Flying high with Great Snipe

As tagging devices get smaller and more sophisticated, they are revealing even more wonders of shorebird migration. We already know that Great Snipe are amazing – flying up to 7,000 km non-stop – but a 2021 paper by Åke Lindström and colleagues describes a striking daily cycle of altitude change during their long migratory journeys.

In their new paper in Current Biology, Åke Lindström and colleagues have used activity and air pressure data from multisensor dataloggers to show that Great Snipes repeatedly changed altitudes around dawn and dusk, between average cruising heights about 2,000 m (above sea level) at night and around 4,000 m during daytime. Most birds regularly flew at 6,000 m and one bird reached 8,700 m, an altitude that is just 150m short of clearing the top of Mount Everest! The same daily cycle was apparent everywhere – independently of climate zone, habitat and the height of the land being overflown. Wherever they are, as morning breaks migrating Great Snipes gain altitude – but why?  

Great Snipe

Great Snipe spend the winter in Africa, between 20 degrees south and 15 degrees north of the equator, heading north in spring to breeding areas in Scandinavia and northern Europe, as far east as 95°E (which is the same longitude as Myanmar).

The first paper to reveal the remarkable migration of Swedish Great Snipe appeared in Biology Letters in 2011, when Raymond Klaassen, Åke Lindström and colleagues revealed the tracks from three birds carrying geolocators. During these journeys, these individuals made long and fast autumn movements, covering between 4300 and 6800 km in two to four days and overflying suitable stopover sites that were used in spring. Ground speeds of 15 to 27 m/s are equivalent to between 54 and 97 km/h (33 to 60 miles per hour).

In 2016, using 19 tracks from four years of captures and recaptures, the same team published a paper in the Journal of Avian Biology. About half of the birds flew directly from the breeding grounds to sub-Saharan Africa, the others making a few shorter flights down through Scandinavia before embarking on a long trans-Sahara flight. Birds took advantage of wet seasonal conditions in this Sahel region for three weeks before moving south to the Congo Basin. Spring migration consists of a rapid movement across the Sahara, only a little shorter than the very long non-stop autumn fights, followed by slower movements through Eastern Europe. Birds arrived back on breeding areas in mid-May.

Great Snipes spend about eight months of the year in sub-Saharan Africa. In a 2017 paper in Wader Study, Edouard Debayle, Åke Lindström and colleagues analysed the moult and fattening patterns of over 3,000 hunted birds, to try to learn more about the phenology of migration. They discovered that:

• Adult males arrived in Africa from mid-August, having started and suspended the moult of the main flight feathers before arrival.
• Females on average arrived somewhat later and were about one month behind in the progress of flight feather moult.
• The adults of both sexes resumed primary and secondary moult immediately upon arrival and typically completed it by the end of November, in males, and the end of December in females. Juvenile Great Snipes arrived later than adults and did not moult their flight feathers in the first autumn/winter.
• Males apparently departed northwards between late March and late April, and the females about two weeks later. There is information about rates of fat deposition in the paper.

Great Snipe watches on as team members set a mist net

Flying high

Processing the catch

Several factors could influence the flight altitude of migratory birds. For example, how high is the land over which birds fly, what are the best temperatures and humidity conditions for efficient flight, at what height can a bird find the most helpful winds, can a bird use navigation landmarks and how can predation best be avoided?

Recent tracking of migratory birds of a range of species has shown that individuals change flight altitude more commonly and dramatically than previously thought but why? In their paper in Current Biology, Åke Lindström and colleagues reveal information from 25 tracked Great Snipe journeys and discuss the reasons that may lie between the patterns that they see.

Methods

Information about behaviour and flights was collected from multisensor dataloggers, consisting of an accelerometer for activity measurements, a barometric pressure sensor with internal temperature sensor, a light-level sensor, a real-time clock, and memory. The dataloggers weighed 1.4–1.7 g (about 1 % of a bird’s total body mass) and were attached to a plastic ring on the bird’s tibia.

In total, 107 dataloggers were put on Great Snipes between 2015 and 2019. Of these, 36 birds were retrapped one, two or three years later (but four birds had lost their loggers). This is an overall recapture rate of 34%, which is similar to the figure for ringed birds. In total, 25 out of the 32 retrieved loggers had functioned for some time, and 16 carried information on flight altitude for at least one of the long flights.

The methods section provides full details of how geolocator data were interpreted and altitudes were calculated and adjusted. Information on air temperatures at different altitudes and the topological features on flight paths provided a background against which to try to understand migration patterns.

