Steve Westerman
Wharfedale Naturalists Society
The Ilkley section of the River Wharfe has undergone a lot of changes over recent months. Earlier in the year the flood moved substantial quantities of stone downstream, forming new ‘islands’. In addition, large areas of the river bed have been exposed through the summer with the low river levels. Many new paths down to the water have been created through the vegetation – some for people, many made by dogs. I think all of this has influenced the wildlife of the river. For example, Dippers and Kingfishers don’t seem as prevalent as last year – perhaps because some nesting and feeding sites are now less secluded.
However, Goosanders (Mergus merganser) seem to be doing relatively well, and on a couple of occasions I have seen a small ‘flotilla’ swimming around. Goosanders are diving, fish-eating birds and consequently aren’t always popular with the angling community. They can often be seen swimming with their faces in the water, looking downwards for their next meal.
Mandarin ducks (Aix galericulata) also seem to be establishing more of a presence. These are non-native and – although loved by many - the exotic, flamboyant appearance of the male is not to everyone’s taste. Originating in east Asia, there were releases/escapes from captive groups in the southeast of this country (Surrey) in the early part of the 20th Century, and this was the beginning of the wild population. Over time they have (been) dispersed more widely, and for some years there have been numbers at Bolton Abbey and the Yorkshire Wildlife Trust reserve at Adel Dam.
Some weeks ago, I was surprised to see one of these usually timid birds in the line-up of mallards and black-headed gulls on the Riverside ‘dock’ in Ilkley. It may also be a little unexpected, but Mandarins are ‘perching ducks’ that can sometimes be seen in trees alongside the river (see photograph). Fairly recently I watched a small group – a female and what I think may have been a couple of juveniles - edging their way along a quieter section of the river. Could it be that Mandarins are now breeding along this stretch?
Both Goosanders and Mandarin Ducks nest in holes in trees – although Goosanders will consider alternatives and Mandarins will use nest boxes. Of course, neither species is equipped to make holes, and so must rely on those that have been created by others (eg woodpeckers) or that have been produced naturally, perhaps in broken or dying trees. This can place these species in direct competition (as well as with some others, eg Jackdaws). So, if suitable holes are in short supply, numbers of these birds may be jointly restricted.
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