Improving the design of road ecology research

Written by Christopher Johnson

CITIES Research Institute, Griffith University, Brisbane, QLD, Australia

25th January 2023

To start

The focus of our research was on birdlife. Birds have long been regarded as being less affected by roads compared to other groups of wildlife. Indeed, most research attention in road ecology has overwhelmingly been on mammals, especially larger mammal species such as predators and ungulates. Birds are, however, highly susceptible to the impacts of roads but this impact is less conspicuous. Our previous studies, in fact, revealed not only significant declines in richness and abundance near roads but a general unwillingness of many bird species to cross all but the narrowest of roads. The implications of this are substantial as birds perform many valuable ecosystem services such as pollination and seed dispersal of medically and economically important plant species, and are predators of agriculturally important pests. In addition, birds provide a significant role in human-nature interactions through birdwatching and backyard feeding.

The problem and what we did next

The context of birds within the general field of road ecology has been summarised in two important studies published around a decade ago (Kociolek et al. 2011; Morelli et al. 2014) when experimental approaches were still being developed. At that stage, several factors were generally accepted to influence birds in areas adjacent to roads: road traffic (wildlife mortality), vegetation management, physical barriers (e.g., fences, drains, etc.), artificial light sources, and road infrastructure (powerlines, fencing, etc.). In particular, traffic noise and wildlife-vehicle collisions were deemed to exert the greatest impact on nearby populations. However, these findings were mainly observational and based on studies with low inferential strength. Since then, there has been some discussion of best research practices (Roedenbeck et al. 2007; van der Ree et al. 2015), but little follow-up.

With this perspective in mind, we performed a systematic quantitative literature review to synthesise and articulate the latest research (2016-2021) to see how the research field responded to previous findings. We framed this in the context of their limitations and biases.

What did we find?

Our systematic search of eight journal databases returned nearly 1,500 articles. From these, we identified 102  studies that sought to quantify road impacts on birds – 52 of these involved the collection of road and bird data from field sites (i.e., roads).

Overall, the recent literature supported the proposition that roads significantly impact birds. This conclusion arises from changes in habitat quality, as well as the presence of associated road infrastructure. However, as we delved further into the research, we noticed several recurrent problems. Numerous studies:

  1. Did not collect data that was comparable. For example, some studies attempted to compare ‘numbers’ data (e.g., traffic volume) with ‘descriptive’ data (e.g., vegetation descriptions);

  2. Collected data for one aspect of the road environment (e.g., noise) but ignored other potentially significant influences (e.g., vegetation parameters). These two examples can have the same effect on birds and can mask each other (i.e., they are confounded);

  3. Used methods that can lead to bias (e.g., ‘eye-balling’ song frequency graphs)

  4. Lasted less than two years. This is a very narrow window through which to draw reliable conclusions based on observation of broader patterns; and,

  5. Studied roads without providing a comparison with at least one non-road area (i.e., no experimental control).

Herein lies the issue at the heart of the practice: road ecology studies often lack a genuine analytical comparator, something that can enable meaningful conclusions to be drawn. Diversity in study design and experimental approach can be beneficial. But, without an appropriate baseline to support this, conflict and confusion may arise that appreciably limits the real-world application of project outcomes.

The ‘Roads for Wildlife’ study framework

Our proposed framework, a simplified version of which can be seen below, addresses the recurrent problems identified in this review by offering a uniform and standardised approach to evaluating road impacts on wildlife generally, not just birds. Importantly, our framework builds upon the previous works of Roedenbeck et al. (2007) and van der Ree et al. (2015) and includes:

  1. Road assessments that measure traffic volume, traffic noise, and ambient background noise;

  2. Habitat surveys that measure habitat composition, vegetation cover, density, and height;

  3. Bird surveys (point count and acoustic) that measure species richness and abundance;

  4. A survey protocol that will ensure spatial and temporal consistency of data collection within and among studies; and,

  5. Statistical analyses that minimise the risk of bias from confounding variables (assuming data for the above are collected).

This framework could improve the reliability of road ecology research outputs, that in turn may enhance their application in the real world. Likewise, the framework will enable transport planners and engineers to implement and undertake a targeted evaluation of transport infrastructure, especially wildlife crossing structures, that yields high-quality data for use in future road projects.


Author information

Christopher Johnson

Cities Research Institute, Griffith University, Brisbane, QLD, Australia

Source citation

Johnson, C., Jones, D., Matthews, T., & Burke, M. (2022). Advancing avian road ecology research through systematic review. Transportation Research Part D: Transport and Environment, 109. doi:10.1016/j.trd.2022.103375

Further reading

Kociolek, A., Clevenger, A., St. Clair, C., & Proppe, D. (2011). Effects of Road Networks on Bird Populations. Conservation Biology, 25(2), 241-249. doi:10.1111/j.1523-1739.2010.01635.x

Morelli, F., Beim, M., Jerzak, L., Jones, D., & Tryjanowski, P. (2014). Can roads, railways and related structures have positive effects on birds? – A review. Transportation research. Part D, Transport and environment, 30, 21-31. doi:10.1016/j.trd.2014.05.006

Roedenbeck, I. A., Fahrig, L., Findlay, C. S., Houlahan, J. E., Jaeger, J., Klar, N., . . . Van der Grift, E. (2007). The Rauischholzhausen Agenda for Road Ecology. Ecology and Society, 12(1), 21. Retrieved from http://www.ecologyandsociety.org/vol12/iss1/art11/

van der Ree, R., Jochen, J., Rytwinski, T., & Van der Grift, E. (2015). Good science and experimentation are needed in road ecology. In R. van der Ree, D. J. Smith, C. Grilo, & D. Smith, Handbook of road ecology: John Wiley & Sons.

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Editor:

Clara Grilo

Cite this summary:

Johnson, C., (2023). Improving the design of road ecology research. Edited by Grilo, C. TransportEcology.info, Accessed at: https://transportecology.info/research/road-ecology-research

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