Abstract: During the non-breeding season, shorebirds, a large and important group of wetland vertebrates, divide their time between foraging, resting and maintenance activities. We examined factors affecting time budgets, foraging techniques and rates, and spacing patterns of 14 to 92 individuals each of 10 shorebird species spending the non-breeding season in Cayo Guillermo, Cuba. We hypothesized that all species would spend the majority of their time foraging. Time spent foraging ranged from 20–85% of total time and was significantly negatively related to average body size. Apparent aggression (e.g. chasing or being chased) occurred in < 10% of individuals in all species and was not related to maximum counts of conspecifics. Aggression was most common in the black-necked stilt but did not vary in frequency as a function of activity. Vigilance varied in occurrence from 0–53% of individuals, but the frequency was not related to maximum counts. Intraspecific distances were generally greater between foraging than non-foraging birds. For most species interspecific distances were similar to intraspecific distances during foraging but greater than intraspecific differences during non-foraging, suggesting some overlap in foraging habitat and niche partitioning during non-foraging. Shorebirds that used primarily tactile techniques foraged closer together than primarily visual foragers. Low rates of aggression, as an index of potential competition, suggest that species-specific energy requirements rather than competitive interactions are the main determinants of foraging behaviour on these tropical non-breeding grounds.
Brook, R. W., L. A. Pollock, K. F. Abraham, and G. S. Brown. 2021. Bird trends from long-term observation data at sites in the Hudson Bay Lowlands. Avian Conservation and Ecology 16(1):10. https://doi.org/10.5751/ACE-01821-160110
We examined diet of nonbreeding Semipalmated Plovers (Charadrius semipalmatus Bonaparte, 1825) in the Cumberland Island estuary, Georgia, USA, through fecal sample analysis. We also examined prey size selectivity by Semipalmated Plovers for the most common prey item found in the fecal samples, which are polychaetes in the family Nereidae (= Nereididae). We compared the size distribution of polychaetes in Semipalmated Plover fecal samples from salt marshes and mudflats with the size distribution of polychaetes sampled from the two habitats. Semipalmated Plovers foraging on mudflats had less variable diets than those foraging on salt marshes, although the mean number of prey per Semipalmated Plover fecal sample was similar between the two habitats. Size selectivity by Semipalmated Plovers of nereid (= nereidid) polychaetes varied as a function of habitat, with Semipalmated Plovers eating larger polychaetes in salt marshes than in mudflats, although in both habitats Semipalmated Plovers avoided extremely small and (or) large ones. Semipalmated Plovers took fewer of the available prey groups and were more selective in sizes of the dominant prey group on mudflats, where prey densities were the highest. These observations are consistent with predictions from optimal foraging theory.
The evolutionary transition from diploidy to polyploidy is prevalent in flowering plants and may result in correlated changes in mating system (outcrossing rate). Most theory predicts a shift toward self‐fertilization (decrease in outcrossing) in polyploids, but empirical evidence for this pattern and its underlying mechanisms is inconclusive or restricted to a few cases. In an analysis of variation in outcrossing rates among diploid‐polyploid species pairs from the literature, polyploids had lower outcrossing rates (higher selfing; $$t=0.23$$, $$\mathrm{SE}\,=0.09$$) than diploids ($$t=0.52$$, $$\mathrm{SE}\,=0.12$$). Among polyploids, however, allopolyploids were predominantly selfing ($$t=0.20$$, $$\mathrm{SE}\,=0.099$$), whereas autopolyploids had significantly higher outcrossing rates ($$t=0.64$$, $$\mathrm{SE}\,=0.087$$), raising the question of what limits the evolution of selfing in autopolyploids. To address this, we examined the magnitude of inbreeding depression in synthetic polyploids of the plant Chamerion angustifolium. The intrinsic cost of selfing in newly formed polyploids was negligible compared with extant polyploids, thus promoting the spread of selfing. However, there was weak evidence that inbreeding depression increases with history of inbreeding, suggesting that the rise in selfing may be ephemeral and that selection ultimately favors mixed or outcrossed mating systems in autopolyploids. Such constraints on selfing have some theoretical support, but additional research on patterns of variation and genetic mechanisms governing polyploid mating systems are needed.
'%3e%3cpath fill='%23012169' d='M0 0v30h60V0z'/%3e%3cpath stroke='%23fff' stroke-width='6' d='m0 0 60 30m0-30L0 30'/%3e%3cpath stroke='%23C8102E' stroke-width='4' d='m0 0 60 30m0-30L0 30' clip-path='url(%23b)'/%3e%3cpath stroke='%23fff' stroke-width='10' d='M30 0v30M0 15h60'/%3e%3cpath stroke='%23C8102E' stroke-width='6' d='M30 0v30M0 15h60'/%3e%3c/g%3e%3c/svg%3e)
