Banded stilts fly hundreds of kilometres to lay eggs that are over 50% of their body mass

File 20171017 5062 1qwrxue.png?ixlib=rb 1.1
Banded Stilts feed on a range of invertebrates (including brine shrimp and snails) at saline wetlands across southern Australia.
Ben Parkhurst, Author provided

Reece Pedler, Deakin University; Andy T.D. Bennett, Deakin University, and Raoul Ribot, Deakin University

The hot, dry Australian desert may not come to mind as an ideal location for waterbirds to breed, but some species wait years for the opportunity to do just that.

New research has shed light on one of Australia’s most enigmatic birds, the banded stilt. This pigeon-sized shorebird has long been a source of intrigue due to its bizarre and extreme breeding behaviour. They fly hundreds or thousands of kilometres from coastal wetlands to lay eggs that are 50-80% of their body mass in normally dry inland desert salt lakes, such as Lake Eyre, on the rare occasions they are inundated by flooding rain.

Such behaviour has been a mystery for decades; described for the first time in 1930, just 30 breeding events had been documented for the entire species in the following 80 years.

To investigate this behaviour, and to assess the stilts’ conservation status, we began a study in 2011, during which I was based in outback South Australia, ready to jump into a small plane after every large desert rainfall. We also satellite-tagged nearly 60 banded stilts, using miniature solar powered devices around half the size of a matchbox.

Sixty banded stilts were tagged with solar-powered satellite trackers.
Author provided

This focused survey effort – which required overcoming the logistical challenges of very remote sites, knee-deep mud, heat and flies – has revealed major new insights into how banded stilts breed and the incredible distances they travel: we recorded one bird that flew 2,200km in just two nights.

Fast movers

The research revealed that, on average, banded stilts respond within eight days to unpredictable distant flooding of outback salt lakes. They leave their more predictable coastal habitat to travel 1,000-2,000km in overnight flights to arrive at the newly flooded lakes and take advantage of freshly hatched brine shrimp.

Brine shrimp eggs lie dormant in the lakes’ dry salt crust for years or decades between floods, but upon wetting they hatch in their billions, creating a “brine shrimp soup” – a rich but short-lived banquet for the nesting stilts.

Banded Stilt nests, with clutches of eggs representing over 50-80% of female body weight, litter an island in recently flooded Lake Ballard, in the Western Australian Goldfields 2014.
Lynn Pedler, Author provided

During the six-year study, we detected this nomadic movement and nesting behaviour seven times more often than it had been recorded in the previous 80 years. Although the banded stilts were previously thought to require large once-in-a-decade rains to initiate inland breeding, we found that small numbers of banded stilts respond to almost any salt lake inundation, arriving, mating and laying eggs equivalent of 50-80% of their body weight, despite high chances of the salt lake water drying before the eggs could hatch or chicks fledge.

Many times the eggs were abandoned as salt lake water dried. On other occasions some chicks survived long enough to learn to fly – although late-hatching chicks ran out of food or water and starved.

Once we found out that stilts needed much less rain to breed than previously thought, we used satellite imagery to reconstruct the past 30 years of flooding for ten salt lakes in South and Western Australia.

These models showed that conditions have been suitable for breeding more than twice as often as breeding events have actually been recorded. It seems that stilts’ nesting behaviour is so remote and hard to predict that scientists have been missing half the times it has happened.

Threats to banded stilt survival

Salt lakes in northwestern Australia are vital for banded stilts’ breeding. Our satellite tracking showed that birds from across the continent can reach these lakes after rain. Satellite images also suggested these lakes fill with water much more frequently than southern breeding sites.

These lakes are also largely free of native silver gulls (the common seagulls seen around our cities), which are predators of stilt chicks.

Silver Gulls fighting over a banded stilt chick on Lake Eyre. These gulls found in Australian cities also fly inland after rain and can decimate some Banded Stilt breeding attempts – eating thousands of eggs and chicks.
Reece Pedler, Author provided

But other southern Australian breeding lakes are dramatically affected by gull predation. In one instance, a colony of 9,500 pairs (around 30,000 eggs) had less than 5% of its chicks survive, despite abundant water and brine shrimp on offer. Observations made near the colony suggested that a chick was being eaten by gulls every two minutes. Nearly 900 chicks and 350 eggs were eaten in the 30 hours we watched the colony.

