Owl population restoration in Luxembourg

Central European cultural landscapes used to be mosaics of meadows, orchards, hedgerows, fields, and forests.  Unfortunately, most of these landscapes have been recently homogenized and converted to monocultures.  This process has been a typical result of agricultural intensification.  In the second half of the 20th century, this homogenization has further increased due to land being used to grow plant resources for producing "green energy" such as biofuel and biogas.  The intensification of farming techniques such as the use of inorganic fertilizers and pesticides, and the conversion of diverse landscapes into intensive monocultures, has resulted in widespread severe population declines for a variety of different animal groups.  Local- and country-specific management actions are being implemented to prevent further losses of farmland birds.  For successful conservation, measures need to include actions like hedgrow provision to improve the feeding and breeding habitats of farmland birds.  However, conservation measures vary between species, thus for effective species conservation we must consider species-specific habitat requirements.

The little owl (Athene noctua) is a nocturnal raptor.  It is a small owl, usually 22 cm tall with a wingspan of 56 cm, and weighing about 180 g.  The core of its distribution is located in the temperate steppes and deserts of the Mediterranean region, including north- and northeast Africa; but it inhabits much of the temperate and warmer parts of Europe, and Asia eastward to Korea (figure 1).  This bird uses meadows, grasslands, and fields for hunting, and it nests in trees.  The destruction of forests, and the conversion of these ecosystems to open agricultural land allowed A. noctua to colonize major parts of central Europe.  Today, it often nests in old trees of high-stem orchards, and in buildings and quarries with suitable cavities.  But A. noctua populations have severely declined throughout Europe in recent decades, and the species is now red-listed in several European countries.  Local conservation measures have included the installation of nesting boxes in potentially-suitable habitats, preferrably in high-stem orchards.

Figure 1:  Geographical distribution of the little owl (Athene noctua).

In Luxembourg, A. noctua is near extinction.  85% of Luxembourg's land surface is agriculture and forest, and in recent decades there have been strong increases in agricultural intensification, livestock, and urban expansion.  These landscape changes have resulted in the loss of shrubs and trees; and this loss in landscape- and habitat diversity has led to the loss of many arthropods and small mammals, these being the main food sources for A. noctua.  Inventories of breeding pairs of A. noctua in Luxembourg during recent decades shows a severe population decline:  In 1960, there was an estimated 4200 breeding pairs; but only 15 to 20 breeding pairs existed in 2002.  To prevent further population collapse, 450 nesting boxes were installed since 1999 in major parts of Luxembourg.

63 study sites in high-stem orchards were randomly selected.  The presence- or absence of A. noctua at nesting boxes was recorded for each study site, and the distance to the next settlement was measured.  Presence/absence was assessed during the mating season (march and april) by using audio recordings of male territory calls, invoking responses from other members of the species.

28 of the 63 study sites (27 of the 38 sites with nesting boxes) were occupied by A. noctua in 2012.  The probability of A. noctua presence was much higher at sites with nesting boxes than sites without nesting boxes.  This pattern was consistent across the entire study region, and proximity to other A. noctua breeding pairs had no detectable effect on presence/absence of the species; this further suggests that, in Luxembourg, nesting-site availability is the limiting factor for this species.  The high relevance of nesting boxes for conservation was also seen in studies in Germany, where about 90% of all A. noctua pairs were breeding in artificial nesting boxes.  Originally, old trees in high-stem orchards, as well as old buildings, provided important nesting sites.  However, these structures have largely vanished in today's landscapes.  It should be noted that, for many species, nesting-site availability has been shown to be crucial for maintaining populations.  A combination of fields suitable for hunting and nesting sites for breeding will be the most successful conservation measure for A. noctua.

A. noctua colonized central Europe during the beginning of traditional farming practices in this region.  A. noctua is a Eurasian- and Mediterranean steppe species.  There is the question of whether species whose biogeographical core-distribution is located outside of central Europe should be target-species for nature conservation in central-European countries.  More than 70% (136 species) listed in the European Birds Directive have their core distribution outside of Europe.  Nevertheless, this secures investment in the designation of protected areas for these species.  However, it may be of higher conservation value for these countries to focus on species whose core distribution is in central Europe.

LINK to Habel et al.'s 2015 article in Biodiversity and Conservation.