Clément Calenge

The exploratory analysis of autocorrelation in animal-movement studies

Studies of animal movements have been popularized for many large and shy species by the increasing use of radio telemetry methods (VHF and GPS technologies). Data are collected with high sampling frequency, and consist of successive observations of the position of an individual animal. The statistical analysis of such data poses several problems due to the lack of independence of successive observations. However, the statistical description of the temporal autocorrelation between successive steps is rarely performed by ecologists studying the patterns of animals movements. The aim of this paper is to warn ecologists against the consequences of failing to consider this aspect. We discuss the various issues related to analyzing autocorrelated data, and show how the exploratory analysis of autocorrelation can both reveal important biological insights and help to improve the accuracy of movement models. We suggest some tools that can be used to measure, test, and adjust for temporal autocorrelation. A short ecological illustration is presented.

Spatial avoidance of invading pastoral cattle by wild ungulates: insights from using point process statistics

Traditional rangelands in many developing countries are currently being encroached by cultivation, driving some herders to illegally use protected areas for grazing their cattle. Since cattle are an exotic species in these ecosystems, they might have an impact on the local wild herbivore communities, notably through competition. We used point pattern statistics to characterise the spatial relationships between wild ungulate species and cattle herds within a protected area in west Africa undergoing seasonal intrusions by cattle. We predicted that the wild ungulate species that are ecologically and morphologically similar to cattle, in terms of body mass and diet, would be more sensitive to grass depletion by cattle and would be separated from cattle to a larger extent. The spatial distribution of browsing and mixed-feeding antelopes did not seem to be affected much by cattle presence, whereas most grazing species showed spatial separation from cattle. Interestingly, elephants also showed significant separation from cattle herds. We discuss the likely processes that may have contributed to the observed spatial patterns. The spatial displacement of certain wild species, including megaherbivores, affects the whole community structure and, thus, other components of the ecosystem.

Reintroduction of roe deer Capreolus capreolus into a Mediterranean habitat: female mortality and dispersion

Abstract During 1995–1997, 52 male and 52 female roe deer Capreolus capreolus, captured in the Forest of Trois-Fontaines in northeastern France, were introduced into the Petit Luberon state forest in southern France; of these 49 females (21 young that were < 1 year old and 28 adults that were > 1 year old) were monitored by radio-tracking. The overall mortality rate among the females monitored was 47% within one year of release. The first month following the release (February) was critical for the success of the operation as 35% of introduced animals died within this time span. It appears that stress was a major cause of mortality at this time, but traumatic deaths caused by drowning, collision with cars, and falling off cliffs were also frequent. The survival rate increased to 0.9 in spring, summer and early fall and decreased again during late fall and early winter. The high mortality rate occurring during this period may be explained by an increased mobility resulting from disturbance from wild boar Sus scrofa hunting. After the reintroduction, the animals stayed close to the release site (50% within 2.4 km, and 75% within 4 km), though the adults established themselves at longer distances than the young. The dispersion pattern of the females was not uniform throughout the study area: they preferentially settled down northwest of the release site, which may be explained by the topography of our study area and by the absence of human structures (roads, canals) in this area.

Influence of fish-farming management on duck breeding in French fish pond systems

Fish ponds host a relatively important share of the breeding population of waterfowl in Europe. The objective of this study was to investigate the influence of fish-farming management on the distribution of dabbling and diving duck breeding, in 103 fishponds from four regions important for duck breeding in France. Duck breeding in fish ponds was apparently influenced by food resource and nesting site availability. Dabbling duck pair density was generally higher when invertebrates were abundant in macrophytes beds and when competition for food with carps Cyprinus carpio was potentially decreased by lower fish stock biomass. Diving duck pair abundance seemed to be negatively influenced by low invertebrates biomasses in pond sediment and by the absence of large reed beds at the edge of waterbodies. The difference between dabbling and diving ducks was also confirmed by a study of the variation in brood numbers standardized by pair numbers. This brood:pair ratio corresponded to a measure of nesting success and the possible attraction of fish ponds for some broods hatched in neighbouring waterbodies. Dabbling duck brood:pair ratio was lower in one of the study regions where most of meadow areas surrounding fish ponds have been transformed into cereal crops in the past few decades. Diving duck brood:pair ratio was positively linked to pond fertilization due to fish farming. Fish farming, therefore, influenced duck breeding by an interaction between carp density and fertilization. We hypothesize that fertilization increases zooplankton density, thereby decreasing the competition between carps and waterfowl for benthic prey.