Unfortunately, even the lakes that are relatively gull-free are now under threat from human development, despite being in one of the most remote parts of the world. Lakes Disappointment, Mackay, Dora, Auld and others surrounding them in the Little Sandy and Great Sandy Deserts are the subject of plans for potash mining.

The most advanced plans relate to Lake Disappointment, where Reward Minerals plans to construct a series of drainage trenches and 4,000 hectares of evaporation ponds on the lake bed to harvest potash for use in fertilisers.

This action will create permanent brine pools in some parts of the lake, and prevent other areas from receiving any water. As surface water drains into evaporation ponds, it’s likely the first rains after a long dry spell will no longer prompt mass brine shrimp hatching. Without this brine shrimp “soup”, banded stilts cannot breed at the site.

A tiny island on Lake Torrens SA, covered by 70,000 Banded Stilt nests in 2010.
Paul Wainwright, Author provided

Meanwhile, the coastal habitat that supports banded stilt for the rest of the year is also changing. Sites that are home to thousands of birds, such as parts of the Dry Creek Saltfields and Bird Lake in South Australia, have been drained in the past two years.

If both the stilts’ inland breeding and coastal refuges are under threat, how can they survive?

Lessons for managing mobile species

This research offers insight into the conservation of highly mobile species, which may travel hundreds or thousands of kilometres in a year. Banded stilts are listed as vulnerable in South Australia, but have no conservation rating in the four other states in which they are found.

Individual banded stilts appear to operate over vast spatial scales, crossing between state jurisdictions in single overnight flights. Their episodic breeding events are hard to find and even more difficult to manage. Between breeding events, long-lived adults depend on refuges around the country which are being impacted by human activity, including potentially longer, harsher dry periods from climate change into the future.

These birds epitomise adaptation to unpredictable changes in their environment, but habitat loss and a warming climate may threaten them as much as any other species.

The ConversationThe authors would like to acknowledge L. Pedler, M. Christie, B. Parkhurst, R. West, C. Minton, I. Stewart, M. Weston, D. Paton, B. Buttemer and the South Australian Department for Environment, Water and Natural Resources, and Western Australian Department for Parks and Wildlife._

Reece Pedler, PhD student, Deakin University; Andy T.D. Bennett, Professor, Deakin University, and Raoul Ribot, Lecturer in Ecology, Deakin University

This article was originally published on The Conversation. Read the original article.


Africa: Scimitar-Horned Oryx Reintroduction to Wild

I am a massive fan of rewilding and of the reintroduction of species back into the wild, so the link below to an article on the reintroduction of Scimitar-Horned Oryx into the Southern Sahara is great news.

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How insight into southern Africa’s dolphins is being deepened

Simon Elwen, University of Pretoria

South Africa has a wide range of oceanographic conditions around the coast. As a result, there is a diversity of cetacean species. These are large-bodied, fast-moving top predators like dolphins and whales. Globally, at least a quarter of these species are listed as endangered. Understanding how these species move and live is crucial to understanding their ecological relationships with the environment.

The E3C – Effect of Climate Change on Cetaceans – project looks at the impact climate change has on these species. The Conversation Africa’s energy and environment editor Ozayr Patel spoke to Dr Simon Elwen, a researcher with South Africa’s University of Pretoria working on the project.

Globally, at least a quarter of whale and dolphin species have been listed as endangered. What are the main reasons?

Many of the large whale species and populations that were subjected to commercial whaling have been very slow to recover, notably the Antarctic blue whale and the North Atlantic right whale. But the majority of large whale populations have been increasing slowly over the past few decades. Species are gradually leaving the threatened lists, thanks to wide-ranging international conservation efforts. The most important of these is the end of whaling, showing that stopping directed take – in other words “not killing animals” – is one of the most effective conservation strategies.

But the bad news is that many dolphin and porpoise populations are the ones now facing extirpation. The Maui’s dolphin of New Zealand and the vaquita of the gulf of California are both critically endangered. The baiji, the Chinese river dolphin, has already been declared extinct due almost entirely to habitat loss in the Yangtze River in China.

What is the state of dolphin species around Africa’s coasts? What threats do they face?

In southern Africa most dolphin populations are thought to be fairly healthy. There are five species that are regularly seen from shore, including the Heaviside’s and dusky dolphin on the west coast and the Indo-Pacific bottlenose and Indian Ocean humpback dolphin, which are found to the east of Cape Point in Cape Town. There are several other species that inhabit the shelf and offshore waters, with the common dolphin being one of the few of these regularly seen close to shore, especially along the south-eastern part of the continent. The only species that is currently thought to be of concern is the humpback dolphin, Sousa plumbea.

