The little Owl (Athene noctua) is a red-listed species in Denmark . The species is widespread in North America, Asia and in Europe where the Danish population represent the northern part of the distribution area. In big parts of Europe the population has been declining the last 30 ‘ 40 years, and in Denmark the population has been declining dramatically since 1965, where the Little Owl was about the most common owl species in Jutland . The species disappeared from Zealand and ‘Lolland-Falster’ in the 1940, and in 2004 it disappeared from Funen . In 2014 there was only registered 13 pairs in Jutland, for one of those pairs there was not given an exact location and in 2 of the remaining 12 pairs it was not sure whether they were pairs at all. One of them was probably only females (they laid 10 eggs and no was hashed) and another was registered the year before but was not seen in 2014. In the same year there was also discovered 3 lonely owls, for one of them there was no exact location . If the negative population trend continues, the species will become extinct in Denmark in the near future . Conservation strategies is needed to prevent further decline of the population. In order to make correct strategies, determine the reason(s) for the decline of the population is essential. In this assignment some of the most important studies of reason(s) for the decline and the results are presented, and how those should be used to make the Danish population of Little Owls (Athene noctua) increase again is explained.
THE POPULATION GENETIC
Since the Danish little Owl population has declined dramatically during the last 40 ‘ 50 years, it is important to look at the genetic consequences of the decline, because genetic diversity is important in populations. For every species it is expected that fragmentation and reduced population sizes will eventually lead to loss of genetic diversity and reduced fitness . Cino Pertoldi et al. (2012), found that the Danish Little Owl populations exhibit relatively low genetic variability. The recent population decline has resulted in genetic bottlenecks, and a historical low effective population size even though the Danish population probably always has been geographically more isolated than Central European populations because it is a peninsular population. The present population is genetically divergent from the historical population, which can be explained by genetic drift. Genetic drift acted strongly as a consequence of the low effective population size and has probably accelerated in the last few decades. If this is to go in the opposite direction, it is important to make available patches of suitable habitats and connection between them. Today these conditions are limited in both number and size .
Knowledge of the species spatial behavior is essential for understanding its behavioral ecology, which is also important when planning conservation strategies for a species . In the case of the Danish little Owl population, the study by Peter Sunde et al. (2008), shows that the mated owls is resident at nesting sites year-round with mean nightly distance from the roosts that peaks in January at 249 m and is shorten in May to 89 m, and was strongly influenced by temperature (determine available food, we’ll get back to that in another study of Meriam H. Holseg??rd ‘ Rasmussen et al., 2007). Home range size varies more than tenfold between pairs, and pairs with neighbors maintaining 2 ‘ 3 times larger ranges than isolated pairs independent of habitat composition. Mean home range is 2.6 ha and males and females behaved similarly, except in breeding season where females foraged closer to the nest. The areas there was close to the nest were very intensively used, especially during summer time, when the owls attempted to breed, but often failed to do so because of energetic limitations. According to this study; management initiatives that wants to improve the quality of Danish Little Owl foraging habitats during the breeding period should give priority to areas close to the nesting sites (preferably within 100 ‘ 200 m) .
According to L. B. Jacobsen (2006), The Little Owl (Athene noctua) lives in the open landscape, especially in agriculture areas close to farms or other houses on the countryside. The species also lives near villages, where the landscape has hedgerows and variation of grass and cultivated areas. The nesting locations today are mostly assigned to human settlement, but in earlier times they also nested in open areas away from humans with nest located mostly in hollow trees. When they are nesting near humans, it is normally located under roofing, which means in a stern box or between roofing sheets and under isolation materials, but the variation is huge. The placement of the nest has varied a lot though the years, the latest years there has not been many nests in hollow threes or in churches where they also used to build nests in previously. In order to stop population decline there has previously been tried to establish 150 nest boxes but it did not increase the population, even though they were used by the owls over several years (1981 ‘ 2000). The fact that they have been using the nest boxes and not increased in the population size might lead to the understanding that nesting places is not the main reason for the population decline. It is, however, part of the reason because the little Owl has been observed nesting in European Magpie nests, in harvesters, under pile of bricks etc., and weird nesting locations like those has been more common the latest years. The conclusion to this is that Danish Little Owls is in lack of nesting locations in suitable breeding habitats, mostly it is because of better isolation of houses today and that there is lack of natural tree cavities in orchards in Denmark . It seems important to improve nesting locations, in order to get a higher reproduction. Improvement of outdoor microhabitat by mounting nest boxes and insuring hollow trees, near preferred foraging areas should be an important part of the conservation strategies. The nesting places in buildings or close to humans should be improved with caution, the reason will be explained in the next section.
