Gulls that are only observed during the migration period

I have various locations in the city where I live that I regularly check for the presence of gulls, primarily to see if any ringed individuals are present.

As a result, I have a good indication of the species and individuals that can be seen at any of those locations at any point of the year.

Most of these individuals I will see almost weekly during either the breeding season or wintering season and I will therefore be very familiar with these birds. Also, for most of the season, little variation in the number of gulls and the number of ringed individuals can be seen.

Apart from 2 times each year: the migration periods.

These are the months in which birds travel between the breeding grounds and the area where they spend the winter. It turns out that some of these birds briefly visit my local gull patches where they can be seen for only a short period of time before they move on.

Helsinki ST185.550

A good example is a Black-headed Gull (Chroicocephalus ridibundus) ringed in Finland: Helsinki ST 185.550. I have seen this individual over the last 4 years but only on 1 occasion each year, including today:

  • 18 March 2010
  • 22 October 2011
  • 13 March 2012
  • 19 March 2013
Helsinki ST185550, 18 March 2010, Leiden, The Netherlands.

Helsinki ST 185.550, 18 March 2010, Leiden, The Netherlands.

Helsinki ST185550, 22 October 2011, Leiden, The Netherlands.

Helsinki ST 185.550, 22 October 2011, Leiden, The Netherlands.

Helsinki ST185550, 19 March 2013, Leiden, The Netherlands.

Helsinki ST 185.550, 19 March 2013, Leiden, The Netherlands.

The observation dates in March are especially fascinating: they are all within a very short period of time.

Unfortunately I have no information where this individual breeds or spends the winter.

Yellow H.501

Another good example is a gull which I have described on this blog before: Lesser Black-backed Gull (Larus fuscus graellsii) with ring Yellow H.501.

Lesser Black-backed Gull Yellow H.501. Leiden, The Netherlands, 1 October 2011.

Lesser Black-backed Gull Yellow H.501 completes its wing moult in Leiden shortly after the breeding season. Leiden, The Netherlands, 1 October 2011.

It differs from the Finnish bird in that I have more than 30 observations over 5 years and over a longer time period in each of these years, but they too are all from shortly before or after the breeding season:

Month Year Number of observations
June 2009 2
September 2010 4
March 2011 2
September 2011 2
October 2011 4
July 2012 2
August 2012 6
September 2012 7
October 2012 2
March 2013 2

I should add that in 2009, H.501 was in its 3rd calendar year and that a more stable observation pattern is only starting to emerge now that it has reached adulthood.

What is clear from this individual is that it spends a large part of the post-breeding season here to complete its wing moult.

What does this tell us?

Being able to observe ringed individuals this way provides a fascinating insight into their life and the “time schedules” that they follow. These schedules are so precise that it is possible to anticipate their return or departure on a yearly basis almost to the day.

It also shows that they are very much driven by seasons but also that they follow a set route with specific locations that they visit instead of just “wandering about”.

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