Hiby L.,Conservation Research Ltd. |
Paterson W.D.,University of St. Andrews |
Redman P.,University of St. Andrews |
Watkins J.,University of St. Andrews |
And 2 more authors.
Methods in Ecology and Evolution | Year: 2013
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. 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. The data may contain individuals identified only from the left side or the right side, as well as individuals identified from both sides. 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. 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. 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. 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. 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. © 2012 British Ecological Society.
Cheung A.,University of Queensland |
Hiby L.,Conservation Research Ltd. |
Narendra A.,Australian National University
PLoS ONE | Year: 2012
Home is a special location for many animals, offering shelter from the elements, protection from predation, and a common place for gathering of the same species. Not surprisingly, many species have evolved efficient, robust homing strategies, which are used as part of each and every foraging journey. A basic strategy used by most animals is to take the shortest possible route home by accruing the net distances and directions travelled during foraging, a strategy well known as path integration. This strategy is part of the navigation toolbox of ants occupying different landscapes. However, when there is a visual discrepancy between test and training conditions, the distance travelled by animals relying on the path integrator varies dramatically between species: from 90% of the home vector to an absolute distance of only 50 cm. We here ask what the theoretically optimal balance between PI-driven and landmark-driven navigation should be. In combination with well-established results from optimal search theory, we show analytically that this fractional use of the home vector is an optimal homing strategy under a variety of circumstances. Assuming there is a familiar route that an ant recognizes, theoretically optimal search should always begin at some fraction of the home vector, depending on the region of familiarity. These results are shown to be largely independent of the search algorithm used. Ant species from different habitats appear to have optimized their navigation strategy based on the availability and nature of navigational information content in their environment. © 2012 Cheung et al.
Hammond P.S.,University of St. Andrews |
Macleod K.,University of St. Andrews |
Berggren P.,University of Stockholm |
Borchers D.L.,University of St. Andrews |
And 26 more authors.
Biological Conservation | Year: 2013
The European Union (EU) Habitats Directive requires Member States to monitor and maintain at favourable conservation status those species identified to be in need of protection, including all cetaceans. In July 2005 we surveyed the entire EU Atlantic continental shelf to generate robust estimates of abundance for harbour porpoise and other cetacean species. The survey used line transect sampling methods and purpose built data collection equipment designed to minimise bias in estimates of abundance. Shipboard transects covered 19,725km in sea conditions ≤Beaufort 4 in an area of 1,005,743km2. Aerial transects covered 15,802km in good/moderate conditions (≤Beaufort 3) in an area of 364,371km2. Thirteen cetacean species were recorded; abundance was estimated for harbour porpoise (375,358; CV=0.197), bottlenose dolphin (16,485; CV=0.422), white-beaked dolphin (16,536; CV=0.303), short-beaked common dolphin (56,221; CV=0.234) and minke whale (18,958; CV=0.347). Abundance in 2005 was similar to that estimated in July 1994 for harbour porpoise, white-beaked dolphin and minke whale in a comparable area. However, model-based density surfaces showed a marked difference in harbour porpoise distribution between 1994 and 2005. Our results allow EU Member States to discharge their responsibilities under the Habitats Directive and inform other international organisations concerning the assessment of conservation status of cetaceans and the impact of bycatch at a large spatial scale. The lack of evidence for a change in harbour porpoise abundance in EU waters as a whole does not exclude the possibility of an impact of bycatch in some areas. Monitoring bycatch and estimation of abundance continue to be essential. © 2013 The Authors.
Hasler B.,Veterinary Epidemiology Economics and Public Health Group |
Hasler B.,Leverhulme Center for Integrative Research on Agriculture and Health |
Hiby E.,Conservation Research Ltd. |
Gilbert W.,Veterinary Epidemiology Economics and Public Health Group |
And 4 more authors.
PLoS Neglected Tropical Diseases | Year: 2014
Background:One Health addresses complex challenges to promote the health of all species and the environment by integrating relevant sciences at systems level. Its aication to zoonotic diseases is recommended, but few coherent frameworks exist that combine aoaches from multiple disciplines. Rabies requires an interdisciplinary aoach for effective and efficient management.Methodology/Principal Findings:A framework is proposed to assess the value of rabies interventions holistically. The economic assessment compares additional monetary and non-monetary costs and benefits of an intervention taking into account epidemiological, animal welfare, societal impact and cost data. It is complemented by an ethical assessment. The framework is aied to Colombo City, Sri Lanka, where modified dog rabies intervention measures were implemented in 2007. The two options included for analysis were the control measures in place until 2006 (“baseline scenario”) and the new comprehensive intervention measures (“intervention”) for a four-year duration. Differences in control cost; monetary human health costs after exposure; Disability-Adjusted Life Years (DALYs) lost due to human rabies deaths and the psychological burden following a bite; negative impact on animal welfare; epidemiological indicators; social acceptance of dogs; and ethical considerations were estimated using a mixed method aoach including primary and secondary data. Over the four years analysed, the intervention cost US $1.03 million more than the baseline scenario in 2011 prices (adjusted for inflation) and caused a reduction in dog rabies cases; 738 DALYs averted; an increase in acceptability among non-dog owners; a perception of positive changes in society including a decrease in the number of roaming dogs; and a net reduction in the impact on animal welfare from intermediate-high to low-intermediate.Conclusions:The findings illustrate the multiple outcomes relevant to stakeholders and allow greater understanding of the value of the implemented rabies control measures, thereby providing a solid foundation for informed decision-making and sustainable control. © 2014 Häesler et al.