Reedbed selection and colony size of breeding Purple Herons Ardea purpurea in southern France

Abstract

Reedbeds of Phragmites australis have declined in Europe in recent decades. Moreover, in some European countries the remaining reedbeds are intensively managed for industrial reed cutting, hunting or grazing. Several species of conservation concern, such as herons and pelicans, use reedbeds as their principal breeding habitat. At the same time, data on habitat use and colony size of these species in relation to reedbed management practices are scarce. We investigated habitat characteristics of 71 reedbeds occupied or unoccupied by breeding Purple Herons Ardea purpurea in the Rhône delta (Camargue) and in other Mediterranean coastal marshes in southern France. In addition, data on colony size in occupied reedbeds were collected from aerial surveys. Reedbeds occupied by breeding Purple Herons were unharvested, or only partially harvested, in winter and had higher water levels in spring compared with unoccupied reedbeds. A logistic regression model with reed harvesting intensity and water levels in mid‐April as independent variables correctly classified reedbed use for 94.7% of the reedbeds in the study. A model with water levels in mid‐April alone was only 90.9% accurate, suggesting that low water level in spring is the most important factor limiting reedbed occupation by breeding Purple Herons. A general linear model indicated significant effects of harvesting intensity and reedbed surface area on colony size. Within occupied reedbeds there was a strong tendency for colony size to increase with increasing reedbed surface area. Given the recent developments in reed harvesting and wetland management in southern France and elsewhere in Europe, these results provide the first information on potential effects of these practices on reed nesting herons, and suggest that Purple Heron conservation is likely to be favoured by maintaining large uncut reedbeds with relatively high water levels in spring. The possible effect of changes in habitat on the Purple Heron population in southern France is discussed.

Analysing spatial and temporal variation in colony size: an approach using autoregressive mixed models and information theory

“…5). This evidence supporting an effect of the number of competitors per unit of habitat indicates that, as expected according to theory, the size of rook colonies in Spain decreased with a greater number of competitors relative to foraging habitat within 6 km from the colony site, which is in agreement with the findings of Griffin and Thomas (2000) for rooks in England, and is also compatible with that found for Scottish rooks (Gimona and Brewer 2006), and for other colonial species (for competence: Furness and Birkhead 1984;Forero et al 2002;for habitat: Gibbs et al 1987;Gibbs 1991;Ambrosini et al 2002;Barbraud et al 2002;. For the first time a derived variable made up of the combination of both number of competitors and area of foraging habitat is found to be associated with colony size.…”

“…Evidence for this comes from positive relationships between colony sizes and indices of food availability (e.g., apparent foraging habitat) around nesting sites (e.g., Gibbs et al 1987;Gibbs 1991;Griffin and Thomas 2000;Barbraud et al 2002;, but this has not been found for some bird species or populations (see references in . If food is a determinant of colony size and foraging ranges overlap between colonies, competition for food by members of the same colony (competition intra-colony; Ashmole 1963) and the neighbouring colonies (competition inter-colony; Furness and Birkhead 1984) may reduce net food availability around colonies and ultimately affect their population sizes.…”

Effect of seasonal water level decrease on a sensitive bird assemblage in a Mediterranean wetland

“…When these areas go dry, they are abandoned by sensitive species that move to areas with permanent wetlands (van der Walk 2006). Therefore, local temporary departure of these species and modification of bird assemblage structure may occur (Báldi and Kisbenedek 1998;Moskát and Báldi 1999;Barbraud et al 2002).…”

Using historical political ecology to understand the present: water, reeds, and biodiversity in the Camargue Biosphere Reserve, southern France

“…At the same time, the number of nesting pairs of purple herons appeared to be decreasing. This was significant because the site was regarded as the Mediterranean bastion of the species (Barbraud et al 2002). Research in the 1990s indicated that the regulations governing the administration of communal land use rights, passed down from barons and abbots since the 13th century (Teulade 1999), were being changed and expanded, allowing a shift from a declining manual reed harvest (reserved to residents) to mechanical harvest by few residents and a growing number of operators coming from neighboring communities (Mathevet 2004).…”

“…Reed beds also provide food, refuge, and shelter for many animal and fish species. The Camargue's reed beds provide nesting areas for birds today designated as rare and/ or vulnerable in Europe (Barbraud et al 2002) such as the bearded tit (Panurus biarmicus), the purple heron (Ardea purpurea), and the Eurasian bittern (Botaurus stellaris). Bitterns are a heron of great importance to the EU Birds Directive ).…”