Spotlight: Curiosity-driven conservation across continents

Often when scientists follow their curiosity, they find something surprising. These unexpected discoveries are one of the joys of scientific research. Of course researchers have well thought-out plans, but within those plans there needs to be freedom to wander and take risks, especially when it comes to species conservation. Within well-studied systems, this is like discovering a new path in a neighbourhood you have known for years. If your neighbourhood spans continents, there may be surprises still to discover.

In this issue of Wader Study scientists working in the Northern and Southern Hemispheres report surprising discoveries about a well-studied shorebird: the rufa Red Knot of the Western Atlantic Flyway. These findings highlight the complexity of conserving species that rely on stopover sites that span continents.

In the Northern Hemisphere, McKellar and colleagues from various government and conservation agencies in Canada and the United States followed their curiosity to confirm a whole new stopover site for the Red Knot¹. The researchers were intrigued by recent studies using light-level geolocators to track Red Knot migratory routes^{2, 3}. The geolocator data showed that Red Knots from flyways along both the North American east coast and mid-continent were stopping near the Nelson River, Hudson Bay, during northward and southward migration. What piqued the researchers’ interest was that this is an area not previously identified as important for Red Knots. They knew more data was needed to determine the precise locations and habitats being used and to estimate the total number of shorebirds occurring in the area.

Therefore in spring 2014, the researchers investigated these geolocator clues further by visiting the Nelson River Estuary on the west coast of Hudson Bay. The team collected data through ground surveys and radio telemetry from 31 May to 6 June 2014, aerial surveys on 1 and 2 June 2014, and a radio tower to automatically log detections of any radio-tagged Red Knots in the vicinity after the team left the site. They also studied data from a total of 53 Red Knots fitted with geolocators between 2009 and 2013.

Results confirmed that the coastal area near the mouth of the Nelson River is a stopover site of major importance. The aerial surveys revealed a total of 25,202 shorebirds over the two days, of which 4,259 were Red Knots. This means at least 10% of the rufa Red Knot population was observed in the Nelson River area in spring 2014. The telemetry data reinforced this finding, confirming that 18.4% (16/87) of Red Knots radio-tagged at Delaware Bay were detected within the study area in 2014. The geolocator data showed that 36 of the 53 tagged birds (68%) used the Nelson River area during northward migration, and 45% also used the area during southward migration.The geolocator data confirmed that birds wintering in Texas also use the Nelson River area, at least in some years.

The authors suggest that the area be designated as an Important Bird Area (IBA) and/or a Western Hemisphere Shorebird Reserve Network (WHSRN) site. Potential threats to the site include ongoing hydroelectric development and continuing increases in the abundance of geese. IBA or WHSRN designations would raise the site’s profile and build connections with Red Knot stopover sites throughout the flyway. In the long term, such designations might help the Nelson River Estuary gain legally protected status.

In the Southern Hemisphere, Martinez-Curci and colleagues from conservation agencies in Argentina and Uruguay have been studying Red Knots in Punta Rasa, Argentina, for 30 years. In their study⁴, the researchers describe over 200 counts tracking abundance patterns of Red Knots from 1985 to 2014. Punta Rasa, which forms the southern tip of Samborombón Bay in Buenos Aires province, is recognized as internationally important within the WHSRN‎.

The researchers found that in the late 1980s and early 1990s Red Knots were more abundant at Punta Rasa during northward migration than during the austral winter (over-summering) – but now that pattern has switched. In the last decade more birds have used the site for over-summering than as a northward migration stopover.

‘Over-summering’ refers to birds from populations that breed in the Northern Hemisphere, but fail to migrate, and remain in the south during the northern summer⁵. Mostly such birds are one-year-olds for which the risks of migration and low chances of breeding successfully in their first year mean that they optimise their lifetime reproductive potential by remaining in their non-breeding area.

The flyway knot population has declined and that must be one reason why numbers using Punta Rasa during northward migration have dropped. However, the proportion of the flyway population using Punta Rasa has also declined. Why is this? The researchers suggest several possibilities, including that recreational tourism has increased. More people driving vehicles, kite-surfing and kite-bugging along the coast mean fewer birds are able to use the area.

Surprisingly, Martinez-Curci and colleagues’ more worrying discovery is that the number of knots over-summering at Punta Rasa has remained relatively high. This would be good news if they were all immatures (indicating successful reproduction), but large proportions were mature birds in full breeding plumage including some individually marked birds that were at least 3-7 years old.

Why do these mature adults fail to fly north to breed and contribute to the population’s reproductive output? The truth is that we do not know. Poor pre-migratory physiological condition or parasite infestation have been proposed as answers⁵. The researchers found that at least some birds that over-summer in Punta Rasa do so temporarily, perhaps to heal. For example, a bird with orange-flag E7N over-summered at Punta Rasa in 2013 when it was seven years old; but presumably it recovered from whatever stopped it migrating because in spring 2015 it was seen in Georgia, USA, during northward migration.

Curiosity drives new conservation discoveries and careful planning and process makes these results strong. In the north, McKellar and colleagues were intrigued by geolocator data that pointed to the Nelson River as a significant stopover site. Their research confirmed it as a site of key importance. In the south, Martinez-Curci and colleagues were curious about over-summering birds. They recognized more adults in over-summering flocks and confirmed this from the flag resighting data. Their curiosity spotlighted Punta Rasa as a site important as providing a place for mature adults to recover from disability. Their discovery also highlights the possibility of a larger loss to the adult breeding population because a lot of potential habitat is not surveyed in the austral winter; therefore many more adults might over-summer and fail to breed than are known. If so, the implications for the population’s demography could be serious.

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Deborah M. Buehler

Outreach Editor, ‘Wader Study’

1. McKellar, A. E., R. Kenyon Ross, R. I. Guy Morrison, L. J. Niles, R. R. Porter, Burger, D. J. Newstead, A. D. Dey & P. A. Smith. 2015. Shorebird use of western Hudson Bay near the Nelson River during migration, with a focus on the Red Knot. Wader Study 122(3).

2. Niles, L.J., J. Burger, R.R. Porter, A.D. Dey, S. Koch, B. Harrington, K. Iaquinto & M. Boarman. 2012. Migration pathways, migration speeds and non-breeding areas used by northern hemisphere wintering Red Knots Calidris canutus of the subspecies rufa. Wader Study Group Bulletin 119 (3): 195–203.

3. Newstead, D.J., L.J. Niles, R.R. Porter, A.D. Dey, J. Burger & O.N. Fitzsimmons. 2013. Geolocation reveals midcontinent migratory routes and Texas wintering areas of Red Knots Calidris canutus rufa. Wader Study Group Bulletin 120 (2): 53–59.

4. Martínez-Curci, N. S., E. Bremer, A. B. Azpiroz, G. E. Battaglia, J. C. Salerno, J. P. Isacch, P. M. González, G. J. Castresana & P. Rojas. 2015. Annual occurrence of Red Knot Calidris canutus rufa at Punta Rasa, Samborombón Bay, Argentina, over a 30-year period (1985-2014). Wader Study 122(3).

5. McNeil R., M.T. Diaz & A. Villeneuve. 1994. The mystery of shorebird over-summering: a new hypothesis. Ardea 82: 143-152.

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