How high?

The new data from a small number of multisensor data-loggers greatly enriched the migration story of Swedish Great Snipe, as revealed byÅke Lindström and colleagues. The key results in the Current Biology paper are:

Breeding habitat in Sweden

Flight duration: There were three long flights, two legs on the way south and one on the way north. As noted earlier, northerly migration slowed once birds landed in Europe.

• On average, male Great Snipe left Sweden on 24^th August and flew across Europe and the Sahara for 73.4 hours, before landing in the Sahel.
• The mean departure date from the Sahel was 24^th September. An average of 23.2 hours later a bird would land in the Congo basin.
• Northerly flights commenced on 18^th April, lasting an average of 82.4 hours and concluding in Europe.

Cyclic flight altitudes: There was an overall strong and consistent daily cycle in the altitudes used by the Great Snipes, in all three long flights. After a night at moderate to high altitudes the birds ascended to very high altitudes in early morning, stayed at these levels during the day, and descended again in late afternoon. They then repeated this cycle for one or two more days.

• The mean individual daytime flight altitude in the first Autumn flight was on average 4,549 m, compared to 2,126 m at night.
• For the In-Africa autumn flights, comparative figures were 3,874 m in daytime and 1,860 m at night.
• For the Spring flights, comparative figures were 4,114 m in daytime and 1,612 m at night.

These altitudes were estimated from air pressure readings and may be underestimates. For comparison, the highest point in the Alps is 4807 m.

Peak altitudes: Some Great Snipes occasionally flew extremely high and then always during daytime. Three birds in Autumn and two birds in Spring reached 7,000 m or more. Migratory waders are able to carry out flapping flight at such high altitudes due to several physiological adaptations of the heart, lungs and muscles. The single highest altitude estimate of 8,077 m was reached in Autumn. If air pressure is accounted for this bird may have been flying above 8,000 m for five hours, perhaps reaching an altitude of 8,700 m, and coping with an air temperature of -21.3 °C. Putting this in a local context for readers: Mount Everest is 8848m high and the high points in other regions of the world are: Africa (5895 m Kilimanjaro), South America Aconcagua 6959 m, North America Denali 6190 m and New Zealand Mt Cook 3754 m.

Ambient temperature, wind condition and humidity appeared not to influence the differences in day and night altitudes chosen by Great Snipes.

Discussing the results

Great Snipe with a datalogger

The daily pattern of altitude changes for Great Snipes was very similar between Autumn, In-Africa and Spring flights, suggesting a common cause that is largely independent of climate zone (temperate or tropical), topography and landscape overflown (forest, savanna, farmland, desert or water). Altitude changes have been reported for other waders, such as Black-tailed Godwits, that have been linked to both ambient temperatures and finding more beneficial winds.

The authors discuss the possibility that landmarks are easier to see from a higher altitude when flying in daylight and suggest that predator avoidance may also account for higher day-time elevations. It would be interesting to know if a daily cycle is apparent in long flights over areas largely lacking bird predators, such as vast oceans.

There is no daily cycle in ambient air temperature or wind conditions at high altitudes that could explain the overall regular pattern of flight altitude selection found in Great Snipes but the authors discuss the theory that the warming effect of solar radiation may be countered by flying through colder, higher air. The temperatures at these heights would be too cold at night.

There are still few papers that provide altitude data for long-distance migrating birds but all of them report altitude changes and have revealed some surprisingly high flight altitudes. With more studies we may well find that migration is even more impressive than we already thought!

Paper

The full methods, results and discussion can be read in the paper in Current Biology.

Extreme altitude changes between night and day during marathon flights of Great Snipes Gallinago media: Åke Lindström, Thomas Alerstam, Arne Andersson, Johan Bäckman, Peter Bahlenberg^, Roeland Bom, Robert Ekblom, Raymond H. G. Klaassen, Michał Korniluk, Sissel Sjöberg & Julia K. M. Weber.

---

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.

Dunlin: tales from the Baltic

Veli-Matti Pakanen, Kari Koivula  and colleagues have been studying Finnish Dunlin for nearly twenty years. These are schinzii birds that breed in coastal grazing meadows around the Baltic Sea. Several papers have been published, as you will see below, some of which are based on information collected using geolocators attached to leg-flags. Dunlin numbers in coastal Finland are dropping quickly, so this research is important to the conservation of the species. In a 2020 paper, Veli-Matti and colleagues ask whether intensive geolocator-based studies are having a negative effect on individual birds in this already-declining study population.

