Parasitized or non-parasitized, why? A study of factors influencing tick burden in roe deer neonates.

Ixodes ricinus , the most common species of tick in Europe, is known to transmit major pathogens to animals and humans such as Babesia spp. or Borrelia spp.. Its abundance and distribution have been steadily increasing in Europe during recent decades, due to global environmental changes. Indeed, as ticks spend most of their life in the environment, their activity and life cycle are highly dependent on environmental conditions, and therefore on climate or habitat changes. Simultaneously, wild ungulates have expanded their range and increased dramatically in abundance worldwide, in particular roe deer ( Capreolus capreolus ), have allowed tick populations to grow and spread. Currently, tick infestation on newborn wild ungulates is poorly documented. However, newborn ungulates are considered more sensitive to tick bites and pathogen transmission because of their immature immune system. Thus, improving knowledge about the factors influencing tick infestation on newborns is essential to better understand their health risks. This study was conducted at Trois-Fontaines forest, Champagne-Ardenne, France (1992-2018). Based on a long-term monitoring of roe deer fawns, we used a novel Bayesian model of the infestation of fawns to identify which biotic or abiotic factors are likely to modify the level of infestation by ticks of 965 fawns over time. We show that tick burden increased faster during the first days of life of the fawns and became constant when fawns were 5 days old and more, which could be explained by the depletion of questing ticks or the turnover of ticks feeding on fawns. Moreover, the humidity, which favors tick activity, was weakly positively related to the tick burden. Our results demonstrate that tick infestation was highly variable among years, particularly between 2000 and 2009. We hypothesize that this results from a modification of habitat caused by hurricane Lothar.

Efectos de la variación ambiental sobre la reproducción de dos especies de ciervos ampliamente distribuidas

El objetivo principal de esta tesis doctoral ha sido evaluar el efecto de la variación ambiental sobre la reproducción de diferentes poblaciones de ciervo (Cervus elaphus) y corzo (Capreolus capreolus) situadas en el límite de su área de distribución, como son la región Mediterránea y la región Alpina. Estas poblaciones marginales pueden aportar una información muy valiosa en el contexto actual de cambio climático ya que pueden ayudar a predecir futuros cambios demográficos y de distribución de las especies. Como resultado principal, se ha observado que el incremento en la duración e intensidad de las sequías en ambientes mediterráneos y el adelantamiento del comienzo de la primavera en ambientes alpinos como consecuencia del cambio climático pueden provocar un desacople entre las principales etapas del ciclo reproductivo de ambas especies (como los partos o la formación de las cuernas) y el máximo de producción primaria. Todo esto podría afectar negativamente al éxito reproductivo de los ciervos y corzos que viven en estos ambientes.

An Update on Cephenemyiosis in the European Roe Deer: Emergent Myiasis in Spain

Cephenemyia stimulator is a Palearctic species developing in the nasal cavity and pharynx of roe deer (Capreolus capreolus). It is widely spread in the range of distribution of this ungulate in Europe. Since the first report of C. stimulator in Spain in 2001, a rapid geographic expansion has been observed, first in the north of the country, with high prevalence and intensities of infestation that caused some mortal cases, and, lately, also in Extremadura and Andalucía, the southernmost populations of European roe deer. These observations suggest an adaptation of this parasite to different ecosystems of the Iberian Peninsula. Almost simultaneously, C. stimulator is also expanding its range to northern Europe, with the first cases being reported in Sweden. Thus, Cephenemyia stimulator may be an example of a parasite currently displaying distributional changes along its southernmost and northernmost range margins. Thus, it is of the utmost importance to unravel all the epidemiological and clinical aspects of this myiasis, as well as implementing surveillance measures including reliable and non-invasive diagnostic techniques to monitor its expansion and adaptation to different ecosystems and/or hosts and to reduce the negative impact on roe deer populations.

Population density and plant availability interplay to shape browsing intensity by roe deer in a deciduous forest

Browsing damage in forests relies on a complex interaction between herbivore density and both forest understory composition and relative availability. Although variation in the amount of browsed twigs is sometimes used to assess abundance of large herbivores, the potential confounding effect of resource availability on this relationship has not yet been investigated. To fill the gap, we measured how browsing intensity of the woody plants varied in response to changes in both roe deer (Capreolus capreolus) abundance and vegetation availability from an intensive long-term monitoring. We estimated plant availability and consumption by roe deer from a modified Aldous method throughout a 14 yearlong period during which we experimentally manipulated population density. The functional response was strongly non-linear and density-dependent. When plant availability was low (< 12.5%), browsing intensity strongly increased with plant availability with an increasing rate with roe deer density, whereas beyond this threshold, browsing intensity slightly increased with both plant availability and population density in an additive way. Thus, forest susceptibility to browsing increases with increasing competition for food, especially when plant availability is low. Moreover, the interplay between browsing intensity and population density at low plant availability prevents the use of browsing intensity to monitor roe deer abundance when plant availability is low. Our findings provide clear evidence that relying on key ecological concepts such as functional responses improves the accuracy of management tools when monitoring changes of the herbivore-plant system over time.

Settle Down! Ranging Behaviour Responses of Roe Deer to Different Capture and Release Methods

The fitting of tracking devices to wild animals requires capture and handling which causes stress and can potentially cause injury, behavioural modifications that can affect animal welfare and the output of research. We evaluated post capture and release ranging behaviour responses of roe deer (Capreolus capreolus) for five different capture methods. We analysed the distance from the centre of gravity and between successive locations, using data from 14 different study sites within the EURODEER collaborative project. Independently of the capture method, we observed a shorter distance between successive locations and contextual shift away from the home range centre of gravity after the capture and release event. However, individuals converged towards the average behaviour within a relatively short space of time (between 10 days and one month). If researchers investigate questions based on the distance between successive locations of the home range, we recommend (1) initial investigation to establish when the animals start to behave normally again or (2) not using the first two to three weeks of data for their analysis. We also encourage researchers to continually adapt methods to minimize stress and prioritize animal welfare wherever possible, according to the Refinement of the Three R’s.