Wildlife & Traffic

A European Handbook for Identifying Conflicts and Designing Solutions

9 Monitoring and Evaluation
Original version (2003)
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9.1 General principles of monitoring

9.1.1 The need for monitoring and its objectives

After the construction of roads, railways and waterways the application of monitoring is of crucial importance as it is this mechanism that allows planners to check the effectiveness of measures which have been applied in order to reduce the infrastructure's impact on habitat fragmentation. A well-designed monitoring scheme will help to achieve several goals:

  • To detect failures in the installation, construction or maintenance of measures.
  • To establish if the mitigation measures fulfil their purpose.
  • To evaluate if the measures provide long term mitigation for the species and habitats.

In short, monitoring will contribute to establishing whether or not suitable and sufficient mitigation measures have been provided for during the planning and construction phases of a transport infrastructure, guaranteeing minimum impact on the fragmentation of animal populations and habitats.

The dissemination of the results of the monitoring scheme is also very important for gaining knowledge on the development of more effective and less expensive measures. Therefore, important objectives of monitoring include helping the infrastructure planners to:

  •  Avoid repeating mistakes.
  • Provide new information for improving the design of mitigation measures.
  • Identify the measures with an optimum relationship between cost and benefit.
  • Save money for future projects.

Monitoring schemes should be an integral part of the routine technical management that leads to the adaptation and improvement of the design of measures which avoid or reduce the effects of transport infrastructure on habitat fragmentation.

9.1.2 Definition and types of monitoring

In general, monitoring should consist of regularly repeated measurements of selected variables. An activity can only be called monitoring if the following requirements are met:

  • Measurements are standardised.
  • The variables selected indicate ecological processes of interest or properties that need to be detected.
  • The scale (both in time and space) of measurement is appropriate for the detection of change.

Without clear objectives for monitoring, these requirements cannot be fulfilled. The establishment of these objectives and the selection of methods, standards, scale and criteria for the evaluation of the effectiveness of measures requires basic ecological knowledge of the systems affected. Therefore, the involvement of ecologists or wildlife biologists in the design of monitoring schemes is fundamental.

It is possible to distinguish between two types of monitoring, described below.

Monitoring of measures: routine monitoring

This type of monitoring focuses on the inspection and control of the effectiveness of measures by measuring local variables such as the number of animals using a passage or the number of animals run over per kilometre of infrastructure. Construction standards (materials, dimensions, location, etc.) and maintenance are verified and variables are measured to evaluate if they fulfil their purpose. When failures appear, corrective measures can be applied to amend the problems.

Monitoring can be focused on an isolated measure but more often than not it is advisable to monitor the measures which show interrelationships or have a combined effect to achieve the same objective.

This type of monitoring can be included in the routine management and maintenance plan of the infrastructure and in some countries is developed as a statutory procedure in all new transport infrastructure developments. It includes activities that do not require high specialisation of the professionals who implement it and can be achieved with reasonable budgets.

Some examples of activities that can be included in this type of monitoring are:

  • Identifying if fauna passages are used or not by the target species and the frequency of use. If they are not used, an attempt should be made to identify the causes of failure and to design corrective measures.
  • Registering the number of road and railway casualties, locating black spots where a large number of animals per unit length are run over, and identifying which species are affected.
  • Identifying other problems such as pits that can act as lethal traps, fences which are not properly installed, etc.
  • Verifying the noise reduction effect of barriers installed to reduce this disturbance.
  • Checking if a new pond which has been constructed as a compensatory measure is being used by the target species.
Figure 9.1 - Monitoring of fauna passages or registering road casualties to locate black spots can be carried out by standard procedures included in the infrastructure maintenance plans. (Photo by C. Rosell)

Monitoring the effects of measures on species and habitats: ecological monitoring

This focuses on the ecological effects of mitigation and compensation measures. It tries to identify changes in genetic diversity, species distribution, population dynamics, habitats and landscapes. Selected habitat features, landscape patterns and natural processes are registered after the construction of a new transport infrastructure and compared to baseline conditions.

Ecological monitoring requires long-term and large-scale approaches, which take into account the whole number of measures that have been applied and the synergistic effects that occur when new transport infrastructure is added to the existing network. For this reason, this type of monitoring can only be applied as routine in special cases, for example when a wildlife overpass has been constructed to link the habitats of endangered species or to connect natural protected areas.