Global Dunlin

Up to ten races of Dunlin have been identified, which together encircle the globe. Most Dunlin spend the non-breeding season in the northern hemisphere and all migrate north in spring. The breeding and wintering ranges of the various races are summarised at the end of this blog. Here, the focus is on Baltic schinzii Dunlin, a small part of a race that largely winters in coastal North Africa and breeds in southern Scandinavia, Northern Europe, the British Isles, Iceland and southern Greenland.

According to Wetlands International, there were between 4.3 and 6.8 million Dunlin worldwide in 2015, with about one million breeding birds within Europe (BirdLife International). Whilst it is acknowledged that numbers are declining, the large range of the species means that it is still considered to be of ‘least concern’.

Different populations are faring differently. In his description of the changing Dunlin distribution in European Breeding Bird Atlas 2, John Calladine points out that there have been major losses across Europe, including Britain & Ireland, and that Baltic populations ‘are now considered threatened’. The Baltic schinzii population was most recently estimated as between 500 and 640 pairs – less than a fifth of the estimate in the 1980s. John highlights gaps in knowledge that research by the team in Finland and other groups elsewhere are helping to fill.

Migration and survival of schinzii

Dunlin that visit the UK are mostly of the schinzii and alpina races, as indicated in this map. There has been a noticable drop in the number of schinzii birds stopping off in July.

In pre-geolocator days, Ole Thorup and colleagues analysed recovery information available for Dunlin breeding around the Baltic, using 40 years of ringing data from Finland, Sweden, Denmark and Germany. At that stage there were only six mid-winter recoveries in N and NW Africa. The analysis emphasised the importance of wintering and stop-over sites in the Baltic, the Wadden Sea, SE and S England, the Atlantic seaboard of France, and the Iberian Peninsula. Paper in Ardea (2009).

Pakanen et al investigated changes in the survival rates of schinzii Dunlin nesting in Denmark, based on ringing and recaptures of a marked population. They found that annual apparent survival rates dropped from 0.817 to 0.650 between 1990 and 2006, equivalent to a doubling of the chance of dying in any given year. Paper in Bird Study (2016). The importance of monitoring survival rates is discussed in the WaderTales blog: Measuring shorebird survival.

Nests in these flat coastal marshes along the Baltic coast are increasingly susceptible to summer flooding

The use of geolocators enabled Veli-Matti Pakanen to add more detail to the migration story in the 2018 paper, Migration strategies of the Baltic dunlin: rapid jump migration in the autumn but slower skipping type spring migration. He and his colleagues showed that autumn migration is faster than spring migration, characterised by fewer stationary periods, shorter total stopping time and faster flight. The Wadden Sea was found to be an important autumn staging area for all of the tagged birds. Some birds stopped once more before reaching Mauritania. On spring migration, more sites were visited on the way north. The important conservation message from the paper is that Baltic Dunlin may be especially vulnerable to rapid environmental changes at their staging and wintering areas. (In Travel advice for Sanderling there is a suggestion that annual survival is relatively low for birds that winter in Mauritania).

In a 2015 paper in Ornis Fennica, Pakanen et al reported on the results of a single-year analysis of survival rates, concluding that there were no strong effects of leg-flagged geolocators on return rates or reproduction in schinzii Dunlin. However, they did suggest that “long term evaluations that capture the full suite of environmental conditions and assess impact on brood care are needed”. This is a question which leads us neatly on to the 2020 paper: Survival probability in a small shorebird decreases with the time an individual carries a tracking device.

Long-term tracking of individuals

To understand the range of pressures that migratory birds face, one needs to know where individuals spend their time, as was demonstrated in Spoon-billed Sandpiper: Track & Trace and Teenage Waders. Waders of a range of species have been wearing geolocators for ten or more years now, either the same devices on birds which have evaded capture, or a series of tags, when data have been downloaded and replacement tags fitted. These long-term surveys are developing our understanding of the repeatability of migratory behaviour and how birds deal with variable weather patterns, but is there a long-term cost to the individual birds that are tasked with finding out this important information?

This Dunlin wore a ring-mounted geolocator for one year, to collect movement data

Effects of tracking devices on survival are generally considered to be small. However, most studies to date have focused on birds that were caught in one breeding season and recaptured in the following season, to retrieve the geolocator and download the data. In their 2020 paper, Veli-Matti Pakanen and colleagues were able to investigate the possible accumulation of negative effects when individuals have carried the tracking devices for longer periods. Survival rates for tagged birds were compared with 338 colour-ringed birds that were followed for all or part of the period 2002 to 2018.

