| Habitat and Ecology: |
Behaviour Populations breeding on the Atlantic coast of Europe, in the Mediterranean and in South Africa are largely sedentary due to the relatively mild winters6 (although they may make local dispersive movements related to rainfall)4. Continental populations are mainly migratory however2, 6 with a marked post-breeding dispersal of immatures2. The species breeds from March to June in Eurasia and during the rains from September to January in South Africa1. It usually nests solitarily although males are polygamous and may mate with up to five females nesting on a large wetland site1. The species remains solitary throughout the year1 (although migratory individuals may travel in small flocks)2, and is mainly crepuscular in its activities2. Habitat Breeding The species has highly restrictive breeding habitat requirements1. It shows a strong preference for quiet lowland marshes around lakes and rivers (less than 200 m above sea-level)2 with extensive dense young reedbeds of Phragmites spp. (e.g. with 1- 3 years worth of new growth3, 11 but still maintaining some old or dead stems1) that are flooded but are fairly shallow1 (less than 30 cm deep)6, have few fluctuations in water-level1, have low acidity2 and are surrounded by clear open areas1 of deeper water is maintained into the driest part of the breeding season8. Breeding adults are more attracted to unfragmented11 reedbeds over 20 ha in area, although smaller sites with networks of reed-fringed waterways or open wetland habitats with a number of small reedbeds6 (greater than 100 m)8 over a wide area may also be used6. The species avoids saline waters2 but is equally abundant in fresh or brackish habitats1 (e.g. in estuarine or delta marshes)5, and may occasionally nest in stands of rushes Scirpus spp.1 or Papyrus spp. if reeds are unavailable2. Non-breeding The species frequents a more varied range of habitats outside of breeding season, foraging on rice-fields, watercress beds, gravel pits, fish farms, ditches, sewage farms1, small ponds and wet grassy areas2 as well as marshes and reedbeds1. It also forages in running water (e.g. streams) when still waterbodies freeze during the winter4. Diet Its diet varies depending on the site and season although it predominantly takes fish (particularly cyprinids and eels) and amphibians as well as adult and larval insects, spiders, crustaceans, molluscs, snakes, lizards, birds, nestlings and small mammals1. Breeding site The nest is a pad of reeds and other vegetation2 constructed close to or floating on water1 amidst dense reedbeds1, 2. Although it is a solitary nester, breeding densities from 2 per 100 ha to 100 per 100 ha may occur depending on the quality of the habitat2, nests sometimes being placed close together in areas where the species is particularly numerous4. Management information Breeding adults in Europe may be more attracted to unfragmented11 reedbeds over 20 ha in area, although smaller sites with networks of reed-fringed waterways or open wetland habitats with a number of small reedbeds over a wide area may also be used6. There is evidence that females in Britain preferentially nest in locations surrounded by less scrub but more vegetated open water, with a higher proportion of Phragmites spp. than other plant species, and in areas where deeper water is maintained into the driest part of the breeding season8. The European Action Plan for this species recommends raising water levels, harvesting and burning reeds, cutting invasive scrub, or digging out reedbeds on a rotational compartmental basis as methods of slowing reedbed succession6. It also recommends the regular cutting of small areas of reedbed to maintain Phragmites spp. monocultures6, to provide a range of multi-age reed stands2 and to favour the retention of water levels in spring and summer (promoting rapid growth, preventing a build-up of reed litter and providing foraging sites)6. Large-scale reed cutting should be prohibited in the late-winter however2. Wetlands should also be managed to enhance the carrying capacity of fish and eel populations (thus increasing food resources for bitterns)7, 9, 10. In Britain it was found that suitable habitats should be provided for all fish life stages (including spawning, refuge and overwintering), the movement of fish throughout reedbeds should be promoted (e.g. by changes in hydrological management regimes and sluice design)7 and issues relating to water quality, zooplankton and macrophyte community structures should be addressed10.
|
