| Bar-tailed Godwit | Red Knot |
The Bar-tailed Godwit is one of the largest wading birds on the East Asian-Australasian Flyway (EAAF), and is readily distinguished by its long, slightly upcurved bill, browny, rather than grey, non-breeding plumage, and variable barring on its lower back and rump. In flight it has only a small pale wingbar, in contrast to the bold wingbar of Black-tailed Godwits. The most similar species is the Asian Dowitcher, which is smaller, leggier, has a shorter 'rear end' so it shows long leg projection during flight, is thicker- and straighter-billed and has a whiter underwing.
The sexes differ substantially in size, with females being much larger and longer-billed. Before northward migration, males moult into a colourful breeding plumage, while females moult into a much duller breeding plumage. See the breeding plumage and sex page for more details.
Figure 1. A male godwit in late March in New Zealand, in virtually full breeding plumage. Photo: Phil Battley. Click here for larger image
There are four subspecies that are generally recognised around the world (Table 1). Two of these occur in the EAAF. Menzbieri occur in Northwest Australia, while baueri occur in eastern Australia and New Zealand. There are subtle differences in proportions between these subspecies (menzbieri is slightly longer-billed and shorter-winged) but the most obvious difference is in the plumage of the lower back and rump. Menzbieri has a whitish back with relatively little dark feathering, whereas baueri has an essentially dark back with a barred rump and upper-tail coverts (see photos below).
Table 1. Bar-tailed Godwit subspecies, distribution and migration lengths
| subspecies | breeds | winters | migration distance (km) |
| lapponica | Scandinavia | Europe | 2,000 |
| taymyrensis | central Siberia | West Africa | 8,500 |
| menzbieri | eastern Siberia | Northwest Australia | 10,000 |
| baueri | Alaska | New Zealand, east Australia | 11-14,000 |
Figure 2. Left - menzbieri godwit from Northwest Australia. Photo: Heather Gibbs. Right - baueri godwit
from New Zealand. Photo: Brent Stephenson. Click here for larger images
As can be seen from the photographs, the barring on the tails itself is variable between individuals.
Figure 3. Close-up of the tails of two baueri godwit from New Zealand.
Photos: Brent Stephenson. Click here for larger images
Figure 4. Baueri godwits from New Zealand in flight. Waipu, New Zealand, 11 October 2005.
Photo: Phil Battley. Click here for larger image
Figure 5. Menzbieri plus baueri godwits in flight. Japan, April 2006.
Photo: Koichi Kudo. Click here for larger image
Godwits leave New Zealand from the second week of March to the end of the month. Flight range calculations suggest that godwits may be able to fly direct from New Zealand to eastern Asia (Japan, Korea and China), but only if favourable winds are assumed (download PDF). There are no counts at potential staging sites that show whether or not New Zealand godwits make a brief stopover en route. Nor have detailed counts and leg-flag checks been made through March in potential arrival sites in Korea and Japan that indicate when New Zealand birds first arrive. Colour-banded birds have been seen in Japan and Korea 15 and 12 days after being last seen in New Zealand, which neither proves nor disproves a direct flight.
Counts of birds in Asia show that the largest number of Bar-tailed Godwits (up to 80,000) congregates at Yalu Jiang National Nature Reserve in Northeast China, by the border with North Korea (Figure 6). Both subspecies of godwit are known to occur at Yalu Jiang. Birds marked in New Zealand have been seen only around the eastern side of the Yellow Sea, and further east (Figures 7 and 8).
Figure 6. Counts of Bar-tailed Godwits in the Yellow Sea during northward migration. Circles are roughly proportional to the maximum count. Adapted from Barter 2002 and articles in The Stilt. Click here for larger image
Figure 7. Number of sightings of godwits leg-flagged in New Zealand. Note - this is now out of date and will be updated after migration 2006. Click here for larger image
Figure 8. Number of sightings of godwits colour-banded in New Zealand. Note - this is now out of date and will be updated after migration 2006. Click here for larger image
Birds leave Asia for the breeding grounds in Alaska in May, and after breeding refuel on the coasts of Southwestern Alaska, particularly on the Yukon-Kuskokwim Delta and the Alaska Peninsula. After what for many birds is thought to be a direct flight across the Pacific, birds return to New Zealand from the third week of September to mid-October. Juveniles may not necessarily follow the same paths as adults, as a sighting of three juveniles in New Zealand on 1 December 2004 that had been flagged in South Australia only eight days earlier indicates.
