Research can involve a lot of reading — especially when you find yourself in a new field of study that has a long history, which means there is a substantial pile of previous research to catch up with. While my current project uses methods that have only been developed over the past few years, some of the study species have been observed for decades, and various fundamental aspects of their behaviour and lifestyle are exactly the things people were describing in the early studies.
Over the past two years, I have read (parts of) hundreds of scientific articles about all manner of vaguely related subjects. For some of these, I have looked back at particular sections so often that it’s perhaps only a matter of time before I can quote them from memory! Others I have only quickly glanced over, and sometimes I find myself reading something, only realizing when I’m already halfway through that I had in fact read it before…
Especially when browsing a lot of text for something specific, most of what you encounter is not particularly memorable. It all just blurs into one, all irrelevant for one reason or another: wrong species, different context, outdated method, and so on, and so on, and.. wait, what? Did I seriously just read that?!
Case in point:
“Moreover, these larvae were not particularly distasteful to the human tongue“
In the middle of a perfectly unassuming text about some small birds and the various insects they have been observed eating, Mr. T. Royama included a little throwaway line about, apparently, having tried some of these caterpillars for himself too. Nowhere in the 50-page text could I find any further reference to the culinary experiments that led to this conclusion. Although the article has 561 citations at the time of writing according to Google Scholar, I can find no further references to this particular peculiar line anywhere on the web.
Earlier this year, I have tried to reach out to Mr. Royama’s last known place of work and listed email-address, but with no luck. Given that the above is already half a century old and some of T. Royama’s articles predate these, there is a chance this intriguing opportunistic insectivore is perhaps unfortunately no longer alive, although he at least appears to have authored an article as recently as 2017. I have now tried to contact one of his last known collaborators, in the hope they might have any means of contacting him. Within seconds, I received a reply: “I will be away from my office for an extended period. For important matters, I can be reached at […]”. I guess this doesn’t *quite* qualify as an “important matter”, so I will simply wait and see.
Maybe whatever happened in the woods near Oxford during the 1960s will simply remain a mystery forevermore…
Let’s start the new year with a new series, detailing the ongoing research of my PhD. As is customary in scientific articles and a good idea in general, I will commence with some background information to explain why we do the things we do.
As nowadays can’t have escaped anybody’s attention, the world is undergoing a bit of change. Many of the warmest years, months and days on record have taken place in the last decade, and whichever of the predicted scenarios of climate warming one follows, such extreme weather events are only going to become more common. (I will not be tackling the existence of climate change and greenhouse gasses here, but perhaps at a later date, after establishing that evolution is real and the Earth is a sphere. Well, technically an oblate spheroid, but.. anyway.) In many different fields of study, people are now trying to predict how the world around us may be altered under the influence of these changing environmental conditions.
Some decades ago now, researchers started to monitor how the seasonal timing in various organisms was shifting with increasing temperatures, and found that from a biological point of view, spring was indeed occurring earlier. Deciphering clear annual patterns for some species could prove difficult, however, let alone understanding whole ecosystems: complex networks of many different species interacting in countless ways.
In 1998, Visser, van Noordwijk, Tinbergen and Lessells  calculated whether the breeding times of a widely studied small bird, the great tit Parus major, might be shifting, and crucially whether this was in line with the peak abundance of the prime food for their young: caterpillars. Those caterpillars, in turn, would want to emerge earlier in the year too, so as not to miss the optimal timing for their own food: the new leaves of deciduous trees (locally predominantly oak, Quercus spp.). They found that while the availability of caterpillars was advancing, the birds were not shifting their egg laying dates accordingly. This suggested that over time, a problematic (for the birds at least) mismatch between food availability and food requirements might start to arise.
But, as often is the case in research, that was not the end of it. While they found no shift in the birds’ timings in the Netherlands, this was in contrast with a long-studied population in the United Kingdom, near Oxford . When a later study compared more populations across Europe of the same and a closely related species (the blue tit Cyanistes caeruleus), no consistent pattern could be found . Overall, breeding periods typically advanced more in southern than in northern populations, and at the time the temperatures in those northern areas had not been rising much yet. Neighbouring populations differed in their responses, however, indicating that other factors must be playing a role.
