Danny I. Rogers

Migratory connectivity magnifies the consequences of habitat loss from sea-level rise for shorebird populations.

Sea-level rise (SLR) will greatly alter littoral ecosystems, causing habitat change and loss for coastal species. Habitat loss is widely used as a measurement of the risk of extinction, but because many coastal species are migratory, the impact of habitat loss will depend not only on its extent, but also on where it occurs. Here, we develop a novel graph-theoretic approach to measure the vulnerability of a migratory network to the impact of habitat loss from SLR based on population flow through the network. We show that reductions in population flow far exceed the proportion of habitat lost for 10 long-distance migrant shorebirds using the East Asian–Australasian Flyway. We estimate that SLR will inundate 23–40% of intertidal habitat area along their migration routes, but cause a reduction in population flow of up to 72 per cent across the taxa. This magnifying effect was particularly strong for taxa whose migration routes contain bottlenecks—sites through which a large fraction of the population travels. We develop the bottleneck index, a new network metric that positively correlates with the predicted impacts of habitat loss on overall population flow. Our results indicate that migratory species are at greater risk than previously realized.

Intake rates and the functional response in shorebirds (Charadriiformes) eating macro-invertebrates

As field determinations take much effort, it would be useful to be able to predict easily the coefficients describing the functional response of free‐living predators, the function relating food intake rate to the abundance of food organisms in the environment. As a means easily to parameterise an individual‐based model of shorebird Charadriiformes populations, we attempted this for shorebirds eating macro‐invertebrates. Intake rate is measured as the ash‐free dry mass (AFDM) per second of active foraging; i.e. excluding time spent on digestive pauses and other activities, such as preening. The present and previous studies show that the general shape of the functional response in shorebirds eating approximately the same size of prey across the full range of prey density is a decelerating rise to a plateau, thus approximating the Holling type II (‘disc equation’) formulation. But field studies confirmed that the asymptote was not set by handling time, as assumed by the disc equation, because only about half the foraging time was spent in successfully or unsuccessfully attacking and handling prey, the rest being devoted to searching.

High-tide habitat choice: insights from modelling roost selection by shorebirds around a tropical bay

High tides force shorebirds from intertidal feeding areas to sites known as roosts. We investigated the roost selection of great knots, Calidris tenuirostris, and red knots, Calidris canutus, on a tropical coastline in northwestern Australia, assessing several roost attributes and recording the frequency of use of each site through automatic radiotelemetry. To model roost choice we used two approaches: (1) conditional logistic regression models that assumed roost selection to be a trade-off based on a probabilistic assessment of several environmental characteristics; and (2) bounds-based models that assumed that birds selected the nearest roost site to their feeding grounds, provided that threshold values for certain environmental characteristics were met. Bounds-based models were more effective, and we suggest that they offer a closer approach to real roost choice mechanisms. By day, roost choice was affected by distance from the feeding area and microclimate; birds selected nearby roosts where they could stand on cool, wet substrates. Different roost selection criteria were used at night when birds chose safer, but more distant, roosts. Models that assumed that roost choice was influenced by recent experience of roost sites performed better than models that assumed constant assessment of roost quality. This effect was significant only at night, suggesting that memory was used more when information on roost quality was limited. Evidence that roost availability may influence selection of foraging areas is also presented. Our results suggest that shorebirds select roosts by using simple mechanisms, making roost choice models a potentially valuable tool in conservation planning.

Behavioural evidence for heat-load problems in Great Knots in tropical Australia fuelling for long-distance flight

Abstract Migratory shorebirds that live in the tropics prior to embarking on long (>5000 km) flights may face heat-load problems. The behaviour of a large sandpiper, the Great Knot (Calidris tenuirostris), was studied in Roebuck Bay, north-west Australia, from February to April 2000. We determined the incidence of heat-reduction behaviour in foraging and roosting birds in relation to breeding-plumage score (an index of migratory preparation) and microclimate variables. Heat-reduction behaviour (primarily raising the back feathers) was significantly related to breeding-plumage score and solar radiation. Raising back feathers may reduce the external heat load for a bird, or increase convective or cutaneous evaporative cooling. The results suggest that managing heat loads in tropical-wintering waders may become more difficult close to departure on migration.

