occurrence, timing and distribution in the Netherlands
Greenish Warbler, Den Haag, The Netherlands, 2 June 2017 (Natalia van Gilst)
Once a rarity, Greenish Warbler (Phylloscopus trochiloides) is nowadays a very scarce, but annual migrant. This article gives an overview of the occurrence of Greenish Warblers in The Netherlands between 1965 and 2017. When‘s the best time to see one? And what are the best places?
An increasing rarity
The first record dates back to 13 September 1965, when one was collected on the Dutch island of Vlieland, Friesland. Up till the early nineties records were still erratic, but since 1998 Greenish Warblers have been recorded annually. In 2003 no less than three adults were present at Schiermonnikoog, two singing males and a female. One pair successfully bred and produced three fledglings (Ebels, 2003); this is the western most breeding record for the species to date.
Up till 2014 the species was reviewed by the Dutch rarity committee CDNA. Up till then, 75 records of 81 birds were accepted. Between 2015 and 2017 there are another 11 proven records (12 birds; source: www.waarneming.nl), resulting in a grand total of 86 records (93 birds) between 1965 and 2017. The best year so far was 2013, with ten. The species is annual since 1998, though there have been six years with only one record and three years with two ever since (Figure 1).
Figure 1. Annual number of Greenish Warbler records in The Netherlands 1985-2017 (orange; n=79) and the number of individual birds involved (blue; n=86) . There are another 7 pre-1985 records.
The average number of sightings a year has grown significantly over the past fifty years (Figure 2). Increased knowledge amongst birders combined with an increased coverage most likely contributed to the increasing numbers, but the species has also been expanding its range westwards since the 19th century (Clement 2017).
Figure 2. Average number of Greenish Warbler records a year in the Netherlands over the past 50, 40, 30, 20 and 10 years.
Temporal distribution: when to see or find a Greenish Warbler?
All Greenish Warblers in The Netherlands have been recorded between May and October. With exactly 43 records in both the first and last six months of the year, their numbers are equally divided over spring and autumn (Figure 3). In this respect The Netherlands takes an interesting middle position: in Belgium, France, Ireland and the UK it's mainly an autumn migrant, while it is mainly a spring bird in Germany (Thoma & Althaus, 2015). However note that spring records are increasing and the pattern is shifting: it used to be more common in autumn.
In spring Greenish Warblers are late migrants that suddenly arrive and peak immediately after. The earliest record in The Netherlands is on 23 May and most birds pass through between the end of May and mid-June. From July to the beginning of August, Greenish Warblers are rare. Most July sightings concern long staying birds that arrived in June. After a very slow build up, autumn migration peaks between the end of August and mid-September. It dies out as quickly as it began. The latest bird ever dates from 17-21 October, but this really is an exception: there are only three October records.
Figure 3. Temporal distribution of Greenish Warblers in the Netherlands. Orange displays when birds were first found. Blue represents the birds that remained present in the period after they were first found.
By far most birds are gone very quickly: both the median and the mode is one day (46 out of 86 records; Figure 4). However, occasionally spring birds are territorial and stick around for quite some time. In all 11 birds stayed for more than a week. 30 and 60 days (the latter concerns the breeding record) days are the records.
Figure 4. Number of days Greenish Warblers remained present in The Netherlands (n=86)
Where to see one?
Greenish Warbler has been recorded in 10 out 12 provinces: only land-locked Drenthe and Utrecht are still waiting for their first record (table 1). With only six inland records, it's a bird of the coastal provinces. The vast majority (about 70%) of the birds have been recorded in the northern and northeastern part of the country. Noord-Holland has most records, but Friesland has had more individual birds. A little over half of all records are from one of the Dutch Wadden Sea islands. Texel, Noord-Holland (15) and Schiermonnikoog, Friesland (12) are by far the best places in the country. On the latter island, long staying territorial birds have been found in several years (the four longest staying birds from Figure 4 are all from there), incl. the breeding record. Breeding in new areas is often preceded by regular appearances of singing males in late spring at suitable sites (Clement 2017). With another long staying, late season singing male on Schiermonnikoog in 2017, this remains the site to keep an eye on for another breeding record. With so many records in the Wadden Sea, it’s surprising that Terschelling, Friesland has no records at all and that Ameland, Friesland only got its first in 2017 – though the latter island is also the least visited by birders.
Since it’s my hometown, Den Haag (The Hague), Zuid-Holland cannot be left unmentioned. There are probably not many cities in Europe that have a larger species list than The Hague (373), yet it has taken long before Greenish Warbler was added to the list. It finally happened in June 2017. In my own street!
Table 1. Number of records per province 1965-2017
The Dutch Wadden Sea islands are by far the best places to see a Greenish Warbler, especially Texel and Schiermonnikoog. At the latter island long staying territorial birds have been present in several years, resulting in a successful breeding attempt in 2003. When a Greenish Warbler pops up in an area nearby, it’s wise to twitch it the same day, as the majority of the birds is gone within a day. Late spring and early autumn are by far the best times to see one. With an increasing number of spring records, it's tempting to see a correlation with the species’ range expansion. Can we expect more long staying territorial birds, or even another breeding attempt in the future?
Thank to Natalia for the lovely pic of the Greenish Warbler that sang right next to my house in 2017!
Clement, P., 2017. Greenish Warbler (Phylloscopus trochiloides). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from http://www.hbw.com/node/58887 on 12 July 2017).
Dutch Avifauna: https://www.dutchavifauna.nl/species/grauwe_fitis (on 16 June 2017)
Ebels, E., 2003. Broedgeval van Grauwe Fitis op Schiermonnikoog in mei-juli 2003. Dutch Birding 25: 304-311
Thoma, M. & S. Althaus, 2015. Erstnachweis des Grünlaubsängers. Der Ornithologische Beobachter 112:4.
Waarneming.nl: https://waarneming.nl/soort/info/252 (on 8 July 2017)