On the burrowing impacts of ice rats Otomys sloggetti robertsi at a wetland fringe in the Afro-alpine zone, Lesotho

Abstract

Recent work has indicated that the southern African ice rat (Otomys sloggetti robertsi) is responsible for negative habitat change due to its foraging and burrowing activities in the Lesotho Highlands. Previous work has only focused on short-term ( ≤ 1 year) monitoring and thus the impact of such rodent activity over longer temporal scales remains unknown. To this end, the current study evaluates vegetation cover and O. s. robertsi's burrowing over a 10-year period (1998–2009) across a portion of a wetland fringe/wetland in eastern Lesotho. A 6 m × 11 m plot was established in 1998 and marked out with permanent stakes. Percentage cover and number of tunnels were recorded, with repeat measurements taken in 2001, 2005 and 2009. The findings indicate an overall 69.2% increase in vegetation cover and associated 71% decrease in burrow densities between 1998 and 2009. The area monitored closest to the wetland fringe recorded the most substantial burrow density decrease (by 80%) and vegetation recovery (by 43%) within a three-year period from 1998 to 2001. With a slight shift of burrow density increases towards the wetland centre, particularly between 2001 and 2005, the standard deviation of burrow density (per m²) from the wetland periphery towards the wetland centre had decreased from 1.25 to 0.32 over the 10-year period. It is proposed that the environmental influence of O. s. robertsi may be less dramatic at some landscape and longer temporal (i.e. years rather than months) scales due to spatial shifts of colonies, bioengineering and rapid vegetation recovery at abandoned, formerly ‘degraded’ burrow sites.

Keywords:

• ice rat
• burrowing
• cover change
• Lesotho

Acknowledgements

This project was funded through the University of Witwatersrand Research Incentive Funding Scheme, for which I am grateful. I thank the two referees and Paul Sumner who provided constructive input to help improve the manuscript.