Godwits eat predominantly marine polychaete worms, using their long bills to probe deep into muddy or soft sandy sediments to extract buried prey. They also eat small bivalves whole, and crabs that they may dismember before swallowing. Because females have much longer bills than males, they often feed in slightly different habitats, males using firmer substrates where they do more surface foraging, females feeding in soft mud, plunging face-deep to extract prey from their burrows.
Godwits are not the easiest bird to study, as they often swallow their prey before removing their bill from the sediment. On Farewell Spit, godwits eat a variety of polychaetes, from stout shallow worms such as Travisia olens, through to tube-building worms of the families Maldanidae and Oweniidae, and the deeply buried lug worm Abarenicola assimilis that godwits can only catch when the worm defaecates on the surface. Shellfish such as small cockles (Austrovenus stutchburyi), nut shells (Nucula hartvigiana), wedge shells (Macomona lilliana) and pipi (Paphies australis) are also probably taken. Male godwits in the Firth of Thames have been observed prising small mussels (Xenostrobus pulex) off rocks.
Barter, M. 1989. Bar-tailed Godwit Limosa lapponica in Australia. Part 1: Races, breeding areas and migration routes. Stilt 14: 43-48.
Barter, M. 1989. Bar-tailed Godwit Limosa lapponica in Australia. Part 2: Weight, moult and breeding success. Stilt 14: 49-53.
Barter, M. 2002. Shorebirds of the Yellow Sea: Importance, threats and conservation status. Canberra, Australia: Wetlands International Global Series 9, International Wader Studies 12.
Battley, P.F. 1997. The northward migration of Arctic waders in New Zealand: departure behaviour, timing and possible migration routes of Red Knots and Bar-tailed Godwits from Farewell Spit, North-West Nelson. Emu 97: 108-120.
Battley, P.F. & T. Piersma. 2005. Body composition and flight ranges of Bar-tailed Godwits (Limosa lapponica baueri) from New Zealand. Auk 122: 922-937. Download PDF (340 kb)
Gill, R.E. & B.J. McCaffery. 1999. Bar-tailed Godwits Limosa lapponica in Alaska: a population estimate from the staging grounds. Wader Study Group Bulletin 88: 49-54.
Gill, R.E., Jr., T. Piersma, G. Hufford, R. Servranckx & A. Riegen. 2005. Crossing the ultimate ecological barrier: Evidence for an 11 000-km-long nonstop flight from Alaska to New Zealand and Eastern Australia by Bar-tailed Godwits. Condor 107: 1-20. Download PDF (645 kb)
Landys, M.M., T. Piersma, C.G. Guglielmo, J. Jukema, M. Ramenofsky & J.C. Wingfield. 2005. Metabolic profile of long-distance flight in a shorebird. Proceedings of the Royal Society of London B 272: 295-302.
Landys-Ciannelli, M.M., T. Piersma & J. Jukema. 2003. Strategic size changes of internal organs and muscle tissue in the bar-tailed godwit during fat storage on a spring stopover site. Functional Ecology 17: 151-159.
McCaffery, B.J. and R. Gill. 2001. Bar-tailed Godwit (Limosa lapponica). The Birds of North America, No. 581. The Birds of North America Inc., Philadelphia.
Piersma, T. & R.E. Gill, Jr. 1998. Guts don’t fly: Small digestive organs in obese Bar-tailed Godwits. Auk 115: 196-203.
Piersma, T., J.M. Everaarts & J. Jukema. 1996. Build-up of red blood cells in refuelling Bar-tailed Godwits in relation to individual migratory quality. Condor 98: 363-370.
Piersma, T. & Jukema, J. 1993. Red breasts as honest signals of migratory quality in a long-distance migrant, the Bar-tailed Godwit. Condor 95: 163-177.
Piersma, T. & Jukema, J. 1990. Budgeting the flight of a long-distance migrant: changes in nutrient reserves levels of Bar-tailed Godwits at successive staging sites. Ardea 78: 315-337.
