ABSTRACT
The nonbreeding season refers to the stationary period when birds are neither breeding nor migrating, and is generally the longest period of the avian annual cycle. Among plovers, some move only short distances or not at all from their breeding grounds, whereas others migrate thousands of kilometers to spend 4–6 months on their nonbreeding grounds. The temporal limits of the nonbreeding period are difficult to assess for both sedentary species and migrants because birds can and do move during this period, but not in the regular patterns that constitute formal migration, as birds often move to follow food resources. In this chapter, I review the evidence that food, habitat (either foraging or roosting), or predation limit plover populations during the nonbreeding season. Plovers are rarely territorial, observations of aggressive interactions and potential competition for food are rare, and few data exist to suggest that food during the nonbreeding season can be depleted with negative consequences for individuals and populations. However, spacing of plovers while foraging might limit the total number of birds that can use a site and the positive relationship between habitat patch size and number of birds suggests that habitat limitation is important. At medium and large geographic scales, plovers track habitats with the most food resources. Habitat quality (either through size of the patch or the degree of disturbance on the patch) appears to also have carryover effects to annual survival. Plover behavior and social organization during the nonbreeding season is also altered by the presence of predators, which affect their habitat selection, and may translate into population-level effects. I conclude that, while the exact mechanism of population limitation is not always clear, nor will it necessarily be the same for all plover species, sufficient evidence suggests that events on the nonbreeding grounds are critical for the determining the health of plover populations.
