Evolving dispersal: where to go next?
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Journal Article↗
Biomedical subjects
JR Belthoff
Publications and source records attributed to JR Belthoff.
Effects of social status on the dispersal behaviour of juvenile western screech-owls.
Variation in timing and distance of dispersal movements of juvenile birds may result from differences in competitive ability. Dispersal by low-ranking juveniles may be initiated before dominants if the latter force subordinate siblings from natal areas. Conversely, when vacant territories are limited and are acquired on a first-come first-served basis, selection could operate on young to disperse as early as possible. In this case, dominant individuals with priority of access to resources in the natal area will mature more quickly and are expected to disperse first. If costs of dispersal increase with dispersal distance, dominant juveniles are expected to disperse shorter distances. Alternately, if there are advantages to long-distance dispersal, then dominants, which are in better condition, should disperse further than subordinates. We examined effects of social rank on the timing and distance (to wintering area) of dispersal movements by juvenile western screech-owls, Otus kennicottii, in southwestern Idaho. Based on observations of aggressive interactions made using video cameras attached to nestboxes, we assigned dominance ranks to nestlings within nine broods. We radiotracked young throughout the postfledging period to determine order of dispersal, and we located them after leaving their natal areas to determine distances to apparent overwintering areas. In six of seven broods, for which dispersal information could be recorded, the most dominant juvenile dispersed first. Moreover, in five of seven broods, the least dominant individual was the last individual to disperse, and the order of dispersal matched the dominance hierarchy in four of seven broods. In contrast, social status did not affect postfledging dispersal distance. We conclude that social dominance relationships influenced the timing of dispersal in juvenile western screech-owls but not distance travelled to overwinter sites. Copyright 1999 The Association for the Study of Animal Behaviour.
Journal Article↗
Corticosterone, body condition and locomotor activity: a model for dispersal in screech-owls
A model that explains natal dispersal in resident screech-owls is presented and examined. The model is based on interactions among hormonal changes, body condition and social stimuli. It predicts that corticosterone, an adrenal glucocorticoid known to stimulate locomotor and foraging activity, increases in blood plasma prior to dispersal through a combination of endogenous and exogenous events. This mediates the locomotor activity that underlies dispersal behaviour. Juveniles in good body condition (i.e. those with sufficient fat reserves) will disperse when corticosterone increases. Birds in poor body condition will not, but they will increase their foraging activity under the influence of corticosterone. Dispersal of siblings will reduce aggression and/or competition for food, enabling the remaining juveniles to improve their body condition and disperse. Initial studies on screech-owls, Otus asio and O. kennicottii, have produced results that are generally consistent with the model. For example, captive juvenile screech-owls showed increased locomotor activity in the weeks leading up to the time when free-living juveniles are dispersing, and activity levels declined thereafter. Peaks in corticosterone corresponded with periods of high locomotor activity (i.e. at the time of dispersal) in captive owls. Finally, field studies indicate that dominant juveniles, which are presumably in better physical condition, initiated dispersal before their more subordinate siblings. Copyright 1998 The Association for the Study of Animal Behaviour.
Journal Article↗