Climate change and migration

We all know that climate change is happening – there is no denying it. We are already seeing the effects that it is having on the planet. An increase in the severity of storms, freak weather events, loss of sea ice, a rise in sea level, longer heat waves, increased rainfall and consequent flooding, are just a few examples of the impact of a warming climate. The changes will affect the behaviour of all species, as they attempt to acclimatise to them. If they cannot adapt fast enough, or there is not enough genetic diversity to enable adaptation, then extinctions will happen. Species are already going extinct at an alarming rate. Scientists have estimated that we’re losing species at 1-10,000 times the natural background rate of one-five species per year, with dozens going extinct each day. We are currently undergoing the sixth mass extinction the planet has experienced – the biggest since the elimination of the dinosaurs 65 million years ago. Unlike previous mass extinctions, this one is caused by us.

The question has been raised more than once about the potential impact of climate change on the migration of ospreys. Of course, we can’t really know for sure, but can speculate based on what we do know. Animals that migrate do so due to the abundance of food, and must therefore time their movements to match those of their prey. They use environmental cues for the timing of their migration, and also for navigation, therefore any changes in these cues will undoubtedly have an effect. In terms of ospreys, they have to migrate to places where their prey, fish, are most plentiful. Fish are ectotherms, i.e. they depend on external sources of heat, and cannot regulate their own temperature internally. As such, their physiology is linked to the temperature of their environment. As temperatures decrease towards the end of summer, fish tend to migrate towards deeper water, making them impossible to catch, hence the need for ospreys to migrate to warmer climates.

A rise in temperature will influence the metabolism of the fish, which is likely to affect their movements. This means that fish in the UK could potentially remain available to ospreys for a longer period, and the beginning of the ospreys’ migration could thus be delayed. In some species, migration patterns have already altered, or indeed halted altogether, as a result of changes to their environment and the movement of their prey. However, having the ospreys stay longer in the UK and even potentially all year round is not a good thing at all. Migration has a role in reducing the occurrence and spread of diseases and infections, as individuals are vacating potentially contaminated habitats, and are separated from one another during the migration process. Also, diseased individuals are less likely to survive any long-distance travel, i.e. only the strong survive, therefore leaving the population more or less healthy. Consequently, staying sedentary and not migrating can lead to increased incidences of disease, which can then be transmitted to others in the population, and infect offspring through the breeding of infected individuals. In closely knit populations, and particularly those that contain low genetic diversity, a disease outbreak could wipe out an entire local population.

Migration is an important, innate process that certain species have been undertaking for thousands of years. Almost 20% of all bird species migrate. It is a necessary part of their lives, and that of their prey species. If these normal patterns, and indeed other aspects of animal behaviour, become disrupted, the consequences could be far reaching and there may be more serious and complicated effects that we cannot yet predict.

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