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The Peregrine Fund Notes From The Field
October 1999-April 2000 - Bush Pigs in Underpants
Ruth Tingay — in Madagascar Project    Share
As the season progressed, so the temperatures soared. By 7 am I would be soaked to the skin in sweat, trying to dodge the 35°C heat by rigging up makeshift shades of t-shirts and towels at the observation site. Our female fledgling was still keeping close to the nest tree, although the four attending adults had stopped delivering fish to the nest and were taking it directly to the eaglet instead. She was very vocal for much of the time and made sure her parents knew when she was hungry, which seemed to be constantly. We hadn’t seen her fly further than 200 metres from the nest tree and most of her time was spent lurking in dense foliage, only giving her position away by the frequent food begging call.

Decken's Sifaka Lemur
Decken's Sifaka Lemur
Our season was beginning to draw to a close and we finished trapping the remaining eagles and started to wind things down a little. Rather than sleeping at night, we were able to take more interest in our surroundings and most evenings we would head off into the forest at dusk to try and locate and identify some of the lemur species with our flashlights. We also searched for the tiny scops owls whose calls had lulled me to sleep so often, and then when we wanted to frighten ourselves we would stand at the edge of the lake and try to pick up the orange glint of the crocodiles’ eyes in our headlamps.

We would usually retire back to our tents by 10 p.m., after long discussions of all our food cravings and the home comforts we were missing. There is no question that I would have traded all those comforts for the experiences I’d enjoyed with these fish eagles, but one can think a lot of thoughts over a five-month period, from the height of philosophical theory to the most abject longing for a cheeseburger.

I would lie in my tent and listen to the now familiar nocturnal sounds of the scops owls, the geckos, the nightjars, the lemurs and, oh yes….the bush pigs. They were easy to identify, crashing through the leaf litter, huge ginger beasts with grizzly faces. Martin was desperate to see them and clad only in his underpants and headlamp, he would tumble from his tent when he heard them approaching and stagger off through the forest, in a pathetic attempt to keep up with them. Unbeknownst to Martin, I spent many amusing nights following him following the bush pigs. It’s difficult to tell which ginger beast had the most comic appeal.

Towards the end of October it was time to leave Camp Handkerchief. Only I had a feeling it wouldn’t be for the last time. Even though I hadn’t yet analysed any of the behavioural data I’d collected, I knew from what I’d seen that we were probably only scratching the surface of this fish eagle’s behaviour and that there was still much more to learn and understand about what appeared to be a bizarre and unusual social hierarchy.

I was looking forward to returning to England, not only to see my friends and family and to go wild in a supermarket, but also to get on and work through my field notes to try and make sense of it all. Then there was the small matter of having to write my dissertation, too. Martin was also keen to get moving, as he was heading up to the north-east Masoala Peninsula to work as a volunteer on the other Peregrine Fund project in Madagascar.

Ruth in canoe on Lake Ankerika.
Ruth in canoe on Lake Ankerika.
I took the canoe out one last time this year and headed over to say goodbye to my friend Cut Off. He was in his usual perch tree overlooking the lake, his bulging crop giving away his morning breakfast. He ignored me as only a fish eagle can and I turned around and headed back over the lake for home.

November 1999 – April 2000: Results

The run up to the Millennium and its aftermath is all something of a blur. Having spent five months of my year eating, sleeping, and breathing fish eagles on their home patch, I had moved halfway back around the world to England but still they invaded my every waking hour.

The blood samples were shipped off to my colleague, Dr. Melanie Culver, at Virginia Tech, USA, as she was conducting the genetic analyses, whilst I got stuck into the pile of field notebooks I’d amassed during the summer. The results are quite revealing, but yield more questions than answers.

I discovered that the four trio groups I’d been studying were polyandrous groups, i.e. they comprised at least two males and one female at each nest. In addition to this, there was a very distinct dominance hierarchy amongst the males at each nest, with one male contributing the highest amount of paternal investment over the second male. Both males contributed to the breeding effort, but the dominant male spent more time incubating the eggs, brooding the nestling, brought in the highest number of fish, and spent the most amount of time guarding the nest and its contents. (For those who are interested, Cut Off fell into the category of dominant male!). However, the subordinate male at each nest managed to gain the most number of copulations with the female, in fact almost four times as many as the dominant male.

The dominant male at each nest appeared to assert his authority by continuously chasing away the subordinate male, although there were many occasions when the two males appeared to swap incubation duty with no apparent aggression seen between them. The female at each nest seemed to be having her cake and eating it – she didn’t fight with either of the males and she readily accepted fish from both of them!

The results become even more confusing when the genetic analyses are added to the equation. Melanie found that the extra pair bird (the subordinate male) was not related to the primary pair as we had first suspected, but in actual fact, the primary pair appears to be closely related to one another (i.e. mother/son or father/daughter).

The final icing on the cake came when we looked at the paternity of the young from my study nests. I had assumed that the dominant male would be the true genetic father, as he had put in the most time and effort at the nest. Wrong! The subordinate male was actually the true father of each chick!

It was clear from these results that further investigation was warranted. My sample size was very small, and probably too small to draw broad conclusions about the Madagascar Fish Eagle social hierarchy in general. What it did tell us was enough to know that the species was exhibiting a highly unusual breeding strategy (polyandry), which is usually seen as a response to an environmental condition. For example, it has been demonstrated in other species to be a response to low food availability, where two males have to cooperate in order to supply enough food for one nest. If this is the case with the fish eagles, it could lead us to conclude that the fish eagle population is severely stressed, which may be affecting the distribution and abundance of the species throughout its range. However, we know from earlier studies that fish eagles at the three lakes have a high foraging success rate, which does not support the theory that fish are in short supply.

Additionally, the fact that the subordinate males sired all the chicks during my field season could just have occurred by chance (we only had three chicks to test). We don’t know if this happens with all trios every year.

Full moon on Lake Soamalipo.
Full moon on Lake Soamalipo.
Other big questions are why are some territories on the lakes occupied by pairs, whilst trios occupy others? Do the trios stay together each year or do they swap with other individuals? Is there an advantage to being in a trio over being in a pair? Do trios produce more offspring than pairs? Are all trios polyandrous or are some polygynous (1 male + 2 females)? Are trios present throughout the island population or do they just occur at the three lakes? All of these questions and more need to be answered to enable us to understand and design a suitable conservation policy for this critically endangered species.
It seemed I had done enough to satisfy the examiners and gain my masters degree, but not enough for me to want to move on to something else! After discussions with my advisors both at the University of Nottingham and The Peregrine Fund, I found myself enrolled onto a Ph.D. programme to expand the study on the Madagascar Fish Eagles and their perplexing behaviour. Fieldwork was scheduled to begin all over again in May 2000.

This year’s fieldwork was funded by The Peregrine Fund, University of Nottingham, and Hawk Mountain/Zeiss Optics Student Research Award.

Ruth's notes of three years in Madagascar continues next month with an account of her return for another season studying the fish eagles.

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