by Geoffrey Carpentier
About this time of year, several acquaintances call me to tell me, excitedly, they just saw their first migrant robin! The excitement in their voice belies the fact they are simply tired of winter and are anxious to face the dawning of spring and all the joy which mild weather and sunshine brings.
Some may think this annual phenomenon is linked to climate change as assuredly a bird like a robin shouldn’t be here in winter, should it? I hate to do it, but the scientist in me feels compelled to ‘set the record straight’. I sheepishly tell them, a February robin is not necessarily a harbinger of spring, but more likely a remnant of an overwintering population of these thrushes which have survived on berries from last year’s growth. As the winter progresses, these hardy souls, simply move about in search of new food and as such become more visible.
That’s not to say, some birds don’t start to migrate as early as January in some cases. This is, of course, species and circumstance dependent. Yet, is climate the causal factor or is something else at work? Assuredly, climate change has an impact on the migratory patterns of some species. Recent studies show, some species are returning earlier than in the past, while others are returning on or about the same time as they did historically.
Generally, the return of migrants is impacted by weather, the amount of sunlight and hormonal changes which semi-annually occur within avian species. That is to say, when the conditions are ideal (i.e. the right amount of daylight, the ideal hormonal level in the bird and the weather to a lesser degree), migrants move northward or southward depending on the season.
In spring, where extended warm days occur, early migrants, such as blackbirds, larks, some sparrows, some hawks, certainly ducks and other water birds, may move north in good numbers before the expected dates of their ‘normal’ return. Although waterfowl movements are also linked to the availability of open water, in the areas to which they are migrating. However, these birds will readily migrate back southward, if conditions are unfavourable over the days following their return. This is called reverse migration and is a common phenomenon.
Climatic impacts are an entirely different thing. Recall, climate change isn’t about short-term changes in environmental conditions, but rather the long-term change in weather patterns. So as the earth warms (or cools), many species can and will be impacted. These long-term trends can have several outcomes. The most serious one affects those species which arrive too early and the food they rely on is not yet available. For example, Tree Swallows often return in late March, as do Eastern Phoebes (a flycatcher) and of course, being insect eaters, if the flies and such aren’t available, the birds must either fly back south, find another food source or starve. Luckily, these are adaptive species which can switch from their insect-based diet to one which relies on berries for nourishment. Other species are not so suited and the outcomes may be catastrophic.
So, the simple outcome of this is, if the prey species cycle does not match the migrant’s food source and the migrant can’t adapt to other foods, climate will have a very negative impact on those species. Conversely, exactly the opposite is true for adaptive species. In fact, early return may be beneficial, as there may be less competition for food.
Other species, such as hawks and waterfowl, are not nearly as impacted by their early return, as long as open water or prey exists, so they are not as negatively affected by ‘early’ springs. The onset of milder springs and shorter winters also means some species may be able to expand their range northward, as the conditions become more conducive to what they would normally experience in their traditional ranges.
So you can see this becomes quite challenging and simple interpretations, such as climate change is always bad, and anything anomalous must be triggered by climate change, may in fact be incorrect. Food for thought!
Geoff Carpentier is a published author, expedition guide and environmental consultant. Visit Geoff on-line on LinkedIn, Facebook and Instagram.