Comparison of population estimators and indices for monitoring house mice in sorghum crops

House mice(Mus musculus domesticus Schwarz&Schwarz,1943)are monitored in Australia and China to track changes in mouse population densities and forecast their potential damage to cereal crops.The present study compared population indices based on the number of different mice caught and overall trap success from live-trapping with an oil card index(OC)and a tracking index(T)for monitoring mice in sorghum crops immediately before crop maturation.T was measured as the percentage of track board covered with mouse footprints night-1,and OC as the percentage of card removed by mice night-1.The reliability of these abundance indices was quantified by Pearson correlation coefficient with the trappable population size(Ñ),which was estimated by capture-recapture over eight consecutive nights on 175×5 trapping grids,in sorghum crops on two properties on the Darling Downs,Queensland.Because of differences among individual mice in capture probability,Model Mh of program MARK was used to account for such heterogeneity and to estimate the size of each mouse population.The number of individual animals caught was more strongly correlated withÑthan trap success and,therefore,might be a more reliable index;the data suggest that three trapping occasions provide optimal precision for this index.T correlated significantly withÑonly at sites where the canopy of sorghum plants was closed,and its use should,therefore,be restricted to this habitat.OC did not correlate withÑbecause none or very little of the cards was eaten at low to moderate mouse densities.T and the number of animals caught over three trapping nights are recommended for monitoring mice in sorghum crops immediately prior to crop maturation.

Rodent management in Aotearoa New Zealand: approaches and challenges to landscape-scale control

Aotearoa—New Zealand has only four rodent species,all introduced.In order of arrival,they are Pacific rat Rattus exulans,brown rat R.norvegicus,house mouse Mus musculus,and black rat R.rattus.Rodent management in New Zealand aims mainly to conserve indigenous biodiversity rather than to protect crops or manage diseases,as is usual elsewhere.We describe four major“regimes”and one major vision for rodent control in New Zealand to meet ecological restoration objectives.Current challenges for island eradications are for large islands that are remote or populated by people.Aerial 1080 is the only large-scale(tens of thousands of hectares)option for black rat control,but its application requires adjustment to counter subsequent rapid black rat repopulation.Unfenced“ecosanctuaries”(mean 720 ha)use ground-based traps and poisons to target mainly black rats and face constant reinvasion.Ecosanctuaries with mammal-resistant fences(up to 3500 ha)limit reinvasion and target more pest species and have enabled the return of previously extirpated taxa to the main islands.Predator Free 2050 aims to eradicate the rat species(but not mice)plus some other introduced mammals from New Zealand by 2050.This vision is not attainable with current tools,but research and experimental management is exploring techniques and technologies.The large scale(to 100000 ha)at which black rats are now targeted for control to extremely low abundance seems to be unique to New Zealand.