On and off in The Netherlands a discussion continues on a nightly bird call, which according to some is produced by Long-eared Owl and to others is produced by Coot. One of the problems in this discussion was the lack of sound recordings to illustrate the case. Some recordings are presented here now.
Up till last spring I was myself convinced that this call was produced by Long-eared Owl. I never mingled in previous discussions, since I was convinced this to be true. Only once I mentioned my view on a local email forum, to get a response that this was untrue by someone I considered an expert. I started reconsidering my view.
Why was I happy with Long-eared Owl at first?
1 In my early birding days this was tought to me by birders which I took seriously, somewhere in the early seventies.
2 I never did any observations giving reason to doubt it, the sound always moved around slowly at low altitude, in an owl-like manner, in areas one could expect Long-eared Owls to occur.
3 I even did a visual observation, some years ago at home, of an owl-like creature flying at low altitude apparently producing this call.
4 The call sounds like an agitated Coot, similar to the calls I met when Coot where attacked by Marsh Harriers or quarelling during daytime in the breeding season. It didn't seem logic that a Coot was flying low at night, producing a call which did not at all seem to be meant to attract a mate.
Owl researchers sometimes explained that they didn't know this call from owls, nonetheless I never took this very seriously, since these people usually study owls close to the nest and not out hunting further away.
Moorhen type calls
For some time I even assumed, as I know others did, that Long-eared Owls also produced Moorhen type calls, since I also met with these when flying low and slow at night. Sometimes I heard similar calls when flying high and fast, but then always ascribed those to Moorhen, as I did with calls of Water Rails to that species. I did consider it odd that Long-eared Owls apparently where able to produce perfect copies of the calls of both Coot and Moorhen, but left it there. In spring 2004 however, on a nightly visit to a marsh area, I came across a bird making such a call when circling over my head at low altitude (with a sound similar to this or this). After a while it suddenly plunged down on the water and started calling as a Moorhen in a more normal way. This of course skipped the owl as possibility and made me wonder whether the Coot-like call was actually an option for Long-eared Owl, especially when birder Ruud van Beusekom told me he had actually seen Coot making such calls at night when flying over lighted greenhouses. That season (2004) I tried to make sound recordings of the call, but failed.
Sound recordings
Guus van Duin was the first to make a sound recording and published this on the site of Dutch Birding early 2005. It was recorded on March 21 in 2004 flying over his house in Amsterdam (koet1). He continuously recorded sounds of birds flying overhead at night and listened to these from inside. I copied this method and was able to make a similar recording at home in Hilversum on February 18 in 2005 (koet2).
On April 11 2005 I recorded this call type again in an area with meadows and canals to the south of Hilversum (koet3). In all cases the sound slowly moved around at low altitude at night, in an owl like manner. These sounds differ in rhytm, but give a proper impression of the call type.
During daytime
During daytime I also came across similar sounds in marshland area's. These were always produced by Coot. When producing these calls Coot seemed agitated: under attack by a predator or quarelling. On July 7 2004 I recorded these calls accidently when recording Purple Herons (heard in the background) in Naardermeer nature reserve (koet4).
None-flying at night
Recently (July 8 2005) I recorded similar calls at night, close to Naardermeer nature reserve. Normal calls of Coot are interspersed with the special call type. I have heard similar combinations before and after (koet5).
Sonagrams
Sonagrams (spectograms) were produced to illustrate that these calls - in my view - are produced by the same species. In all 5 examples similar images are shown, with similar base tones and overtones. Its frequencies are about 850 Hz, 1700 Hz, (2500-)2600 Hz, (3200-)3500 Hz and (4300-)4500 Hz. At close range more overtones are shown, further away less of them. All 5 sonagrams are shown here.
Field experiment
When finally sound recordings became available in early 2005, I decided to confront some local Coot and Moorhen with these. In the late afternoon of February 20 2005 I played calls 1 and 2 to them as well as a nightly call of Moorhen. During the first test they appeared interested, started calling, then decided to move away. Two later tests did not give any proper extra response and they kept at a distance. When I moved away there was a lot of calling going on, both of Coot and Moorhen.
Not much can be concluded from this, apart from the fact that they seemed to recognise their own species and were chasen away rather than attracted by it. I produced small films of it.
Conclusions
So far I have been unable to produce solid evidence that the birds producing these nightly calls, when flying low and slow, were in fact Coot (and Moorhen), I only made it very likely. I am convinced, however, that this evidence (by video) will come sooner or later. Several other observers have actually observed and identified Coot showing this behaviour. Observers identifying such birds as Long-eared Owls should provide proof of this themselves now, since I consider it rather unlikely (though still possible) that two unrelated species should be capable of producing identical sounds.
Rail species flying at night are not uncommon at all, but usually they migrate at higher altitutes and at speed, producing calls which are easy to identify. Confusion has arisen when they fly around more slowly at low altitutes, in an owl like manner, and producing a rather uncommon call in the case of Coot. In the meantime both Guus van Duin and myself have made recordings at home of Coot and Moorhen flying low and slow producing more common call types too.
Questions
I still have some questions, as shown above under bullets 3 and 4. Of course my simultaneous observation of this call type and an owl may have been a misidentification: I expected to see an owl, saw some bird, but possibly not well enough to be aware that it might have been something else. But why would a Coot flying around at night produce an 'agitation call' which other Coot did not seem to like much? What could be the function of this? Do they actually perform this at places far away from their normal habitat as observed by others? This in fact was the main reason why these observers assumed that Coot was not an option and therefore still consider Long-eared Owl as the most likely species. This is especially so in cases when this call type was observed as coming from a tree. Since Coot are considered unable to sit in a tree because of the backward position of their legs (so unlike Moorhen), this still asks for an answer. Observers should try to make proper sound- or video including sound recordings of this behaviour. It will be very interesting to hear the opinion of other birders and researchers on these matters, especially from other countries!
Sonagrams (spectograms) were produced to illustrate that these calls - in my view - are produced by the same species. In all 5 examples similar images are shown, with similar base tones and overtones. Its frequencies are about 850 Hz, 1700 Hz, (2500-)2600 Hz, (3200-)3500 Hz and (4300-)4500 Hz. At close range more overtones are shown, further away less of them. All 5 sonagrams are shown here.