In the summers of 2013 & 2014, fifty-three adult schinzii Dunlin were fitted with leg-flag mounted geolocators, with a mass equivalent to 1.5 – 2.0% of body-mass. Of these birds, 17 tags were retrieved after one year and 9 after two years. Other marked birds could not be caught and carried their tags for longer periods (3 or 4 years). The research team found that Dunlin carrying a geolocator had reduced chances of survival. Their models suggest that annual survival of colour-ringed males was 0.813. For a bird that carried a geolocator for a year, annual survival probability declined to 0.748 and to 0.581 for birds that carried the geolocator for at least 2 years. Their data suggest that the reduction in survival rates was greater for females than males, even though females are larger than males.

Summer flooding of coastal breeding area is becoming an increasing problem, and likely to get worse with sea-level rise and more chaotic weather patterns

In a thorough Discussion, the authors consider reasons why tags on small waders may be reducing survival, either through ongoing stresses, impacting on things such as feeding efficiency and the energy needed during migration, or because the extra burden means that tagged birds find it harder to cope with occasional periods of tough environmental conditions. They comment on the condition of the skin under removed geolocators – something that other researchers night want to look out for.

As anyone studying breeding waders will know, nest-trapping to retrieve tags is not easy, especially if adults lose their clutches when incubation has only just started, due to flooding, predation etc. Birds may end up carrying tags for longer than intended. The authors “recommend that the detrimental effects of tagging may be avoided by developing attachment methods that are automatically released after one year, e.g. biodegradable materials”.

Balancing costs and benefits

The results from the Pakanen study of long-term survival suggest that requiring a small wader to carry a geolocator for several years may have an impact on survival. As in all mark-recapture studies, researchers are urged to assess the costs to the individual when seeking to understand what might be affecting the viability of a population.

Four previous WaderTales blogs have discussed tag effects:

• Are there costs of wearing a geolocator? (a multi-species analysis of leg-mounted geolocators)
• Leg flags and nest success (four small species of American shorebird)
• Green Sandpipers and Geolocators (geolocators mounted on harnesses)
• Flagging up potential problems (flag/geolocator effects in Common Sandpipers)

Details of the Dunlin tagging effects study:

Survival probability in a small shorebird decreases with the time an individual carries a tracking device.

Veli-Matti Pakanen, Nelli Rönkä, Thomson Robert Leslie, Donald Blomqvist, Kari Koivula. Journal of Avian Biology (2020): https://doi.org/10.1111/jav.02555

Four other papers relating to this Finnish Dunlin study

Grazing by cattle is an important management tool in coastal meadows. Pakanen et al studied the impact of trampling on artificial nests and concluded that even recommended stocking rates were too high for chick numbers that could deliver a sustainable population. Paper in Biodiversity and Conservation (2011). (Redshank on British estuaries are similarly vulnerable to trampling – see Big Foot and the Redshank Nest).  

In a follow-up paper in 2016, Pakanen et al concluded that Dunlin populations could be sustained in grazed coastal meadows as long as there was no active grazing before 19 June. Meadows with grazing cattle attracted breeding birds but there was insufficient breeding success for sustainability. Paper in Ecology & Evolution (2016).

If these schinzii Dunlin chicks return to breed they are likely to try to nest nearby; something that needs to be considered when considering conservation measures

Dunlin are strongly philopatric, with both male and female chicks recruiting to suitable habitat close to natal sites. In a paper in Ibis (2017), Pakanen et al show that natal dispersal of Dunlin is strongly linked to the size of their natal site and how isolated the site is. They suggest that inbreeding may be avoided by creating a network of suitably sized patches (20–100 ha sites), no more than 20 km apart from each other. These may work as stepping stones for recruiting individuals. These results are corroborated by a 2021 microsatellite study in BMC Ecology and Evolution which shows genetic differentiation and isolation by distance within the Baltic Dunlin population.

Up to ten races

In western Europe we see three races of Dunlin – alpina, arctica and schinzii. Wintering birds are almost exclusively of the alpina race, which head north and east to northern Scandinavia, Russia and Siberia in spring. The other northern race is arctica, a very small Dunlin that breeds in low numbers in NE Greenland and possibly Spitzbergen. Schinzii has a very large breeding range, spanning the Baltic, southern Scandinavia, Northern Europe, the British Isles, Iceland and SE Greenland. There is huge variation in the timing of breeding of schinzii, as birds do not return to breeding sites in SE Greenland until the end of May, at the same time as schinzii Dunlin being studied by Veli-Matti Pakanen and colleagues in Finland will have their first young chicks.