Treatment of capture myopathy in shorebirds: a successful trial in northwestern Australia

Abstract Shorebirds held during banding activities can develop muscle cramps, especially when temperatures are high and birds are heavy. Such capture myopathy can be fatal or render birds vulnerable to predators. We rehabilitated Great Knots (Calidris tenuirostris), Red Knots (C. canutus), Bar-tailed Godwits (Limosa lapponica), and Red-necked Stints (C. ruficollis) in northwestern Australia. We kept birds in slings (if cramped) or in a small cage (if able to walk) and gave them daily standing exercises. Recovery of severely cramped birds took up to 14 d, which may reflect a critical period of tissue regeneration. Of 15 knots (8 Red and 7 Great) taken into captivity, 12 were rehabilitated and released. The resighting rate after the breeding season of the rehabilitated birds was the same as for other birds color-banded during our research, indicating that the rehabilitation was successful. We conclude that rehabilitating cramped shorebirds is possible though time-consuming. A sex bias in susceptibility to capture myopathy is suggested by seven of the eight Red Knots treated being male; the sex ratio in the local population was 1:1.

Rapid population decline in migratory shorebirds relying on Yellow Sea tidal mudflats as stopover sites

Migratory animals are threatened by human-induced global change. However, little is known about how stopover habitat, essential for refuelling during migration, affects the population dynamics of migratory species. Using 20 years of continent-wide citizen science data, we assess population trends of ten shorebird taxa that refuel on Yellow Sea tidal mudflats, a threatened ecosystem that has shrunk by >65% in recent decades. Seven of the taxa declined at rates of up to 8% per year. Taxa with the greatest reliance on the Yellow Sea as a stopover site showed the greatest declines, whereas those that stop primarily in other regions had slowly declining or stable populations. Decline rate was unaffected by shared evolutionary history among taxa and was not predicted by migration distance, breeding range size, non-breeding location, generation time or body size. These results suggest that changes in stopover habitat can severely limit migratory populations.

Continental-scale decreases in shorebird populations in Australia

Abstract Decreases in shorebird populations are increasingly evident worldwide, especially in the East Asian—Australasian Flyway (EAAF). To arrest these declines, it is important to understand the scale of both the problem and the solutions. We analysed an expansive Australian citizen-science dataset, spanning the period 1973 to 2014, to explore factors related to differences in trends among shorebird populations in wetlands throughout Australia. Of seven resident Australian shorebird species, the four inland species exhibited continental decreases, whereas the three coastal species did not. Decreases in inland resident shorebirds were related to changes in availability of water at non-tidal wetlands, suggesting that degradation of wetlands in Australias interior is playing a role in these declines. For migratory shorebirds, the analyses revealed continental decreases in abundance in 12 of 19 species, and decreases in 17 of 19 in the southern half of Australia over the past 15 years. Many trends were strongly associated with continental gradients in latitude or longitude, suggesting some large-scale patterns in the decreases, with steeper declines often evident in southern Australia. After accounting for this effect, local variables did not explain variation in migratory shorebird trends between sites. Our results are consistent with other studies indicating that decreases in migratory shorebird populations in the EAAF are most likely being driven primarily by factors outside Australia. This reinforces the need for urgent overseas conservation actions. However, substantially heterogeneous trends within Australia, combined with declines of inland resident shorebirds indicate effective management of Australian shorebird habitat remains important.

