Nicholas J. Aebischer

Compositional Analysis of Habitat Use From Animal Radio‐Tracking Data

Analysis of habitat use based on radio-tagged animals presents difficulties inadequately addressed by current methods. Areas of concern are sampling level, data pooling across individuals, non-independence of habitat proportions, differential habitat use by groups of animals, and arbitrary definition of habitat availability. We advocate proportional habitat use by individual animals as a basis for analysis. Hypothesis testing of such nonstandard multivariate data is done by compositional analysis, which encom- passes all MANOVA/MANCOVA-type linear models. The applications to habitat use range from testing for age class effects or seasonal differences, to examining relationships with food abundance or home range size. We take as an example the comparison of habitat use and availability. The concepts are explained and demonstrated on two data sets, illustrating different methods of treating missing values. We compare utilized with available habitats in two stages, examining home range selection within the overall study area first, then habitat use within the home range. At each stage, assuming that use differs from random, habitats can be ranked according to relative use, and significant between-rank differences located. Compositional analysis is also suited to the analysis of time budgets or diets.

Multi-way comparisons and generalized linear models of nest success: extensions of the Mayfield method

The Mayfield method of estimating a constant probability of daily nest success adjusts for the fact that nests found part-way through a nesting stage (egglaying, incubation or brood-rearing) have, by definition, not failed since the stage began. The equality of two independently estimated probabilities can be tested using their associated standard errors. However, published Mayfield methodology does not extend to testing the equality of three or more probabilities, considering multi-way comparisons, or fitting complex regression-type models. It is important that such flexibility is accessible to biologists. I present an overview of the statistical model underlying the Mayfield method and of its assumptions, and present a test of goodness-of-fit based on the deviance. The model is extended to one-way classifications numbering two or more categories. A hypothesis test of the equality of all category-specific probabilities is derived based on the likelihood-ratio statistic. Relevant formulae are given explic...

Assessing pesticide effects on non-target invertebrates using long-term monitoring and time-series modelling.

One way of assessing ecotoxicological effects of pesticides at the farm level is by longterm environmental monitoring coupled with time-series modellinrg. This is illustrated with 20 years of data on the density of sawflies (Symphyta: Hymenoptera) in cereals on a 62-km2 area of West Sussex. The summer use of aphicides in the area first became important in 1989, when 7km2 were treated with dimethoate. Based on pre-1989 data, annual sawfly densities were found to be related, with a 1-year lag, to the proportion of cereal fields which were undersown and to summer rainfall and temperature, with a strong autoregressive component. In 1989, sawfly density in the area treated with dimethoate was less than one-tenth of that predicted by the model. Key-words: Dimethoate, environmental monitoring, pesticides, sawflies, Symphyta, time-series

Quantitative Comparison of Two Methods of Assessing Diet of Nestling Skylarks (Alauda arvensis)

atics. Cambridge Univ. Press, Cambridge, Great Britain. MILLER, A. H., H. FRIEDMANN, L. GRISCOM, AND R. T. MOORE. 1957. Distributional check-list of the birds of Mexico, part 2. Pacific Coast Avifauna 33. OBERHOLSER, H. C. 1974. The bird life of Texas. Univ. Texas Press, Austin. PETERS, J. L. 1951. Check-list of birds of the world, vol. 7. Museum of Comparative Zoology, Harvard Univ., Cambridge, Massachusetts. PETERSON, R. T., AND E. L. CHALIF. 1973. A field guide to Mexican birds. Houghton Mifflin Co., Boston, Massachusetts. PHILLIPS, J. C. 1911. A years collecting in the state of Tamaulipas, Mexico. Auk 28:67-89. RICHMOND, C. W. 1896. Partial list of birds collected at Alta Mira, Mexico, by Mr. Frank B. Armstrong. Proc. U.S. Natl. Mus. 18:627-632. RICHMOND, C. W. 1899 [1900]. Description of a new bird of the genus Dendrornis. Proc. U.S. Natl. Mus. 22:317-318. RIDGWAY, R. 1911. The birds of North and Middle America, part 5. Bull. U.S. Natl. Mus. 50(5):1-859. SIBLEY, C. G., AND B. L. MONROE, JR. 1990. Distribution and taxonomy of birds of the world. Yale Univ. Press, New Haven, Connecticut. WETMORE, A. 1942. New forms of birds from Mexico and Colombia. Auk 59:265-268. WINKER, K. 1995. Neotropical stopover sites and Middle American migrations: The view from southern Mexico. Pages 150-163 in Conservation of migratory birds in Mexico (M. Wilson and S. Sader, Eds). Maine Agric. For. Exp. Stat. Misc. Tech. Publ. 727. WINKER, K., R. J. OEHLENSCHLAGER, M. A. RAMos, R. M. ZINK, J. H. RAPPOLE, AND D. W. WARNER. 1992. Bird distribution and abundance records for the Sierra de los Tuxtlas, Veracruz, Mexico. Wilson Bull. 104:699-718.