Further east, centralis Dunlin replace alpina. Many of these birds use the Central Asian Flyway. Further east still, we find sakhalina that use the East Asian/Australasian Flyway (EAA). Two other subspecies have been identified breeding within the EAA Flyway, the more southerly kistchinski birds and actites, which breeds furthest south, on the Russian island of Sakhalin, on a similar latitude to the UK.

It is generally accepted that there are three Dunlin subspecies in North America. In autumn, arcticola head west from northern Alaska and NW Canada and follow the EAA Flyway, pacifica fly south along the Pacific coast from SW Alaska and hudsonia migrate from central northern Canada using the Atlantic Americas Flyway.

---

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.

More Curlew chicks needed

There are three ways to increase the number of Eurasian Curlew in the UK; boost chick production across the breeding range, find ways to ensure more chicks recruit to the breeding population and/or maximise the lifespan of breeding birds. In a paper in Biological Conservation, Aonghais Cook and colleagues show that, while continued protection of wintering sites is really important, there appears to be little scope for conservation action that can further increase annual survival rates. The focus for conservationists has to be on increasing chick productivity and recruitment.

Curlew in Britain and Ireland

The once-common breeding Curlew is becoming harder to find in many areas. We know that productivity is generally low but could reduced annual survival rates also be contributing to the speed of disappearance? Here’s a quick summary of the story so far.

• The Eurasian Curlew is designated as ‘near threatened’, as discussed in this WaderTales blog.
• A 2017 paper by Sam Franks and BTO/RSPB colleagues described the main factors associated with the species’ decline in Great Britain. This work is summarised in a WaderTales blog called Curlews can’t wait for a treatment plan.
• Estimated breeding population declines since 1995 are 69% in Wales, 59% in Scotland and 31% in England (Breeding Bird Survey). This is not as bad as in Ireland, where 96% were lost between the 1980s and 2015-2017. See Ireland’s Curlew Crisis.
• Huge numbers of Curlew cross the North Sea at the end of the summer, particularly from Finland. Recent population estimates show that British wintering numbers dropped by 14% in just eight years, with an Irish decline of 13% in five years. See two reviews of wader population estimates, based upon waterbirds papers in British Birds and Irish Birds.

Survival of adult Curlews

As discussed in Measuring shorebird survival, a change in adult survival rates can have a huge effect on shorebird populations. If a species’ annual survival rate drops from 90% to 80% then numbers can half in just six years. We have seen these sorts of dramatic declines in populations of waders that travel between Russia/Alaska and Australia. There’s more about this in Wader declines in the shrinking Yellow Sea.

There are several factors that could be affecting survival rates of British-wintering Curlew:

• Warmer winters might be expected to lead to increased survival rates.
• The shooting ban, introduced in 1982 in response to declining Curlew numbers, was specifically designed to increase survival rates.
• As local wintering populations have dropped, competition for resources could have dropped, potentially leading to increased survival rates.

In their paper about survival rates of Curlew in North Wales, published in Bird Study in 2013, Rachel Taylor and Steve Dodd detected an increase in apparent survival from 86.9% to 90.5% that coincided with the cessation of hunting. They also found that mechanical cockle harvesting in the mid-1990s occurred at the same time as a reduction in apparent survival rate of Curlew from 95% to 81%, indicating the potential for management changes to have huge, unintended consequences for wintering Curlew.

Amassing the data

The research team analysed recoveries of Curlew marked as chicks and adults in the breeding and winter periods, in order to estimate annual survival and the proportion of birds available to recruit into the breeding population.

Thanks to the efforts of skilled, volunteer ringers, two large data-sets were available, collected during the period 1970 to 2018:

• A total of 1293 adult birds, 144 juveniles and 14,277 chicks were ringed in their breeding grounds across Great Britain.
• During the winter period, 4403 Curlew were caught and ringed in five key sites – the Severn Estuary, the Tees Estuary, the Wash, Traeth Lavan and the Moray Firth (see map). Supplementary colour-ring sightings were available for the Wash, Tees and Severn.

Full details of how data were used and how models were developed are provided in the paper.

How well do Curlew survive?

