Barn Owl Productivity Response to Variability of Vole Populations

Abstract

We studied the response of the barn owl annual productivity to the common vole population numbers and variability to test the effects of environmental stochasticity on their life histories. Current theory predicts that temporal environmental variability can affect long-term nonlinear responses (e.g., production of young) both positively and negatively, depending on the shape of the relationship between the response and environmental variables. At the level of the Czech Republic, we examined the shape of the relationship between the annual sum of fledglings (annual productivity) and vole numbers in both non-detrended and detrended data. At the districts’ level, we explored whether the degree of synchrony (measured by the correlation coefficient) and the strength of the productivity response increase (measured by the regression coefficient) in areas with higher vole population variability measured by the s-index. We found that the owls’ annual productivity increased linearly with vole numbers in the Czech Republic. Furthermore, based on district data, we also found that synchrony between dynamics in owls’ reproductive output and vole numbers increased with vole population variability. However, the strength of the response was not affected by the vole population variability. Additionally, we have shown that detrending remarkably increases the Taylor’s exponent b relating variance to mean in vole time series, thereby reversing the relationship between the coefficient of variation and the mean. This shift was not responsible for the increased synchrony with vole population variability. Instead, we suggest that higher synchrony could result from high food specialization of owls on the common vole in areas with highly fluctuating vole populations.

The relationship between intra–guild diet overlap and breeding in owls in Israel

“…We detected an increase in barn owl breeding attempts in those years when the diet overlap with long-eared owls was higher. Voles (Microtus species) are known to be the preferred prey of both barn owls (Taylor 1994;Klok and De Roos 2007;Pavluvčík et al 2015) and long-eared owls (Village 1981;Korpimäki and Norrdahl 1991;Tome 2009;Sergio et al 2008), and in the present study, the proportion of voles in the diet of long-eared owls increased in years with more barn owl breeding pairs. Vole populations are known to fluctuate between years (Klok and De Roos 2007) and are the favored prey of both owl species, not only because of the large population sizes in peak years but also because of this rodent's relatively high body mass and ease of capture (short legs, small ears, and small eyes) (Taylor 1994).…”

“…Since barn owl breeding success increases when their diet is mainly made up of Levant voles (Microtus guentheri) (Charter et al 2015) and because long-eared owls switch from capturing rodents (mainly voles) to birds when these rodents are less abundant, diet overlap between the two owl species could be positively correlated with barn owl population dynamics. There is a possibility that the two species compete for the same resources because they are similar in size (although barn owls are slightly larger) and hunt similar prey species in the same agricultural landscapes (Village 1981;Korpimäki and Norrdahl 1991;Taylor 1994;Klok and De Roos 2007;Tome 2009;Sergio et al 2008;Pavluvčík et al 2015). Our hypothesis is that barn owl breeding numbers will be highest when diet overlap is greatest between the two owl species, whereas barn owl breeding parameters will be lower in years when long-eared owls eat more birds.…”

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

“…Most evidence in birds of prey abundance comes from variations in breeding performance. During good trophic years pairs produce more young compared to poor trophic years (e.g., Long-eared Owl-Korpimäki 1992;Sergio et al 2008;Montagu's Harrier;-Millon and Bretagnolle 2008;Barn Owl Tyto alba;-Pavluvčík et al 2015). Beyond these relationships various behavioural adaptations such as hatching asynchrony (e.g., Valkama et al 2002) and siblicide or fratricide (e.g.…”

Can temporal covariation and autocorrelation in demographic rates affect population dynamics in a raptor species?

“…Predictions for autocorrelation patterns are more difficult to formulate because they will depend on the temporal pattern in the abundance of their main prey. Vole populations may cycle over short periods, for example 3 years, as well as longer periods or not at all according to both location and time (Brommer, Pietiäinen, & Kolunen, 2002;Millon et al, 2014;Pavluvčík et al, 2015;Tkadlec & Stenseth, 2001), making prediction impossible at this point. Finally, we tested the food availability hypothesis directly by assessing the relationship between reproduction and vole abundance.…”