Action: Manage grazing regime
- One replicated, controlled study in the UK found that grazed plots did not have higher abundance of natterjack toads than ungrazed plots and had lower abundance of common toads. Five studies (including four replicated studies) in Denmark, Estonia and the UK found that habitat management that included reintroduction of grazing increased green toad populations, maintained or increased natterjack toad populations and maintained common toad populations.
- One before-and-after study in the USA found that the decline in amphibian species was similar under traditional season-long or intensive-early cattle stocking.
Livestock grazing changes habitats in a number of ways such as reducing vegetation height, changing plant diversity, creating openings for seed growth and preventing reed and shrub growth. Such changes can have beneficial or detrimental effects on amphibian populations, depending on the amphibian species, grazing intensity and timing.
For an intervention that aims to reduce the detrimental effects of grazing see ‘Exclude domestic animals or wild hogs by fencing’.
Supporting evidence from individual studies
A replicated, controlled study in 1992–1995 of natterjack toad Bufo calamita terrestrial habitat in southern England, UK (Denton & Beebee 1996) found that natterjacks did not use grazed plots more than ungrazed plots. There was no significant difference between average numbers in grazed and ungrazed plots for toadlets (13 vs 13) or adults (5 vs 5). Total common toad Bufo bufo numbers were lower in grazed compared to ungrazed plots and surroundings (1 vs 11). Four plots (20 x 20 m) of each of four habitats were established: grassy clearfell, sandy clearfell, heath and moss habitat. Two plots of each were grazed in May–September by highland cattle (1 adult/3 ha). Captive-reared natterjack toadlets were released onto each square in summer, 75 in 1992 and 20 in 1993. Toads were monitored twice monthly in April–September 1992–1995.
A replicated, before-and-after study in 1989–1997 of coastal meadows and abandoned fields on two islands in Funen County, Denmark (Briggs 2003) found that the green toad Bufo viridis population increased significantly following reintroduction of grazing to fields, along with pond creation and restoration. The population increased from 92 to 2,568. Pond occupancy increased from 10 to 29 ponds and ponds with successful breeding from four to seven. In 1989–1997, cattle grazing was reintroduced to 48 ha of coastal meadows and abandoned fields. Four ponds were created and eight restored by removing plants and dredging. Populations were monitored annually in 1990–1997 during two or three call, visual and dip-net surveys. One population was also monitored in 1987–1989.
A replicated, before-and-after study in 1986–2004 of coastal meadows in Funen County, Denmark (Briggs 2004) found that green toad Bufo viridis and natterjack toad Bufo calamita populations increased significantly following reintroduction of grazing of fields, along with pond creation and restoration. On 10 islands, the total number of green toad adults increased from 1,132 to over 10,000 in 2004. Numbers remained stable on four islands without management. Pond occupancy increased from 27 in 1988 to 61 ponds in 1997 and ponds with successful breeding doubled from 11 to 22. Natterjacks increased from 3,106 in 1988 to 4,892 adults in 1997. Ponds with successful breeding remained similar (28–34). In 2000–2004, numbers dropped and small populations were lost due to insufficient grazing. In 1987–1993, cattle grazing was reintroduced to 111 ha of coastal meadows on six islands and continued on a further 10. From 1990, farmers could get financial support from EU agri-environmental schemes. In addition, 31 ponds were created and 31 restored by removing reeds on 16 islands. Green toad eggs were translocated to one island. Four populations were monitored annually and others less frequently during two or three call, visual and dip-net surveys.
A before-and-after study in 1994–2004 of a coastal meadow on a small island in Estonia (Lepik 2004) found that reintroduction of grazing along with aquatic and terrestrial habitat restoration resulted in a stable population of natterjack toads Bufo calamita. A total of 17 natterjacks were counted in 1992 and seven in 2004, with numbers ranging from 1–17/year. The author considered that without management the population may have declined or become extinct. Common toad Bufo bufo counts were eight in 1992 and four in 2004 and ranged from 3 to 40/year. Restoration on the 16 ha island involved implementation of sheep grazing, reed and scrub removal and mowing. Toads were counted along a 1 km transect.
A replicated, before-and-after study in 2001–2004 of three coastal meadows in Estonia (Rannap 2004) found that reintroduction of grazing along with aquatic and terrestrial habitat restoration increased the population of natterjack toads Bufo calamita on one island and halted the decline on the other two islands. In 2001–2004, habitats were restored where the species still occurred. Restoration included reintroduction of grazing where it had ceased, reed and scrub removal and mowing. Sixty-six breeding ponds and natural depressions were cleaned, deepened and restored.
A before-and-after study in 1989–2003 of tallgrass prairie in Kansas, USA (Wilgers et al. 2006) found that there was no significant difference in the decline in amphibian species richness during season-long cattle stocking compared to intensive-early stocking. Although not significant, species richness tended to decline faster during season-long stocking than during intensive-early stocking. Authors considered that strong conclusions could not be reached because of confounding effects of changes in both grazing and burning. From 1989 to 1998, the ranch was managed with traditional season-long stocking (0.6 cattle/ha) with burning in alternate years. From 1999, management changed to intensive-early stocking (1.0 cattle/ha) for three months from late spring combined with annual burning. Amphibians were surveyed in April each year along a 4 km transect.
A replicated, site comparison study in 1985–2006 of 20 sites in the UK (McGrath & Lorenzen 2010) found that natterjack toad Bufo calamita populations increased with species specific habitat management including introduction of grazing to fields. Populations declined at unmanaged sites. Individual types of habitat management (aquatic, terrestrial or common toad Bufo bufo management) did not significantly affect trends, but length of management did. Overall, five of the 20 sites showed positive population trends, five showed negative trends and 10 showed no significant trend. Data on populations (egg string counts) and management activities over 11–21 years were obtained from the Natterjack Toad Site Register. Habitat management was undertaken at seven sites. Management varied between sites, but included introduction of grazing, pond creation, adding lime to acidic ponds, maintaining water levels and vegetation clearance. Translocations were also undertaken at seven of the 20 sites using wild-sourced (including head-started) or captive-bred toads.
- Denton J.S. & Beebee T.J.C. (1996) Habitat occupancy by juvenile natterjack toads (Bufo calamita) on grazed and ungrazed heathland. Herpetological Journal, 6, 49-52
- Briggs L. (2003) Recovery of the green toad Bufo viridis Laurenti, 1768 on coastal meadows and small islands in Funen County, Denmark. Deutsche Gesellschaft für Herpetologie und Terrarienkunde, 14, 274-282
- Briggs L. (2004) Restoration of breeding sites for threatened toads on coastal meadows. Pages 34-43 in: Coastal meadow management - best practice guidelines. Ministry of the Environment of the Republic of Estonia, Tallinn.
- Lepik I. (2004) Coastal meadow management on Kumari Islet, Matsalu Nature Reserve. Pages 86-89 in: Coastal meadow management - best practice guidelines. Ministry of the Environment of the Republic of Estonia, Tallinn.
- Rannap R. (2004) Boreal Baltic coastal meadow management for Bufo calamita. Pages 26-33 in: Coastal meadow management - best practice guidelines. Ministry of the Environment of the Republic of Estonia, Tallinn.
- Wilgers D.J., Horne E.A., Sandercock B.K. & Volkmann A.W. (2006) Effects of rangeland management on community dynamics of the herpetofauna of the tall grass prairie. Herpetologica, 62, 378-388
- McGrath A.L. & Lorenzen K. (2010) Management history and climate as key factors driving natterjack toad population trends in Britain. Animal Conservation, 13, 483–494