Analysis of photo-id data allowing for missed matches and individuals identified from opposite sides.

1. In many species, photo-identification could be used as an alternative to artificial marking to provide data on demographic parameters. However, unless the population is very small or fragmented, software may be required to pre-screen and reject most image pairs as potential matches. 2. Depending on the species and method used to obtain images, currently available software may falsely reject some matches. We estimate the false rejection rate (FRR) of the ExtractCompare (EC) program when used to pre-screen images of female grey seals. Filtering images manually to reduce the FRR involves subjective assessment of image quality, reduces the amount of data available and may bias the results in favour of relatively well-marked individuals. 3. The data may contain individuals identified only from the left side or the right side, as well as individuals identified from both sides. 4. Missed matches resulting from false rejections by pre-screening software and/or inclusion of individuals identified only from opposite sides cause some individuals to generate multiple encounter histories. 5. We describe an open population model for data of this type which, given a measured risk of missing a match between a randomly selected pair of images of the same individual, provides maximum likelihood (ML) estimates of initial population size, survival/emigration and immigration/recruitment by calculating the expected frequency of any encounter history that could be generated. 6. As a case study for the method, we used EC to pre-screen photographs of female grey seals on a breeding colony and generate encounter histories over five successive seasons. Allowing for the measured FRR, we calculated ML estimates for comparison with estimates from previous studies. 7. We also used the model with encounter histories simulated using the same FRR to give the same mixture of left side, right side and both sides histories and derived ML estimates for comparison with the values used to drive the simulation. 8. With FRR set at up to 33%, the method gave estimates of the abundance and survival parameters used in the simulation model that were biased by at most 4·7% up and 3% down, respectively. The results of the grey seal case study were consistent with previous estimates of apparent survival and trends in abundance

Estimating bird density using passive acoustic monitoring: a review of methods and suggestions for further research

Passive acoustic monitoring is a non-invasive tool for automated wildlife monitoring. This technique has several advantages and addresses many of the biases related to traditional field surveys. However, locating animal sounds using autonomous recording units (ARUs) can be technically challenging and therefore ARUs have traditionally been little employed to estimate animal density. Nonetheless, several approaches have been proposed in recent years to carry out acoustic-based bird density estimations. We conducted a literature review of studies that used ARUs for estimating bird densities or bird abundances in order to describe the applications and improve future monitoring programmes. We detected a growing interest in the use of ARUs for estimating bird density in the last 6 years (2014–19), with a total of 31 articles assessing the topic. The most common approach was to estimate the relationship between the number of vocalizations per recording time with bird density or bird abundance estimated in the field (61%). In 26 studies (79%), bird estimates obtained by human surveyors agreed with those obtained using ARUs. Some approaches have proven able to reduce biases in acoustic surveys, such as considering imperfect detection (spatially explicit capture–recapture, using microphone arrays), applying paired acoustic sampling to control for different sampling radius between humans and ARUs, or including relative sound level measurements that allow researchers to estimate bird distance to recorder. However, several studies did not include any covariates to reduce existing biases and some did not estimate the sampling radius of the recorder, which may hamper future comparisons between human and ARU surveys. Future studies should include a measurement of the sampling radius of the recorder employed to be able to obtain density estimations using ARUs. Finally, we provide some guidelines to improve the applicability of ARUs to infer bird population estimates in future studies.The authors wish to thank several projects that have financed their studies in bioacoustics. Special thanks to the Research and Conservation Program of Zoo de Barcelona, within the project ‘Nuevas tecnologías para viejos trabajos. Uso de grabadores automáticos para la detección y censo de especies raras y amenazadas. El caso de la alondra ricotí en Lleida y otras poblaciones pequeñas’; the LIFE-Ricotí-project (LIFE15-NAT-ES-000802), granted by the European Commission; and the project BBVA-Ricotí granted by the BBVA Foundation. This is a contribution to the Excellence Network REMEDINAL TE-CM (P2018/EMT- 4338), supported by Comunidad de Madrid

Design and field methods for sighting surveys of cetaceans in coastal and riverine habitats

1. Dolphins and porpoises in coastal and/or riverine habitats face serious conservation threats, yet surveys of their abundance are often especially difficult due to the challenges imposed by the habitats. Because many of these species occur in developing countries, lack of resources imposes a further set of challenges. 2. We offer advice on designing and conducting line-transect surveys with a focus on sound, practical, design rather than analytical sophistication, and we attempt, where possible, to offer simple, inexpensive solutions. 3. We guide the reader through the questions of what kind of survey should be done, whether by boat or aircraft, and we discuss ways to avoid bias and increase precision. 4. Our treatment of field methods focuses especially on robust, but low-cost, approaches. We provide two case studies to illustrate the implementation of these ideas

Consequences of maternal size for reproductive expenditure and pupping success of grey seals at North Rona, Scotland

1. The reproductive performance of individually marked mothers aged between 4 and 36 years breeding at the established grey seal colony of North Rona, Scotland was studied. Natality rate was between 0.805 and 0.975 for these females during 1979-95 and 57% of females produced 74% of the pups born. Mothers pupped successfully on N. Rona after absences of up to 5 years.2. The average maternal postpartum mass (MPPM) of mothers was 190 +/- 23 (SD) kg. larger than had been recorded from this colony previously. Although annual mean MPPM increased during the study, there were increases and decreases in individuals MPPM between years.3. Pup mass at birth and pup growth rare were related to MPPM and date of parturition. No evidence of differential postpartum expenditure in the sexes was found. Relative pup birth mass decreased with MPPM but relative pup weaning mass remained constant over the range of MPPM.4. Maternal mass expenditure during lactation averaged 39% of MPPM, and the consequences for MPPM in the year following either high or low relative expenditure were inversely related to relative expenditure in the first year. However, mothers increased their mass after skipping breeding in a year.5. General Linear Models and REML analyses indicated that expenditures were significantly different between mothers when other variables and Factors had been taken into account. In general, maternal expenditure was greater for animals of larger masses and duration of lactation, but corrected maternal expenditure of longer individuals was less than expected. Pup mass at weaning was influenced by mother's identity and year and there was evidence that individual mothers which were longer for their weight raised smaller pups.6. The life history consequences of reproductive expenditure in any year appeared in subsequent breeding patterns. The cost of breeding for larger animals and larger expenditures was indicated by lower pupping success rates in years following births and skipped breeding years.</p