Guest Blog by Dr Alex Bond, RSPB Senior Conservation Scientist

Situated 350km south of the main group of islands in the Tristan da Cunha group is Gough Island, a seabird Mecca home to 23 breeding species of seabirds from tiny diving-petrels to massive great albatrosses.  In September 2014, I went to Gough on the SA Agulhas II as part of the annual takeover as the team transitions from Gough 59 to Gough 60 (yes, there have been 60 overwintering teams!).  The crew of biologists, meteorologists, a medic, radio operator, and mechanic will be there until next September.

One of the most important tasks during takeover is the Tristan Albatross (Diomedea dabbenena) chick count.  These wanderer-type albatrosses breed only on Gough (with one pair on Inaccessible Island; they were extirpated from Tristan over 100 years ago) where mice – yes, mice! – are the main predator of their chicks.  You might be wondering how a 25g mouse can take down a 9kg albatross chick, but I can assure you that a) it does happen, and b) it’s a big problem.

Dr Alex Bond with Tristan albatross chick

Typically, these large albatrosses raise a chick successfully in 60-70% of their breeding attempts, and it takes so long (about 10-11 months) that they only breed every other year. But because of mouse predation, the albatrosses on Gough raise a chick successfully in only 30% of their breeding attempts. 

Worst ever year for Tristan Albatross chicks

Combined with mortality of adults in longline fishing operations in the Southern Ocean and mouse predation, Tristan Albatross are struggling.  But knowing this did nothing to prepare me for the 2014 albatross chick count.

163 chicks. From just less than 1,700 nests counted in January. The lowest ever recorded for Tristan Albatross. Ever.

Searching the empty hills for missing chicks

When we landed in Giant Petrel Valley on the west end of the island, we immediately knew something was wrong.  Instead of seeing tens or hundreds of white dots sitting in nests on the hills from the helicopter, we saw none.  Where there were 541 adults happily tending nests in January, there were now 14 chicks in Giant Petrel Valley and West Point.  When the three teams met at the end of a long day of hiking (and not seeing many albatross chicks), we were all worried we had missed some chicks, or forgotten to check certain places, but we hadn’t – the birds just weren’t there.

Giant Petrel Valley, Gough Island with very few Tristan albatross chicks this year.

The second day went much the same as the first – 16 chicks out of 192 nests on Green Hill, 23 chicks where 274 adults were found only months before on Spire Crag, and on, and on.

Predation by mice

But how does this happen?  The albatrosses, having evolved to breed on islands without land predators, have no behavioural experience with mice.  The mice attack the chick (and sometimes the parents simply sit). After one or two nights, and attacks of three, four, five or more mice, the chick dies, and just like that, the adults’ investment in incubating and egg for months, and feeding a chick for weeks is for naught.

Conservation efforts

The RSPB Centre for Conservation Science recently published a paper on the prioritization of UK Overseas Territories for eradications of introduced species, and Gough came out on top.  We’ve spent the last 15 years gathering evidence on the effects of mice, studying their biology and behaviour, conducting bait trials, and consulting with our partners on Tristan da Cunha, in South Africa, and with experts overseas. 
We’re hoping for a green light soon on an eradication of mice from Gough, and should have a decision in early 2015.  In the meantime, the remaining albatross chicks are preparing to depart, and in a few short months, the adults will return to try again, and I’ll be back on Gough next September, hopefully with more albatross chicks.

Find out more about our work on Tristan da Chuna and also see coverage of the Tristan Albatross breeding season on the Agreement on the Conservation of Albatrosses and Petrels (ACAP) website.

Our work on the Tristan Islands has been supported by many funders including OTEP, Darwin, Darwin Plus, the European Union’s EDF-9 and ACAP.