Intraspecific variation in size and density of Avocet colonies: effects of nest‐distances on hatching and breeding success

Abstract

In many colonial bird species there is considerable intraspecific variation in colony size and inter‐nest distance (colony density). Possible causes of this variation and its effects on hatching success (survival of eggs) and breeding success (probability of a pair raising chicks) were studied in 48 Avocet Recurvirostra avosetta colonies in Schleswig‐Holstein (Germany) between 1991 and 1996. Colony density was influenced by time of year and habitat (categories: island or mainland, close to or far from feeding grounds). Colonies on islands had the highest densities. When all available space at a colony site was used, colonies became very dense (mean nearest‐neighbour nest distance less than 1 m). Colony size (number of clutches) was influenced by time of year, but not by habitat. Hatching success was low in high density colonies and in very low density ‘colonies’ (single nests) and high over a broad range of intermediate nest densities. The low success rate of single nests was caused by a very high predation rate, whereas the low success rate in very dense colonies was caused by a high rate of nest abandonment. Nest abandonment in very dense colonies was associated with a high level of aggressiveness among Avocets during the egg‐laying period. Due to territorial behaviour, Avocets seemed to be expelled from the densest breeding sites. In very dense colonies, high frequencies of clutches of unusual size occurred due to conspecific nest parasitism. The number of Avocets taking part in attacks on potential egg predators was small and (in colonies of more than one clutch) depended neither on colony size nor on colony density. Despite a low hatching success in very dense colonies, individuals breeding in the densest colonies had significantly better chances of raising chicks than Avocets breeding in less dense colonies. Coloniality seemed to be obligatory for Avocets in order to ensure hatching success. The size and density of colonies seemed to be associated with the availability of suitable nesting habitats (islands).

Nest-site selection and characteristics in a mixed-species colony of Avocets Recurvirostra avosetta and Black-winged Stilts Himantopus himantopus

“…Inter-nest distance was slightly larger than the minimum mean values found in the literature both for Black-winged Stilts (Goutner 1989, Tinarelli 1990 and Avocets (Goutner 1985, Casini 1986, although much larger than in some extremely dense Avocet colonies described by Hötker (2000). Here Avocet nests were significantly closer to a conspecific nest and to the geometric centre of the colony than Blackwinged Stilt ones, revealing a higher degree of gregariousness.…”

Effect of intraspecific interactions on seasonal decline in productivity of Common TernsSterna hirundo

“…2a), which although higher than published values for Magellanic Penguins Spheniscus magellanicus (< 0.05 per hour) (Stokes & Boersma 2000), is less than that observed for Avocets Recurvirostra avosetta breeding at high densities (4.8 per hour) (Hötker 2000). It is also lower than the observed frequency of other breeding activities of Common Terns, such as provisioning (Fig.…”

“…However, median laying-dates of late-breeding terns in the two treatments were no different, and other parameters often associated with parental quality, such as clutch size (Coulson & Porter 1985), were similar (Table 3), allowing direct comparison of mixed-laying and late-laying treatments. Focal pairs were also matched with respect to mean nearest-neighbour distances and there were no differences between treatments in nesting density, a variable known to influence frequency of introspecific interactions (Hötker 2000, Stokes & Boersma 2000.…”

“…Nesting density of Common Terns in North America commonly ranges from 0.06-0.5 nests/m 2 but is unusually high at Bird Island (Massachusetts, USA) where distances between nests can be less than 0.5 m (Nisbet & Drury 1972In areas of high nesting density, colonial seabirds are often subjected to a higher frequency of intraspecific interactions (Hötker 2000, Stokes & Boersma 2000, Coulson 2002). Arnold et al (2004) found some evidence that the frequency of intraspecific interactions at the nest was higher at Bird Island for Common Terns breeding late in the season.…”

Spatial differences in breeding success in the pied avocet Recurvirostra avosetta: effects of habitat on hatching success and chick survival

“…Movements from nesting sites to feeding areas regularly occur in both waders and ducks (Walters 1984, Sedinger 1992). Pied avocets usually nest in dense colonies in which pairs occupy tiny nesting territories (Cadbury and Olney 1978, Tschernitschko 1980, Cramp and Simmons 1983), and colonial nesting is thought to be essential for successful hatching in this species (Hötker 2000). Factors affecting breeding success in coastal populations of avocets include competition for nest sites by other species, nest predation, flooding of nests, adverse weather, abundance of food for chicks and predation on chicks (Cadbury et al 1989, Hötker and Segebade 2000).…”