Scheiffarth, G. 2001. The diet of Bar-tailed Godwits Limosa lapponica in the Wadden Sea: combining visual observations and faecal analyses. Ardea 89: 481-494.
Scheiffarth, G., S. Wahls, C. Ketzenberg & K.-M. Exo. 2002. Spring migration strategies of two populations of bar-tailed godwits, Limosa lapponica, in the Wadden Sea: time minimizers or energy minimizers? Oikos 96: 346-354.
Red Knots in non-breeding plumage (Figure 9) are one of the least distinctive waders, which is why lone birds are often mistaken for other invariably much rarer species. Grey above and white below apart from some light barring on the breast and sides, they have some pale barring on the rump and uppertail coverts (Figure 10). The legs range in colour from mustard (as young birds) to blackish (adults). They are gregarious, roosting and feeding in dense flocks.
Figure 9. Red Knot in non-breeding plumage. Photo: Phil Battley. Click here for larger image
Figure 10. Red Knot showing barred rump. Photo: Phil Battley. Click here for larger image
In breeding plumage, Red Knots are much more impressive (Figs. 11 and 12). Their breast and underparts becomes rich red-orange, which in some birds spreads up around the face and head also, and their upperpart feathers become grey or blackish with red spots or notches and white tips. It is easy to see why the name "Red Knot" is preferably to the name generally used in New Zealand, "Lesser Knot".
Figure 11. Red Knot entering breeding plumage, roosting among New Zealand's endemic Wrybill. Photo: Phil Battley. Click here for larger image
Figure 12. Red Knot in full breeding plumage. Photo: Phil Battley. Click here for larger image
The species most easily confused with the Red Knot is its larger cousin, the Great Knot. Great Knots are always longer-billed than Red Knots, and have a whitish rump that shows up in flight. In non-breeding plumage they have bolder chevrons ('vees') down their sides, more dark markings on the breast, a less cleanly marked supercilium, heavier streaking on the forehead, and the feathers of the upperparts are browner with darker centres than those of the smooth grey Red Knots. Great Knots look less uniform above as a consequence. In breeding plumage there is no room for confusion - Great Knots have a gorget of black spots across the breast, and varying amounts of large red spots and patches on their scapulars (shoulder feathers).
There are six described subspecies around the world (Table 2, Figure 13). The main subspecies reaching New Zealand is rogersi, which breeds in Chukotka Peninsula in Russia's far east, and winters in eastern Australia and New Zealand. Red Knots are among the most northerly-breeding bird species in the world, with some populations reaching 76-78 degrees north. While rogersi knots breed comparatively far south in knot terms, those reaching New Zealand make the longest migration of any subspecies.
Table 2. Red Knot subspecies, distribution and migration lengths
| subspecies | breeds | winters | migration distance (km) |
| islandica | Notheast Canada, Greenland | Europe | 4,000 |
| canutus | central Siberia | West Africa | 8,500 |
| piersmai | New Siberian Islands | Northwest Australia | 10,500 |
| roselaari | Wrangel Island | Gulf of Mexico | 7,500 |
| rogersi | eastern Siberia | New Zealand, east Australia | 14,000 |
| rufa | northern Canada | South America | 12,000 |
Figure 13. Red Knot Flyways, showing breeding areas (grey) and non-breeding locations (black circles, which are shown proportional to population size). Click here for larger image
The main differences in plumage between piersmai and rogersi are the colour and extent of the red plumage on the underparts, and the darkness of the upperparts. The base colour of piersmai breeding plumage is typically a rich, dark red, whereas rogersi is paler, more peachy coloured (Figure 14 and 15). The red plumage on the underparts generally ends before the vent in rogersi though, as Figure 14 shows, some birds from Chukotka may have some red on the vent.
Figure 14. Range of variation in underpart plumage of Red Knots of the subspecies rogersi from the breeding grounds. Specimens are from the Zoological Museum in Moscow. Photo: Phil Battley. Click here for larger image
Figure 15. Range of variation in underpart plumage of Red Knots of the subspecies piersmai from the breeding grounds. Specimens are from the Zoological Museum in Moscow. Photo: Phil Battley. Click here for larger image
On the upperparts, piersmai plumage consists largely of blackish feathers with dark red patches (Figure 16) whereas rogersi has more greyish fringes, paler reddish patches, and generally looks paler. A classic rogersi, photographed on the breeding grounds, is shown in Figure 17.
