The results of surveys at key sites in South America has revealed one of the highest numbers for wintering rufa Red Knot (Calidris canutus rufa) in 10 years!
During the 2022 winter season (austral summer), counts were performed of the Red Knot (Calidris canutus rufa) at key sites in Southern South America: The Bahía Blanca Estuary and the Bahía San Blas Reserve (Buenos Aires, Argentina); the Gulf of San Jorge (Chubut, Argentina); the coasts of the Province of Santa Cruz (Argentina); the Atlantic Coast Reserve (Tierra del Fuego, Argentina) and Bahía Lomas (Tierra del Fuego, Chile).
The aerial surveys of Bahía Lomas revealed one of the highest counts recorded for the Red Knot subspecies rufa in the last 10 years at Bahía Lomas, approaching the numbers observed in 2012 (14,000) and 2014 (14,200 birds). The count of 193 birds at the Atlantic Coast Reserve (Reserva Costa Atlántica) was also close to the highest numbers recorded in recent years at that site. Previously this site was the second most important in the Southern wintering area for the species, with counts in the range of 3,500 to 5,000 birds in 2008, and it remains today the site with the second greatest concentration of wintering birds for the Southern wintering region. However, the number of individuals has been drastically reduced at this site since then.
Beyond these areas, another notable count was that of 1,893 birds in the bays in the south of Buenos Aires Province (Argentina). This may represent a significant and previously unaccounted for number as part of the Southern wintering population of Calidris canutus rufa, and it demonstrates the importance of surveys and monitoring at other sites in southern South America, in addition to those at Bahía Lomas.
Left: Aerial survey team for Bahía Lomas, Chile, on January 8 and 9, 2022. From left to right: Heraldo Norambuena (observer 1), Hernán Cabrera (pilot), Ricardo Matus (observer 2) and Antonio Larrea (photographer). Right: Survey team working in the bays south of Buenos Aires (Argentina) defining the itinerary to be covered during the aerial surveys. From left to right: Leandro Marbán (navigator), Marcelo Davel -standing out of picture- (pilot) and Pablo Petracci (observer 1). Photo: Martín Sotelo (observer 2).
The critical conservation status of the rufa Red Knot is due to a dramatic population decline in the last 25 years and has increased the concern of conservationists and scientists in the Western Hemisphere. This issue was highlighted when the count at Delaware Bay in 2021 returned the lowest numbers in recent years, when just 7,000 individuals were estimated at this site during the migratory stopover, on route to the breeding grounds.
Monitoring activities have been carried out for the last several years at key sites for the species along its migratory route, with the aim of understanding the state of the population to determine if the apparent decline is real, measure the scale at which it is occurring, and identifying the causes of it, as well as suggesting priority actions to halt and reverse the decrease.
Census Results
In recent years, almost all of the Knots counted during the annual aerial monitoring in the Southern wintering region have been found at Bahía Lomas (Chile), and 2022 was no exception. Bahía Lomas is a tidal flat, with a wide range of tidal variation which exceeds seven kilometers per day (measured from the line of maximum height reached by the rising tide to the sea). This bay contains an extensive area of continuous and channeled marshes, beyond which large sandy areas predominate. This site is considered to be the most important South American wintering area for Calidris canutus rufa, and in 2009 was declared a WHSRN Site of Hemispheric Importance.
Mixed flock of Hudsonian Godwit and Red Knot recorded during the aerial survey in Bahía Lomas. January 8, 2022. Photo: Antonio Larrea
Members of the Bahía Lomas Center (Universidad Santo Tomás) carried out aerial surveys over the bay on January 8-9, 2022. During these aerial counts the estimates of the different flocks of shorebird species were performed by an observer supported with a digital audio recorder, whilst two other observers took photographs for the comparison of estimates in the field with counts obtained from the photographs. The final total of Red Knot at this site was 14,073 individuals.
Bahía Blanca Estuary (Estuario de la Bahía Blanca) and the Bahía San Blas Reserve (Reserva Bahía San Blas) were surveyed by airplane due to their large size and difficulty in access. The Bahía San Blas Reserve survey incorporated the bays of Unión, Anegada and San Blas (listed north to south). These sites are located in the extreme south of Buenos Aires Province. The aerial surveys were carried out by members of Gekko (Universidad Nacional del Sur) on January 21, 2022 and recorded 1,893 individuals.
The coast of the Province of Chubut was also surveyed in the area of the Gulf of San Jorge (Golfo San Jorge). The monitored sites were (from north to south): Bahía Melo, Playa Médanos, Playa Ezquerra, Playa Arroyo Marea and Estancia Bahía Bustamante. At high tide, islands in the Caleta Malaspina were visited by boat to detect the potential presence of Knots roosting in this area. Despite best efforts, no Red Knots were recorded during these surveys.
Large flock of shorebirds at Bahía Lomas. Photo: Antonio Larrea.
On January 4-8, members of Asociación Ambiente Sur carried out ground surveys along the coast of Santa Cruz Province (Argentina) at Puerto San Julián, Puerto Santa Cruz, Puerto Coyle and Río Gallegos. On January 4, three Knots were seen at Puerto San Julián and on January 8, 23 were found at the Río Gallegos Estuary. Between January 18 and March 11 a second block of periodic visits to this site took place. The highest count for Puerto San Julián during this period was of 25 Knots on January 23 and the same number was recorded again on January 28. For the Río Gallegos Estuary, the highest count during the period was of 33 individuals on February 2. No Knots were recorded at Puerto Coyle or Puerto Santa Cruz during any of the visits to these two sites.
Finally, surveys were undertaken for the species from January 3-6 and February 3-4 at the Atlantic Coast Reserve (Reserva Costa Atlántica). In both cases all-terrain vehicles were used to reach the most remote areas of the site to cover the maximum amount of ground possible. The highest count during this survey was of 197 individuals on January 4 on the coast of Río Grande. During the survey in February, the highest count here was 86 Knots, this time at Bahía San Sebastián.
The results obtained during the annual monitoring of wintering individuals indicates that the low numbers observed at Delaware Bay in 2021 cannot be explained by a decrease in the population of rufa Red Knot in Tierra del Fuego. It remains a priority to continue monitoring at the hemispheric level to understand the species’ population and changes in site use through all phases of their life cycle, to better target conservation actions required for the recovery of the species.
Acknowledgements:
These census was possible thanks to the support of Environment and Climate Change Canada, WHSRN Executive Office — Manomet, and the local members at each site (Gekko, Universidad Nacional del Sur; IDEAus-CONICET; Asociación Ambiente Sur; Estepa Viva and Centro Bahía Lomas, Universidad Santo Tomás).
Cover Photo: Aerial image of the bays in the south of the province of Buenos Aires. Photo: Pablo Petracci.
