Chris J. Hassell

Simultaneous declines in summer survival of three shorebird species signals a flyway at risk

Summary 1. There is increasing concern about the world’s animal migrations. With many land-use and climatological changes occurring simultaneously, pinning down the causes of large-scale conservation problems requires sophisticated and data-intensive approaches. 2. Declining shorebird numbers along the East Asian–Australasian Flyway, in combination with data on habitat loss along the Yellow Sea (where these birds refuel during long-distance migrations), indicate a flyway under threat. 3. If habitat loss at staging areas indeed leads to flyway-wide bird losses, we would predict that: (i) decreases in survival only occur during the season that birds use the Yellow Sea, and (ii) decreases in survival occur in migrants that share a reliance on the vanishing intertidal flats along the Yellow Sea, even if ecologically distinct and using different breeding grounds. 4. Monitored from 2006–2013, we analysed seasonal apparent survival patterns of three shorebird species with non-overlapping Arctic breeding areas and considerable differences in foraging ecology, but a shared use of both north-west Australian non-breeding grounds and the Yellow Sea coasts to refuel during northward and southward migrations (red knot Calidris canutus piersmai, great knot Calidris tenuirostris, bar-tailed godwit Limosa lapponica menzbieri). Distinguishing two three-month non-breeding periods and a six-month migration and breeding period, and analysing survival of the three species and the three seasons in a single model, we statistically evaluated differences at both the species and season levels. 5. Whereas apparent survival remained high in north-west Australia, during the time away from the non-breeding grounds survival in all three species began to decline in 2011, having lost 20 percentage points by 2012. By 2012 annual apparent survival had become as low as 0� 71 in bar-tailed godwits, 0� 68 in great knots and 0� 67 in red knots. In a separate analysis for red knots, no mortality occurred during the migration from Australia to China. In the summers of low summer survival, weather conditions were benign in the Arctic breeding areas. 6. We argue that rapid seashore habitat loss in the Yellow Sea is the most likely explanation of reduced summer survival, with dire (but uncertain) forecasts for the future of these flyway populations. This interpretation is consistent with recent findings of declining shorebird numbers at seemingly intact southern non-breeding sites.

Unexpected diversity in socially synchronized rhythms of shorebirds

The behavioural rhythms of organisms are thought to be under strong selection, influenced by the rhythmicity of the environment. Such behavioural rhythms are well studied in isolated individuals under laboratory conditions, but free-living individuals have to temporally synchronize their activities with those of others, including potential mates, competitors, prey and predators. Individuals can temporally segregate their daily activities (for example, prey avoiding predators, subordinates avoiding dominants) or synchronize their activities (for example, group foraging, communal defence, pairs reproducing or caring for offspring). The behavioural rhythms that emerge from such social synchronization and the underlying evolutionary and ecological drivers that shape them remain poorly understood. Here we investigate these rhythms in the context of biparental care, a particularly sensitive phase of social synchronization where pair members potentially compromise their individual rhythms. Using data from 729 nests of 91 populations of 32 biparentally incubating shorebird species, where parents synchronize to achieve continuous coverage of developing eggs, we report remarkable within- and between-species diversity in incubation rhythms. Between species, the median length of one parent’s incubation bout varied from 1–19 h, whereas period length—the time in which a parent’s probability to incubate cycles once between its highest and lowest value—varied from 6–43 h. The length of incubation bouts was unrelated to variables reflecting energetic demands, but species relying on crypsis (the ability to avoid detection by other animals) had longer incubation bouts than those that are readily visible or who actively protect their nest against predators. Rhythms entrainable to the 24-h light–dark cycle were less prevalent at high latitudes and absent in 18 species. Our results indicate that even under similar environmental conditions and despite 24-h environmental cues, social synchronization can generate far more diverse behavioural rhythms than expected from studies of individuals in captivity. The risk of predation, not the risk of starvation, may be a key factor underlying the diversity in these rhythms.

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.

Mandora Marsh, north-western Australia, an arid-zone wetland maintaining continental populations of waterbirds

Abstract Mandora Marsh in north-western Western Australia floods at intervals of several years to many decades. It flooded in 1999 and 2000, supporting 480000 ± 40000 and 490000 ± 50000 waterbirds in August of each year. Counts of Black-winged Stilts (~180000 and 220000) represented 70% and 80%, respectively, of the estimated Australian population, and counts of Hardheads (~100000) and terns (~110000) comprised considerable portions of the Australian populations of these species. Breeding was prolific and the Marsh appears to be an important breeding site, on the rare occasions it floods, for many species. Waterbird numbers, breeding and movements are discussed in the context that, collectively, the network of arid-zone wetlands, including Mandora Marsh, has a major role in maintenance of Australian waterbird populations. The significance of flooding history and grazing on the biological value of arid-zone wetlands are also discussed briefly.

