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Papers by Pierre-Alain Ravussin

Tengmalm’s Owl has been studied for over 30 years within an area of 150km2 in the Jura Mountains ... more Tengmalm’s Owl has been studied for over 30 years within an area of 150km2 in the Jura Mountains in the northern part of the Canton of Vaud (CH) and in the Department of
Doubs (F). From 1985 to 2015, 639 nests were found:
179 in Black Woodpeckers Dryocopus martius cavities
and 460 in artificial nestboxes. Each year the
number of nests varied from 2 (minimum in 2013) to
57 (maximum in 1992) with an average of 20 nests.
Overall and on the long-term, there has been a noticeable
reduction in the presence of breeding Tengmalm’s Owl. The average number of nests calculated on a period of 5 years has declined from 19 in 1985-89 to 11.2 in 2010-14. Recaptures and controls of locally ringed birds highlight a considerable nomadism which fluctuates through time. Most adult females and young birds leave the area after “goodyears”, i.e. years with relatively high population
densities. Philopatry is highest between the peaks of
prey abundance and seems to be male-biased.
However, a very low number of them are captured and
ringed compared to females. Pine Marten Martes
martes is the most important predator of this owl species
and can destroy up to two thirds of the nests in
specific years. In order to decrease this predation
pressure, several mechanical protection systems were
tested. These systems give good performances during
the first years, but become thereafter less effective
and their weakness spreads quickly. Other studies
clearly highlighted that predation increases
with nestboxes age. The important fluctuations
through time of appearance or disappearance of
Tengmalm’s Owl in some regions are an adaptation
to environmental fluctuation of food conditions and
to high vulnerability to Pine Marten predation.
Cohabitation of these two predators in mountain forests
must have caused adaptation in Tengmalm’s
Owl in order to minimize these risks. Among these
adaptations, selecting a new nest site rather than an
old one seems obvious. A new cavity has less risks
to be known and regularly visited by Pine Marten. In
order to test this assumption, we moved and reinstalled
part of our nestboxes in autumn 2014 and 2015.
The first results from 2015 and 2016 seasons are in
agreement with this prediction. Nestboxes installed
recently or shifted in the previous autumn have a higher
occupancy rate (35.5%, N = 42) than those left
in place (10.5%, N = 105). Displacement of nestboxes
in favourable sectors could be an effective measure
to support Tengmalm’s Owl populations. It would stimulate
colonization by philopatric males and decrease
the risk of predation on breeding nests.

Food resources used by Tengmalm’s Owl in the Jura between 1982 and 2014 at two distinct sites wit... more Food resources
used by Tengmalm’s Owl in the Jura between 1982 and 2014 at two distinct sites within the Canton of Vaud were determined by the analysis of food remains in nest cavities and nest boxes. Remains of more than 23 000 prey items from 357 nest sites were identified. Mammals were predominant and made up 98 % of the total. Seventeen species were
identified but varied considerably in their abundance.
Amongst the dominant species figured the Eurasian/Crowned Shrew Sorex araneus/coronatus, Bank Vole Myodes glareolus and Field Mice of the Apodemus genus. Birds only made up 1.7 % of the prey items but consisted of 21 different species. Thrushes were in a majority, in particular Song Thrush Turdus philomelos. Field Mice of the Apodemus genus appear to be the characteristic prey item of Tengmalm’s Owl in the Jura Mountains. This would go towards explaining the fluctuations of the species as opposed to the situation in Fennoscandinavia, but corresponds
with the situation in other parts of Central Europe.

Journal of evolutionary biology, Jan 14, 2015

Geographic variation in phenotypes plays a key role in fundamental evolutionary processes such as... more Geographic variation in phenotypes plays a key role in fundamental evolutionary processes such as local adaptation, population differentiation and speciation, but the selective forces behind it are rarely known. We found support for the hypothesis that geographic variation in plumage traits of the pied flycatcher Ficedula hypoleuca is explained by character displacement with the collared flycatcher Ficedula albicollis in the contact zone. The plumage traits of the pied flycatcher differed strongly from the more conspicuous collared flycatcher in a sympatric area but increased in conspicuousness with increasing distance to there. Phenotypic differentiation (PST ) was higher than that in neutral genetic markers (FST ), and the effect of geographic distance remained when statistically controlling for neutral genetic differentiation. This suggests that a cline created by character displacement and gene flow explains phenotypic variation across the distribution of this species. The diffe...

Proceedings of The Royal Society B: Biological Sciences, 2004

La Chouette de Tengmalm est étudiée dans les forêts du massif du Jura, au nord du canton de Vaud ... more La Chouette de Tengmalm est étudiée dans les forêts du massif du Jura, au nord du canton de Vaud et dans le département français du Doubs, depuis plus de 30 ans. Chaque année, les nids sont recherchés tant en cavités qu'en nichoirs et ils font l'objet de contrôles détaillés portant sur la ponte et sur la réussite de la nichée, de même que sur la nourriture apportée aux jeunes. Tous les poussins sont bagués, tout comme la plupart des femelles ainsi que quelques mâles. Cet énorme travail bénévole de longue haleine a fourni des données très originales sur la stratégie de reproduction de cette petite espèce forestière et montagnarde. Cependant, à l'heure actuelle, son statut inspire des craintes quant à son avenir dans les forêts du massif du Jura. En effet, si les fluctuations très importantes du nombre de couples nicheurs caractérisent toujours cette espèce, elle a perdu en moyenne plus de la moitié de ses effectifs ces 20 dernières années. Chouette de Tengmalm Aegolius fu...

