From October to March, many Black-headed Gulls Chroicocephalus ridibundus visit my home town of Leiden, the Netherlands to spend the winter here.
Because many of these individuals are ringed, we can recognize them and follow their whereabouts. We therefore know that these birds always stay at a specific location throughout the winter, such as a park, a street in a suburban area and so on. Each year they return to that very same spot (usually around a specific date as well) and can only be seen at that location or within a small area around that location.
But exactly how small or large is that area?
Today I got a nice insight into the kind of area that a wintering gull can cover.
While doing my local gull watching round today (during which I attract gulls with bread to get them close enough to read the rings that they are fitted with), I was ‘followed’ by White E5RE over a 50-minute time period during which I observed her at 5 different locations covering an area of some 1,000 meters by 300 meters.
Note that some of these locations are very close to each other and it is not surprising therefore that E5RE would show up at one location shortly after having observed it at another location.
For example: location B is close enough to location A for any activity to attract E5RE to come over from location A. The same goes for location D which is in clear view of location C.
However, the distance between locations B and C and the distance between locations A and E are too far apart with too many buildings and obstructions between them to apply that same rule. This would suggest that E5RE ‘patrols’ these locations and happened to be close enough for it to notice the activity that was going on there.
Note also that although the shaded area covers the area between location D and E, I actually believe that E5RE travels between each location by following the waterways: from A to B, C and D and back from D to C, B, A and E with a possible detour from B to E.
I actually went from location D back to location B again before I went to location E, but I did not observe her at location B (although there was a lot of gull activity there at that time).
Although much of this is speculation and no conclusions can be drawn on a single observation, it does at least give a nice insight into the whereabouts of a single gull within a 50-minute time period on a given day.
About White E5RE
I know White E5RE well because she (it’s a female) was ringed in 2010 in the Black-headed Gull colony of Zoetermeer some 10km to the south-west of Leiden where I observe her regularly and often each breeding season. I also see her regularly in Leiden during the winter months (mostly in November and December), indicating that she doesn’t travel far away from the breeding grounds. She is actually one of my most observed gulls with over 80 observations.
My encounters with her on 5 different locations today is very much an exception to the rule, and something that I have not observed in any other wintering Black-headed Gulls that I have been following over the last 6 winters here. I am more used to observing her in the area shaded red in the map above (locations A and B) and it is the first time that I have observed here at locations C, D and E.