Migration:

A paradox of 

dangers

Photo by Barth Bailey on Unsplash

Mass migrations are perhaps one of the greatest marvels of behavioural evolution, from the wildebeest crossing the Serengeti to the migration of Australian white shark to South Africa each year, the need to move great distances can be seen across the natural world. However, few can consider themselves as well adapted for migration as birds, with the Arctic turn travelling more than 35,000 miles each year to reach its breeding grounds. 

But why do species migrate?

With such a demanding passage often killing many of those that attempt it, why not simply stay put? 

For some species including most mammal migrations, the answer is food. Whether it’s the currents of our oceans moving whole ecosystems to new areas, or the seasonal rain finally returning to the great plains of Africa, there is a need to follow your food source or risk starving. 

Image by Rohan Reddy from Unsplash

For other species it is due to changing climatic conditions. Unlike many terrestrial species this is where birds have the advantage, with the novel movement strategy of flight. Being able to relocate to areas with more favourable conditions allows individuals to survive in a world where climates can vary greatly between seasons, even in the same location. For many species this challenge is overcome by having large bodies capable of storing fat to insulate themselves when the weather gets colder, or by having fur that they can shed when it becomes too warm. Neither of these are things that birds are capable of, with feathers rather than fur and too much fat stopping them being able to fly or hunt. 

Instead some avian species have adapted behaviourally to changes in climate, moving to suit their needs for each season. This type of movement also overcomes an issue that many species face over winter, with food supplies often becoming scarcer. The trade-off for birds having these advantages is a single high energy expenditure event, migration. This trade off can be fatal for some individuals who may already be injured, old or less fit than others, but for a taxonomic group or species it is a novel way of balancing the requirements of surviving on planet earth.

But even with the apparent advantages of this lifestyle, there are still a litany of risks that are ever present during the perilous migrations that happen every year. 

What are the risks?

The substantial energy requirements of long-range movements make efficient routes a necessity, causing many species to fly from point A to point B as directly as possible. This method of movement has its advantages, but it also poses a number of risks to individuals who can end up caught in storms or environments different to those they were expecting. 

Storms are a major risk to many species, with one sudden and unexpected storm in 2014 killing more than 20,000 migrating sea birds between France and the UK. In one day 14,455 dead puffins were recorded on the beaches in south west France, with thousands more washing up in the UK. As the climate changes and weather patterns become more extreme, this could become a more regular occurrence. However as the climate changes it is possible so too will the routes taken by some species, hopefully meaning they can avoid events like this in the future.

Food shortages are also another major risk to migrating birds who are unaware of the conditions at the sites they aim to reach. In 2004 after travelling almost 30,000 miles to the UK, Arctic turns arrived to find a significant shortage of sand eels, their chosen food source. This shortage led to one of the biggest single die offs of a UK species ever recorded. Of the estimated 50,000 eggs laid by more than 20,000 breeding pairs, the RSPB reported that not a single chick survived to join their parents on the flight back to the arctic. While numbers did recover in the following years, it was in part due to the 30-year lifespan of the species. If a similar event happened for a migratory species like the Blackpoll Warbler which only has one mating event, it could cause a single mass extinction event for the species.

However, the largest and most constant threat to migratory birds is human persecution.  

The UK is currently home to more than 600 species of birds, but many of these are not full-time residents. From Ospreys to Quail thousands of birds from over 250 species leave our shores to find more suitable conditions somewhere else. These migratory or passing birds often visit a dozen countries on the way to their final destination, a fact that puts them all at risk of something other than the journey itself. As humans and countries draw lines on maps to differentiate themselves, these lines also represent where some laws stop and others begin. This is true when it comes to wildlife conservation as well, with some countries doing more to protect their visiting species than others.

While our little island might be the perfect breeding site for many birds, there is another smaller island that is currently pushing 160 migratory species closer to extinction. Malta has a population of around 500,000 people, under half the population of London and is the 10th smallest country in the world. Yet it is having an unprecedented impact on many bird species including turtle doves.

 

In total it is estimated that 3 million birds are shot each year in the country, including almost 100,000 birds of prey. While the official hunting season in the country only includes stocked Quail, hunters in the country have gained infamy by shooting anything and everything. One study found 84 different migratory species had been killed on the small island, with ringed birds from 17 diffirent countries included. A German Osprey that was being tracked as part of a conservation scheme was shot inside bird sanctuary within minutes of arriving in the country. Thankfully a concerned citizen reported it and members of Bird Life International (Malta) rescued the bird and sent it for treatment. As such, it is important to highlight that there is a proportion of the population on Malta that are vital to stopping these events occurring and are doing their part for conservation.

Photo by Jongsun Lee on Unsplash

Additionally, while much of the focus has been on this small island nation, it is not just Malta that are killing migratory species in large numbers. It is estimated that 25 million migrating birds are killed each year by European Union member states, despite strong laws protecting many of the species. Italy is the largest killer in Europe at 5.6 million wild birds killed annually, often on an industrial scale to sell the seasonal birds as a delicacy to the restaurant industry. This includes many species that come to our shores here in the UK, like chaffinch (2.9m killed) blackcap (1.8m), quail (1.6m) and song thrush (1.2m). The scale of the issue is hard to comprehend in some cases, with the study also finding a 70km long continuous network of nets present along the Nile river, decimating migratory species that fly through that region by killing almost 5.7 million birds in one year. 

While poaching wild animals may seem to be a problem often attributed to developing countries, when it comes to birds it is most defiantly western “first world” countries that do the most damage.

The case of the Osprey

Osprey have one of the longest migratory routes of any bird of prey and in an attempt to help numbers of the species recover, the RSPB has sought to track the movements of our local birds on their journey. Satellite tagging of two birds affectionally known as FR3 and FR4 in Scotland helped shine a light on their journey, as well as the size of the task facing conservationists who aim to safeguard their travels. 

After leaving their breeding grounds in Scotland the pair travelled through eight countries on the way to warmer wintering grounds.  From France to Spain, Morocco to Senegal they eventually settled in Gambia. But as they travelled South, where were they most at risk?

 

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In France an untagged but ringed osprey was shot and killed in 2009, but events like this appear to be uncommon. Deaths in Spain are seemingly more likely with a number of ospreys killed in collisions with sometimes faulty powerlines. But these risks are for the most part out of our control. In comparison persecution of the species in Africa seems generally low, although detailed information is not available for many regions. Death rates for young birds are high but this is likely due to predators and conditions that are extremely different to those in the Scotland.

But what about the UK?

According to the RSPB's bird crime data, six ospreys’ have been shot in England, with at least 1 nest being destroyed since 2007. However total numbers of reports of birds of prey illegally killed in the UK number more than 700, indicating the scale of the issue. But these are not the only risks, less than 1 month ago a successful male that had migrated 14 times to Gambia was killed by a collision with a lorry on the M6. As such, it is likely that European countries likely pose more of a threat to the species than African countries. With the UK possibly being the riskiest country for our ospreys’ due to the time spent here. 

However, with that being said we are also one of the safest for our and other countries bird species. We as a nation still shoot over 10 million birds each year, but these are stocked birds and not wild birds. This is a clear and important difference that limits the damage to natural ecosystems and limits the killing of endangered or protected species. The UK is a an almost perfect example of how a country can have a shooting industry while not impacting wild species and wildlife conservation as significantly as seen in other countries. Although there is still room for improvement.