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Flooding and breeding birds - A question

With much of the Somerset levels still flooded, there must be a risk that birds that would normally breed on or around water are likely to start building nests in areas that will soon be dry. Excluding the winter migrants, does anyone know if there is any research or informed knowledge on whether birds would normally return to the more traditionally wet areas on the levels or is there a real risk of many being unsuccessful when the flood finally recede as their nest are left high and dry. Is a good food supply the key factor when selecting breeding sites?

Something to discuss on what looks like being a wet Sunday!!

Re: Flooding and breeding birds - A question

Parts of the story are well understood, but there are some important knowledge gaps.

You're right - the food supply is hit badly. Earthworm populations get decimated by floods and this affects birds that largely depend on them during the breeding season - notably the waders. There are other invertebrates in these habitats, some of which are better at surviving flooding. Many beetles make use of whatever cover is left above water and others appear to be able to survive in air pockets in the soil. The extent and duration of the current floods is likely to be particularly damaging to all the prey groups, as so little cover was left above water and oxygen may run out for insects trying to survive in the soil. We were discussing this issue at Otmoor recently - there is scope (there, at least) to retain more rough grass vegetation on raised banks, to allow more inverts to survive big floods (this was in connection with a rare, floodplain specialist that occurs there and at West Sedgemoor - Badister meridionalis ... now on my list!). Some prey will bounce back quickly - rotting vegetation specialists, like hoverflies (rat-tailed maggots), may do well when the waters recede, but overall, food for breeding birds will probably be scarce this spring, until invert/worm populations bounce back.

There is another intriguing side to this. Big floods also remove the nest predators, so there can be a period of high nest survival for a year or two, before predator populations recover. The dramatic reduction in fox/badger prey (earthworms and small mammals) might discourage them from returning quickly to the low-lying ground. Nest predation is the big limiting factor nowadays, so a reduction, however short-lived, could compensate for the reduced prey levels. It's possible that waders used these bursts of high-productivity on flood aftermaths to make good their losses during drier times. You may have heard experienced wader researchers making this suggestion (Dave Chown may have more to add on this and reserve wardens elsewhere say the same, e.g. on the regularly-flooded Nene Washes). However, this is where the evidence base gets gappy, so this remains a theory, however plausible. If floods are benficial in this way, then it is more likely be smaller, short-lived, occasional floods that provide the benefits (and help maintain soil fertility on pastures/meadows) and NOT the big, persistent floods like the current one & last year's.

Dave Buckingham

Re: Flooding and breeding birds - A question

The bigger issue here are those species that do not normally breed on the Levels doing so, then finding their attempts futile as the water recedes leaving high and dry. Thereby wasting a whole breeding season. This is now happening with BH Gulls and Coot in particular, 100s of pairs are involved.
So a massive egg bonus for the local Fox, Badger and Crow population awaits!

Re: Flooding and breeding birds - A question

Hi Dave, many thanks for the detailed reply to my question. There is clearly more reason to be hopefully than I would have thought.

Hi Nigel, many thanks for your comments, it might be that the crows are the ones that will benefit most.