Action: Use humans to assist migrating amphibians across roads
- Two studies (including one replicated study) in Italy and the UK found that despite assisting toads across roads during breeding migrations, 64–70% of populations declined over 6–10 years.
- One study in the UK found that despite assisting toads across roads during breeding migrations, at 7% of sites over 500 toads were still killed on roads.
- Five studies in Germany, the UK and Italy found that large numbers of amphibians were moved across roads by patrols. Numbers ranged from 7,532 toads moved before and after breeding to half a million moved during breeding migrations annually. In the UK, there were over 400 patrols and 71 patrols spent an average of 90 person-hours moving toads and had been active for up to 10 years.
Many amphibians are killed by vehicles, particularly where their annual migration routes between breeding and over-wintering habitats cross roads. In some areas local volunteers may try to reduce deaths by collecting animals and releasing them on the other side of the road. Temporary drift-fencing and pitfall traps are often used to capture amphibians so that they can be assisted across the road. Patrols often focus on migrations to breeding sites rather than migrations of adults and juveniles away from those sites.
Ideally evidence of the effectiveness of this intervention would consist of survival rates, counts of animals in the population or numbers killed on the road before and after or at sites with and without human assistance. However, such evidence is rarely available and so here we not only present data on population trends, but also numbers of animals that were moved across roads and numbers and effort of patrols assisting amphibians.
For other interventions that involve engaging volunteers to help manage amphibian populations or habitats see ‘Education and awareness raising – Raise awareness amongst the general public through campaigns and public information’ and ‘Engage landowners and volunteers to manage land for amphibians’.
Supporting evidence from individual studies
A study in 1986 of 114 sites that included at least 23 human-assisted road crossings, 60 amphibian barrier fences and 11 road closure sites in Nordrhein-Westphalia, Germany (Feldmann & Geiger 1989) found that 131,061 amphibians were protected from death on roads. Between one and 116,515 individuals of 14 species were recorded at each hand-assisted, barrier fence or road crossing site. Animals were collected by hand and assisted across roads during breeding migrations at 23 sites. Nine sites had a combination of two of the interventions and for 20 sites it was unknown which of the interventions were used.
A study in 1980–1988 of a human-assisted road crossing in Bad Tölz, Bavaria (Haslinger 1989) found that thousands of toads were moved across the road each year. In 1980, a total of 15,000 toads were collected and in 1988 the figure was 7,532. Eight tunnels with wire-netting fences on both sides of the road were installed. Animals did not use tunnels and so those at the fence were collected by hand and moved across the road twice a year, before and after breeding.
A review in 1989 of toad patrols in the UK (Langton 1989) found that by 1988 there were more than 400 human assisted toad crossings which moved over 500,000 amphibians annually. Most crossings were for populations of common toads Bufo bufo, with breeding populations of over 12,000 adults.
A replicated study in 1981–1987 of toad patrols in the Netherlands (Zuiderwijk 1989) found that assisting common toads Bufo bufo across roads did not prevent the decline of nine out of 14 (64%) populations over six years. About 80% of toad crossings had fences and pitfall traps, from which toads are collected and released on the other side of the road.
A study in 1995 of 76 toad patrol projects in the UK (Froglife 1996) found that 20,000–39,000 toads were moved across roads in the spring by 71 patrols. The most frequent number moved by each patrol was 500–1,000 animals (28% of patrols). Despite human assistance, 65% of patrols reported that up to 100 toads were killed on the road, 28% reported 100–500 were killed and 7% over 500 toads. Many patrols reported that an ‘appreciable proportion’ of the total number of migrating toads were moved by humans. However, only 20% of populations were believed to be stable or increasing. Patrols involved an average of 90 person-hours, as they tended to have 1–3 volunteers/night (range: 1–14) for 11–20 nights (1–49) each lasting two hours (1–7 hours). Most patrols had been active for 3–10 years (49 of 53 patrols). Forty-four sites had toad warning road signs. A questionnaire survey of most of the known and established toad patrols was undertaken. Seventy-six replies were obtained.
A study in 1993–2010 of toad patrols during in Central and Northern Italy (Bonardi et al. 2011) found that although 1,042,966 common toads Bufo bufo were assisted across roads breeding migrations, 70% of 30 populations declined substantially from 2000 to 2010. Only 10% of the populations increased over the same period. Data on population trends were gathered mainly from volunteer toad patrol groups, with some from other volunteer groups, herpetologists and the literature. Sampling effort was taken into account when examining population trends.
- Feldmann R. & Geiger A. (1989) Protection for amphibians on roads in Nordrhein-Westphalia. Amphibians and Roads: Proceedings of the Toad Tunnel Conference, Rendsburg, Federal Republic of Germany, 51-57.
- Haslinger H. (1989) Migration of toads during the spawning season at Stallauer Weiher lake, Bad Tölz, Bavaria. Amphibians and Roads: Proceedings of the Toad Tunnel Conference, Rendsburg, Federal Republic of Germany, 181-182.
- Langton T.E.S. (1989) Reasons for preventing amphibian mortality on roads. Amphibians and Roads: Toad Tunnel Conference, Rendsburg, Federal Republic of Germany, 75-80.
- Zuiderwijk A. (1989) Amphibian and reptile tunnels in the Netherlands. Amphibians and Roads: Proceedings of the Toad Tunnel Conference, Rendsburg, Federal Republic of Germany, 67-74.
- Froglife . (1996) Toad patrols: a survey of voluntary effort involved in reducing road traffic-related amphibian mortality in amphibians. Froglife Conservation Report No.1.
- Bonardi A., Manenti R., Corbetta A., Ferri V., Fiacchini D., Giovine G., Macchi S., Romanazzi E., Soccini C., Bottoni L., Padoa-Schioppa E. & Ficetola G.F. (2011) Usefulness of volunteer data to measure the large scale decline of ‘‘common’’ toad populations. Biological Conservation, 144, 2328-2334