L. B. Jacobsen (2006), further clarifies that most of the Danish Little Owls annual mortality is caused by accidents, which generally occur in the breeding season. A relatively large part of the observed death of adults is caused by traffic killing, the owls getting stuck in buildings and other human ‘ related accidents like nesting in harvesting machines or owls drowning in barrows with water. Most of these accidents is likely to have been constant over time from the start when using breeding sites near humans. This situation reflects that there in Denmark is no pairs breeding in the outdoor habitats, such as natural tree cavities in orchards and hedgerows anymore, possibly because those spaces are no longer present in the modern Danish rural landscape. To stop the decline of the Danish Little Owl population, it is important to reduce mortality caused by these human-related accidents. The mortality rate are lower when they are not nesting near buildings, so re-establishment of suitable breeding habitats in outdoor microhabitats (hedges and tree lots with natural tree holes or nest boxes in vegetation) might be considered as initiative that would improve survival of adults and fledged young . Other factors such as predation also influence survival. The Marten has potential to threat small populations of Little Owls, and making predator secured nest for the Little Owls might be a solution . Since the mortality rate are higher when they are nesting near humans, it is important to secure areas, where Little Owls are observed nesting.
L. B. Jacobsen (2006) suggests that the decline may be related to the large-scale landscape changes in agricultural practices. The use of pesticides and fertilizers has increased, and has led to a dramatic decline in the abundance and biomass of larger insects , and appearance of worms on the agriculture areas are today normally less than on other grass areas. Meriam H. Holseg??rd ‘ Rasmussen et al., 2007, tells that the mean part of the Little Owls food is insects and worms, and the availability of grazed or other areas with short vegetation (like meadows) is therefore important, especially for adults when providing food to the young . For that reason there should be at least 10 ‘ 15 % short vegetation in their breeding habitat . At temperatures below 0 degrees C, earthworms and insects are no longer available, and Little Owls switch to vertebrates, like rodents and birds .
Kasper Thorup et al. (2010), made a study of food limitations, and found that the closer the Little Owl is to preferred foraging habitats, the higher is the reproductive parameters. The production of young is affected by distance to grass habitats, proportion of seasonally changing land cover, weather conditions and food supply . This study alone shows problem with the conditions in Denmark at the moment. Further the study by Meriam H. Holseg??rd ‘ Rasmussen et al. (2007) shows that it is the male how forage over large distances due to females more active in care and defense of the young . Females are needed in protecting the nest from predators, and when food is scare close to the nest, it is mostly the male who is bring food home. It seems to be a huge challenge to bring enough food home, because he might have to fly over large distances and by that suffers great cost.
Kasper Thorup et al. (2010), further found out that the decrease in production of young with increasing distance to preferred habitat is probably a direct result of adults only being able to bring a smaller amount of food to the nest if they have to fly larger distances to forage . When food supplementation to breeding pairs is offered (from humans), it increases the number of eggs that results in fledged young from 27 to 79 %! The main reason for the population decline in Danish Little Owls seems to be reduced productivity because of the energetic cost of raising young. The conservation efforts should focus on enhancement of food availability during the breeding season .
To make the population of Danish Little Owls (Athene noctua) increase again, the conservation efforts should first of all focus on enhancement of food availability during the breeding season. The main reason for the population decline in Danish Little Owls is reduced productivity because of the energetic cost of raising young. In short term food supplementation should be used to stop the population from further decline. That provides time to make available patches of improved foraging habitats with short vegetation (grazed vegetation), close to the nesting locations (100 ‘ 200 m). To make sure that short vegetation is kept short, creatures such as cows, horses and goats could be used to grass at the owls foraging habitat. This kind of management makes sense given that the Little Owl breeds near farms, so farmers might be more likely to accept the management strategy since they could be benefitting for it as well. Foraging habitats that provides small birds and rodents should also be located close to the breeding site.
When those patches of foraging/ breeding habitats are made, it is important that there is connection between them to make genetic flow possible. This makes inbreeding as small as possible and helps increase fitness and survival. Even if those connections are made it should be investigated whether it is possible to get Little Owls from other countries (populations) to the Danish population, to provide new genes to the population and thereby make inbreeding and reduced fitness even less likely.
The nesting locations should also be improved in safety if they are near farms or villages, but also in the outdoor microhabitat where they (like the ones near/in buildings) are in danger of predators like the Marten. Nesting boxes should be used, if there is lack of suitable nesting places, these could be made predator secured.
The decline in the population of Danish Little Owls (Athene noctua) seems to be because too few young is being produced. According to Peter Sunde and Lars Bo Jacobsen (not publish yet), the necessary number of young produced is 2.3, to ensure a stable population under normal population conditions . Today there is under 20 pairs left in Denmark and actions needs to take place know! Otherwise what is left of once the most common owl in Jutland, will go extinct in near future.
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