One of our most important tasks is monitoring the population of Barn Owls in our study zone. With the help of the Swiss Ornithological Institute and thanks to the many artificial nestboxes that have been installed, every year we carefully monitor each brood. These nestboxes are vital for the owls who are otherwise lacking in natural breeding sites.
1/10 The artificial nestboxes that we install look like large boxes. We often place them on the walls of barns. Which means that most of our nestboxes are located on land belonging to farmers, vital partners for us. An ideal nesting site is located up high and not far from fields. © Jeremy Bierer
2/10 At the University of Lausanne, we study Barn Owls across a study zone that is approximately 1000 square kilometers. Each blue dot represents the location of one or several nestboxes. Map data © Google 2018
3/10 Between March and April, we do a nighttime check of each nestbox once a month to see if eggs have been laid. We can also check for owl pellets, small balls containing the undigested parts of prey that the owls regurgitate. These pellets are a good indication of an occupied nestbox. © Jeremy Bierer
4/10 Each egg is measured, weighed, and dated. This is done by candling the eggs (placing a light behind the egg) to estimate their developmental stage. Dating the eggs enables us to predict when the eggs will hatch and thus plan our visit for ringing the owlets. © Jeremy Bierer
5/10 The birds’ rings are made from aluminum and are therefore very light. Attached to the bird’s leg when they are very little, the rings allow researchers to monitor how the population evolves. This system enables us to know that this owl, ringed M026255, was born in 2010 and was mother to a brood of chicks in 2019. © Paul Béziers
6/10 This approximately 20-day-old owl is being weighed. Along with wingspan, weight is a good indicator of growth. An abnormally weak growth alerts us to a possible abandonment or the death of the parents. If this happens, the nestlings are brought to the care center and released into the wild once they are healthy adults. © Daniel Aubort
7/10 To determine the sex of each owl, we take a blood sample. This also enables us to record various other data (stress, DNA gathering, etc.). We jab the owls and gather a drop of blood using a glass capillary tube. © Jeremy Bierer
8/10 The populations are also monitored in the lab, to determine the sex of the owls, for example. Félix Imhof © UNIL
9/10 We also count how many parasites are on the owlets’ wings. Here is a tick (at the top of the image), an infrequent finding, along with parasitic flies (white bodies) which are commonly found. © Jeremy Bierer
10/10 When the young are ready to leave the nest, at approximately 55 days, we return to measure them. Among other things, we carefully check their color (from reddish-brown to white). © Jeremy Bierer
Installation of nestboxes
Our study zone is located in Switzerland and extends from Lausanne to Morat, covering areas in the canton of Vaud and Fribourg. Each year, researchers from our group and from the Swiss Ornithological Institute regularly visit the nestboxes of this region. Currently, there are about 400 nestboxes installed, and the number continues to increase. Installing nestboxes creates new nesting sites for Barn Owls, an essential measure for the conservation of the species. Traditionally, these owls reproduce using cavities in old trees or cliffs. They then moved into human habitations, but our renovations often deprive Barn Owls of these breeding sites. Common Kestrels will also willingly reproduce in artificial nestboxes.
Follow up and study
During the breeding season, we regularly check each nestbox for new eggs, and then we monitor their development. Using DNA analyses, we’ve been able to establish a genealogy of the Barn Owls in our study zone for over 25 years. What’s more, each owlet is given a ring (provided by the Swiss Ornithological Institute) on which is engraved an ID number for the bird. It will keep this ring for its entire life. We take advantage of the ringing stage to track the growth of the nestlings as well as gather various essential information for monitoring the species, like the number of eggs and owlets.
When the young owls are ready to leave the nest, usually at about two months, we visit the nestbox for the last time. All the owlets are measured: beak, wing, feathers, weight, colors, etc. In addition to furthering our research, these data enable us to track the number of owlets who reach maturity, as well as monitor overall headcounts and the health of the population.
