Deer gradually disappearing from Sonian Forest

Fewer deer can be seen in Belgium’s Sonian Forest, according to the most recent deer monitoring survey from the Flemish government’s Research Institute for Nature and Forests (INBO).

Since 2008, survey volunteers have walked 473km per year and counted deer on a fixed route in the forest near Brussels that also takes in parts of Flanders and Wallonia.

While the institute said that this method does not give a clear picture of the population, trends are still revealed.

From 2009 to 2013, numbers were stable, with around 1.07 deer observed per kilometre, but between 2014 and 2023, the figure fell to an average of 0.6 deer.

The institute, whose function is to “underpin and evaluate biodiversity policy”, said that there were no clear answers as to why roe deer sightings have diminished over the years.

The most likely reason is disruption caused by people and dogs who leave the footpaths to enter the forest, therefore disturbing the habitat of these shy animals.

Now, to find proper answers, the institute is starting photo surveillance with a network of hidden cameras.

Preliminary results show that the behaviour of deer that come into contact with humans – for example, people going on walks with or without their dogs or cycling in the forest – is different from the habits of a deer population that does not see anyone.

The new camera monitoring can also map the possibility of the deer coming into contact with potential predators – such as foxes and wild boars – which would also impact on deer numbers.

“We use population modelling to predict the influence of human and other factors on populations of large mammals, game and other species in Flanders,” the institute’s website says.

“Thanks to these models, we are able to form more rapid estimates of the impact of ‘new’ species such as wolves and raccoons.

“We develop new methods such as uniform monitoring protocols, environmental DNA, camera traps, citizen science and automation of data processing.”