A new approach to estimate fecundity rate from inter‐birth intervals

Abstract

Abstract. Accurate estimates of fecundity rate are key to population assessments and effectively direct conservation efforts. We present a new approach to estimate fecundity rate based on the probability of a female giving birth, conditional on a previous birth t years ago, from which an expected inter-birth interval (IBI) can be estimated. We use generalized linear mixed-effects models to account for individual and temporal variability and apply the approach to individual reproductive histories of bottlenose dolphins (Tursiops truncatus) from the east coast of Scotland. We estimate a fecundity rate of 0.222 (95% CI = 0.218-0.253) and an expected IBI of 4.49 yr (95% CI = 3.94-4.93 yr). We use simulated data samples to show that the approach produces estimates with a minimum bias of <3%. Simulations are also used to investigate the effect of the most common data-driven biases in the estimates of birth intervals and fecundity rate; we recommend longitudinal studies of at least 10 yr and capture probabilities of at least 0.3 when using this methodology. The approach may be modified to incorporate other parameters of interest and should be applicable to any population with comprehensive data on birth intervals.

Variations in age‐ and sex‐specific survival rates help explain population trend in a discrete marine mammal population

“…Individual dolphins were identified from high‐quality photographs (Wilson et al, ) based on unique markings in the dorsal fin (Würsig & Jefferson, ), and matched against a catalogue of previously identified bottlenose dolphins from the east coast of Scotland. Because bottlenose dolphin calves do not tend to have permanent marks that can be tracked across years, individuals in the first 3 years of life were aged and identified based on body size, skin coloration, presence of fetal folds and repeated association with a known adult dolphin (i.e., the mother; Grellier, Hammond, Wilson, Sanders‐Reed, & Thompson, ; Arso Civil, Cheney, Quick, Thompson, & Hammond, ). Capture histories of marked juveniles (at least 4 years of age) and adults (i.e., dolphins with distinctive long‐lasting nicks on the trailing edge of the dorsal fin) and of calves were constructed to model survival probabilities.…”

Decline in abundance and apparent survival rates of fin whales (Balaenoptera physalus) in the northern Gulf of St. Lawrence

“…In marine vertebrates, robust estimation of reproductive (birth) rates is available for several seabird, sea turtle and pinniped species, facilitated by the confinement to terrestrial birthing and breeding colonies (Cury et al, ; Pomeroy, Fedak, Rothery, & Anderson, ; Troëng & Rankin, ). In cetaceans, robust estimates of birth rates are more difficult to obtain and are limited to a few well studied populations (e.g., Arso Civil, Cheney, Quick, Thompson, & Hammond, ; Mann, Connor, Barre, & Heithaus, ; Rolland et al, ).…”

Joint estimation of survival and breeding probability in female dolphins and calves with uncertainty in state assignment

“…Adult female bottlenose dolphins invest heavily over several years to raise their offspring (Arso Civil, Cheney, Quick, Thompson, & Hammond, ), like other mammal species such as elephants (Lee, ) and chimpanzees (Van Lawick‐Goodall, ). Providing such intensive parental care may have an impact on the female's subsequent reproduction (cost of reproduction, Paterson, Rotella, Link, & Garrott, ), as well as other demographic traits (trade‐offs) such as survival, which is the predominant trait for long‐lived species.…”

“…Adult female bottlenose dolphins invest heavily over several years to raise their offspring (Arso Civil, Cheney, Quick, Thompson, & Hammond, 2017), like other mammal species such as elephants (Lee, 1987) and chimpanzees (Van Lawick-Goodall, 1968…”