Purabi Deshpande is undertaking her PhD at the University of Helinksi. She is an urban ecologist, with an interest in understanding how climate change and anthropogenic disturbance affect bird communities. Purabi shares her recent work on the interaction between climate and habitat on over-wintering bird abundance in Finland.
Purabi, watching early spring migrants in winter whilst surrounded by tens of centimeters of snow on the ground. (Photo credit: Ricky Nencini)
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Institute. University of Helinski
Academic life stage. PhD
Major research interests. Urban ecology, ornithology
Current study system. I study the response of birds to changing environments at the intersection of urbanisation and climate change. Human impacts on ecosystems are often studied at a local scale (e.g. habitat destruction due to a city’s growth) or at the global scale (e.g warming temperatures due to anthropogenic climate change). I am interested in understanding how birds respond to both these local- and large-scale changes caused by humans. Part of my research is carried out in Bangalore, a megacity in India, and the other part in Finland, which at 60 to 70 degrees north faces the brunt of climate change.
Recent paper in JBI. Deshpande, P., Lehikoinen, P., Thorogood, R., & Lehikoinen, A. (2022). Snow depth drives habitat selection by overwintering birds in built‐up areas, farmlands and forests. Journal of Biogeography. 10.1111/jbi.14326
Motivation for this paper. Snow cover in Finland, especially in the south of the country, is decreasing drastically as a result of warming climates. At the same time in human inhabited areas across the country, there is a lot of supplementary feeding, either directly, indirectly (think garbage), or in the form of introduced plant species. Species that would typically be classified as “migrants”, which would leave Finland during the winter, are now seen overwintering in Finland. This change in migratory behaviour is possibly due to milder climates and/or constant food supply. We therefore wanted to explore how different environmental variables and their interaction with different habitats affected the abundance of overwintering birds in Finland.
A brambling, seen in a snowy winter (Photo: Petteri Lehikoinen)
Key methods. We explored if abundances of birds in three different habitats (built-up, farmland and forest) changed with snow depths and temperature across 32 winters and whether species traits could explain the observed changes. We expected most variation in abundance to occur in built-up habitats as snow depths were likely to be lower and food availability higher, which would allow more birds to overwinter here. This work would not have been possible without brilliant long-term climatic monitoring datasets that are maintained in Finland. The Finnish Meteorological Institute maintains mean daily snow depth data for 10 by 10 km grids across the country (among other climatic variables). More importantly, the Finnish winter birds census which is an effort undertaken by citizen scientists every winter for more than half a century is a mind-blowing effort. This is especially true when you consider that some of the data collection is done at temperatures as low as minus 30 degrees centigrade!
Major results. There are two major results from this recent paper. First, there is an interaction between habitat and climatic conditions. As expected, decreasing snow depth led to increased bird abundance in farmlands and forests. However, as snow depth increased, there was increasing abundance in built-up areas. These results indicate that built-up areas could provide refuges for birds to over-winter when climatic conditions become less favourable. With climate change there are expected to be more extreme weather events. Overwintering species that can occupy urban areas might benefit, compared to those species that avoid built-up areas. Secondly, we found that snow depth is a better predictor of bird abundance than temperature. Even though there is a correlation between temperature and snow depth, snow depth may better reflect climatic harshness because food or roosting sites will be covered at high snow depths. However, collecting snow depth data is more difficult than temperature, so it is often overlooked while studying the effect of climatic factors on species.
Unexpected outcomes. As I was interested in seeing how urban environments are affecting birds, I had expected that the largest changes in abundances of overwintering birds would be observed in built-up areas, due to low snow depths and easy access to food. On conducting the analyses, we discovered that this was not the case and most of the changes were driven by farmland areas! The most exciting finding of this work is that the variation in bird abundances is explained better by snow depths rather than temperature. Data pertaining to snow depth is often difficult to collect at a level that is relevant to study animal ecology. So, most research uses temperature instead. Few studies investigate how habitat preferences of animals change with changing snow depths. Here we show that even though temperature and snow depth are often correlated they might be affecting animals differently and warrant separate investigation.
Barnacle geese foraging on a thawing farmland.
Next steps. As a result of warming climates we know that many species are moving their ranges along latitudinal and altitudinal gradients. Most of this work is focused on movements in the spring, However, weather is more variable in the winter. We are currently working on a manuscript which explores not only the poleward shifts in wintering bird communities in Finland, but also whether birds are moving poleward faster in certain habitats, and how changing snow depths are affecting these shifts.
If you could study any organism on Earth, what would it be? I have always been excited about birds and I am quite happy sticking with them! More than particular organisms I would like to get my hands on some long-term monitoring datasets of different taxa and explore similar questions with all of them.
Anything else to share? My PhD journey so far has been a real adventure. Before I moved to Finland (from India), I had only seen snow once before. Carrying out fieldwork in sub-zero temperatures, thinking about winter ecology and shifting my “home-range” has been an excellent experience!