Reclamation of tidal flats and shorebird declines in Saemangeum and elsewhere in the Republic of Korea

Abstract Saemangeum, in the Republic of Korea (ROK, commonly called South Korea) was one of the most important shorebird staging sites in the Yellow Sea. It supported at least 330 000 shorebirds annually between 1997 and 2001, including ∼30% of the world population of Great Knots (Calidris tenuirostris) during both northward and southward migration. Construction of a 33-km long sea-wall was completed in April 2006. We show that shorebird numbers at Saemangeum and two adjacent wetlands decreased by 130 000 during northward migration in the next two years and that all species have declined at Saemangeum since completion of the sea-wall. Great Knots were among the most rapidly affected species. Fewer than 5000 shorebirds were recorded at Saemangeum during northward migration in 2014. We found no evidence to suggest that most shorebirds of any species displaced from Saemangeum successfully relocated to other sites in the ROK. Instead, by 2011–13 nearly all species had declined substantially in the ROK since previous national surveys in 1998 and 2008, especially at more heavily reclaimed sites. It is likely that these declines were driven by increased mortality rather than movement to alternate staging sites given that other studies have shown concurrent declines in numbers and survival on the non-breeding grounds. This is the first study in the East Asian—Australasian Flyway to confirm declines of shorebirds at a range of geographical scales following a single reclamation project. The results indicate that if migratory shorebirds are displaced from major staging sites by reclamation they are probably unable to relocate successfully to alternate sites.

A global threats overview for Numeniini populations: Synthesising expert knowledge for a group of declining migratory birds

The Numeniini is a tribe of 13 wader species (Scolopacidae, Charadriiformes) of which seven are Near Threatened or globally threatened, including two Critically Endangered. To help inform conservation management and policy responses, we present the results of an expert assessment of the threats that members of this taxonomic group face across migratory flyways. Most threats are increasing in intensity, particularly in non-breeding areas, where habitat loss resulting from residential and commercial development, aquaculture, mining, transport, disturbance, problematic invasive species, pollution and climate change were regarded as having the greatest detrimental impact. Fewer threats (mining, disturbance, problematic native species and climate change) were identified as widely affecting breeding areas. Numeniini populations face the greatest number of non-breeding threats in the East Asian-Australasian Flyway, especially those associated with coastal reclamation; related threats were also identified across the Central and Atlantic Americas, and East Atlantic flyways. Threats on the breeding grounds were greatest in Central and Atlantic Americas, East Atlantic and West Asian flyways. Three priority actions were associated with monitoring and research: to monitor breeding population trends (which for species breeding in remote areas may best be achieved through surveys at key non-breeding sites), to deploy tracking technologies to identify migratory connectivity, and to monitor land-cover change across breeding and non-breeding areas. Two priority actions were focused on conservation and policy responses: to identify and effectively protect key non-breeding sites across all flyways (particularly in the East Asian- Australasian Flyway), and to implement successful conservation interventions at a sufficient scale across human-dominated landscapes for species’ recovery to be achieved. If implemented urgently, these measures in combination have the potential to alter the current population declines of many Numeniini species and provide a template for the conservation of other groups of threatened species.

Gull-billed Terns in north-western Australia: subspecies identification, moults and behavioural notes

Abstract Two subspecies of the Gull-billed Tern (Sterna nilotica) occur along the coasts of north-western Australia: the large, pale Australian subspecies macrotarsa, and a smaller, darker migratory subspecies from northern Asia. On the basis of banding data we describe the measurements and moult strategies of both subspecies in north-western Australia and identify the Asian migrants as subspecies affinis. Asian migrants have a predictable plumage cycle including regular alternation between breeding and non-breeding plumage in adults. The moult strategy of Australian macrotarsa is more varied and we argue it is adapted to exploit unpredictable breeding opportunities. Plumage and structural characters described in this paper allow the two subspecies to be distinguished in the field, and field observations demonstrate some broad ecological differences between them. Adult affinis occur in Australia from August to April, with smaller numbers of immatures remaining during the dry season; they are strictly coastal, occurring in highest abundance over intertidal flats near mangrove systems where they pluck prey from the surface of mud while in flight. Subspecies macrotarsa uses the north-western Australian coast as a non-breeding area, but it does so mainly during the dry season and also uses grasslands and inland wetlands; unlike affinis, in Roebuck Bay it is regularly kleptoparasitic, stealing large crabs (Macropthalmus sp.) from Whimbrels (Numenius phaeopus).