Establishing numbers of breeding Little Owls on Quinta da Rocha, Portugal

Little Owl at Quinta da Rocha

Although the Little Owl (Athene noctua) is widespread in Europe, Asia and North Africa, in many countries its numbers appear to be declining and in Europe it is classified as a category 3 ‘Species of European Conservation Concern’ (SPEC) with unfavourable conservation status. Three-quarters of the European population are found within arable land and improved grasslands. It is generally accepted that changes in this land-use type, resulting in habitat loss, has been a significant factor in the decline of the species. Little Owls thrive in sparsely-wooded areas of rough grassland and arable land that has received little or no fertiliser or pesticide. Quinta da Rocha, A Rocha Portugal’s study area, contains many of these habitat features and an initial study by A Rocha in 2003 recorded a high density of the species in the area.

The aim of the study was to establish an accurate estimation of the current status of Little Owl in the area. The methods used to establish the breeding population of Little Owls at the site were based on those set out in the 2003 study. As Little Owls are nocturnal and possess a powerful and distinguishable call they are most readily identified and recorded through voice recognition. Four transects were laid out across the site, following tracks that provided access through potential habitat areas. Three of these transects were additional to those set out in the initial 2003 investigation and were added to give greater coverage of the study site. Research has demonstrated that the majority of Little Owl calls are not recognised over a distance of 400m. To minimalise over-counting the study site was divided up into 500m squares with survey points placed as close to the centre of these as possible.

Each transect was walked once a week from mid-February till the end of March. In April, during the pre-breeding season when males are normally displaying territorial behaviour, four surveys were conducted per week. The surveys were conducted between 9:00pm and 11:00pm, when calling activity is at its highest. At each survey point any heard calls were recorded for one minute a mindisc player. This was followed by playing a territorial call for 45 seconds through a loudspeaker to trigger any individuals in the area to respond and then nine minutes of listening and plotting on a map the position of any responding owls. Only the territorial calls, made by the males, were used to define the territories, whilst alarm calls were also noted to help establish the population numbers. Calls were only considered to be from different owls if they were either heard simultaneously or from distinctly different directions. A territory was considered to be defined once at least three calls had been heard on separate nights within the same cluster.

Old farmland habitat on Quinta da Rocha

The investigation identified 17 territories within Quinta da Rocha and the estimated density of Little Owls at 6.44 territorial males per km2. This is comparable with other findings in the Mediterranean region but considerably higher then in the rest of Europe. The study also incorporated sonogram analysis of the owls recorded in the 17 territories. Out of the 17 individuals, 11 could be identified as different through their sonograms. A limiting factor in this approach was the length of each record call. The shorter the call the harder it was to distinguish from others. In addition if two owls were calling at the same time or there was background noise then the use of the sonogram proved limited.

Quinta da Rocha’s landscape of extensive farming and long-term fallow grassland mixed with mature olive, carob, fig and almond stands provides high-quality habitat conditions for Little Owls. The site also contains a number of disused buildings, mature and dead trees that are appealing nesting sites for the species. These conditions appear to be the key factors in the healthy local populations of Little Owls.

***

Project leader: Anouschka Hof. For further information please contact portugal@arocha.org