Analysis of breeding season data for the period 1970 to 2018 indicates that the average annual survival was 89.8% (confidence interval 0.871–0.920) for adults and 32.6% (0.278–0.378) for first-years. The period of steepest population decline, between 1983 to 1991, coincided with lower survival in both age classes. Encouragingly, since 1996, survival has increased to 92.2% (0.886–0.948) for adults and 39.0% (0.304–0.484) for first-years.

The British and Irish wintering population of Curlew is drawn from a vast area, with birds arriving from as far as Russia and lots of birds from Finland. In a recent breeding wader report covering the Fennoscandia region, no overall change in Curlew numbers was detected, with declines in Norway and Sweden balanced by increases in Finland (see Fennoscandian Wader Factory). From 1970 to 2018, survival rates of UK wintering Curlew averaged 88.4% (0.875–0.893), consistent with survival rates of the British breeding population (above).

Survival varied over time and between the five study sites but has been generally greater than 90% in recent years. Increases in survival were recorded on the Severn Estuary and The Wash.

Curlew struggle in winters with large number of frost-days and survival rates drop significantly, both in that winter and over the subsequent year

Survival was lower in winters with a greater number of days of air frost, an effect exacerbated in successive cold winters. Cold weather may have contributed to low survival in the 1980s, a pattern also evident in the analysis of breeding season data.

Resources may limit numbers. The study suggests that, for four out of five sites, survival was lower in years in which the number of Curlew on a site was higher.

Nationally, the research team found no strong evidence that the hunting ban had increased survival rates. However, there appeared to be local effects on The Severn Estuary and on the Wash. It is unfortunate that national bag data are not available to indicate whether Curlew hunting was particularly prevalent in these two estuaries in the period prior to 1982.

What does this all mean for Curlew conservation?

Birdwatchers are helping to monitor annual survival rates by reporting sightings of colour-marked birds

Since 1996, the mean annual adult survival rate of the British Curlew breeding population has been about 92%. Despite this high number, the Breeding Bird Survey tell us that there has been an observed decline in breeding numbers of 3% per year. Demographic modelling suggests that four breeding pairs must be producing an average of only one chick per year between them. This low figure may come as no surprise to Curlew fans.

To achieve sustainability, the authors conclude that the current figure of 0.25 chicks per pair needs to rise to 0.43 chicks per pair. There are estimated to be 58,000 pairs of Curlew in Great Britain (paper in British Birds). Currently they might be producing about 14,500 chicks each year, on average, and they need to produce nearly 25,000 chicks. British Curlew need to fledge 10,000 more youngsters – every year – just to arrest the decline in numbers.

Personal reflections

Currently, annual survival rates of adults are consistently high but a couple of cold winters, changes to shellfish policy, tidal barrage developments, inappropriately-sited wind turbines and unrestricted disturbance could all have serious negative effects. It is important that we continue to protect the UK’s estuaries and the grassland feeding and roost sites that fall outside their boundaries.

Many Curlew spend significant amounts of time on farmland and recreational land that is not protected in the same way as estuarine habitats

There are a couple of gaps in our knowledge about Curlew demography. When do Curlews first breed and what are survival rates during the ‘teenage’ pre-breeding years? A working hypothesis would be that most breed at age two, with possibly some earlier and probably some later. More colour-ringing of chicks will hopefully provide better data on recruitment age and teenage survival rates. This issue was discussed in Teenage waders. In the meantime, perhaps more thought needs to be applied to avoiding disturbance of non-breeding flocks during the summer holiday season?

It is going to be important to understand how quickly juveniles recruit to breeding populations

It almost goes without saying – Curlews need to produce more chicks. Local conservation initiatives, whether by tenant farmers or dukes with vast estates, will help but raising 10,000 more chicks per year will likely require changes in land management policies. Can agri-environment initiatives be refined to deliver more Curlew? How do we integrate tree-planting and upland conservation priorities? Where should wind turbines be sited? And so much more!

Paper

In their summary of their paper, Aonghais Cook et al concluded that “In addition to increasing productivity, effective conservation strategies will need to maintain high levels of survival, which requires an improved understanding of population connectivity and demographic variation throughout the annual cycle.”

The full paper can be read here:

Temperature and density influence survival in a rapidly declining migratory shorebird.

Aonghais Cook, Niall Burton, Stephen Dodd, Simon Foster, Robert Pell, Robin Ward, Lucy Wright & Robert Robinson. Biological Conservation

---

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.