Tawny Owl Strix aluco as an indicator of Barn Owl Tyto alba breeding biology and the effect of winter severity on Barn Owl reproduction

Abstract

In the temperate zone, food availability and winter weather place serious constraints on European Barn Owl Tyto alba populations. Using data collected over 22 years in a Swiss population, we analysed the influence of early pre-breeding food conditions and winter severity on between-year variations in population size and reproductive performance. To estimate pre-breeding food conditions, we attempted a novel approach based on an index that combines Tawny Owl Strix aluco reproductive parameters and the occurrence of wood mice Apodemus sp. in their diet. Tawny Owls breed earlier in the season than Barn Owls and are strongly dependent on the abundance of wood mice for breeding. This index was strongly positively associated with the number of breeding pairs and early breeding in the Barn Owl. Winter severity, measured by snow cover and low temperatures, had a pronounced negative influence on the size of the breeding population and clutch size. Food conditions early in the breeding season and winter severity differentially affect the Barn Owl life cycle. We were able to use aspects of the ecology and demography of the Tawny Owl as an indicator of the quality of the environment for a related species of similar ecology, in this case the Barn Owl.A major goal for ecologists is to monitor population trends and make predictions about them. This is not an easy exercise because it not only requires a precise knowledge of ecological factors that are responsible for population size fluctuations but also the ability to measure these factors reliably. Given the complexity of ecosystems and the need to distinguish changes due to anthropogenic activities from those caused by natural processes (Magurran et al. 2010), we need to derive integrative measures of the factors that influence the population dynamics of the species of interest. The difficulties in monitoring some ecological factors known to drive population size variation may require consideration of surrogate measures. This approach may be particularly fruitful in ornithology when, for instance, the aim is to identify the determinant role of food supply on reproductive parameters. In many species, such as passerines and raptors, measuring the availability of caterpillars or rodents is time-consuming and technically difficult when applied at a large scale and over many years.To address these problems, we tested the ecological correlates of reproductive success and population dynamics of one bird species using as a proxy the reproductive parameters of a second species that is highly sensitive to certain ecological factors. Specifically, our aim was to investigate the role played by food supply early in the season on the breeding performance of Western Barn Owls Tyto alba. This species shows pronounced inter-annual variation in population size (Taylor 1994) but the extent to which pre-breeding food conditions account for these inter-annual variations is unclear,

Signalling value of maternal and paternal melanism in the barn owl: implication for the resolution of the lek paradox

“…This suggests that offspring that inherit genes from smaller‐spotted mothers may have a selective advantage in years when few pairs breed. Because the breeding population size is lower after a harsh winter and in years when pre‐breeding food conditions are poor (Altwegg et al ., ; Chausson et al ., ), we conclude that small‐spotted mothers may have a selective advantage over large‐spotted mothers under those conditions, at least in terms of offspring growth. Furthermore, when breeding conditions were poor (i.e.…”

“…This was done for morning (8 a.m.), midday (12 a.m.) and evening (8 p.m.). As surrogates of ecological parameters, we considered number of breeding pairs, mean annual laying date and mean number of fledglings at the first annual breeding attempt (Chausson et al ., ). Since the latter two variables were strongly correlated (Pearson's correlation: r = −0.75, N = 14 years, P = 0.002), we performed a principal components analysis.…”

Apodemus mice as the main prey that determines reproductive output of tawny owl (Strix aluco) in Central Europe

“…Similarly, the representation of the two most available rodent groups in tawny owl diet (Apodemus mice and Microtus/Myodes voles) is variable and probably relects their availability in the ield (Obuch 2011). More recently, there is a growing body of evidence that Apodemus mice and not Microtus/Myodes voles are the main prey of several Central European owl species (Marchesi et al 2002;Roulin et al 2009;Zárybnická et al 2013;Chausson et al 2014).…”

Breeding decisions and output are correlated with both temperature and rainfall in an arid-region passerine, the sociable weaver

“…In temperate regions, where temperature is an important determinant of food availability and acts as a cue that triggers reproduction, warmer springs can lead to earlier laying dates [ 5 , 7 ]. By contrast, lower-than-average winter temperatures may affect female condition [ 24 ] and lead to fewer individuals breeding and to reduced output in the following breeding season [ 25 , 26 ]. In arid regions, temperature may also be used as a cue for breeding [ 23 ] and can exert a strong influence on food availability: lower-than-average temperatures can reduce primary productivity, independent of rainfall [ 27 ], and may directly affect insect activity patterns and phenology, for example by increasing developmental times [ 28 ].…”