Wednesday 28 April 2021

Advanced forest nest-finding

What an exciting time to be outside! The breeding season of Ural Owls Strix uralensis turned out to be really promising, as predicted by the large numbers of rodents present in the forest this spring, after last autumn's abundant beech crop. At the end of last week we discovered two Ural Owl nests in natural cavities in two consecutive days! The first nest was found completely by chance (as it frequently happens), while searching for White-backed Woodpecker's nests in the Dinaric forests of mount Snežnik. A greyish tail, sticking out of the side of a large Sycamore Acer pseudoplatanus caught our attention. On closer inspection we realised we were looking at a female Ural Owl incubating the eggs (probably) in a rather small natural cavity in the tree. These owls have such a long tail that they rarely fit well into a natural cavity. Nearby was also the male which gave us a warning hoot. We took a few pics and left the owls to their nesting. After all we had another mission - to find a White-back's nest.

IMPORTANT NOTE: all photos of birds on nests in this blog were taken for scientific purposes and from a safe distance, to prevent disturbance to the birds. Equipment used included powerful superzoom cameras (up to 2000 mm) and/or digiscoping through a telescope. The stay at each nest location was minimal - only the time to take a few photos and collect some basic parameters.

Female Ural Owl Strix uralensis incubating in a Sycamore's natural cavity.
Ural Owl's habitat in the forests of Snežnik.

After an entire day of unsuccessful search for nesting signs of White-backed Woodpecker Dendrocopos leucotos ssp. lilfordi, working on foot a large and rugged forest area in the Snežnik plateau, perseverance finally paid off. In the late afternoon we came across a territorial male that brought us directly to its nest, located on a tall beech, some 12 metres from the ground. The nest was excavated almost on the very top of the tree, where the wind has broken part of the tip. The male went into the hole rather quickly and silently and didn't came out for some time, so we deduced it must have been incubating. Later we also found a female (probably its female), feeding several hundred metres away from the nest. In the next two weeks we'll concentrate more carefully on the nesting of this pair as well as try to find other active nests in the area - probably more about the subject in the future posts.
White-backed Woodpecker Dendrocopos leucotos ssp. lilfordi - male.
White-backed Woodpecker Dendrocopos leucotos ssp. lilfordi - female preening.
White-back's nesting hole, on a beech 12 metres from the ground.
The height of the nest tree.
Excellent dead wood elements in the White-back's nesting habitat.
Horvath's Rock Lizard Iberolacerta horvathi - an endemic of the SE Alps, Slovenia and NW Croatia.

The next day we were in our local forest in the Karst, where we have been regularly observing a pair of Ural Owls Strix uralensis (since 2014), already widely presented in several other blog posts. Every spring we check a nice "chimney" (a large hollow beech snag) that would serve as an excellent nesting site for owls. So far we never found anything nesting in it, although Ural Owls use the area around it. So imagine our surprise when, upon approaching the tree from a distance and taking a look with binoculars, we spotted a semi-hidden owl's head staring fiercely at us! It was a female Ural Owl on the nest... at last!! The find doesn't really come as a huge surprise as this tree is perhaps one of only 3-4 available natural cavities that might host a Ural Owl in this forest. Moreover, forest owls don't necessarily breed every year, but follow natural cycles of food abundancy. Given the huge amount of rodents roaming the forest this year, a successful breeding of the owls (or at least an attempt) was kind of expected this season. Let us hope the birds manage to breed successfully, despite nearby forestry activities!
Nevertheless this remains an important record as it represents the first confirmed breeding of Ural Owl in the Karst - a region that 200 years ago used to be almost completely treeless.
The perfect natural cavity for...
Ural Owl Strix uralensis, nesting in the Karst.
The wider oak-beech forests in the Karst, around the Ural Owl's territory, host an excellent array of other breeding birds. The traditional nest of Black Woodpecker Dryocopus martius that we usually followed through the years has been "usurped" and diligently walled by a pair of Nuthatches Sitta europea, while the former owners have moved to a nearby tree. Last week male and female Black Woodpecker were still finishing the nest and not incubating yet. This week they probably are. Other woodpeckers in the same area include Middle Spotted Leiopicus medius and Grey-headed Picus canus, as well as the commoner Green Picus viridis and Great Spotted Dendrocopos major. This year we got the impression that also Nuthatches are having an excellent breeding season (possibly due to beech mast availability & major winter survival?) as we came across 6 different nests in the course of a few days. In the developing new foliage of oaks it was also good to see and hear the first returning (although only migrant) Wood Warblers Phylloscopus sibilatrix.
Black Woodpecker Dryocopus martius, male finishing the nest.
Nuthatch Sitta europaea using an old Black Woodpecker's cavity.
Beech Fagus sylvatica - the April joy of chlorophyll explosion!
Beech seedlings are sprouting everywhere on the forest floor, even in clumps!
Sessile Oaks Quercus petraea are the last to put out their new leaves.
Middle Spotted Woodpecker Leiopicus medius
Two different Nuthatches Sitta europaea on their nests.
Male Great Spotted Woodpecker Dendrocopos major on its drumming post.
Active nest of Blackbird Turdus merula in a Black Woodpecker's feeding hole.

Finally, an extremely brief, but emotionally intense visit to our recently-found nest of Black Storks Ciconia nigra (the only known in western Slovenia), for a quick check on the breeding situation. The female was sitting on the nest and incubating, while we observed it from a strategic and distant enough position to prevent stress. Soon the fresh foliage of the nearby canopies will take over and the storks will have their absolute privacy. Hopefully we'll be able to see the fledged juveniles taking into the air in mid summer!

Black Stork Ciconia nigra
Black Stork's breeding habitat in western Slovenia.