From the RSNZ journals: Road kill, parasites, plant invasion

A number of papers appearing in journals published by the Royal Society of New Zealand are now available online and reference decades of methodical research,

Road kill survery – 25 years of flattened fauna

Abstract available here – log into the SMC Resource Library to download.

On three independent surveys over 21 years (1984, 1994 and 2005), Bob Brockie and Richard Sadleir counted dead animals seen on the roads between Lower Hutt, Wellington through Taumarunui and Whangarei to Awanui in Northland, and returning through Dargaville and Rotorua (Brockie et al. New Zealand Journal of Zoology 2009). Each round trip totalled 1660?km. The authors, including Wayne Linklater, compare these counts with others going back to 1949.

The three most frequent road casualties found were possums, hedgehogs and rabbits, plus lesser numbers of cats, hares, rats, ferrets, stoats and a dog. Far fewer birds were counted, of which only mynas, pukekos, harriers and magpies were found frequently. All the counts were made in February while travelling at speeds between 50 and 100 km.

There was no consistency in patterns of change over time in the three species: counts of rabbits rose, counts of hedgehogs dramatically fell, and counts of possums both rose and fell, all surveyed on the same roads over the same 21-year sampling period. The researchers suggest that these fluctuations are correlated not with traffic volumes but with real fluctuations in the animal populations.

A steep fall in possum numbers between 1994 and 2005 coincided with intensified activities by the Animal Health Board, whose expenditure on control of potential TB carriers (especially farmland possums) rose from about $10?million in 1994 to $54?million for the year ending June 2005 (Animal Health Board 2006).

The research authors conclude: “The relationship between road-kill and traffic volume indicates that roads carrying more than 3000 vehicles per day act as barriers to larger mammals, while vehicles on less busy roads are more dangerous for crossing animals. We suggest that regular counts taken at annual intervals over the same roads is a useful method for gathering information about the changing distribution and relative abundance of certain animals on a provincial or national scale and over long periods of time. Regular counts at seasonal, monthly or weekly intervals are also a rich source of information.”

What’s eating you?

Abstract available here – log into the SMC Resource Library to download the paper.

Did you know there are about as many different species of parasites hosted by man (though not necessarily all at the same time) as there are hosted by an ox, a pig, a goat, a horse or a sheep? You can find out who your parasites are now in an updated checklist of helminth and protozoan parasites of terrestrial mammals in New Zealand compiled by P. B. McKenna and published in the New Zealand Journal of Zoology (June 2009).

It’s 10 years since the publication of two earlier checklists and since then a number of new records have been added. Some parasite names have been updated, and the list includes the additional records and corrects omissions from the previous versions. The checklist, which is divided into two parts, includes a total of 301 parasites (151 nematodes, 27 cestodes, 8 trematodes, 2 anthocephalans and 113 protzoans) from 37 hosts.

Check out the list and find out about a parasite near you.

Plant invasion best limited by sheep grazing

Abstract available here – log into the SMC Resource Library to download the paper.

Results, from sites studied by Dianne Sage, David Norton and Peter Espie, published in the New Zealand Journal of Agricultural Research (June 2009), suggest that a regular grazing regime may limit the invasion of sweet brier and reduce the overall abundance and vigour of existing sweet brier populations in semi-arid high country environments. Sweet brier plants were significantly taller, occurred at higher densities and had a greater cover in ungrazed compared to grazed sites.

The total numbers of plants in all size classes were reduced with grazing, except for the smallest size class at one site, and size class distributions markedly skewed towards the smaller sizes suggesting limitations on recruitment into larger size classes. However, as other studies show, while grazing reduces recruitment in woody species, it does not necessarily prevent plants from growing into larger size-classes once they have become established (Milton 1995; Walker 2000).

It therefore seems likely that any reduction in grazing pressure will result in sweet brier expanding across suitable sites in the high country.

Soil cores reveal high water contamination

Abstract available here – log into the SMC Resource Library to download the paper.

Zoonoses are organisms carried by animals that can cause disease in humans. Important zoonotic bacteria that can be carried in animal faeces include a form of toxin-producing subspecies of Escherichia coli known as E. coli O157:H7, and species of Campylobacter. After being shed in faeces, these organisms can travel through the soil in drainage water or over the soil surface in run-off into streams and rivers.

Andrea Donnison and Colleen Ross of AgResearch, Ruakura wanted to find out how long these bacteria could survive in the soil and on the soil surface, and to what extent they were moved through or across the soil by rainfall. To avoid spreading these disease-causing organisms in the environment, their research was carried out on soil cores in the laboratory.

They studied behaviour of bacteria in two soils, a Topehaehae gley and a Kereone sandy loam. Both soils are found near the Toenepi Stream in the Waikato region, and any bacteria washing from them could be expected to enter the stream.

In the laboratory, simulated dairy effluent was applied to cores of both soils. The simulated effluent contained cow manure, distilled water, and a mixture of E. coli O157:H7, and Campylobacter. Water was dripped onto the surface of the cores to simulate rainfall at various times up to 28 days after the effluent was applied. The water draining through the soil or running off the surface was collected and the bacteria in it counted. Bacteria surviving in the soil were also counted.

Both bacteria survived in both soils for 28 days, but numbers of Campylobacter declined faster than E. coli O157:H7. The Topehaehae soil continued to release large numbers of E. coli O157:H7 for 28 days after effluent application, and Campylobacter for at least 21 days. Numbers of bacteria in drainage from Kereone soil fell more quickly than from the Topehaehae soil; few E. coli were found after 21 days, and few Campylobacter after 14 days.

Donnison & Ross (New Zealand Journal of Agricultural Research, June 2009) conclude that rainfall will transfer faecal bacteria from poorly drained gley soils bordering a stream for at least 28 days after deposition.