Bycatch – part I

Time flies and the days are full. More than two weeks have passed since we are here. It is extremely tempting to spend all our time catching birds. So many new birds need to be equipped with a new tiny geolocator backpack. And so many geolocator birds from last year have returned: 14 birds! This is 37% of the 38 we deployed. For me this is surprisingly high; way more than I hoped for. I expected lower return percentages, since this was what we encountered in our own Dutch population last year and what we heard from researchers in various other European populations. Especially those birds equipped with geolocators may pay a higher price when circumstances, like last spring, were likely harsh during migration.

Giant Cola cordifolia in ‘the strip’

Most birds with geolocators started to pop up in the area we called ‘the strip’, which is a small narrow forested strip that is situated around a small dried out gully. It contains some tree giants such as Khaya senegalensis, Cola cordifolia and some beautiful big African oaks that we referred to as the ‘pod-tree’ (due to the distinct big pods)1. African birches mostly cheer up the edges of the forests. Already at the first day, we2 managed to see several colour ringed pied flycatchers of last year: including our ‘star’ bird from the last blog on the balance: miss ‘yellow-Alu’. Wender & Rob had the honour of catching her in our second day. I was pleased to see how good habituation can work, and to see how strait away she remembered what it meant when humans place a bowl in her territory: food!

The strip is also a great place to work in, given it’s great visibility (and hence ease for observing birds), coolness, clear open forest floor, and other great species that you encounter in sight and nets. Rob and I were lured by a calling, young greater honey guide to a bee hive in the strip (which, to our humble opinion, Wender indicated more accurately than this ‘guide’). Common bycatches in our nets include African Pygmy kingfisher, Common wattle-eye, Common bulbul, Snowy- & White-crowned Robin chats and Square-tailed drongo’s. The latter are screaming black drama queens with blood red eyes that attract the attention of the whole forest (including our target pied flycatchers), while driving their sharp beak and claws into your skin when you try to get the bird from the net, while keeping our hair-nets alive.

Square-tailed Drongo
Snowy-crowned (l) & White-crowned (r) Robin chat

From the edge of the strip, you can see flycatchers, Willow warblers and Senegal eremomela foraging high up in the African birches, and enjoy a wider view over the savanna, now and then showing a ‘bell’ full of raptors with species such as White-backed (and rarer, White-headed) vultures, Black kites, Red-necked buzzards. Also the Grasshopper buzzards are around, which is – in addition to our sense of smell and hazy sky – a sign that the annual burning from the savanna grasses is getting closer to the station. With their long legs, they are specialized in snacking on the escaping insects that are chased when the fires race across the savanna. Now that the savanna grass is still so long and tiring to walk through, I realize again how tempting it is to spend a lot of time in the forest strip, and how easy you get an observational bias. Especially, when you see you targets well, and recapturing feels so urgent, one too easily falls in the trap to pick and spend most research time in the areas where you can work, see, and walk most easily. I decide then, that I should stay sharp and not forget to spend more time in the other sites: by ploughing our way through the savanna grass, and spend enough time searching birds and doing, often frustrating, observations (‘I think 1 leg was unringed..’) and catching attempts in the denser riverine gallery forest and dryer forests island. This is important for more reasons. Not in the last place, because we see that Pied flycatchers use the gallery forest now much more than the savanna.

savannah
Grassy savanna with gallery forest in the back

You could say that ‘miss yellow-Alu’ from the strip is representing the ease why which fieldwork can go. While ‘mister pink’ and ‘mister orange’ represent the other end of the spectrum, by respectively skulking through the denser forest island, and gallery forest, and by showing behaviour that we not yet fully understand. Why does ‘mister orange’ appear now in the gallery, and did we see him last year having a spot on the savanna? We also noticed that most of the birds that we resighted now with geolocators, are either younger birds born last year, birds that occupy a new sight and birds that we never saw again after the catching event from last expedition. Such movements are very interesting in itself.

Janne with Pied flycatcher equipped with geolocator
Do I see this pied flycatcher again in late winter and again next year? And in which habitat?

Volker Salewski already suggested habitat switching in his research from the nighties. Why do birds move between habitats? What can this tells us about the food conditions now (and later in the season) in these different habitats? And if birds move or need to occupy a wintering site for this first time, what sort of information do they use to make these decisions? I’m happy that I decided – at the last moment – to take less muesli, but rather already bring some of the malaise traps with me. Rob and I set up these insect traps to study how many arthropods occur at this moment in these habitats.

Wender and I refresh our thoughts on our ‘safe-haven theory’3 from last year, and add new complexity, while thinking of simple rules they may underlie this apparent complexity. Isn’t it overwhelming and beautiful, to think and take the freedom to ‘play’ with these thoughts about behaviour of wild animals, the processes of establishment and enjoy field ecology for the sake of science. It’s a luxury to work on this puzzle in this beautiful place with people with whom you share this passion.

verrekijkers
Wender with a Blue-bellied kingfisher (l) and birding time on the ‘sahel-like’ plains (r: Christiaan Both, Wender Bil, Rob Bijlsma). 

Paradoxically, in contrast to the dynamics of the wintering areas and flycatcher research system, I dislike this change in human dynamics with its sudden disruption of the absence-of-time-feeling. My sense of time here is dictated by the sounds of nature, and by people coming or going. The first singing Common bulbul in the morning tells us that our breakfast time is over, and it’s time to head into the field to catch birds. The arrival of postdoc Pauliina told me that at least 10 days have pasted. It will be only a week until Rob and Christiaan go home. When Rob and Christiaan leave, this will create a weird silence, since they are also true experts in coffee table ornithology talk and hypotheses, and are great to have on board…

[You can read in the next blog posts what the other team members have to say, about their experiences here.]

Rob brings an endless amount of stories and bird knowledge, sees things differently. Christiaan also has an important role in maintaining our high4 catching score of 1 bird per day, by now and then compensating days of emptiness in our nets, by catching several birds in a day. We caught over 15 birds by now, including 4 recaptured geolocators of last year (all with data!) My aim of catching 60+ birds this expedition was overly ambitious, we have to see how close we get… Go-go Christiaan, to break the 4 birds a day record!

Foot notes

1 But more importantly, because I forgot their latin name, Afzelia africana.

2 Mostly found by our king of the resightings: Wender.

3 This expresses our thoughts about how flycatchers use their wintering homes, with a core territory (the ‘safe haven’) from where they can more flexibly roam and move across a wider area (‘home-range’).

4 This is pretty good for our 10 nets (of 3m and 6m) the wintering period.