One potential factor was the timing window for the birds. The period of peak food requirements, when the chicks are rapidly growing (see this previous post), occurs quite a while after the parents commence their breeding behaviour. A nest has to be built (which takes a few days), after which they lay their eggs (around 10 days, as their clutches average about 10 eggs and they lay 1 egg/day), which have to be incubated (another 2 weeks), after which the chicks finally emerge. As those young require the most food when they are around 1.5–2 weeks old, well over a month has now elapsed since the start of the breeding period. Not only does this make the optimal timing difficult to predict based on the conditions at the start of the season, the increase in temperatures is not necessarily uniformly distributed over the year. Furthermore, weather in any individual year can of course simply vary a lot, which means any natural selection towards early breeding is not very straightforward.
And then we haven’t even considered many other factors that can play a role. In some populations, the birds frequently have second broods, and those birds may breed earlier in order to have the ability to raise another brood in the same year. The birds may further be constrained in time by a demanding overwintering period before the breeding season, or the timing of their moult in summer, although these latter factors are unlikely to significantly differ between neighbouring populations.
Then, of course, there are the prey themselves. The insect community in oak-dominated woodlands is unlikely to be the same as that found in birch forests or pine plantations. Different species have different overwintering strategies, and will emerge at different times in different forms (for example as tiny, freshly hatched caterpillars, or as adult moths). In studies on the birds’ food availability and requirements, it has been common to either assume that all local caterpillars would be on the birds’ menu, or that a particulary common prey species would be representative of all others in the diet. Such simplifications were basically required, as identifying hundreds of different prey species quickly and accurately is practically impossible. Or at least: it used to be. New DNA-based techniques have opened the doors to studies not thought to be possible before, and they have been particularly useful for otherwise tricky dietary studies. With these techniques, we will for the first time delve into the availability and consumption of all the different prey species in this food web. This should give us a much better understanding of how the populations of these birds may actually be affected by climate change, and with that, how the natural world could be altered in the decades to come. In the next blog post, I will go into more detail about these methods, how they work, and how we are using them.
 Visser ME, Van Noordwijk AJ, Tinbergen JM, Lessells CM (1998) Warmer springs lead to mistimed reproduction in great tits (Parus major). Proceedings of the Royal Society of London B 265: 1867–1870.
 McCleery RH, Perrins CM (1998) . . . temperature and egg-laying trends. Nature 391: 30–31.
 Visser M, Adriaensen F, Van Balen JH, Blondel J, Dhondt AA, Van Dongen S, Du Feu C, Ivankina EV, Kerimov AB, De Laet J, Matthysen E, McCleery R, Orell M, Thomson DL (2003) Variable responses to large-scale climate change in European Parus populations. Proceedings of the Royal Society London B 270: 367–372.
Among the many amazing traits of the birds I currently study is their remarkably rapid development as nestlings. When the chicks hatch from their eggs after a two-week incubation period, they look like tiny pink monsters, capable of little and requiring constant food and looking after. (In other words, not unlike human babies.)
Less than three weeks later, the fledglings leave their nest; seeing the world outside of their nesting cavity and flying for the first time in their lives (somewhat unlike human babies, to the best of my knowledge). The transformation isn’t far off that of a caterpillar to a butterfly.
To see how and how rapidly the young birds change, I visited a pied flycatcher (Ficedula hypoleuca) nest and took pictures of one of the chicks every day until it fledged. A €2 coin (approx. 2.5cm/1″ diameter) was included in the pictures for scale, to better show the extent to which the nestlings grow.
Normally, we only visit the nests when the eggs are expected to hatch, and again a few days before the chicks fledge and leave their nests. Although the difference in the chicks between these visits is obvious, it hardly stands out when monitoring dozens of nests simultaneously — especially as one typically ends up losing any concept of time over the course of the field season anyway. Seeing the very notable changes after just 24 hours each time was quite astounding. Even after going back and forth through the photo series several times, and indeed having seen it happen in the first place, it remains hard to believe how this strange pink shape with black tufts of fluff becomes a complete bird so rapidly.
So, what fuels this rapid growth? As it happens, that is one of the main questions I am looking to answer in my current research. Watch this space!