The consequences of predator control for brown hares (Lepus europaeus) on UK farmland

The brown hare Lepus europaeus is a valued game species but also a species of conservation concern owing to its severe decline in abundance on farmland throughout Europe during the twentieth century. Changes in the farmland habitat and predation have both been cited as causative factors. Their relative roles have been unclear, but most conservation action has focused on improving habitat. We analyse data from a sequence of three unique studies (one experiment and two demonstrations) covering the period 1985–2006 in which control of several common predator species was undertaken to increase densities of wild game on farmland in England. Across the three studies, regression modelling of the proportional change in hare numbers between successive years showed that—after site, year differences and harvesting were accounted for—predator control was a significant determinant of hare population change. Where habitat improvement also took place, hares reached autumn densities that were exceptional for the UK and which could sustain substantial harvests. When predation control was stopped, hare densities fell, even where habitat improvements remained in place. This analysis demonstrates that even where farmland habitat is greatly improved, uncontrolled predation prevents hares making full use of its carrying capacity. This helps explain the mixed—and at best modest—success of agri-environment schemes in the UK and elsewhere in Europe to increase hare densities. Game-shooting estates, on which effective predator control takes place, probably have a special significance within the landscape as source areas for brown hares.

Trends in pesticide use and efficacy during 26 years of changing agriculture in southern England

We report on trends in agricultural pesticide use from1970 to 1995 inclusive in arable crops on the SouthDowns, West Sussex, U.K. Information is given on theproportion of cropped area treated with pesticides,the percentage spray area, the number of pesticideapplications per field, and the number of compoundsapplied per field for herbicides, foliar fungicidesand insecticides. Compared to national publishedfigures, our data are broadly representative of thenational picture; they provide a complete and detailedtime series whereas national figures are available foronly 7 out of the 26 yr. In general, the areatreated (fungicides, insecticides) and the intensityof use (all three types of pesticide) increased overthe 26 yr. The spectrum of activity of theherbicides applied to arable crops increased from anaverage of 22 weed taxa susceptible in 1970 to 38 weedtaxa susceptible in 1995. The odds on herbicide andfungicide use in break crops were, respectively, 93%and 99% lower than average; odds on insecticide usein spring cereals were 98% lower than average. Comparing winter wheat on the most traditional farm(grass/cereal rotation) with the most modern one(monoculture winter wheat), the proportion of fieldstreated with herbicides was similar, but the odds onbeing treated with fungicides were 129% higher on themodern farm. Insecticides were used in only 2% ofthe fields on the traditional farm, while on themodern farm over the same time period, 79% of thefields were treated. This fits previously observeddifferences in wildlife abundance on the two farms.

Breeding ecology of Turtle Doves Streptopelia turtur in Britain during the period 1941-2000: an analysis of BTO nest record cards

