Browsing by Subject "Birth intervals"

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Open Access
Life History Parameters and Social Associations of Female Bottlenose Dolphins (Tursiops Truncatus) in North Carolina, USA
(2008-04-25) Thayer, Victoria Graves
In this study, I describe the seasonality of reproduction in bottlenose dolphins by examining data from stranded animals, photographic surveys and focal follows. I examined inter-birth intervals from focal follows of known female dolphins. I found bottlenose dolphins that frequent the coastal waters of North Carolina to be comprised of at least two populations; one with a primarily spring birthing peak and a presumed second (or second and third) with two smaller birthing peaks in the fall and winter. These animals are reproducing at 2-3 year inter-birth intervals, which are shorter than bottlenose dolphin inter-birth intervals in the Moray Firth, Scotland, Shark Bay, Australia, or Sarasota Bay, FL. A decrease in reproductive intervals can indicate a density-dependent response to an anthropogenic disturbance or a natural change. Association patterns between and among these known females revealed relationships that have persisted for more than a decade. Most association patterns of the female dolphins in this area are long-term casual acquaintances which are evident in the fission-fusion grouping pattern, and individuals are not highly gregarious. Females appear to associate with most other females in the local area and do not form bands, as defined by researchers in Sarasota, FL (Wells et al. 1987). However, females do exhibit preferred associates, with whom they associate, regardless of reproductive state. Associations of females with young of the year were slightly stronger than associations between females with different aged calves, except for preferred associates. Future work will include genetic research on some of these known females, and continued study of the life and reproductive histories of these known females and their offspring.
Open Access
New Evidence on the Timing and Spacing of Births
(1985) Heckman, JJ; Hotz, VJ; Walker, JR
This is a progress report on an ongoing empirical study of the determinants of life cycle fertility. "The main objective of the early stage of [the] work is to codify the 'facts' in a coherent statistical framework that provides the duration data analogue of the conventional simultaneous equations model." After reviewing the relevant literature, the authors present an empirical analysis of data on fertility, marital status, and work histories for 570 Swedish women born between 1941 and 1945. The data are from a survey conducted by the Swedish Central Bureau of Statistics in 1981