Functionality of underpasses as wildlife crossings on Route 34, Hacienda Barú National Wildlife Refuge, Puntarenas, Costa Rica.
Written By Marta Venegas-Vargas
8th December 2021
Route 34: Section Hacienda Barú, the first site with underpasses for wildlife in Costa Rica
The Hacienda Barú National Wildlife Refuge is a 335 hectare protected area in the province of Puntarenas in the South Pacific of Costa Rica. It is in a tropical rainforest zone, and contains primary and secondary forests, wetlands, mangroves, riparian forest and the sea (Figure 1).
Figure 1. . Route 34 and Hacienda Barú National Wildlife Refuge, Puntarenas, Costa Rica..
Hacienda Barú was fragmented by 3 km of Route 34, also known as the Costanera Sur highway, which was upgraded from gravel to asphalt in 2010. The project's environmental impact study predicted an increase in wildlife roadkill because the speed limit increased from 60 km/h to 90 km/h, and a significant increase in traffic volume. For this reason, the refuge manager requested the developer to build wildlife underpasses as part of the negotiation during the expropriation of the land
As a result of this negotiation, 33 crossing structures were installed, including four aerial crossings for arboreal mammals and 29 underpasses (7 round culverts and 22 square structures) (Figure 2). Of these 22 square structures, 13 are specifically for wildlife and were 1.5 x 1.5m, while the remaining nine were combined with drainage and were larger in size.
As a result, this was the first road project in Costa Rica that had crossing structures installed specifically to reduce the barrier effect of the road and to reduce wildlife mortality due to vehicle collisions.
Figure 2. Map showing the location of underpasses along Route 34 that divides Hacienda Barú National Wildlife Refuge, Puntarenas, Costa Rica.
The aim of this research was to evaluate the functionality of these wildlife underpasses and to generate information to improve the design of future underpasses in the region. Camera traps were used to determine the species of terrestrial vertebrate using the underpasses. The data collection was carried out in 23 of the structures and a camera remained in each of the structures for two months, between September 2015 and July 2016.
In addition, the effectiveness of these structures was evaluated based on their structural characteristics (shape, size, substrate), and spatial characteristics (distance to water bodies, distance to the nearest underpass). For this purpose, cameras were placed in 16 structures and only photographic records of mammals were considered for this analysis, in order to avoid the bias generated by camera traps in the capture of other groups of vertebrates.
Are the underpasses really functional?
A total of 1279 photographic records belonging to 21 species were obtained of animals using the 23 underpasses in the Refuge. Fourteen of these were mammal species (Figure 3), four were reptiles, two were amphibians and only one bird. Prior to our study, seven of these 21 species had not been observed using underpasses in Costa Rica.
According to the Costa Rica Wildlife Friendly Roads Guideline, eight of the 14 mammal species recorded using the underpasses are considered vulnerable to road impacts. In addition, nine of the species recorded (more than 60%) are subject to high rates of mortality on the Costanera Sur highway, demonstrating the importance of underpasses as effective mitigation measures.
The only feline recorded in our study was the ocelot, which is endangered in Costa Rica, mainly due to habitat loss and fragmentation. Of the six species of felines existing in our country, this is the one most impacted by roadkill, with an average of three roadkill incidents per month in the country.
Figure 3. Mammals recorded using underground structures under Route 34: section Refugio Hacienda Barú. A. Common Opossum. B. Common Gray Four-Eyed Opossum. C. Northern Tamandua. D. Nine-Banded Long-Nosed Armadillo. E. Central American Agouti. F. Paca. G. Northern Raccoon. H. White-Nosed Coati. I. Tayra. J. Striped Hog-Nosed Skunk. K. Ocelot. L. Collared Peccary.
Characteristics influencing functionality
No statistically significant relationship was found between the relative abundance of animal detections and the shape and size of the structure; however, a higher abundance of crossings was obtained in the large drainage culverts. The Costa Rica Wildlife Friendly Roads Guideline suggests that specific passages should be at least 3 x 3 m and 3 x 4 m, for medium and large mammals, respectively, which could be linked to the high crossover rate obtained for these structures. Importantly, large stormwater drains also played a significant role in the permeability of the road, highlighting the importance of retrofitting them to increase their functionality.
Maintaining passages with a natural substrate and adjacent vegetation cover will increase their functionality as most species preferred these types of structures. Each structure should also be designed for the species of interest. Before the development of any road project, a study should be undertaken to identify habitat and determine the main natural crossing areas for the different species and target mitigation for those areas.
Evaluating the rate of use of crossing structures is critically important in Costa Rica and other areas where road ecology is a relatively new discipline to ensure future crossing structures are the optimum design. Well-designed monitoring programs should start soon after construction and continue for many years, thereby taking into account the adaptation period where the vegetation regrows and animals become accustomed to the structures. This is necessary to generate robust data on rate of use allow for better decision making.
Author information:
Marta Venegas-Vargas
Contact: martavv28@gmail.com
Source:
Venegas-Vargas, M. 2018. Functionality of underground structures as wildlife crossings in Hacienda Barú National Wildlife Refuge, Puntarenas, Costa Rica. Bachelor's thesis. National University of Costa Rica. Heredia, Costa Rica.
Editor:
Wendy Collinson & Rodney van der Ree
Cite this summary:
Venegas-Vargas, M.. (2021): Functionality of underpasses as wildlife crossings on Route 34, Hacienda Barú National Wildlife Refuge, Puntarenas, Costa Rica. Edited by Collinson, W & van der Ree, R. TransportEcology.info, Accessed at: https://transportecology.info/research/underpass-functionality-route34-costa-rica[Date accessed].
