Bye Bye Birdie(s)

Needless to say, it’s getting hotter. It may not yet be scorching hot, and England may not have been transformed into the nouveau California like many (yes I’m looking at you) secretly hope, but it is definitely getting hotter. Walther et al.(2002), veterans of last week’s blog, put this warming at around 0.6^oC for the past 100 years. This may not seem like much, but for flora and fauna, who are far more specialised and fine-tuned to their environments than us super-adaptable humans, this is quite literally the biggest thing since sliced bread.

Not quite the adaptation I had in mind

Take, for example, birds. Birds are having quite a hard time adapting to current warming trends, and, whilst many succeed with (literally) flying colours, others are finding themselves somewhat left behind.

One of the biggest changes in the life of birds, highlighted by Crick et al. (1997), is that birds are laying eggs earlier. Between 1986 and 1997, Crick et al. noted that the growing season of plants advanced by around 8 days in Northern latitudes. This had huge effects for plant and bug communities, as not only did average flowering and leafing dates come forward, but so did the peak in abundance of bugs that make it their business to feed on these plants. Consequently, as birds in turn are somewhat dependent on peaks of bug abundance for food, it is suggested that they have begun laying earlier so that they could re-synchronise feeding their young with the times when arthropod bounties were at their greatest.  

Now I know what you’re thinking - “Joe, this doesn’t actually sound like much of a problem”. And, partly, you’re right. There are lots of benefits of laying eggs earlier, such as the survival of young being being enhanced by a greater pre-winter period. However, not all birds respond to these phenological changes with gusto. Take the Parus major (you know him as the Great Tit) for instance. As revealed by Both and Visser (2001), the Great Tit has shown very little response to temperature change, and is effectively getting left behind.

Local birds however aren’t the only ones who suffer when it comes to earlier optimal laying dates. Those that decide to spend their summer abroad soaking up the sun (a luxury I’m sure we’re all guilty of) are in trouble too. Take the Pied Flycatcher (also known as  Ficedula hypoleuca), for instance, who migrates to sunny West Africa at about 10^o Latitude during winter. While he is away, the time of optimal food resources creeps closer, and he is none the wiser until it is too late.

A Pied Flycatcher doing what it does best... (catching flies)

The trouble for long-distance migrants like the Pied Flycatcher is that most do not rely on temperature as a signal to fly home, and for those that do, regional climate change differences cause them a world of pain regardless. Most rely on endogenous rhythms or environmental stimuli that are entirely unrelated to temperature, such as the Pied Flycatcher’s reliance on day length. So, by the time the Pied Flycatcher has made the return flight to Europe, the time of greatest food resources is all but upon him (Both and Visser 2001).

Both and Visser study this phenomena in the Hoge Veluwe region of the Netherlands.  They found that the Pied Flycatcher, in response to the warming, brought forward its laying by an average of 10 days. This was possible for the bird, as usually they take a while to re-adjust back to the EU climate and recover after their migration before embarking on parenthood. However, Both and Visser noted that even with this adjustment (which put the birds at an initial disadvantage by causing increased stress after migration), the birds were still not arriving and laying early enough to take advantage of peak food availability. They were getting left behind.  

For those of you interested, here are Both and Visser's graphs that show the general trends - You can clearly see that whilst temperature at the breeding ground rises and the mean laying date moves forward, the arrival date generally stays the same. Also of interest is the selection differential - this seems to suggest that later laying birds are selected against.

This is a very interesting study, with some serious connotations. But it must be taken with a pinch of salt, as it only researches one area and one community of Pied Flycatcher. A similar study by Goodenough et al. (2010) that focuses instead on Pied Flycatchers in the UK, whilst sharing the conclusion that climate change is disadvantaging birds, sees it happening in entirely different ways.

They note that the community that migrates to the UK is not turning up too late for peak food availability, but is instead waiting too long to lay their eggs, in complete contrast to their Netherlander cousins. The average wait after arrival before laying is a staggering 27 days. They offer many explanations for this, however the most convincing is the argument that it is due to limits or constraints on their phenotypic plasticity (their ability to adapt their phenology). Perhaps they are constrained because the environmental stimuli is not available for migrant birds (such as the temperature at  the species' breeding ground before their arrival) or perhaps due to a genetic constraint that comes about due to low heritability of different laying dates (to put it simply, the knowledge isn’t passed between generations). Whatever the explanation, it is clear however that the UK Pied Flycatchers are disadvantaged, albeit in a different way than their cousins.

Uncertainty like this makes it really difficult to see the true effects of climate change on fauna and flora such as the Pied Flycatcher. Not only is it hard to thoroughly explain changes (or no changes) in their behaviour, but the behaviour itself differs between different communities in the species. This makes it a seemingly impossible task to assess (at a species level, at least) the effects of climate change on organisms.

There is one solid conclusion we can draw from this though, and that is that climate change is taking a real toll on migratory birds such as the beloved Pied Flycatcher. Regardless of whether they adapt their phenology or not, the environmental trigger of the photoperiod (day length) will never be changed by climate change. Their migratory nature, if warming continues, may spell their doom. As the optimal egg laying period creeps ever forward, and the Pied Flycatchers live ever more in the past, they will become more and more disadvantaged, until, who knows, they may never return from their holiday at all.

For those of you a bit depressed about the state of our flora and fauna - fear not! Potentially we have found some more on another planet that we can destroy as well - see here.