Yuri Zharikov

Intake rates and the functional response in shorebirds (Charadriiformes) eating macro-invertebrates

As field determinations take much effort, it would be useful to be able to predict easily the coefficients describing the functional response of free‐living predators, the function relating food intake rate to the abundance of food organisms in the environment. As a means easily to parameterise an individual‐based model of shorebird Charadriiformes populations, we attempted this for shorebirds eating macro‐invertebrates. Intake rate is measured as the ash‐free dry mass (AFDM) per second of active foraging; i.e. excluding time spent on digestive pauses and other activities, such as preening. The present and previous studies show that the general shape of the functional response in shorebirds eating approximately the same size of prey across the full range of prey density is a decelerating rise to a plateau, thus approximating the Holling type II (‘disc equation’) formulation. But field studies confirmed that the asymptote was not set by handling time, as assumed by the disc equation, because only about half the foraging time was spent in successfully or unsuccessfully attacking and handling prey, the rest being devoted to searching.

Philopatry. nest-site tenacity, and mate fidelity of Semipalmated Plovers

Philopatry, nest-site tenacity, and mate fidelity were examined in a population of Semipalmated Plovers Charadrius semipalmatus breeding near Churchill, Manitoba, Canada from 1992 to 1997. Natal philopatry was low (7 of 445 (1.57%) hatchlings returned to the study area to breed) and no difference in sex of recruits was detected. Adult males returned at a significantly higher rate (58.9%) than adult females (41.2%). For both sexes, but more strongly for females, success in the previous year resulted in higher return rates in the subsequent year. Of pairs that returned, 41.6% divorced. Females that divorced or changed mates through death or disappearance of a partner between breeding seasons were significantly less site tenacious than females that reunited and also less so than males of any pairing status. Females that experienced breeding failure and changed mates in the subsequent breeding season moved farther than successful females that changed mates. In only one of four years did reunited pairs nest earlier and have greater hatching success than novel pairs. After divorce new mates of females did not differ significantly in morphological or plumage characteristics from old mates, nor did they possess territories with greater visibility, or territories nearer to water. After divorce new mates of males were significantly smaller than old mates. Our return rates underestimate survivorship in females because both the probability of return and site tenacity of females are strongly influenced by their previous success.