Subspecies, connectivity and conservation in shorebirds

Rufa’ Red Knot in Delaware Bay

For waders such as Red Knot (Knot), conservation designations such as ‘near-threatened’ or ‘endangered’ are based upon declines and vulnerability of populations that breed in defined areas. What happens when populations mix when they are on migration or in their non-breeding areas? How do we define conservation priorities of mixed flocks? Camila Gherardi-Fuentes, Jorge Ruiz and Juan Navedo invited us to think about this issue in a 2021 Red Knot paper in Bird Conservation International.

Conservation challenges posed by overlapping subspecies

It would be convenient if subspecies of waders kept themselves to themselves but they don’t. In spring, islandica Black-tailed Godwits join limosa in Portuguese and Spanish rice fields. Icelandic populations have been increasing for a century but the Dutch population of limosa dropped by 75% between the 1970s and the period 2007-15 (as described in this blog). Which subspecies should take precedence when assigning conservation importance to a spring flock on the Tagus, or to an autumn flock in France, for that matter? These questions are not abstract; they are relevant to a decision to site a new airport for Lisbon in the estuary and to discussions about the sustainability of autumn hunting on the French coast.

Further south, in the Banc d’Arguin of Mauritania, what is the conservation importance of Dunlin? Birds from Iceland outnumber those that breed around the Baltic coast. There is no suggestion that Icelandic schinzii Dunlin are in trouble, with between 200,000 and 300,000 pairs and no indication of range change, but the Baltic schinzii population was most recently estimated as between 500 and 640 pairs – less than a fifth of the estimate in the 1980s. Does the plight of Baltic (and Irish and UK) schinzii Dunlin confer a ‘threatened’ label on the whole wintering population of the Banc d’Arguin?

Untangling Red Knot in Chile

In their paper, Insights into migratory connectivity and conservation concerns of Red Knots in the austral Pacific coast of the Americas, Camila Gherardi-Fuentes, Jorge Ruiz and Juan G Navedo present the first detailed population morphometrics of Red Knot on the southern Pacific coast of South America, during the non-breeding season, along with information about resightings of these birds throughout the Americas.

Globally, Red Knot Calidris canutus is one of the most extensively studied shorebird species and is considered as ‘Near Threatened’ at the global level (BirdLife International 2018). It is currently accepted that three subspecies are found in the Americas. The general migratory patterns are as follows but the authors of the new paper present evidence of a more complicated picture.

  • roselaari Knot breed in Alaska and Wrangel island (Russia) and migrate along the Pacific coast to spend the non-breeding season mainly in Mexico. The total population is estimated to be 17,000 birds.
  • rufa Knot breed in northern Canada and migrate down the eastern seaboard of the Americas, some travelling as far as Tierra del Fuego. The total population is estimated to be 42,000 birds. This subspecies has been designated as ‘threatened’ in the USA, where there has been an increase in the pressure upon spring staging sites. There is a WaderTales blog about the vulnerability of this subspecies, based upon work in Delaware Bay.
  • islandica Knot breed in NE Canada and Greenland and spend the winter in western Europe. Two WaderTales blogs about changing numbers of shorebirds in Great Britain and Ireland discuss declining numbers of islandica Knot.

Colour-ringing and geolocator studies that track individual birds are providing new evidence that complicates the above pattern, with some rufa Knot spending the non-breeding season on the Pacific coast of South America (Navedo, J.G. & Gutiérrez, J.S. 2019) and some roselaari wintering in Texas. Migration is even more complex, with one roselaari bird flying from Chile to Texas and then switching back west to head to Alaska (see map right). There is more about this on the Wader Study website.

The Red Knot of Chile

The team from the Bird Ecology Lab in Chile have been studying the shorebirds of the Chiloé Archipelago (42˚S, Chile) for several years. This archipelago is a Site of Hemispheric Importance for the conservation of migratory shorebirds, due to its large numbers of Hudsonian Godwit (WaderTales blog Teenage Waders) and Whimbrel.

Red Knot regularly winter in this area, with at least 150 occurring in two well-studied bays of the main island. Although it might be assumed that these birds would be roselaari, there have been colour-ring sightings of a small number of birds that had been marked with lime and green flags within the rufa flyway. With conservation of two subspecies in mind, the research team were keen to know more about the natal origins of the Chiloé Red Knot.

42 Red Knot were caught on Chiloé main island between 2017 and 2020. As well as being aged, ringed, colour-ringed with red flags, measured and weighed, blood samples were taken, in order to determine gender. The biometrics of this small sample of birds combined with sightings of red-flagged Knot has revealed a remarkable amount of information:

  • As in other Red Knot populations, males were smaller than females in all measurements (see paper for details).
  • Measurements suggest that the Chiloé population includes rufa Red Knot.
  • Weights of birds were higher at the end of April than at the start of March, suggesting an increase in body mass of between 2.9 and 3.6 grammes per day; figures that are comparable to other studies of Knot.
  • In spring, marked birds were reported in Peru, the Gulf of Mexico, Minnesota and Manitoba. These last two sightings are on the Mid-Continental Flyway, which is used by waders heading for both Alaska and Northern Canada, as might be expected of roselaari and rufa Red Knot, respectively.
  • The red-flagged birds pictured shown here were photographed by Peter Bergeson (above right) and Jean Hall (below) in South Carolina and Florida, respectively) clearly suggesting that they are rufa Red Knot.

Conservation implications

Chiloé is an important non-breeding area, where Red Knot fuel up for non-stop 8,000 km flights to the Gulf of Mexico, one of the longest migration legs for the species. Now that Gherardi-Fuentes et al have shown that these flocks include ‘Endangered’ rufa, it makes sense to provide some designated protection to the Chiloé Archipelago population of Red Knot. You can download the current Conservation Plan for Migratory Shorebirds in Chiloé.

This relatively small-scale study of Red Knot has emphasised two important points about shorebird conservation.

  • The protection of sites that hold important populations of key species provides benefits for other waders that use similar habitats. In this case, sites designated for Hudsonian Godwits and Whimbrel are being used by two subspecies of Red Knot, at least one of which is ‘threatened’.
  • Waders from one breeding population use a range of sites when migrating and during the ‘wintering’ period. Given that it is hard to know all of the possible sites that link to one breeding area, it is pragmatic to protect as many different sites as possible, across a broad range of countries. There is more about this in Spoon-billed Sandpiper: Track & Trace.
Caulín Bay in Chiloé

Paper

It is interesting that we are still discovering important information about the origins of population of Red Knot, a species that has been at the heart of shorebird research for decades. Will genetic techniques and tracking reveal more surprises? And, more intriguing, how much more is still to be discovered about less well-studied species?

Here’s a link to the paper in Bird Conservation International:

Insights into migratory connectivity and conservation concerns of Red Knots Calidris canutus in the austral Pacific coast of the Americas. Camila Gherardi-Fuentes, Jorge Ruiz and Juan G Navedo (2021).


WaderTales blogs are written by Graham Appleton (@GrahamFAppleton) to celebrate waders and wader research. Many of the articles are based on published papers, with the aim of making shorebird science available to a broader audience.

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