Gaining some insight in a Barn Owl’s diet. Part 1: diet sampling

Today’s afternoon I found some time to collect the pellets that were regurgitated by a Barn Owl Tyto alba that had spent the winter in a wall-mounted nest box in Zwolle, The Netherlands (http://www.timvannus.blogspot.nl/2013/01/barn-owl-tv-zwolle-netherlands.html). After connecting the infra-red camera earlier during the day I noticed the owl was gone, so it was safe for me to climb the ladder and open the box for an inspection. 64 pellets were collected. Based on my observations the owl inhabited the box for at least two months and, assuming that the box was permanently in use, produced about 1.05 pellet there per day. This is considerably less than during previous years, when about 1.3 – 1.5 pellet got produced per day. Additionally, this sample round included a considerable number of small sized pellets, possibly another indication that food had not been abundant during the last couple of months. These pellets will be analyzed by an expert. What exactly the owl was living on during these two winter months will be presented in a later entry.

Most of the pellets had accumulated in the ‘lobby’ of the nest box.

 

 

 The breeding chamber still contains a Eurasian Jackdaw Corvus monedula nest from the previous year. I noticed there was at least one jackdaw present near the nest box today.

 

After being collected, the pellets were put in a plastic bag and frozen. 

 

I am not sure why the owl always abandons this box around this time. I doubt that food shortage is a cause, as I am getting the impression that there currently is a good number of mice present in the garden (and I assume in its surroundings). Therefore I was not completely surprised this evening, when seeing a Barn Owl perched in an apple tree in the same garden, where it was overlooking bird feeders and compost mounds. Now did the jackdaws expel it from its nest box, or did it move in with a mate elsewhere to breed?

Photos of an entertaining stay on the Dutch island ‘Rottumeroog’, March 8 – 11

A colleague and I joined three other Forestry Service employees, as we made preparations for another field season out at Rottumeroog, starting on April 2^nd. Long rains, blizzards, impressive wind forces coming in from the east, bringing in low temperatures, all could not prevent us from finishing the work successfully, while having a wonderful time.

The only moment a scope got used was when an adult female Peregrine Falcon Falco peregrinus perched on ‘the Kaap’ for a short time, after its unsuccessful attempt to catch a Common Shelduck Tadorna tadorna. The bird was not ringed.

More about this visit can be found in the near future on the Forestry Service’s blog: http://staatsbosbeheerrottum.wordpress.com

Moby-Dog

On March 5 a ‘carcass trip’ along three kilometers of beach between Praia de Mira and Areao resulted in the findings of two marine mammals for which I haven't found the time yet for a proper identification. My first thought was that both were Harbour Porpoises Phocoena phocoena (which is what got reported by us to the authorities, I'm afraid), but their sharp nose probably indicates that they are not. Unfortunately I know very little about dolphins and a quick midnight Google search revealed that in Portugal you can in particular spend your money on swimming with them and it does apparently not matter which type of dolphin you’ll be swimming with.

The first remains included a complete spinal cord, skull and tail (http://observado.org/waarneming/view/74168365)

The second was of a more intact Flipper-type that had been laying in the sun for a bit too long (http://observado.org/waarneming/view/74168366). I assume both will get properly identified in the near future.

When we were certain that all the dolphins were out of the water we went in ourselves, together with our own mammal. For free and less smelly.

São Jacinto’s ducks, February 25 – 27: few ducks, but still a lot of work to be done.

On my last of this winter’s visits to the ponds of São Jacinto we were confronted with a serious lack of ducks. Although on the first day of captures we still managed to ring and mark 23 Common Teals (excl. 3 recaptures) and one Mallard, but on the second day our traps only held two Common Teals, including one recapture. The Common Teal was pretty much the only duck species present in our pond during these days and their number was low. There was a more interesting number of ducks present further away in a second pond, including Shovelers, Gadwalls, Wigeons, Pintails and a single Tufted Duck. These birds were obviously not at ease. There was a constant presence of a Goshawk again, which managed to grab at least a single duck during our stay, but more importantly, stray dogs managed to find their way into the fenced area again. I suspect that these are the main reason for the ducks to almost completely abandon the main pond. Thanks to them on the second day of captures we could spend most of our time cleaning up more storm damage, clearing more of the invasive acacia and resight the few ducks that were still there. Hopefully by autumn things are back to normal again.