Some of the aspects of ecological monitoring are:

  • Incidence of mortality caused by road and railway casualties and its effect on the population dynamics of target species.
  • Evaluation of the barrier effect of the whole infrastructure network, taking into account not only the proportion of animals that try to cross and are run over but also the proportion of individuals that attempt the crossing and are dissuaded from doing so by disturbance (noise, light, etc.).
  • Changes in the behaviour of indicator species due to disturbances.
  • Effects of new habitats associated with the infrastructure such as cuttings and verges. Colonisation by invasive species and consequences of the attraction of predators such as birds of prey to these areas.
  • Landscape changes generated by the new infrastructure such as the degree of habitat fragmentation, distance between fragments of the same type of habitat and others.
  • Changes in distribution, composition and quality of the habitats adjacent to roads and railways due to pollutants generated by the infrastructure.

Ecological monitoring provides very valuable information for the design of new infrastructure in order to mitigate its effects, and also improves understanding of the problems. The design of these monitoring projects must be carried out by wildlife specialists because methods and temporal and spatial scale of measurements show a high variation between different species and landscapes. As a result, this chapter does not describe this type of monitoring but rather focusses on the monitoring schemes to be applied as part of the management and maintenance of transport infrastructure.

Figure 9.2 - Telemetry data provide information on the behaviour of the animals in relation to transport infrastructure but it requires high specialisation and investment of time and money. Its application to routine monitoring is limited, but it can be very useful in special cases. (Photo by B.Iuell)

9.1.3 Practical considerations

The main lesson to be learnt from existing monitoring schemes is that successful schemes are simple, cheap, co-ordinated and standardised.

All monitoring schemes are limited by the practical considerations of cost and feasibility, which means that monitoring objectives have to be examined very closely for relevance. Priorities must be linked to objectives in order to identify which parameters are important and which can be omitted.

Some of the practical considerations which are important when planning the monitoring of infrastructure developments are:

  • Clear monitoring objectives should be defined. This is necessary in terms of what information will be provided.
  • Clear achievement targets for mitigation measures should also be defined. Monitoring cannot show which targets to aim for when setting standards: these are value judgements. However, what monitoring can do is indicate whether or not these targets are being achieved.
  • Systematic and standard recording schemes and methods should be used. Training and co-ordination are important.
  • Information on the baseline conditions should be gathered when possible.
  • Species with a recognised value as indicators of habitat fragmentation should be selected. It is not possible to monitor everything.
  • A scale of recording appropriate to the process/animal being monitored should be chosen.
  • Monitoring work should continue beyond the infrastructure development phase. Monitoring requires repeated records.
  • Monitoring records should be stored safely and in such a way that they are accessible to all stakeholders.
  • Records should be kept in a standardised way. Change can only be detected if the original work is geo-referenced and sites can be relocated.

Four points are thus particularly important:

the selection of target species, the selection of the spatial and temporal scale, the methodology and the development of standards.

Standards for evaluating whether goals are achieved

Monitoring provides results about variables that need to be compared with a standard measurement. The existence of standard measurements allows the degree of effectiveness of measures to be evaluated and aids the decision about when corrective actions must be applied to improve their effectiveness. A standard must be a quantitative variable when possible and should be based on clear criteria. Expressing the objectives of mitigation measures in a standard way provides the best basis for the monitoring and evaluation of the effectiveness of mitigation measures.

Selection of target species

Some measures have been designed for a particular species such as species of high conservation value or native species which are sensitive to habitat fragmentation and require large areas of continuous habitat, or the maintenance of migration routes (for example wolf, bear or ungulates). In this case the choice of target species is clear.

Nevertheless in other cases, the measures have a more general goal such as avoiding the loss of quality of an adjacent habitat or maintaining links between fragmented habitats or populations. In these cases, it is necessary to select target species (see Chapter 5) on which to focus the monitoring activities. The following characteristics are suggested:

  • Species for which measures were designed.
  • Species which respond to changes in fragmentation and do so rapidly.
  • Organisms about which substantial ecological knowledge is available and standard monitoring methods have been clearly established.
  • Species that are easy to detect and identify.
  • Taxonomic groups recognised as indicators of habitat fragmentation, which give information about the state of whole ecosystems.


The selection of appropriate spatial and temporal scales for monitoring is of major importance but it is not possible to establish general rules. Essentially, to detect change a sufficiently large area over a long enough period of time needs to be sampled. For example, the duration and periodicity of monitoring will be completely different in an analysis of the effectiveness of a fauna passage and a analysis of a reduction in road casualties caused by a new fence. The selection of spatial scale cannot be generalised.

Standardisation of monitoring techniques

One problem which limits comparisons of the impact of infrastructure developments or mitigation measures is that monitoring methods vary widely. The result of this variation is that few studies can be directly compared and patterns cannot easily be summarised. Standard monitoring protocols are essential if studies are to be compared or results from different monitoring programmes combined. This is essential to enable the analysis of different mitigation measures in different cirumstances. It is therefore important to be open for co-operation.