Over the last decade, deploying small tracking devices on seabirds has been able to provide us with astonishing insights into their offshore life. Today’s blog has been written by Conservation Scientist, Saskia Wischnewski, on some recent findings which take us straight to the West coast of Ireland, where Manx shearwaters ended up breaking records and proving that location matters.
There is something weirdly fascinating about the elusiveness of seabirds. While the buzzing noise of a seabird colony can be heard (and smelled) from far away, they completely disappear from our senses when leaving shore, only to magically return later with food to feed their chicks.
Some seabirds such as Manx shearwaters are even more mysterious and experiencing their colonies located on remote and often inhabited island on the West Coast of the UK and Ireland can turn into a true adventure requiring a minimum of a bumpy boat ride and a good headlight as birds only return to their nest burrows at night.
Adult Manx shearwater in hand © Gavin Arneill
Studying Manx shearwaters (in Ireland)
Studying Manx shearwaters means hours and hours of night-time work on one’s knees with arms down muddy burrows feeling for fluffy chicks and their feisty parents, and even usually simple tasks such as defining the size of the colony can be challenging. Up until recently most of this work was mainly concentrated on few long-term studies within some of the biggest colonies located in and around the Irish Sea.
A study lead by researchers at University College Cork expanded the usual study area with the aim of understanding where, and particularly why, Manx shearwaters from the West Coast of Ireland go to where they go at sea, and how this might differ from birds breeding elsewhere. Over three years, the first local GPS tracking and monitoring data was collected and analysed. Results have been published in multiple scientific publications over the last year and include some exciting findings.
Manx shearwater with fluffy chick in burrow © Saskia Wischnewski
Breaking records
Compared to their counterparts on Welsh islands, Manx shearwaters breeding on Irish islands regularly travelled enormous distances offshore up to the Mid-Atlantic Ridge before returning to their single chick. This is equivalent to the distance from London to Rome and about five times as far as the expected regular breeding range for the species.
These long trips set the record for the longest distance travelled by an actively and successfully breeding seabird in the Northern hemisphere and come as a bit of a surprise as they could last up to 11 days. Are Manx shearwaters bad parents for leaving the chicks alone for that long?
Map of foraging trips during chick rearing © paper by Wischnewski et al. 2019
Balanced parenting
Compared to other cliff-nesting seabirds, Manx shearwater chicks are mostly safe from predators when left alone in their burrows and the second parent will usually still take care of the chick even if the other one is gone offshore. This study additionally showed that Irish Manx shearwaters like numerous other seabirds alternate between short trips aimed at quickly collecting as much food as possible relatively close to the colony to bring it back to their hungry chick, and long trips during which birds restore their own energy reserves. Therefore, birds would only leave on long trips if their chick was in good condition and would then return in better condition. One question remains: Why would they bother flying all the way out there if they could also forage close to the colony?
Photo of chick in cup being processed © Saskia Wischnewski
Why travel further than “necessary”?
It’s a difficult question and finding a clear answer is not easy. There might be less competition for food, food resources might be qualitatively and quantitatively better, or the reason might not be linked to food at all. The newest publication of the study indicates that Irish Manx shearwaters change their behaviour from travelling to foraging in highly productive, potentially food rich areas, suggesting that at least most of their trips are indeed foraging trips aimed to find food. However, the relationship was less clear for offshore trips, maintaining their mystery, at least for now.
Seabirds are one of the most threatened group of animals on the planet and understanding where they go at sea and why is critical to protect them from ever increasing human-made pressures such as climate change, overfishing and energy developments. To complicate things, this tracking study showed that where and how far seabirds go at sea very much depends on where their colonies are located. We cannot simply presume it is the same everywhere but need targeted local studies when developing conservation plans.
Continue reading
Would you like to be kept up to date with our latest science news? Email with the heading 'enewsletter' to be added to our quarterly enewsletter.
Want our blogs emailed to you automatically? Click the cog in the top right of this page and select 'turn blog notifications on' (if you have an RSPB blog account) or 'subscribe by email'.