Hoge Veluwe National Park in the Netherlands has a wildlife survey system that is unique in the world. A network of 50-70 camera traps continuously records the activity of animals across the park, since 2013. Each camera monitors a random patch of habitat in each of the six major habitat types: two types of forest, dry and wet heathland, drift sand and meadow.
Hoge Veluwe National Park is a fenced park of 5.400 ha, including 3.200 ha forest, 2.100 ha heathland and 60 ha of drift sand. The Park has three entrances through which 570.000 visitors enter annually. The area is home to approximately 220 mouflon, 180 red deer, 200 roe deer, 50 wild boar and an unknown number of fallow deer.
The camera-trap network is unique because of the large quantity of cameras and the long duration of the monitoring. The habitat types are rather discrete, and the Park is fenced, hence we know precisely what choices are available to the wildlife. Moreover, as the Park has strict opening hours and gates with ticket boots, we know when there are people in the park and how many.
Snapshot Hoge Veluwe
The cameras collect over a million photographs annually, that we manage and process using the application Agouti. This application groups photographs into sequences that form time-lapse clips of moving animals. Classifying all these images to obtain observations, the actual data, is a major challenge.
One way in which we process these photo sequences is with the public, in the project Snapshot Hoge Veluwe, which runs on the citizen-science platform Zooniverse. Most participants are beginners in wildlife watching, hence the quality of the classifications is highly variable. Nevertheless, the classification of multiple users combined yields a ‘wisdom of the crowd’ that is usually correct.
To the national park, involving citizens in classification is an additional means to increase the knowledge and interest in wildlife among the public, and to encourage wildlife watching at the Veluwe. Snapshot Hoge Veluwe is supported by the SIDN fund, amongst others.
We use the data from this network for a variety of purposes. One is to develop camera trapping as a method to estimate the population size of wildlife. Population size is a vital parameter in wildlife ecology as well as management but notoriously hard to measure in forested habitats.
We test the so-called random encounter model which estimates densities by correcting capture rates for the detectability of the wildlife. Detectability in turn depends on the size of the area that is effectively covered by the camera’s sensor and the total daily distance travelled by an individual.
The big complication that we attempt to tackle is that detectability is highly variable. For example, both the detection distance of the movement sensors of the camera traps and the movement behaviour of the wildlife differ between species, habitat types, and seasons. Hoge Veluwe is an ideal location for this purpose because the managers have quite precise annual counts of four species of ungulates to which we can compare our estimates.
Wildlife responses to recreation
We use the Hoge Veluwe camera network to study how recreation affects the behaviour of wildlife. The Netherlands are one of the most densely populated countries in the world, with numbers of recreations attaining levels that may affect the conservation value of protected areas and the ecology of species. We study wildlife responses to recreation in two ways.
First, we use a unique before-after control-impact experiment that the park provides. Up to 2015, visitors were allowed to wander everywhere, even outside of the paths, except in restricted areas. The camera network was set up to have half of the cameras in restricted area and half in accessible area. Since 2016, however, visitors must stay on the paths, and this rule is actively enforced. Effectively, the entire park is now restricted area. The camera network tells us how the distribution of wildlife activity has changed before and after the policy change.
Second, we take advantage of the fact that the park has strict opening hours that are shifted by one hour several times during the year according to a schedule. Moreover, the number of visitors varies dramatically between days. Since visitors buy tickets to enter, we have a record of recreation pressure. Busy and quiet days, as well as shift in opening hours form experimental treatments to which wildlife may respond.