Figure 16. Comparison of upperpart plumage of Red Knots of the subspecies piersmai (New Siberian Islands) and rogersi (Chukotka) from the breeding grounds. Specimens are from the Zoological Museum in Moscow. Photo: Phil Battley. Click here for larger image
Figure 17. Red Knot of the subspecies rogersi on the breeding grounds. Photo: Evgeny Syroechkovsky Jr. Click here for larger image
It is probable that some piersmai knots reach New Zealand, however. Some birds are a much deeper red colour in breeding plumage than others, have more red on the rump and vent, and often have very red heads. The bird in Figure 18, for example, could well be a piersmai rather than rogersi, though the plumage colour seems more consistent wirh rogersi.
Figure 18. Red Knot, possibly of the subspecies piersmai. Note the red feathering on the uppertail, undertail and flanks. New Zealand, May 2005. Photo: Phil Battley. Click here for larger image
Red Knots are one of the big unknowns in the East Asian-Australasian Flyway. Despite large populations of two subspecies being known on the non-breeding grounds, only around 30% of the expected population migrating has been located on migration in Asia. Possible explanations for this shortfall are that birds congregate densely in a few sites with very high food resources (parallelling Delaware Bay for rufa knots in the Americas) that have not been located yet, birds use areas that are off-limits to ornithologists (North Korea), some populations may migrate later than assumed, and the estimate of how many birds there are may be too high. The last two explanations are more relevant to piersmai than rogersi, for which non-breeding populations and migration timing are fairly well known.
As few knots have been located on migration, it is not surprising that there are few records of leg-flagged birds from Asia (Figure 19). Birds have been seen in Taiwan, South Korea and China.
Figure 19. Number of sightings of knots leg-flagged in New Zealand. Click here for larger image
Only one colour-banded knot has been seen on migration, caught by banders at Chongming Dao near Shanghai on 12 May 2005 (Figure 20). It weighed only 90 g, implying it had only just arrived after a long flight, possibly from northern Australia, where birds flagged in New Zealand have been seen in mid-April.
Figure 20. Colour-banded knot caught on migration in China. Photo: Zhang Kejia. Click here for larger image
Little is known of the southward migration of Red Knots in the EAAF, though it is likely that many knots overfly eastern Asia from launching sites in Russia. Leg-flagged birds from New Zealand have been seen in eastern Australia in early-mid September, indicating that some birds pass through Australia on the way south.
Young birds are a different proposition. Very few juvenile knots make it to New Zealand straight away in their first migration south. Instead, most go as far as Southeast Australia, subsequently moving to New Zealand later in the season or after a year or more.
Virtually everywhere around the world, knots feed on hard-shelled molluscs, particularly small bivalves (generally <15 mm long). Knots are able to locate these buried shellfish efficiently, probably by using pressure-sensors in their bill tip. As shells are swallowed whole and crushed in their stomach knots have the largest gizzard relative to body mass of any shorebird. Because the shell fragments pass out in the faeces, the diet of knots can be studied comparatively easily.
On New Zealand tidal flats, knots are known to eat mostly small pipi (Paphies australis) on sandy flats, cockles (Austrovenus stutchburyi) and nut shells (Nucula hartvigiana) on muddy flats or eelgrass beds, and a variety of small surface-dwelling snails. Where prey densities are high enough, knots may eat tiny crustaceans (such as amphipods and isopods).
Baker, A.J., P.M. González, T. Piersma, L.J. Niles, I. d. L. S. d. Nascimento, P.W. Atkinson, N.A. Clark, C.D.T. Minton, M. Peck, & G. Aarts. 2004. Rapid population decline in red knots: fitness consequences of decreased refueling rates and late arrival in Delaware Bay. Proceedings of the Royal Society of London B 271: 875-882.
Barter, M., A. Jessop, & C. Minton. 1988. Red Knot (Calidris canutus rogersi) in Australia. Part 1: Sub-species confirmation, distribution and migration. Stilt 12: 29-32.
