A new study by Bournemouth University (BU) has discovered that faster recovery of osprey populations relies on a small number of ospreys who, unlike most, prefer to nest away from others of the same species. These birds have been referred to as 'pioneering pairs' and could be the secret to helping conservationists increase their population spread.
The study looked at a rare long-term dataset covering 54 years of recolonisation of ospreys in Northern Scotland. It investigated the distribution and density of nests and the resulting patterns of settlement to understand how populations spread and what drives spatial recovery.
The study was led by PhD Researcher at BU, Brittany Maxted, in collaboration with Dorset charity, Birds of Poole Harbour and The Roy Dennis Wildlife Foundation who monitor ospreys in parts of Northern Scotland. Brittany said: "Ospreys usually like to nest in areas where there are already other ospreys, which we refer to as conspecific attraction. Most males also exhibit natal philopatry, which means they tend to breed close to their own birthplace. Together, these factors lead to very slow population spread for such a large bird. However, in Scotland we noticed that a small number of pairs were choosing to settle more than 20 km away from all the others, in areas with no competition. We call these 'pioneering pairs' as they recolonise new areas, and in doing so create separate subpopulations and increase the speed of recovery for the species."
Restoring lost species is a key goal for conservationists, but very little is known about the process of recolonisation. This study found that the patterns seen in ospreys are very similar to other types of population expansion which have been much better studied, like invasive species. The tools that scientists use to investigate these species could therefore also be used to better understand and help recovering species.
The paper's findings also point to other potential solutions to speed up the recovery of osprey populations. Dr Tim Mackrill, Lead Ornithologist at the Roy Dennis Wildlife Foundation and co-author on the paper said: "This study highlights how much the spatial expansion of ospreys relies on the long-distance dispersal of these rare pioneering individuals. It suggests that the best way to accelerate natural recovery rates is for conservationists to encourage or even replicate these pioneering movements. We can do this by building artificial nests to help entice ospreys into new areas or by physically moving individuals via translocation."
Ospreys once bred across much of Britain, but by 1916 they had disappeared due to hunting and egg collecting. However, after a pair naturally returned to a nest site at Loch Garten in Scotland in 1954, a conservation movement began to protect nesting pairs and help the species recover. Dr Roy Dennis OBE, founder of the Roy Dennis Wildlife Foundation has been monitoring and conserving the Scottish population since the 1960s, leading to the dataset behind this study. Roy said: "It's fantastic that this dataset, which we've collected over many decades, continues to teach us more about these remarkable birds. Our findings reinforce that we're taking the right approach to restore ospreys across the UK and beyond, and suggest that we should be using these measures even more widely to see faster recovery of the species across Europe."
One example of where these techniques have already helped ospreys recover is in Poole Harbour in Dorset. Starting in 2017, the Roy Dennis Wildlife Foundation and Birds of Poole Harbour ran a five-year translocation project in collaboration, moving young ospreys from Northern Scotland to Poole Harbour. Healthy chicks were taken from longstanding nests at seven weeks old and moved temporarily to hacking cages in Dorset to finish developing before being released into the surrounding landscape, which they quickly came to recognise as home. Brittany said: "Through translocation we can essentially create our own pioneering birds to kickstart a new population. The first breeding pair in Poole Harbour was a male named 022 who we had translocated from Scotland, and a female named CJ7 who had visited from a population 200 km away and was attracted to stay by the presence of translocated chicks. In 2022 they hatched two chicks of their own, becoming the first breeding ospreys in Southern England since 1847. If it wasn't for the translocation project, we may have had to wait another 60 years for breeding ospreys to reach Dorset naturally."
The team and volunteers have described it as a "huge success story" with the original Poole Harbour pair returning to breed and producing chicks at the same nest each year since. This summer they have hatched four chicks for the third year in a row, all of which will remain in the area and reliant on their parents for food until they leave on migration around early September. And several pioneering movements have also been recorded, with a second pair breeding away from the harbour and the first wild born Poole Harbour chick now breeding in the East Midlands. Both pairs are forming new subpopulations and starting to close the gap between Poole Harbour and the nearest osprey population in Rutland Water.
Brittany, who is currently leading a team of Birds of Poole Harbour staff and volunteers who monitor the growing population said: "Translocation is an incredible tool, but it can take many years to see the results. We're still in the early stages in Dorset, but are already seeing some of the first wild born chicks returning, with four eligible young males currently exploring suitable nest sites and looking for mates. We hope that in the coming years some of them will become pioneers themselves, helping the population spread along the south coast of England. Artificial nests have already been built for them in neighbouring counties like Devon and Hampshire, and based on the results of our study we'll be aiming to provide lots more."
Brittany and her co-authors hope that their research will help motivate more conservation action for ospreys across Europe, where they are still missing from much of their historical range. They also have many more questions about what determines where ospreys choose to nest and what makes pioneering pairs different, which they plan to investigate in the future.
The full study has been published in the Journal of Animal Ecology . To find out more about the conservation of ospreys and where to see them in Dorset visit the Roy Dennis Wildlife Foundation and Birds of Poole Harbour website.
