011). The bivalves are gulped down whole to be broken up in the gizzard, before the crushed-up shell is returned to the mud in droppings and regurgitated pellets.
Bivalve-guzzling Great Knots leave plenty of evidence behind them. Amongst the dense pattern of footprints left behind by feeding flocks are lots of white splodges of poo and regurgitates. On close inspection, these contain many bits of crushed-up indigestible shell.
They do not, however, rely on bivalves all the time. While nesting in the Siberian mountains, they gobble fruit, arthropods and even hard-shelled Dwarf Pine nuts (see here). In Kamchatka we spotted a couple of Great Knots sampling some other unusual foods. This adult is proudly brandishing some sort of large isopod that it has found, although after wrestling it for a while it thought better of it and went back to bivalves.
Close-up of an isopod crustacean, similar to the one the knot was wrangling.
Even more interesting was this juvenile, which was intently picking at the eye sockets and other soft parts of a dead salmon!
Southbound migration of Great Knots comprises three main overlapping waves of birds. After the failed breeders and females comes the second wave, consisting mainly of adult males. These will have stayed on the breeding grounds until their chicks became able to feed themselves, at which point the fathers begin their journey south, leaving the youngsters to take care of themselves. It was not clear when the transition from the first to second wave of migrants took place, but we did notice flocks of fat birds making their excited southbound departure from the estuary on several occasions when the weather was conducive to migration. This was a most wonderful thing to observe, so we must write much more about this ‘migration watching’ in a future post.
The third wave of Great Knot migration is made up of the juvenile birds, just recently hatched and fledged and now finding their way to Kamchatka on the first leg of their maiden migration. The youngsters began appearing at the start of August and were easy to spot. Their juvenile plumage, although not as boldly patterned and striking as the adults, was immaculate and fresh. Although essentially grey and speckled with a neatly scalloped pattern on the upperparts, the pristine feathers have an almost golden fresh-out-of-the-box sheen to them. The juveniles also had a distinctive sort of wide-eyed naivety and air of bewilderment that the more worldly and experienced adults lacked. They were often found singly or in small groups, pecking around uncertainly in the pebbles or shallow mud around the edge of the estuary, or even in the grass and tundra, as if they hadn’t yet worked out that the Great Knot food was out there on the mud where all the thousands of adults were busy stuffing themselves with yummy bivalves. Actually, this may have been the first time some of the juveniles, whose short lives had so far been spent munching berries and spiders in stony tundra, had even seen mudflats, so perhaps we shouldn’t be so hard on them.
“Why am I here? Where are the berries?” A fresh juvenile looking a bit lost.
As more and more juveniles arrived and began associating with the adults, there was always a degree of segregation, with the youngsters mostly foraging on the periphery of the flocks. Maybe feeding knots have some kind of a social hierarchy, with the adults dominating the best patches of mud and the safest position in the middle of the flock.
Juvenile Great Knots are often less efficient foragers than the more experienced adult birds, and often struggle with food items that are a bit too big. This one is trying to swallow a rather large bivalve.
Juvenile Great Knots were sometimes very approachable, so it was easy to watch them feeding. This bird has found a small pink bivalve, of a kind that was common in the Khairusovo mud.
When we left Khairusovo on 8th August, juvenile birds made up a substantial portion of the Great Knots present. We travelled to our next shorebird study site at Vorovskaya River Lagoon, around 300km south of Khairusovo, where the main species were Dunlins and Red-necked Stints, but small numbers of Great Knot were still seen each day. Here, they were almost entirely juveniles. By the time we said goodbye to Kamchatka altogether and set off to the UK in mid September, the vast majority of the Great Knots we had seen would have been well on their way to Australia.
In fact, on 22nd September, wader-watchers in Broome spotted a Great Knot wearing yellow-over-black Kamchatka flags inscribed with the code AV – the first of the birds we had banded at Khairusovo known to have completed the 9,000km trip. Other sightings of our flagged Kamchatka birds were reported from stopover sites in South Korea, Japan, and Thailand, and a couple more were found in Broome in October.
We snapped this juvenile, D3, at Khairusovo on 7th August. By 30th September, D3 had travelled more than 3200km southwest, where it was seen (by Dmitry, the leader of the our Kamchatka expedition) near Gunsan, South Korea. This location in Korea is close to Saemangeum, formerly a crucial stopover site for about 30% of the world’s Great Knots, but now the site of the world’s longest man-made sea wall and one of its biggest shorebird conservation catastrophes.
The disastrous effect that Saemangeum and other similar mudflat ‘reclamation’ projects in the East Asian-Australasian Flyway are having on migratory shorebirds highlights how crucial their remaining stopover sites are. Bivalve-rich Asian mudflats, such as those around the Yellow Sea coast of China and Korea, are absolutely vital to these birds, which depend on them as refuelling stations on their migrations every year. Protection of these important sites is necessary if we are to continue seeing Great Knots and other shorebird species in their spectacular congregations at both ends of their flyway.