Abstract from BTO Research Report No 220:

Balmer, D.E. & Rehfisch, M.M.

An assessment of the feeding requirements of overwintering waterfowl at Hickling Broad.
ISBN: 1-904870-66-X

Executive summary

1. During 1998, Hickling Broad held 3,588 tonnes mean wet weight biomass of Chara intermedia. As one gramme wet weight of C. intermedia converts to 0.156 g dry weight C. intermedia, and one gramme dry weight has an energy value of 5.212 kJ, Hickling Broad held 2917 million kJ energy in the form of Chara. Some 46.5%, or 1357 million kJ, of this energy was theoretically available to feeding waterfowl.

2. During the 1998/99 winter, Hickling Broad supported on average 17,190 Mute Swan bird days, 10,289 Gadwall bird days, 46,125 Teal bird days, 53,579 Mallard bird days, 5,085 Shoveler bird days, 29,187 Pochard bird days, 94,313 Tufted Duck bird days and 305,229 Coot bird days. The total energy needs of these birds was 622 million kJ energy.

3. The equivalent figures estimated from peak counts of each species are 30,814 Mute Swan bird days, 17,794 Gadwall bird days, 118,916 Teal bird days, 131,502 Mallard bird days, 14,280 Shoveler bird days, 49,000 Pochard bird days, 128,464 Tufted Duck bird days and 463,512 Coot bird days. The total energy needs of these birds was 1053 million kJ energy.

4. Assuming that the birds fed on nothing but C. intermedia and that the C. intermedia standing crop was that present in 1998, then the waterfowl present on Hickling Broad during the 1998/99 winter would take 46% (based on mean bird counts) or 78% (based on peak bird counts) of the available food.

5. The four proposed cutting regimes for the C. intermedia would lead to the following proportions of the Chara being taken by the waterfowl (based on the 1998/99 mean and peak winter waterfowl numbers):

6. Allowing for the assumptions made during the calculations, each cutting regime will potentially have an impact on the the number of overwintering waterfowl that Hickling Broad could hold.

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