City hedgehogs - urban snufflers
Nina KorhonenOuti Ovaskainen needed an unusual assortment of field work instru-ments for preparing her Master's thesis: in her rucksack she carried a torch, a map, a scale, a paintbrush and a can of mace. The mace was necessary for her protection - not against wild animals but possibly aggressive people.
Outi Ovaskainen, 25, is studying at the Population Biology Department of the University of Helsinki. The field work required for her Master's thesis did not lead her to wild jungles but to entirely urban environments, the parks in the centre of Helsinki, Finland's capital. Luckily, she had no use for the mace she was carrying in her rucksack while she was mapping the hedgehog population in downtown Helsinki. Most of the people she met during her nightly walks were just curious about what she was doing, and many were also willing to help her find hedgehogs hiding under bushes.
The hedgehogs Ovaskainen found were marked with a non-toxic paint so that their routes could be detected. Each park had its own colour and each individual hedgehog had a distinguishing marking. Unfortunately, the markings made on the hedgehog spines faded and wore off, and had to be renewed more than once.
In the course of last summer, Outi Ovaskainen explored a total of ten parks in central Helsinki."We started out to the parks at twilight, about 9 o'clock in the evening. Hedgehogs don't usually forage around for food until it's dark," she says.
During many mapping walks Ovaskainen was helped by her supervisor Heidi Kinnunen and by Marco Amati, a student of environmental sci-ences from Ireland, who was writing his thesis in Finland.
"Since hedgehogs are generally regarded as extremely endearing creatures, it was not difficult to enlist voluntary help. Enthusiastic helpers foraged through parks with us, calling out to me as soon as yet another snuffler was located."
The sex and weight of the examined hedgehogs were recorded, and so was the place where they were found. The paint markings were useful later when the routes taken by individual animals between parks were charted.
Omnivorous surviverHedgehogs do not have their own territories, although some old, ill-tempered females seemed to defend their immediate surroundings with considerable noise. During their nocturnal wanderings in search of food hedgehogs can travel up to about two kilometres.
There are no exact data about the numbers of hedgehogs living in Helsinki, and Outi Ovaskainen is also unwilling to go further than just a careful estimate: it is possible that there is a population of thousands of hedgehogs spread over the whole area of the capital city.
Hedgehogs have adapted to urban life very well because they have no natural enemies in towns. They are primarily insectivorous, but they also eat snails, earthworms, bird eggs, fish provided by people, and even dog food.
At least those hedgehogs that Ovaskainen and her helpers found in the Linnanmäki amusement park, located in central Helsinki, are happy with an urban diet. The amusement park is paved, but the hedgehogs find safety under bushes and the various structures, for example under the carousel.
"Hedgehogs investigate rubbish heaps and waste-bins, and pick up items such as half-eaten hot dogs," Ovaskainen explains.
Diversity in parksBesides collecting new knowledge about hedgehogs, Outi Ovaskainen also hopes that her study will help to improve the living conditions of these small mammals in cities and towns. Urban planning is of key importance in this respect, and so is the maintenance of public parks.
"As far as hedgehogs are concerned, it would actually be better if parks were not too carefully cleaned. Hedgehogs need fallen leaves for building their winter nests, and they also examine litter for food. The lawns wouldn't need to be perfectly even in every corner, and when dead leaves are raked in the autumn, some heaps could perhaps be left in the parks over the winter."
Urban life would also be easier for hedgehogs and other small animals if the parks were connected to each other. Ovaskainen believes that the human inhabitants of towns would also welcome some connecting walks or cycling routes between public parks.
"I'm convinced that there will be hedgehogs living in towns in future, too. City people have a heartfelt interest in the living conditions and habits of hedgehogs: those who have observed hedgehogs in their own yards or in the parks hope that their grandchildren will also be able to enjoy the company of these charming creatures."
Northern border of habitatThe hedgehog (Erinaceus europaeus) came to Finland through the Åland Islands, Estonia and Sweden as late as the beginning of the 20th century. It is spread all over Europe, and North and Central Asia. The smaller species of African hedgehogs are popular pets on the American continent. In Finland the hedgehog ranges as far north as Rovaniemi.
The average life-span of hedgehogs in Finland is 2-3 years, although some 6-year-old individuals were reported in a study carried out in Vilppula. Mortality is high in winter; only about one out of five hedgehog babies born in summer survive over their first winter season.
Apart from the long periods of severe cold, foxes, large birds of prey and humans are the enemies of hedgehogs. Other threats are traffic and pollution, and hedgehogs are also endangered by salmonella epidemics, which occur once in a while and easily spread through feeding places visited by large numbers of hedgehogs.
Hedgehogs keep growing all their lives, which means that the oldest individuals are also the largest. The largest one among the hedgehogs marked in the Helsinki parks weighed 1.5 kg and the smallest one only slightly under 300 grams.