Floater strategies and dynamics in birds, and their importance in conservation biology: towards an understanding of nonbreeders in avian populations

Abstract

Over the past 40 years, the study of animal populations has shifted from a relatively simple science that assumed the most crucial regulating mechanisms were the intrinsic properties of breeders, to a more complex and refined discipline that reflects a greater understanding of populations and their dynamics. Part of this shift has been the explicit recognition of the importance of a previously overlooked nonbreeding component of animal populations, the so-called floaters.Here we review and discuss the various effects that pools of floaters can have on the structure, dynamics and persistence of bird populations. Under some circumstances floaters can be both active intruders that can alter the breeding performance and behavioural traits of territory owners, as well as secretive presences reducing the extinction risk of populations. Floaters are crucial elements in conservation biology, and knowledge of their behaviour and dynamics in avian communities can be a key factor in the success of conservation strategies. Firstly, larger pools of floaters are associated with more stable breeding populations, even in cases where breeding output could be impacted through interference by floaters. Secondly, the effects of habitat loss and mortality rates are frequently ignored in areas where floaters settle, and consequently conservation measures tend to overlook these sites, potentially leading to increased risks of mortality among floaters. Thirdly, because an increase in the proportion of juveniles in the breeding component of a population may be because of increased pre-adult and/or adult mortality rates, a change in the age of breeders has the potential to function as a warning of an imminent decline in breeding populations. Most population studies have only considered the breeding components of animal populations, so it is time now to focus attention on the floater component, wherein the solution to many conservation issues may be found.

Habitat selection by Black kite breeders and floaters: Implications for conservation management of raptor floaters

“…The latter adds complexity to strategic management targeting long-term population persistence, especially because non-breeding animals are difficult to study due to their cryptic behaviour, differential habitat selection, spatial separation from breeders, or potential long-distance dispersal (e.g. Zack and Stutchbury, 1992;Rohner, 1997;Whitfield et al, 2009a;Penteriani et al, 2011). As a result, there is little knowledge on the differences in habitat choices between the breeders and floaters of a population, and conservation planning is often biased to protect the habitats preferred by the breeding sector of predator populations (e.g.…”

“…Real and Mañosa, 1996;Whitfield et al, 2006a). Also, most of the (scarce) available knowledge is heavily biased towards large species of solitary birds of prey, whose floaters are typically concentrated in so-called ''temporary settlement areas'', where they select different habitats than breeders (Ferrer and Harte, 1997;Balbontín, 2005;Caro et al, 2011;Penteriani et al, 2011). As a result, little is known of smaller species with different social systems, such as colonial or loosely colonial species.…”

The signaling function of plumage characteristics in female tree swallows and implications for reproductive success and life-history decisions.

“…Many reproductively mature individuals do not breed and are instead "floaters" within the population. Floaters may exist in a population for several reasons (Penteriani et al 2011). One such reason is that they are competitively excluded by conspecifics from breeding (Stutchbury and Robertson 1985;Penteriani et al 2011).…”

More than meets the eye: importance of recognizing life history and population structure in monitoring populations

“…Second, it is fairly easy to monitor individuals during their reproductive cycle, particularly those that initiate, maintain and defend territories and/or nests, or are conspicuous for other reasons, for example, mate attraction. However, by focusing attention only on the breeding population, researchers may neglect an important demographic component influencing species or population trajectory (Penteriani, Ferrer & Delgado, 2011). In species where individuals are long-lived and either require multiple years to achieve reproductive maturity or breeding territories and nest sites are limited, sub-adults or nonterritorial 'floaters' may reside elsewhere geographically, away from breeding individuals and therefore, undocumented during census work.…”

“…Accurate appraisal of population size, including nonbreeding individuals, however, is crucial for conservation planning (Hunt, 1998;Newton, 1998;Penteriani et al, 2011), and coupled with finite resources for conservation, researchers are often limited by their ability to monitor an entire population to assess overall population stability. Rudnick et al (2005Rudnick et al ( , 2008 provided a relatively simple approach using non-invasive 'genetic tags' to assess population size, assuming that the species under study possess behavior where non-territorial individuals roost communally allowing systematic tissue collection.…”