Failure...

Two-egg clutch of Barn Owls (Tyto alba guttata) in a wall mounted nest box located in a green suburb of Zwolle, The Netherlands. An infrared camera connection showed that one of the two breeding birds disappeared during early egg-stage (halfway April), but the true cause of failure remains unknown. The box was installed over 20 years ago and became occupied by a single Barn Owl pretty much every winter and occasionally in summer. During summer 2015 a second bird appeared and a first breeding attempt was made the following year, which also failed during early egg stage. Today the box got cleaned out, the eggs were removed and 85 pellets were collected and will be used to identify prey items.

Eirol landfill, Portugal (January 12, 2015)

One of two adult Herring gulls Larus argentatus present at the site.




Herring gull number two.




Ringed Mediterranean gull Ichthyaetus melanocephalus, from Véron, les Prés Pendus, Yonne, FRANCE 48,07N 3,17E. One of two birds observed.




A Pied wagtail Motacilla alba yarrellii (top) and white wagtail M. a. alba (bottom).




The only signs of the young Peregrine falcon Falco peregrinus that resided at the landfill for some time (see previous posts) were 10 older remains of Black-headed Gulls Chroicocephalus ridibundus…

...and, remarkably, the remains of a 1st winter Lesser Black-backed Gull Larus fuscus. Not a common prey for a Peregrine.

Gull die-off in the Ria de Aveiro

Once a week the dog gets a walk along the a few hundred meter long sand dam on the Ria de Aveiro, at the height of the University of Aveiro. On this walk I identify and count fresh carcasses of birds (and once a feral cat). About three weeks ago I started to notice a rapid increase of dead Lesser Black-backed Gulls and Black-headed Gulls. I usually find (depending on the time of the year and the number of gulls present in the area) about 0-1 gull carcass on each trip. Within the past three weeks I found there the carcasses of 10 LBBG (9 adult and 1 immature) and 4 adult BHG. About two weeks ago I spoke with 'Ines', a UA student who also walks with Juli along the Ria at the height of the university. At that time she told me Juli ran onto the mudflats while chasing a dark gull that could not fly. On October 3 I got informed by an inhabitant of Sao Jacinto that he had noticed an unusual high number of deceased and dying LBBG out on the most southern dam of the peninsula, about 7 kilometers from the earlier location. He told me he found 21 gulls of which a few were still alive. These live birds were unable to walk and were turning their heads backwards in an odd way. Today Flor and I walked our transect again and ran into this adult LBBG showing symptoms of poisoning. About 40 meters from us was another adult LBBG present on the water surface which appeared to be trying to fly, though it did not manage. There were no new carcasses present on the transect, but the recent high tide could have swept away most of the dead matter. I regularly count the number of live LBBG and BHG present at this part of the Ria, which, during today’s upcoming tide, was surprisingly low, compared to earlier high tide visits. I have informed Biology student 'João' from the University of Aveiro about this situation in the hopes that the situation can be investigated. Luis would inform his supervisors about this, what seems to be fair to call, gull die-off in the Ria de Aveiro.

Larus marinus feeding frenzy @ Rottumeroog

On May 23 a dead and marked Harbor seal Phoca vitulina washed up on the North Sea beach of Rottumeroog. The seal got reported by us.

Greater Black-backed Gulls Larus marinus readily took advantage of the carcass. 

Which we could observe from our office...

On May 24 this colour-ringed adult plumage bird showed up. Black J1038 also got reported by us and should originate from the south of Norway.

An adult Lesser Black-backed Gull Larus fuscus eats from the carcass, while in front of a subadult Greater Black-backed Gull (May 25).

On May 26 this impressive immature male showed up and occupied the carcass for some time. It was also ringed, read and reaported. Black JP873, also from the south of Norway, presumably.

Then JP873 was forced to stand in line and wait until the older and even larger birds had taken their share. About 5-9 Greater Black-backed's were present near the carcass on a daily basis, in varying sizes and plumages.

But JP873 was impatient...

...and got his ass kicked by the big boss.

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?