Habitat preferences of Eurasian Bitterns Botaurus stellaris booming in ricefields: implications for management

Abstract

The Eurasian Bittern Botaurus stellaris suffered declines in western Europe during the 20th century, partly because of wetland reclamation. The species has been traditionally considered a reedbed specialist but recent studies identified a greater ecological plasticity than previously believed. We investigated habitat associations of a Eurasian Bittern population that has started to breed in the ricefields of northwest Italy since the early 1990s. Booming Bitterns had a higher probability of occurring in ricefields with taller rice plants, more vegetated field banks, more weeds, a larger surface and closer to remaining natural wetlands. The positive effect of field bank vegetation height on the probability that a ricefield hosted a booming Bittern declined late in the season, in contrast to the effects of weeds and ricefield area, which were stronger later in the season. A decreasing importance of vegetation on field banks to booming Bitterns may be a consequence of seasonal changes in habitat structure through the Bittern's breeding period. The degree of flooding did not affect the probability of occurrence of booming Bitterns, probably because most ricefields were homogeneously flooded during the peak breeding season (June-July). Our findings have important implications for the management of Bittern populations breeding in the ricefields of northwest Italy. We propose simple conservation actions that may favour the occurrence of booming Bitterns and help the species spread in this novel habitat.

Effects of grass management intensity on ground beetle assemblages in rice field banks

“…In many cases, their highly variable physical and chemical conditions lead to the establishment of flexible, opportunistic, and generalist species assemblages. However, when the intensity of management is reduced, bunds may provide a refuge for species vulnerable to disturbance and habitat simplification (Longoni et al, 2011;Naito et al, 2013).…”

“…Moreover, the maintenance of the riparian vegetation on field banks could benefit other species of conservation concern inhabiting paddy fields, such as birds (e.g. Eurasian Bittern, Longoni et al, 2011).…”

“…Some birds nest in the strips of natural vegetation that develop along paddies and irrigation canals (Pierlussi, 2010), while others' field use is affected by the amount of spontaneous flora in the surrounding bunds (e.g. Great Bittern, Longoni et al, 2011). Paddy banks also support high activity densities of some arthropod species (e.g.…”

“…or a belt of bare soil. For all we know, even if evidences exist on the essential role that vegetated bunds could have in the maintenance of a functioning rice ecosystem (Longoni et al, 2011;Naito et al, 2013), no studies were specifically focused on the effect of human disturbance, such as mowing, herbicide application, or chemicals drifting from adjacent fields, on bank's fauna.…”

The introduction of subsidies for grassland conservation in the Italian Alps coincided with population decline in a threatened grassland species, the CorncrakeCrex crex

“…broadcast calls of males) if no male was singing (one minute of playback, three minutes of listening, repeated twice). The number of calling males is used as a population estimate for this (Schäffer 1995, Tyler & Green 1996, Schipper et al 2011) and other elusive species (Poulin et al 2005, Longoni et al 2011. All areas were visited once in May to early June, before mowing (which in the study areas takes place around the 15th June, with inter-annual variations), and once in late June to July, after mowing.…”