A new exploratory approach to the study of the spatio-temporal distribution of ring recoveries: the example of Teal (Anas crecca) ringed in Camargue, Southern France

We use a new method called “product kernel estimator” to explore the spatial and temporal distribution of 9,114 recoveries of Teal (Anas crecca) ringed in Camargue, southern France, and recovered over the whole of Europe. This method allows exploration of the changes in time of the probability density to recover a ringed bird over a grid covering the study area. We thus identified two migration corridors for this species to the north and south of the Alps, whereas earlier analyses mostly suggested a southern route from Camargue, especially in spring. The northern route seems to be used to a greater extent in autumn than in spring, indicating a frequent abmigration (animals switching from one corridor to the other). Moreover, migration of the population seems faster in spring than in autumn. The simultaneous presence of Teal recoveries in many distinct geographical areas in spring is consistent with the idea that these ducks are not limited by their migratory speed in spring, nor do they wait until favorable environmental conditions before colonizing their breeding areas.

Bayesian modelling of hunting data may improve the understanding of host-parasite systems: wild boar diseases and vaccination as an example.

Wildlife diseases are often studied using hunting data. In such studies, inferences about diseases are often made by comparing raw disease prevalence levels, ignoring complications like stochasticity in recruitment. We carried out a field trial to study the effectiveness of oral vaccination of wild boar (Sus scrofa) against classical swine fever (CSF) in the Vosges mountains (Northeastern France) for 3 years (2008-2010). Since August 2004, hunters had carried out three vaccination sessions per year in spring, summer and autumn. During our study period, we determined whether each wild boar hunted in our study area was immunized or not against CSF. We used a Bayesian approach to model the changes in the proportion of vaccinated animals in the population of young animals (i.e., <12 months old). This approach allowed to disentangle the effects of the birth peaks (leading to a decrease) and of both the vaccination sessions and natural infection (leading to an increase) on this proportion. We thus inferred, at the individual level, the probability that a non-immunized animal became vaccinated after a particular session. There was a high between-year variability in the effectiveness of the vaccination: the observed patterns were similar in 2008 and 2010, but 2009 was characterized by an overall greater effectiveness of the vaccination. Within a particular year, the spring vaccination session was more effective than the autumn session, probably because of the higher food availability in autumn that render the vaccination places less attractive to the animals. The vaccination effectiveness was rather low in summer, except in 2009, probably because of higher age identification error this year. This model also highlighted an immunisation of animals occurring outside vaccination periods, which suggests either the presence of the CSF virus in our study area, or the consumption of the vaccine outside the vaccination sessions. Finally, we observed a high spatial variability of the probability of vaccination. The effectiveness of the vaccination was indeed strongly related to both the distribution of the forests and the distribution of the vaccination places in our study area. This study highlights an optimal vaccination effort of 1.25 places per km(2) to maximize the proportion of immune wild boar in that area.

Home range size and reproduction of female roe deer re-introduced into a Mediterranean habitat