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).

Mitochondrial-DNA evidence shows the Australian Painted Snipe is a full species, Rostratula australis

Abstract Despite its distinctive morphology, the taxonomy of the Australian Painted Snipe has been unsettled, with some authors treating it as a full species, Rostratula australis (Gould 1838), and others treating it as a subspecies of the Greater Painted Snipe, Rostratula benghalensis. We sequenced the DNA of five mitochondrial genes (Cyt b, ND5, ATP 6–8, COIII and COI) of Australian Painted Snipe, Greater Painted Snipe and South American Painted Snipe, Nycticryphes semicollaris. The sequences of Australian Painted Snipe were 10% different from those of Greater Painted Snipe from Africa and South-east Asia, which differed from one another by only 2%. Plumage and anatomical characters can also distinguish the Australian and the Greater Painted Snipes. Our results clearly indicate that the Australian Painted Snipe is a distinct species that diverged ~19 million years ago (mya) (95% credible interval 13.0, 27.4 mya).

Fuelling and moult in Red Knots before northward departure: a visual evaluation of differences between ages, sexes and subspecies

Abstract The departure of migratory birds from their non-breeding grounds is thought to be driven by the phenology of their breeding destination. In north-west Australia, two plumage morphs of Red Knot (Calidris canutus) prepare for a 5500-kmjourney to Yellow Sea staging areas. These morphs are recognised as the subspecies C. c. piersmai and C. c. rogersi, which breed at different latitudes and have different seasonalities. From February to May 2011, we observed the migratory preparation of individually marked birds of known age, sex and type. This enabled a comparison of fuelling rates and prealternate moult among these classes. First-year birds did not prepare for migration. Second-year birds accumulated smaller fuel stores and reached lower plumage scores than adults. Adults of both types reached their highest abdominal profile scores by the end of April when they were last observed in Roebuck Bay. This lack of difference between types in the timing of fuelling and departure is surprising. Based on the differences in staging and breeding phenology, C. c. rogersi is expected to leave north-west Australia 2–4 weeks before C. c. piersmai. Assuming that types and subspecies are equivalent, our findings in combination with other research on Red Knots in the East Asian-Australasian Flyway suggest that it takes more than breeding origin alone to explain annual cycles in migratory birds. Concurrent migratory schedules imply that, during northward staging in the Yellow Sea, there is strong variation in fuelling rates between and within subspecies depending on non-breeding origin. The ongoing loss of staging habitat may therefore have differential effects on Red Knots in the East Asian-Australasian Flyway.

The large-scale drivers of population declines in a long-distance migratory shorebird

Migratory species can travel tens of thousands of kilometers each year, spending different parts of their annual cycle in geographically distinct locations. Understanding the drivers of population change is vital for conserving migratory species, yet the challenge of collecting data over entire geographic ranges has hindered attempts to identify the processes leading to observed population changes. Here, we use remotely sensed environmental data and bird count data to investigate the factors driving variability in abundance in two subspecies of a long-distance migratory shorebird, the bar-tailed godwit Limosa lapponica. We compiled a spatially and temporally explicit dataset of three environmental variables to identify the conditions experienced by each subspecies in each stage of their annual cycle (breeding, non-breeding and staging). We used a Bayesian N-mixture model to analyze 18 years of monthly count data from 21 sites across Australia and New Zealand in relation to the remote sensing data. We found that the abundance of one subspecies L. l. menzbieri in their non-breeding range was related to climate conditions in breeding grounds, and detected sustained population declines between 1995 and 2012 in both subspecies (L. l. menzbieri, –6.7% and L. l. baueri, –2.1% year–1). To investigate the possible causes of the declines, we quantified changes in habitat extent at 22 migratory staging sites in the Yellow Sea, East Asia, over a 25-year period and found –1.7% and –1.2% year–1 loss of habitat at staging sites used by L. l. menzbieri and L. l baueri, respectively. Our results highlight the need to identify environmental and anthropogenic drivers of population change across all stages of migration to allow the formulation of effective conservation strategies across entire migratory ranges.