Capsule No trends over time were detected in any aspect of Turtle Dove breeding ecology and only slight regional variation, based on individual nesting attempts recorded. Aim To present information on the breeding ecology of Turtle Doves and identify any temporal or regional trends that may have contributed to the decline of the species. Methods Information on nesting habitat, type of bush used, nest height, clutch size, brood size and nest outcome was extracted from 1925 Turtle Dove nest record cards from 1941 to 2000, and examined for temporal and regional trends. Results The majority of Turtle Doves nest in thorny trees within scrub habitats, where mean nest height was 2.27 ± 0.02 m. Mean first-egg date was 18 May ± 1 day (annual range 28 April to 26 May). Mean clutch size was 1.84 ± 0.01 (annual range 1.65–1.93), producing a mean brood size of 1.82 ± 0.01 (range 1.50–2.00). Based on the recorded fate of individual nests, 41.3 ± 1.4% were successful, 44.9 ± 1.7% were predated and the rest (13.9 ± 1.4%) were lost to other causes. Nest survival rate averaged 0.577 ± 0.019 during the 14-day incubation period and 0.771 ± 0.019 during the 15-day nestling period giving an overall rate during the entire nesting period of 0.445 ± 0.018. Although there was some significant variation in these parameters between time periods and regions, there were no significant linear trends during the period 1941–2000. Conclusion The population decline experienced by Turtle Doves breeding in Britain is not due to lower success of individual nesting attempts. If breeding productivity has played a role in the decline, it must be through a reduction in the average number of nesting attempts per pair.

Habitat availability and use by Turtle Doves Streptopelia turtur between 1965 and 1995: an analysis of Common Birds Census data

Capsule Breeding density on long-term CBC plots fell in proportion to loss of nesting rather than feeding habitat. Aim To investigate the habitat requirements of Turtle Dove and relate changes in breeding density to changes in habitat, at the national scale. Methods Bird and habitat data were extracted from 30 long-term farmland and woodland CBC plots for the period 1965 to 1995. Results Turtle Dove densities declined at an average annual rate of 4.6% on both farmland and woodland plots, equal to a decline of 76% over the period 1965 to 1995. Turtle Dove density on the woodland plots was, on average, 6.5 times greater than on the farmland plots. Overall habitat availability did not change over time, but some finer measures of habitat quality, such as habitat diversity, nesting and feeding habitat availability did change. Changes in Turtle Dove density were positively related to changes in the amount of hedgerow and woodland edge per unit area on the farmland CBC plots, where Turtle Dove territories contained three times more woodland than expected from availability. On the woodland CBC plots, territories were established apparently at random. Conclusion It is likely that the availability of nesting habitat dictates Turtle Dove density, with areas of woodland and scrub supporting on average 6.5-times more breeding Turtle Doves, per unit area, than farmland.

The diet and disease susceptibility of grey partridges Perdix perdix on arable farmland in East Anglia, England

Abstract A three-year field-based study of 85 radio-tagged female wild grey partridges Perdix perdix was undertaken during 2001–2003 in East Anglia, England, to investigate possible links between chick diet and parasite-induced disease. The females produced 30 broods, whose diet measured by faecal analysis was typical of that previously reported. Chicks in some broods, however, consumed large numbers of known parasite vectors, particularly ants. Survival to the age of six weeks of chicks in a brood declined, on average, as the percentage of ants in the diet increased. Additionally 79 wild partridges found dead or in poor condition were submitted for necropsy to assess internal parasite burdens. Of these, 22 (28%) contained parasitic infections, although only 12 (15%) had levels of parasites that may have resulted in death. Internal parasites were found in only 7% of a subsample of 46 birds that died accidentally or were shot, and this was likely to be representative of the background level of infection. In a separate laboratory study of nutrition, no parasites were recorded in 180 six-week-old chicks that had eaten > 16,000 potential parasite vectors during the first three weeks after hatching. Either parasite levels were very low among host invertebrates or other factors contributed to increase disease susceptibility. Our results suggest that poor wild brood survival was indicative of low habitat and food quality rather than of a high rate of parasite infection. Management to conserve and increase wild grey partridge numbers should concentrate on improving foraging habitat quality, i.e. increasing the abundance of nutritious invertebrate chick-food, rather than directing efforts at reducing the small-scale effects of disease.

Ecology: Hunting and fox numbers in the United Kingdom

The potential impact of fox-hunting ban in Britain is a contentious issue that has been explored by Baker et al.. They conclude that a suspension of lowland fox-hunting for nine months during 2001 made no difference to fox density in certain areas. We are not confident, however, that their analysis supports their conclusions — their study does not consider statistical power or account sufficiently for regional variation, and also uses an inappropriate statistic.