UVM Theses and Dissertations
Format:
Print
Author:
Cline, Mason
Dept./Program:
Natural Resources
Year:
2010
Degree:
MS
Abstract:
Breeding dispersal holds consequences for individuals, populations, and species. Despite its importance, knowledge of breeding dispersal remains limited, especially for small migratory songbirds. I studied breeding dispersal patterns in the black-throated blue warbler (Dendroica caerulescens) at the Hubbard Brook Experimental Forest in central New Hampshire, USA. I analyzed,426 breeding dispersal events of banded adults from 1998 to 2008. Uncorrected between-year return rates were 58% for males and 30% for females. Mean breeding dispersal distance for females (mean = 235 m +/-23 SE) was significantly greater than that of males (mean = 151 m +/-11 SE). Older males moved significantly shorter distances than younger males; however there was no difference between age classes for females.
Males occupying territories with fewer deciduous leaves dispersed significantly greater distances than males who occupied territories with a greater number of deciduous leaves; a pattern not found for females. Females exhibited a significant trend of breeding dispersal distance decreasing with increased numbers of young fledged. However, this pattern was not found for males. These results suggest that the costs and benefits associated with breeding dispersal differ between males and females and for birds of different age classes. Additionally, individuals of different sex and age may use different cues when determining whether to disperse or to remain site faithful, likely reflecting different selective pressures.
Breeding dispersal movement can influence the number offspring an individual will produce, thus it can entail fitness consequences. I examined whether BTBW offspring production following breeding dispersal was related to dispersal distance. Analysis indicated that the difference in number of offspring fledged before breeding dispersal and number fledged subsequent to breeding dispersal (i.e., delta offspring fledged, hereafter DOF) was most influenced by year, but not in any consistent direction; some years were good for reproduction while others were poor. For females, reproductive consequences associated with breeding dispersal were unclear. For males, however, a correlation between breeding dispersal distance and DOF approached significance. Males that moved shorter breeding dispersal distances tended to fledge more offspring compared to the year prior to dispersal. Fitness consequences of breeding dispersal for D. caerulescens were equivocal. Possible explanations include breeding dispersal's inability to overcome the effect of predation, insufficient sample size, or that breeding dispersal has no associated fitness consequences.
Males occupying territories with fewer deciduous leaves dispersed significantly greater distances than males who occupied territories with a greater number of deciduous leaves; a pattern not found for females. Females exhibited a significant trend of breeding dispersal distance decreasing with increased numbers of young fledged. However, this pattern was not found for males. These results suggest that the costs and benefits associated with breeding dispersal differ between males and females and for birds of different age classes. Additionally, individuals of different sex and age may use different cues when determining whether to disperse or to remain site faithful, likely reflecting different selective pressures.
Breeding dispersal movement can influence the number offspring an individual will produce, thus it can entail fitness consequences. I examined whether BTBW offspring production following breeding dispersal was related to dispersal distance. Analysis indicated that the difference in number of offspring fledged before breeding dispersal and number fledged subsequent to breeding dispersal (i.e., delta offspring fledged, hereafter DOF) was most influenced by year, but not in any consistent direction; some years were good for reproduction while others were poor. For females, reproductive consequences associated with breeding dispersal were unclear. For males, however, a correlation between breeding dispersal distance and DOF approached significance. Males that moved shorter breeding dispersal distances tended to fledge more offspring compared to the year prior to dispersal. Fitness consequences of breeding dispersal for D. caerulescens were equivocal. Possible explanations include breeding dispersal's inability to overcome the effect of predation, insufficient sample size, or that breeding dispersal has no associated fitness consequences.