Figure 1. Iberian Chiffchaff, April 2016. The Hague, The Netherlands: the 37th record for the country.
Slaterus (2007) analysed all Dutch Iberian Chiffchaff (Phylloscopus ibericus) from 1967-2006 (n=18). With an increase in the number of records, there’s now more data available to both confirm and fine tune his conclusions.
Up till and including July 2017, there are 45 Iberian Chiffchaff records in The Netherlands (40 accepted, 5 still pending at the time of writing*). The first one was recorded in 1967. At the turn of the century, there were ten records. Though the species was already fairly well-known by then (with e.g. seven between 1986 and 1994), there’s a surprisingly long streak without any records between 1995 and 2000 (figure 2). With 35 records between 2001 and 2017, the species has become a regular vagrant. Ever since only 2003 and 2008 drew a blank. The best years are 2010 (6) and 2016 (5).
Figure 2. Iberian Chiffchaff records in The Netherlands 1986-2017 (n=42). There are another three records between 1967 and 1981. Note that this graph includes five pending, not (yet) accepted records.
Iberian Chiffchaff is a typical spring vagrant (figure 3). The earliest ones arrived on 8 and 9 April. Half of all birds were found at the end of April and the beginning of May (n=22). Since most birds stick around for quite some time (see below), the highest presence is at the end of May and the beginning of June. Only a few have been recorded after June (and only one ‘new’ bird was found then). It’s tempting to speculate that at least some birds found in spring hadn’t actually left by July, but fell silent instead and were therefore no longer reported. The latest dates are 10 and 23 September. Both birds were already discovered in spring.
It’s an easy species to twitch: by far most are territorial and these birds often linger on for weeks on end. Only five birds were recorded on a single day, whereas 31 birds were reported for a week or longer. The combined average duration of their stay is 31 days. The record holders stayed for 155 and 135 days, but these birds are exceptions: number three on the list stayed for 76 days and more than half of all the birds were present for less than 30 days. The bird that stayed for 135 days successfully bred with a female Common Chiffchaff (Ph. collybita) (Wester in prep).
The species has been recorded in 9 out of 12 provinces (table 1). Only Drenthe, Flevoland and Noord-Brabant are still waiting for their first record, whereas Overijssel got its first in 2016. With 21 records Noord-Holland has had an amazing number of birds. Friesland comes second, with seven, closely followed by Zuid-Holland with six. The latter province has had no less than four in 2016-2017. There aren’t any specific hotspots and many birds have been found outside protected areas, like city parks. The three largest cities in the country all have records: Amsterdam (4), The Hague (3) and Rotterdam (1). Migrant hotspot Texel, Noord-Holland also has four records. Not a single singing bird turned up at exactly the same place the year after. If at least some of the 45 birds survived until next year, they didn't show site fidelity.
Table 1. Number of Iberian Chiffchaff records per province 1967-2017
Figure 3. Number of Iberian Chiffchaffs found (blue) and present (orange) per 10 day timeframe in The Netherlands 1967-2017 (n=45)
It wasn’t until 2016 and 2017 that the first two calling – and not singing – birds were reported. Identifying calling birds could further boost the number of records in the future, and potentially could also give a twist to the timing of the records (the 2017 bird was the first one to be found in July), with records of calling migrating birds (perhaps even in autumn), females and birds that stopped singing (but are in fact still present) all being possible.
* Note: after all pending records have been reviewed, I will update this page.
Slaterus, R. 2007. Iberische Tjiftjaffen in Nederland. Dutch Birding 29:83-90
Wester, R. in prep. Broedgeval Iberische Tjiftjaf in Enschede.