Predicting the incidence of mohua predation from the seedfall,mouse, and predator fluctuations in beech forests

Abstract

Predator control will be required to save many mohua (Mohoua ochrocephala) populations from extinction. However, control may be required only in years when stoat (Mustela erminea) densities are high. To manage local stoat populations effectively, a reliable predictor of high risk years is required. We examined whether different levels of beech seedfall and mouse capture rates were related to the levels of mohua predation recorded in the Hawdon Valley, Arthur's Pass National Park, and the Eglinton Valley, Fiordland National Park, between 1989 and 1994. During this period there was only one full beech mast year in each study area during autumn. The full mast seedfall in Hawdon Valley was predominantly of mountain beech (Nothofagus solandri var. cliffortioides) and red beech (N. fused), and in Eglinton Valley it was predominantly silver beech (TV. menziesii). During the following summer, mouse and stoat densities, and the predation rate of adult mohua, all increased considerably. There was very little predation on adult mohua in the summers following poor seedfalls when mouse and predator densities remained low. In 1993, a partial mast did not trigger a mouse or stoat irruption.

We conclude that counts of beech seedfall and indices of mouse density are potential predictors of an impending irruption of key predators. Winter mouse density appeared to be the most reliable indicator, because neither stoats nor mice respond to seedfall alone. A combination of these indicators could be used as a basis for management decisions on whether to undertake stoat control to protect mohua populations in the future. However, more information is required on the seedfall thresholds that may trigger sufficient increases in mouse and stoat numbers and, consequently, bird predation.     

Habitat use by yellowheads,Mohoua ochrocephala (Aves: Muscicapidae), in the Hawdon River Valley,Arthur’s Pass National Park. 2. Time budgets and foraging behaviour

Abstract

Instantaneous sampling was used to describe the ecological niche of yellowheads. Observations began during nesting in 1983 and continued until April 1984. Yellowheads spent on average 90% of their time foraging. As daylength decreased, an increasing proportion of time was spent foraging and a decreasing proportion of time was spent on social activities. When feeding nestlings, females spent significantly more time foraging than did males. Yellowheads spent 75% of their time in the upper understorey and the shaded canopy. There was no difference in the relative use of strata in the two canopy tree species, nor a sexual difference in the time spent in each strata. Yellowheads were entirely insectivorous. Prey items were recorded on 33 occasions; most were lepidopteran larvae. The most common foraging method was surface gleaning, most often on foliage and trunks. Time spent foraging on different substrates varied with tree diameter and tree species. Relative use of different foraging methods changed during the study, as did the types of substrates searched for prey and the proportion of time spent in different strata and at different heights in the forest. Presumably these changes were in response to variations in invertebrate availability.     

Fluctuations in the abundance of butterflies, 1976–82

Abstract. 1. A scheme for monitoring the abundance of butterflies at about eighty sites in Britain is described.
2. Indices of abundance are presented for twenty-nine species for the years 1976–82.
3. There are marked differences between species in the scale of annual fluctuations.
4. Some species show correlations between successive index values; for example the summer generation index of Pieris brassicae is highly correlated with the spring generation index.
5. The annual changes in the index values of many species are highly Correlated. The index values themselves also show positive correlations, but these are less strong.
6. The drought of 1976 is believed to have severely depressed populations of many species in 1977.
7. The data do not indicate any general fall in butterfly numbers over the period at the sites in the scheme.
8. The sites are not representative of the countryside as a whole, but, for a number of species, it is considered that the index values reflect wider trends.     

Comparative performance of four survey methods for assessing Lilian’s Lovebird abundance in Liwonde National Park,Malawi

Monitoring abundance of threatened species is important for conservation planning. Lilian’s Lovebird Agapornis lilianae is a near-threatened small parrot found in mopane Colophospermum mopane woodland. Its population has not been investigated in any part of its range. We investigated the abundance and density of the Lilian’s Lovebird in Liwonde National Park, Malawi. Both distance sampling (line and point transects) methods and total counts (waterhole and flyway counts) were applied. The point count method gave very low numbers and was discontinued after the first year. Line transects conducted during the wet season had the highest density estimates of 17 ± 4.8 lovebirds km?2 of mopane woodland. However, number of observations per transect in each year were low. Waterhole counts had the lowest density estimates (10 ± 3.5 lovebirds km?2). Flyway counts gave an intermediate estimate (13 ± 3.0 lovebirds km?2). The total population of Lilian’s Lovebirds in Liwonde National Park is therefore estimated to be about 4 000 individuals. The use of line transect counts at the end of the rainy season is recommended for continued monitoring of Lilian’s Lovebirds abundance in Liwonde National Park.     

Estimating population density from indirect sign: track counts and the Formozov–Malyshev–Pereleshin formula

For many purposes it is often desirable to estimate animal population densities over large areas. Where total counts are not possible and sightings are relatively rare, a range of methods exists to estimate densities from indirect sign. Such methods are frequently unreliable and usually require independent calibration or confirmation. We present an analytical method for estimating population density from track counts. The method, widely known in the Russian Federation but not in the English language scientific literature, requires counts of tracks of known age, together with estimates of animal daily travel distances. We use simulations to verify the theoretical basis of the approach and to indicate potential precision that may be achieved. We illustrate application of the approach using a large data set on ungulate track counts in the Russian Far East. We suggest that under most circumstances, nonparametric bootstrapping will be the most appropriate method for deriving estimates of confidence intervals about density estimates. As with other approaches to estimating density from indirect sign, the method that we discuss is vulnerable to violations of an array of underlying assumptions. However, it is easily applied and could represent an important method by which the relationship between indices of abundance and absolute density can be understood.     

Evaluation of community indices in seasonal assemblages of butterflies (Lepidoptera) at different frequency of transect count

Community indices were evaluated at different frequency of transect counts of butterflies by randomization. Randomized samples were obtained by re-arranging 1, 3, 6, 12 and 18 counts from 18 counts at a study site (Hiraoka), and 1, 2, 3, 5 and 15 from 15 at another site (Narukawa), in 1994. Morisita's new estimate of species richness, QM gave a good estimate when the number of counts was five or more. QM estimated from the sum of both assemblages (58 species) was 70.7, while 73 species were recorded at least once from 1990 to 1994. The Octave method always resulted in an underestimation. Diversity indices, Shannon's H, Simpson's D and , Hurlbert's E(Sn), Itow's b, and Morisita's H gave good estimates when the number of counts was five or more. Temporariness of univoltine species in flight period made a bias in the estimates. We concluded that the count is needed at least six times (once a month) and the estimates were improved by separating the multivoltine species from the univoltine species. Intensive counting during the flight period of the univoltine species was recommended.