Barter, M., A. Jessop, &C. Minton. 1988. Red Knot Calidris canutus rogersi in Australia, Part 2: biometrics and moult in Victoria and North-Western Australia. Stilt 13: 20-27.
Battley, P.F. 1999. Seasonal mass changes of Lesser Knots in New Zealand. Notornis 46: 143-153.
Battley, P.F. 1997. The northward migration of Arctic waders in New Zealand: departure behaviour, timing and possible migration routes of Red Knots and Bar-tailed Godwits from Farewell Spit, North-West Nelson. Emu 97: 108-120. Download PDF of paper (337 kb)
Battley, P.F. & T. Piersma. 1997. The body composition of Lesser Knots Calidris canutus rogersi preparing to take off on migration from northern New Zealand. Notornis 44: 137-150.
Battley, P.F., D.I. Rogers, T. Piersma, C.J. Hassell, A. Boyle & H.-Y. Yang. 2005. How do red knots leave Northwest Australia in May and reach the breeding grounds in June? Predictions of stopover times, fuelling rates and prey quality in the Yellow Sea. Journal of Avian Biology 36: 494-500. Download PDF (133 kb)
Buehler, D.M. & A.J. Baker. 2005. Population divergence times and historical demography in Red Knots and Dunlins. Condor 107: 497-513.
Boyd, H., & T. Piersma. 2001. Changing balance between survival and recruitment explains population trends in Red Knots Calidris canutus islandica wintering in Britain, 1969-1995. Ardea 89: 301-317.
Brochard, C., B. Spaans, J. Prop & T. Piersma. 2002. Use of individual colour-ringing to estimate annual survival in male and female Red Knot Calidris canutus islandica: a progress report for 1998-2001. Wader Study Group Bulletin 99: 54-56.
Dekinga, A., & T. Piersma. 1993. Reconstructing diet composition on the basis of faeces in a mollusc-eating wader, the Knot Calidris canutus. Bird Study 40: 144-156.
Morrison, R.I.G., N.C. Davidson & T. Piersma. 2005. Transformations at high latitudes: Why do Red Knots bring body stores to the breeding grounds? Condor 107: 449-457.
Piersma, T. 1991. Red Knots in New Zealand eat molluscs too: preliminary diet observations at Miranda, Firth of Thames and Farewell Spit in November 1990. Stilt 19: 30-35.
Piersma, T. & N.C. Davidson. 1992. The migration of Knots. Wader Study Group Bulletin 64: Supplement (210 pages).
Piersma, T., Koolhaas, A. & Dekinga, A. 1993. Interactions between stomach structure and diet choice in shorebirds. Auk 110: 552-564.
Piersma, T., G.A. Gudmundsson & K. Lilliendahl. 1999. Rapid changes in the size of different functional organ and muscle groups during refueling in a long-distance migrating shorebird. Physiological and Biochemical Zoology 72: 405-415.
Piersma, T., D.I. Rogers, P.M. González, L. Zwarts, L.J. Niles, I. d. L. S. d. Nascimento, C.D.T. Minton & A. J. Baker. 2003. Fuel storage rates before northward flights in red knots world-wide: facing the severest ecological constraint in tropical intertidal environments? Pages 262-273 in P. P. Marra and R. Greenberg, editors. Birds of Two Worlds. Smithsonian Institution Press, Washington, D.C.
Riegen, A.C. & C.D.T. Minton, R. Jessop & P. Collins. 2005. Movements of Red Knot between Australia and New Zealand. Pp. 175-182 in P. Straw (ed.) Status and Conservation of Shorebirds in the East Asian-Australasian Flyway. Proceedings of the Australasian Shorebirds Conference, 13-15 December 2003, Canberra, Australia. Wetlands International Global Series 18, International Wader Studies 17. Sydney, Australia.
Tomkovich, P.S. & A.C. Riegen. 2000. Mixing of Red Knot populations in Australasia: some thoughts. Stilt 37: 25-27.
Tomkovich, P. S. 2001. A new subspecies of Red Knot Calidris canutus from the New Siberian Islands. Bulletin of the British Ornithologists Club 121: 257-263.
Zwarts, L. & A.-M. Blomert. 1992. Why knot Calidris canutus take medium-sized Macoma balthica when six prey species are available. Marine Ecology Progress Series 83: 113-128.
