Keith Hobson and Migration's Many Mysteries

Blog on the SBS seminar (25th March 2021) from Keith Hobson written by David Watt, student from the “Meet the scientists” course.

One of the marvels of the natural world is the incredible migratory routes animals, both large and small, embark on over the course of their lives or even generations, to survive. Long gone are the days when the ‘disappearance’ of swallows in winter, was a perplexing conundrum that seemed to require a magical explanation. And yet, understanding exactly where a migratory species originated from is still a complex question to this day, one that has grabbed the attention of scientists like Keith Hobson. So why is this area still so mesmerising for him to explore in a globalised world, where we can clearly see where animals ‘disappear’ to? Can the nature of this disappearing act be revealed?

A common way to approach migration that has revealed a lot of what we know has been done by attaching a tag or GPS tracking device to individual animals and mapping out their movements. However, this approach does have its limitations. Whilst we may be able to trace the movements of the tagged animal after tagging has occurred, this practise simply cannot give us information on where that animal was beforehand and often that is precisely the information that could be most beneficial. For example, if an ill animal is found it would be useful to know where it picked up this illness and what other populations may have the illness. Similarly, when dealing with potential animal trafficking, knowledge of the animal’s origins, its past as well as its future movements would provide a much more holistic overview of animal movement. So, how could such an approach be undertaken?

This is where Dr Hobson and his team come in. Rather than using this classical tracking techniques, he focuses on undertaking chemical analysis of sample tissues, such as a bird’s feather, to work out where the animal has been. All cells and tissues are made up of fats, proteins, carbohydrates and other minerals and compounds and ultimately, of course, a wide range of elements (atoms). Two different atoms of differing mass may represent the same element. These are known as isotopes. Typically, when two isotopes are present, the lighter isotope will be more abundant in the tissue sample. This is useful in studying animal migration since the ratio of heavier to lighter isotopes of a given element will reflect the environmental conditions in which the animal was living. If Dr Hobson can identify the factors changing this ratio then conclusions on how that animal lived its life can be made. By working out the effects of various chemical processes on an animals isotope ratios, it is possible to understand which isotopes were assimilated in the animal from their food source. This can be achieved for several different atoms that are characteristic of different food groups. This is particularly useful for identifying the movement patterns of migratory species by allowing Dr Hobson to work out the geographical location where these isotope ratios would be expected to be observed.

Ultimately, it is possible to create maps of common isotopes in a given species. Thus, grouping similar isotope levels with a geographical area, all on a biological basis. This is particularly exciting as it opens up a range of practical applications going even beyond animal migration. By comparing the isotope ratios of similar animals in the same area, we can see if they are using the same or a different dietary strategy and, thus, whether they are in direct competition with each other for resources. We can gather from this how many differing strategies are being used and gain a better understanding of the impacts of human activities. 

This technique certainly opens up many doors to expand our knowledge of migration and even to topics further afield. However, there are additional ideas being explored by Dr Hobson’s team, particularly in determining how animals prepare for and undergo migration. One idea is to determine whether a migratory animal stores or just consumes food in each geographical location encountered during migration by establishing which factors play a role in this decision process. A further development is establishing isotope ratios for different amino acids (the fundamental building blocks of proteins) in an organism. This is because some isotopes in amino acids change drastically according to dietary changes whilst others remain more constant relative to the animal’s origin. A comparison of amino acid isotope ratios can, therefore, reduce the number of steps required to determine where an animal has been and may lead to further developments in the future. This could give a clearer picture of the animal’s behaviour than other methodologies.

Given such advancements, is there really any wonder why the investigation of animal migration is still as relevant as ever? Even though there may still be some hidden secrets to the “Magic of Migration”, research of this kind certainly paves the way to a greater level of understanding of this complex process.