Kestrel-Prey Dynamic in a Mediterranean Region: The Effect of Generalist Predation and Climatic Factors

Auteurs: Juan A. Fargallo, Jesús Martínez-Padilla, Javier Viñuela, Guillermo Blanco, Ignasi Torre, Pablo Vergara, Liesbeth De Neve
Bron: PLoS ONE 4(2): e4311. doi:10.1371/journal.pone.0004311
Abstract:

Background

Most hypotheses on population limitation of small mammals and their predators come from studies carried out in northern latitudes, mainly in boreal ecosystems. In such regions, many predators specialize on voles and predator-prey systems are simpler compared to southern ecosystems where predator communities are made up mostly of generalists and predator-prey systems are more complex. Determining food limitation in generalist predators is difficult due to their capacity to switch to alternative prey when the basic prey becomes scarce.

Methodology

We monitored the population density of a generalist raptor, the Eurasian kestrel Falco tinnunculus over 15 years in a mountainous Mediterranean area. In addition, we have recorded over 11 years the inter-annual variation in the abundance of two main prey species of kestrels, the common vole Microtus arvalis and the eyed lizard Lacerta lepida and a third species scarcely represented in kestrel diet, the great white-toothed shrew Crocidura russula. We estimated the per capita growth rate (PCGR) to analyse population dynamics of kestrel and predator species.

Principal Findings

Multimodel inference determined that the PCGR of kestrels was better explained by a model containing the population density of only one prey species (the common vole) than a model using a combination of the densities of the three prey species. The PCGR of voles was explained by kestrel abundance in combination with annual rainfall and mean annual temperature. In the case of shrews, growth rate was also affected by kestrel abundance and temperature. Finally, we did not find any correlation between kestrel and lizard abundances.

Significance

Our study showed for the first time vertebrate predator-prey relationships at southern latitudes and determined that only one prey species has the capacity to modulate population dynamics of generalist predators and reveals the importance of climatic factors in the dynamics of micromammal species and lizards in the Mediterranean region.

Lees meer: PLoS ONE

Tracking the Flight of Birds, With Tiny Backpacks

Birds are famous for airborne speed and endurance. Some have been clocked flying 60 miles per hour or more. Others make annual migrations from Alaska to New Zealand, nonstop.

But for scientists, tracking birds as they perform those feats has been an intractable problem. Now researchers think they have cracked it with a novel device — a tiny bird backpack that contains sophisticated sensors and weighs less than a dime.

The new technology has opened up vast new possibilities for bird researchers. Already, it is yielding surprising findings — for example, that some birds fly even faster than previously thought. But its real importance, biologists say, is the opportunity to unlock mysteries of bird migration that could help preserve species threatened by habitat loss and climate change.


Lees meer: NYTimes

Does Red Fox Vulpes vulpes affect bird species richness and abundance in an agricultural landscape?

Auteur(s): Kujawa, Krzysztof; Łęcki, Rafał
Bron: ACTA ORNITHOLOGICA, Volume 43, Number 2, December 2008 , pp. 167-178(12)
Abstract: The aim of the study (carried out 25 km south of Poznań, western Poland) was to determine the impact of Red Fox on bird abundance on farmland. Bird abundance was studied in the years 1999-2000 and 2005-2007 in three categories of sampling plots: 1) in small woods — with or without active fox dens, 2) along transects — starting from dens and running across arable land, and 3) around points — located at dens and far from them. Thus, variability in bird density was analyzed in relation to the presence/absence of Red Fox (in woods) and to the intensity of Red Fox penetration of crops (approximated by distance from a den).

Two groups of bird species were distinguished with respect to their vulnerability to Red Fox predation pressure: 1) potential fox prey, i.e. species nesting on the ground and in low vegetation; and 2) birds not threatened by foxes, i.e. species nesting in tree holes and in tall vegetation. To investigate the relationships between bird distribution and Red Fox dens in woods, a step-wise multiple regression of bird density and species number on woodland structure was first performed.

The residuals derived from the model were used to evaluate the impact of foxes by analyzing the differences between woods with and without active dens. Neither the species number nor the bird density differed significantly between woods with and without active dens. The differences in bird density observed between years in woods with or without active dens were not significant, either. No relationship between bird density in crop fields and distance from fox dens was found.

The results are contrary to those of earlier studies and show that Red Fox does not affect farmland bird distribution, diversity and abundance, at least in the short term.

Birds Survived Mass Extinction That Wiped Out Dinosaurs Because Of Their Larger Brains

The Cretaceous–Tertiary mass extinction 65 million years ago may have wiped out the dinosaurs, but those that survived – the ancestors of today's birds – may have done so because of their bird brains.

Analysis of computer tomography (CT) scans of fossilised bird skulls shows they had a more developed, larger brain than previously thought.

'Birds today are the direct descendents of the Cretaceous extinction survivors, and they went on to become one of the most successful and diverse groups on the planet,' says Natural History Museum palaeontologist (fossil expert), Dr Stig Walsh.


Lees meer: ScienceDaily

Bird Song Discoveries May Lead To Refinement Of Darwinian Theory

For Williams College biology professor Heather Williams, the songs birds sing are more than a pleasant part of a spring day. They are a window into how communication works in the natural world. A birdsong is more than just an encapsulated package of information, it is "a behavior frozen in time."

One of her projects is to record and map out the songs of Savannah sparrows that spend the warmer months on a small Canadian island, Kent Island, in the Bay of Fundy. With the help of microphones, binoculars, and a well-documented set of individual birds, her research is beginning to create a richer view of how birdsong moves from neighbor to neighbor and generation to generation in the wild. And it could lead to a refined way of looking at how communication fits into evolutionary theory.


Lees meer: ScienceDaily