SummaryFrom 1995 to 1997, 52 males and 52 females, which had been captured in the Forest ofTrois Fontaines (Northeast of France), were re-introduced into thePetit Luberon state forest (South of France). Among them 49 females (21 young [<1 year old] and 28 adults [>1 year old]) were monitored by radio-tracking. The mean annual home-range sizes (mean 95% MCP = 157 ha) were larger than those estimated in more temperate forests, but were smaller than in cultivated plains. In spring and summer, repeated visual observations allowed us to study the reproduction of the monitored docs and the summer survival of their fawns. The mean number of fawns per adult female was 1.18 (SE = 0.13) and the mean number of fawns per doe with young was 1.59 (SE = 0.09). The fecundity of the does and the summer survival of their fawns were similar in our study area and inTrois-Fontaines (their area of origin).ZusammenfassungVon 1995–1997 wurden 52 männliche und 52 weibliche Rehe. Die im Wald von Trois-Fontaines (Kordostfrankreich) gefangen worden waren, im Staatsforst Petit Luberon eingebürgert. Von den weiblichen Tieren wurden 49 (21 jünger als ein Jahr, 28 älter als ein Jahr) mit Radiosendern versehen. Das durchschnittliche jährliche Streifgebiet (Mittelwert 95% MCP = 157 ha) war grö\er als die für gemä\igte Wälder geschätzten, aber kleiner als diejenigen für landwirtschaftliche Flächen. Wiederholte visuelle Beobachtungen im Frühjahr und im Sommer ermöglichten die Untersuchung der Fortpflanzung der Ricken sowie des Überlebens ihrer Kitze. Die durchschnittliche Zahl der Kitze pro erwachsene Ricke betrug 1,18 (SE = 0,13) und die durchschnittliche Zahl der Kitze pro führende Ricke war 1,59 (SE = 0,09). Die Fruchtbarkeit der Ricken und das Überleben der Kitze während des Sommers war in unserem Untersuchungsgcbiet ähnlich wie in Trois-Fontaines, ihrem Herkunftsort.

Geographic variation in body mass of rock ptarmigan Lagopus mutus in the Alps and the Pyrenees

Abstract We compared the body mass of adult rock ptarmigan Lagopus mutus shot in autumn in the French Pyrenees (Ariège), the French Alps (Hautes-Alpes) and the Italian Alps (Province of Verbania). Mean body mass of adults was greater in the Ariège than in the Hautes-Alpes both for cocks (466 vs 433 g) and hens (429 vs 406 g), with the body mass of Italian birds being intermediate (cocks 448 g, hens 418 g). The relatively large mass of rock ptarmigan in the Pyrenees contrasts with the geographic trends found in capercaillie Tetrao urogallus and grey partridge Perdix perdix in France. For the last two species, birds in the Pyrenees are smaller than those further north. The site differences that we observed in body mass of rock ptarmigan may be related to differences in availability of high quality foods, particularly ericaceous shrubs. However, at the continental scale within Europe, the body mass of rock ptarmigan appears to be greatest in northern latitudes.

Analysis of Spatial Point Pattern Shows No Desertion of Breeding Mute Swan Areas by the Other Waterbirds Within Fishpond

Abstract. Mute Swan Cygnus olor numbers have recently increased in a dramatic fashion in Western Europe and in North America, suggesting there could be potential consequences for the rest of the waterbird community. Breeding Mute Swan pairs may behave territorially towards other waterbirds, taking advantage of their larger size, and hence cause concern regarding their potential effects on waterbird communities. We studied how the within-site distributions of breeding Mute Swans and other waterbirds were related to each other, in order to assess if there is support to the assertion that breeding Mute Swans may affect the distribution of the other waterfowl within waterbodies. We mapped waterbird and swan distribution within fishponds during the Mute Swan breeding period. Relying on spatial point pattern analysis, our first finding is that breeding Mute Swans were located in the vicinity of the other waterbirds, using the same area within fishpond. Waterbirds do not completely desert the area used by breeding swan pairs within a waterbody, hence not supporting the claim that Mute Swans dislodge the other species. If an exclusion process by Mute Swan breeding pairs towards waterbirds exists, it is not strong enough to generate deserted areas by waterbirds around breeding Mute Swans. Our second finding is that breeding Mute Swans were not located where the density probability function for waterbird presence was the greatest within a fishpond, i.e. breeding Mute Swans were not located in the centre of groups formed by other waterbirds within each fishponds. This may indicate slightly different micro-habitat preferences or use within fishponds, or could indicate the potential occurrence of interactions. In conclusion, these results question whether the increasing Mute Swan populations actually directly threaten the other waterbird communities in such habitats, and require population control as is often claimed.