Breeding site fidelity and its effect on reproductive success was investigated in two diving ducks species, i.e. Common Pochard (Aythya ferina) and Tufted Duck (Aythya fuligula) in the Trebon region and the surroundings using caught and individually marked females, searching for nests, and monitoring of marked individuals and its broods. In both studied species, the fidelity ratio (apparent survival, MARK software) was around 65 %. Evaluating the influencing factors, impact of previous reproductive success in the phase of rearing ducklings was found to be the only one statistically significant factor. Furthermore, we compared reproductive parameters (i.e clutch size, laying date, reproductive success) in the first and subsequent year of study. The statistically significant relationship was found between the timing of nesting in the first and in any subsequent year in the Tufted Duck . When comparing the reproductive success in relation to hatched or unhatched clutches and reared or not reared ducklings, we do not confirm any significant shift. Successful females were not able to improve or even repeat their reproductive success in the following years, which could result in subsequent lower degree of fidelity. Subsequently, there is a female dispersion and reduction of the reproductive success of...

I conducted demographic and behavioral studies of Western Sandpipers (Calidris mauri) breeding on the Yukon-Kuskokwim River Delta, Alaska (1998-2005). In chapter one, I estimated apparent annual survival (product of true survival and site fidelity) while correcting for the probability of encounter for 237 males and 296 females. Overall return rates (individual returned to the site in a subsequent season) were lower for females (40%) than males (65%), as was apparent annual survival (± SE, females = 0.65 ± 0.05, males = 0.78 ± 0.03), and encounter rate (females = 0.51 ± 0.07, males = 0.74 ± 0.04). In chapter two, I examined the effects of mate and site fidelity on nesting success (N = 430 nests). Annual divorce rate ranged between 37-83%, with 17-63% of pairs reuniting annually. Reuniting pairs initiated clutches earlier than newly formed pairs, and clutches that were initiated early in the season had higher nest success rates compared to late-season nests. When I controlled for clutch-initiation date, nests tended by individuals with prior breeding-site experience had higher daily survival rates compared to birds breeding at the site for the first time. The effect of site experience was greater for males than females. In chapter 3, I reported that Western Sandpipers exhibited aggregated breeding behavior on a 36 ha plot. Breeding aggregations occurred when dominant and/or older individuals excluded younger, subordinate individuals from preferred habitat. The pattern of habitat occupancy conformed to an ideal despotic distribution with aggregated nesting birds in less preferred habitat experiencing lower reproductive success. In chapter 4, I described and demonstrated the form and function of parent-chick communication in the Western Sandpiper. Through experimental playback of adult vocalizations to chicks in the field, I demonstrated: (1) chicks respond to the alarm call by vocalizing relatively less often and moving away from the signal source, (2) chicks respond to the gather call by vocalizing relatively more often and moving toward the signal source, (3) and chicks respond to the freeze call by vocalizing relatively less often and crouching motionless on the substrate for extended periods of time. I also describe two distinct chick vocalizations (chick-contact and chick-alarm calls). / Ph. D.