Correlates and consequences of coloniality in great blue herons

Abstract

1987. Correlates and consequences of coloniality in great blue herons. Can. J. ZOO^. 65: 572-577. Sixty percent of the breeding great blue herons (Ardea herodias) in a colony at Pender Harbour, British Columbia, were individually marked to test three hypotheses concerning the benefits of colonial breeding. ( i ) Most herons fed near the site of the colony, but neighbours or members of a pair did not tend to choose adjacent feeding sites, as predicted by the information center hypothesis. Food supply was predictably distributed in time and space, and birds that did most of their feeding outside Pender Harbour bred less successfully than locally feeding birds. (ii) Nests that failed because of predation were nearer to the edge of the colony in 1978 but not in 1979. The colony was abandoned in 1980 after 2 years of high predation. Predation may, therefore, select for colonial breeding in herons, but heavy predation may force colony abandonment. (iii) Most herons chose new nest sites and new mates each year. The colony site may therefore serve as an assembly site for mate finding. Mate finding and avoidance of predation are therefore more likely to explain coloniality in great blue herons than are advantages associated with finding food. SIMPSON, K. J., J. N. M. SMITH et J. P. KELSALL. 1987. Correlates and consequences of coloniality in great blue herons. Can. J .Zool. 65 : 572-577. Soixante pourcent des Grands Herons (Ardea herodias) d'une colonie de Pender Harbour, Colombie-Britannique, ont ete marques dans le but de verifier trois hypotheses sur les avantages de la reproduction en colonies. ( i ) La plupart des herons se nourrissaient prks du territoire de la colonie. mais des oiseaux voisins ou les partenaires d'un couple n'avaient pas tendance a se choisir des sites d'alimentation adjacents, comme prevu selon I'hypothese du ((centre d'information >>. Les sources de nourriture etaient reparties dans le temps et dans l'espace selon les modeles, et les oiseaux qui se nourrissaient surtout hors de Pender Harbour avaient un succes reproducteur moins elevi que les oiseaux qui se nourrissaient localement. ( i i ) Les nids victimes de predation etaient plus prks de l'exterieur de la colonie en 1978, mais pas en 1979. La colonie a eti abandonnee en 1980 aprks 2 ans de predation intense. La predation peut donc favoriser la reproduction en colonies chez les herons, mais une predation trop intense peut entrainer I'abandon de la colonie. (iii) Chaque annee, la plupart des herons choisissaient de nouveaux emplacements pour construire leur nid et de nouveaux partenaires. Le territoire de la colonie peut donc servir de territoire de rassemblement pour le choix d'un partenaire. Le choix d'un partenaire et la protection contre les predateurs semblent donc des facteurs plus susceptibles d'expliquer la vie en colonies que ne le sont les avantages relies B l'acces plus facile a la nourriture chez le Grand Heron.[Traduit par la revue]

Colony Development and Density-Dependent Processes in Breeding Grey Herons

“…The Renkoji site was abandoned 4 years after establishment and the colony relocated to a new site in Tama Zoological Park close to Renkoji along the Tama-gawa River. Higher rates of nest mortality lead to significant decreases in colony size, and breeding colony distributions often shift in association with these reductions in colony size [33,34] [8,35]. Heavy predation may thus force colony abandonment by herons.…”

Importance of Proximity to Foraging Areas for the Pacific Great Blue Heron (Ardea herodias fannini) Nesting in a Developed Landscape

“…Kelly et al (1993) reported young herons being pulled from the nest by ravens in the absence of adult herons, and being eaten on the ground. Chick depredation by Golden Eagles (Aquila chrysaetos), Great Horned Owls (Bubo virginianus), Red-tailed Hawks (Buteo jamaicensis), and Raccoons has also been reported (Lopinot 1951;Pratt 1972;Kelsall and Simpson 1979;Hjertaas 1982;Pratt and Winkler 1985;Forbes et al 1985b;Simpson et al 1987;Burkholder and Smith 1991;Kelsall 1992). Several authors have noted that disturbance by humans or eagles facilitated raven or crow depredation (Taylor and Michael 1971;Simpson and Kelsall 1978;Quinney 1983;Drapeau et al 1984;Moul 1990).…”

“…This transient nature of smaller heron colonies in the lower Fraser River valley may be in response to Bald Eagle depredation (Simpson et al 1987), human disturbance, or other undetermined factors. In the interior of the province, Black Bear (Ursus americanus) depredation has been noted at several colonies (R. Packham and D. Peel, MELP, pers.…”

“…Kelsall and Simpson (1979) suggested that the location of heron colonies was far more dynamic than originally thought and that there was considerable interchange between colonies from year to year. Simpson et al (1987) found nest site and mate fidelity to be low from year to 6 year, and suggested that herons may switch colonies readily. Draulins (1988) suggested that heronries probably function as an assembly area for herons to find new mates and nest sites each year.…”

“…Other wildlife species such as Common Ravens, crows, Great Horned Owls and Raccoons are also responsible for egg and chick depredation (Simpson and Kelsall 1978;Forbes et al 1985b;Simpson et al 1987;Gebauer 1995a and1995b) and may affect reproductive success.…”