480 Do Adult Little Egrets Respond to Disturbance at Their Nest by Increased Breeding Dispersal? PIERRE-YVES HENRY 1,2 , ROBERT E. BENNETTS 1,3 , YVES KAYSER 1 AND HEINZ HAFNER 1 1 Station Biologique de la Tour du Valat, Le Sambuc, F-13200 Arles, France Internet:gauthier-clerc@tourduvalat.org 2 Present address: Department of Ecology and Evolutionary Biology 301 Guyot Hall, Princeton University, Princeton, NJ 08544, USA 3 Permanent address: USGS-Florida & Caribbean Science Center 7920 NW, 71st Street, Gainesville, FL 32618, USA Abstract.—When studying breeding dispersal with marked individuals, manipulation-induced disturbance should not affect movement patterns. As part of a study on the Little Egret (Egretta garzetta), we tested whether the capture of breeding adults at their nest and handling (i.e., disturbance) increased their probability to move to a new colony in the subsequent breeding season (i.e., breeding dispersal). The proportion of adults disturbed in a given year that had changed colony in the subsequent breeding season was compared with the dispersal of adults observed during at least two consecutive years at colonies and not disturbed on the previous year: (1) birds marked as chicks and (2) birds marked as adults and observed ≥ two years after capture at the nest. Disturbed birds were not found to have an increased propensity to disperse. We conclude that, for this species, capture did not increase the subsequent breeding dispersal. Received 28 November 2003, accepted 7 August 2004. Key words.—Breeding dispersal, capture, disturbance, Egretta garzetta, Little Egret. Waterbirds 27(4): 480-482, 2004 When studying life history traits, the techniques used should not affect the trait under study. Nevertheless, some studies in- duce unavoidable disturbance. For banding studies, the impact of capture method or marking used is infrequently investigated (Rodgers and Burger 1981; Calvo and Fur- ness 1992). The few studies that have as- sessed the impact of disturbance focused mainly on intra-annual consequences on breeding success, nest desertion, chick mor- tality or parental behavior. But, to our knowl- edge, the hypothesis that such disturbance induces breeding dispersal (i.e., change of breeding location between subsequent years) has not been investigated. As part of a study of the Little Egret (Egretta garzetta), adults were captured at their nest using baits containing a narcotic drug. This disturbance, which included drugging, capture at the nest and handling, may have increased the propensity for birds to change colony in the next year. Two pseu- do-control groups were available to us: birds initially marked as chicks and observed as breeding adults, and adults captured at their nest but observed ≥ two years subsequent to the year of capture. Disturbance at the nest was assumed to affect the breeding dispersal in the season following capture but not on latter breeding attempts. A difference in dis- persal propensity was tested by comparing disturbed (i.e., recently captured) and not disturbed (i.e., control-like groups) birds. METHODS Our study group consisted of five to nine colonies each year from 1981-1997, scattered across the Camar- gue (1,800 km 2 , Rhône Delta, Southern France). Chicks (N = 7,267) and adults (N = 558) were captured and in- dividually marked with color-bands or wing-tags in five colonies each year (Hafner et al. 1998; Fasola et al. 2002). Chicks were captured at the nest and marked be- fore fledging. Adults were narcotized while incubating by placing a small fish containing a capsule of 9 mg of α- chloralose on nest. Once narcotized, adults were caught by hand at their nest, marked, measured, and placed back on their nest; handling lasted less than ten min- utes. All colonies were searched for marked individuals once a week each year, from 20 May to 30 July, re-sight- ing effort being higher in years 1988-1995. To test our prediction, only re-sightings of birds ob- served during incubation or nestling stage in colonies (considered as breeders) in two consecutive years were used. Re-sightings were separated into three groups: (1) disturbed birds (individuals re-sighted the year subse- quent to the year they were captured at their nest), (2) undisturbed birds marked as chicks (never captured at their nest as breeders) and (3) undisturbed birds marked