What future for Tengmalm’s Owl Aegolius funereus in the Jura Mountains ? Thirty years of study re... more What future for Tengmalm’s Owl Aegolius funereus in the Jura Mountains ? Thirty years of study reviewed. Tengmalm’s Owl has been studied for over thirty yearswithin an area of 150 km2 in the Jura Mountains in the north of the Canton of Vaud (CH) and the Department of Doubs (F). Six hundred and one nests were studied, of these 176 in Black Woodpecker Dryocopus martius cavities and the remainder in nest boxes. Annually the number of nests varied from 2 (minimum in 2013) and 57 (maximum in 1992), with an average of 20.
Overall there has been a marked reduction in the number of nests to the extent that if this evolution continues it can be expected that the species will have disappeared from the Jura
Mountains between 2025 and 2035.
Eggs are laid from the end of February to the end of June, with large variations from one year to another both in terms of the average and the length of the season. The clutch size varies from
2 to 9 with major differences in the average from one year to another. The actual number depends on food availability but also predation by European Pine Marten Martes martes which
sometimes can be extremely high. All these factors are closely linked. The annual number of nests is closely correlated with early breeding, the number of eggs and a high reproductive success.
The dominant food brought to the young is dominated by three types of prey : Field mice Apodemus are the commonest and are associated with reproductive success. Bank vole Myodes glareolus also plays an important role.
In opposition to this Eurasian shrew Sorex araneus is a common prey item and present when Field mice and Bank voles are lacking.
Eurasian shrew abundance correlates with poor reproductive success.
Capture and control of ringed birds show their considerable nomadism, which varies from one season to another. The majority of adult females and the young leave a sector after an
abundant year. Sedentarity increases and is at a maximum between two abundance peaks.
Multiple factors are probably responsible for the major reduction in the breeding population. Forest management leading to the elimination of old trees and favouring conifers over beech
is probably one of the causes. Competition with Tawny Owl Strix aluco, which is becoming more and more common, in areas where previously it was absent, is also a factor. Global warming
is probably also a factor as it affects other parameters that are essential to the survival ofTengmalm’s Owl in the Jura Mountains.

Summary – Reproductive success and return rate of the Pied Flycatcher Ficedula hypoleuca in weste... more Summary – Reproductive success and return rate
of the Pied Flycatcher Ficedula hypoleuca in
western Switzerland, at an edge of its
distribution range. We studied two populations
of Pied Flycatchers in western Switzerland
in Baulmes VD (650 m a. s. l.) and in Corcellesprès-
Concise VD (430 m a. s. l.), at the limit of
the distributional range of the species. Flycatchers
started to breed in the seventies in Baulmes,
and their number increased until the
middle of the eighties when population size
decreased to reach one third of the maximal
population size. The population in Corcellesprès-
Concise established in the sixties, and since
then its size is stable. Flycatchers lay their eggs
on average two days earlier in Corcelles-près-
Concise than in Baulmes, and clutches are slightly
larger (5.64 vs. 5.46), although not significantly.
Hatching and fledging successes are similar
in the two populations. Survival prospects
from one year to the next, estimated using
capture-recapture methods, was higher in adults
than in juveniles, and in birds born in Corcelles
than in Baulmes (Corcelles-près-Concise : young
males : 27.7%, young females: 18%, adult
males : 54.8%, adult females: 57.7%;
Baulmes: young males : 14%, young females:
11.5%, adult males: 51%, adult females:
46,3%). We suggest that the decline in population
size in Baulmes is due to a high emigration
rate, a low survival rate and by a low immigration
rate. The maintenance of a stable population
in Baulmes thus implies that immigration
should be more important in Baulmes than in
Corcelles. In conclusion, these recently established
populations benefited from a high rate of
immigrations in the early years, and thus their
current stability now requires a high reproductive success.

Summary – The biology of Tengmalm’s Owl Aegolius funereus ; observations made following the sprin... more Summary – The biology of Tengmalm’s Owl Aegolius funereus ; observations made following the spring 2000 invasion in the Jura Moutains. The 2000 breeding season of Tengmalm’s Owl was
exceptional throughout the Jura Mountains. The number of breeding pairs, the size of clutches, and the number of young leaving the nest were all amongst the highest seen during the last 15 years. The majority of females were one year old in spite of the fact that breeding success in the Jura had been poor the preceding year. Captures of ringed birds confirmed a major influx of birds from the centre and north of Germany. Analysis of the diet shows that trophic conditions vary considerably from year to year. The abundance of Wood Mice Apodemus sylvaticus and Yellow-necked Field Mice A. flavicollis, themselves dependent on the beech nut are a pre-requisite for the success of Tengmalm’s Owl in the Jura. Our observations show that Tengmalm’s Owl populations are able to make rapid long distance displacements in response to variations in the available prey, conditions in 2000 lead to a major invasion of the species.
Unlike the situation in Scandinavia, forests occupied by Tengmalm’s Owl in Central Europe are much more variable and often broken into small sections sheltering a more diversified prey
leading to a wider variation in numbers

Journal of evolutionary biology, Jan 14, 2015

Proceedings of The Royal Society B: Biological Sciences, 2004