The humpback dolphin lives along the southern Cape coast and off northern KwaZulu-Natal province. This entire population in South Africa likely numbers less than 1,000 individuals and lives extremely close to shore, where it regularly encounters humans. This results in things like boat traffic, pollution, habitat loss and prey depletion having an impact on these species.

Why are dolphins, in particular, important in the ocean’s ecosystem?

Dolphins and whales are large, highly mobile top predators. They can eat a lot of food and respond quickly to changes in the environment by moving large distances, depending on the species. As large predators, they can have a top-down role in ecosystems, suppressing the numbers of prey animals. What this means is that sometimes species near the bottom of the food chain, like sardine or anchovy, can increase when medium-level predators are removed by top predators such as seals, sharks and dolphins, a result shown in a number of ecosystems globally.

Dolphins and
whales are known to be top predators.

Simon Elwen

What is unique about the South African coast that makes it so diverse?

South Africa’s marine life at all trophic levels is remarkably diverse, thanks largely to the diversity of habitats available around the coast. It ranges from tropical at the Mozambique border, to temperate along the south coast and cool-temperate along the west coast.

From a mammal point of view, the cold waters of the Benguela ecosystem along the west coast provide a link to sub-Antarctic environments, so some species that are usually only found south of 40 degrees of latitude also occur in the Benguela, like southern right whale dolphins and pygmy right whales.

Commercial fishing practices, gill nets and pollution are viewed as the most serious challenge to dolphins. Are these serious problems in African and South African waters?

To the best of my knowledge, bycatch – the unintentional catching of a species – is thankfully not a major problem in South Africa. There is no gill netting in South Africa. Coastal net fisheries are scarce and most of the large-scale commercial fishing activities in South Africa occur in deeper waters than most of our coastal dolphin species occur.

But entanglement in lobster and octopus trap lines is an increasing concern for large whales in coastal waters. Recent data on organic pollutants in dolphins from the east coast suggests that DDT and polychlorinated biphenyls are still a concern, especially for coastal dolphin species like the humpback and bottlenose.

What effect is climate change having on dolphins?

Essentially, assuming no other changes in the ecosystem – which is somewhat naive – we expect a general pole-ward shift in the distribution ranges of most cetacean species. This isn’t likely to be a major problem for animals that move large distances in the relatively uniform and connected environment of the open ocean. But it will potentially have major impacts on some coastal species, especially those that live in habitats that are “dead ends” in this respect (like the southern coast of Africa).

Along the South African coast, several dolphin species live in the Benguela, which is currently thought to be cooling – against the general trend of climate change – due to increased winds and upwelling of cold water. Right now we don’t really know how adaptable these animals are to massive changes in temperature in either direction, should they occur.

What other major conservation tactics are used to help dolphins survive and thrive?

1) Don’t kill them! In any form, including entanglement or bycatch, hunting or pollutants.

2) Stop polluting the oceans – including noise, plastics and organic pollutants.

3) Stop harassing them – obey the laws and use responsible tour operators.

4) Don’t steal their food – eat sustainably caught fish

You have started a project involving citizen scientists. Why have you taken this route?

Citizen science projects have been extremely successful both locally and internationally. Modern communication methods like mobile phones and the internet allow scientists to rapidly communicate with thousands of interested and knowledgeable observers to increase the number of eyes and ears available to collect data. We can’t be everywhere, and our boat surveys and acoustic methods are limited in the amount of area or time they can cover, so we are trying to take advantage of the large number of keen whale and dolphin watchers around our Cape Town’s coasts to report sightings to us.

Remarkably, the area around Cape Town itself has been quite poorly studied by cetacean scientists in the past. So citizen science offers us a potentially powerful route to massively increase the number of data points of dolphin and whale sightings around the area.

The Conversation

Simon Elwen, Research Fellow, Mammal Research Institute, University of Pretoria

This article was originally published on The Conversation. Read the original article.

Africa’s Fairy Circles

The link below is to an article that looks at the Fairy Circles of southern Africa.

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African Elephant: Another Massacre – Chad

There has been another elephant massacre in Africa – this time in southern Chad. The link below is to an article reporting on the tragic loss.

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Largest Group of Beck’s Petrel Ever Recorded

Though only rediscovered in 2007, Beck’s Petrel appears to have made a significant comeback. The largest group ever recorded was recently found in southern New Ireland, Papua New Guinea.

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