Sean Jellesmark

I did my Bachelor degree in Natural Resources at the University of Copenhagen - Faculty of Science. Here I worked with quantifying the effect sociodemographic variables have on nature management and hunting preferences among Danish hunters. My Master thesis was done on the same faculty in collaboration with the Mara Conservancy in Kenya. Field studies were conducted in the Maasai Mara - northern Serengeti ecosystem and used poaching-related data collected during anti-poaching field patrols. The thesis investigated spatiotemporal bushmeat poaching patterns in order to optimize future patrolling effort and identify differences in poaching magnitude between adjacently located regions. Research findings were utilized to identify where and when improved or altered patrolling would benefit but also to emphasize the need for regional-specific political/community solutions to secure future wildlife.

PhD project [completed]: Measuring the impact of conservation on species' populations

The global biodiversity crisis has sparked a rise in conservation actions. However, the impact of conservation actions on species’ populations is often not evaluated. In particular, studies of the impact of large-scale conservation, such as area protection or national legislation aimed at safeguarding biodiversity, on population trends remain poorly represented in the scientific literature. The resulting limited knowledge of conservation effectiveness potentially hinders effective evidence-based decision making and leads to suboptimal conservation outcomes.

Here, I collated longitudinal records of vertebrate abundance, conservation interventions and ancillary information to measure the impact of conservation on species’ populations across different spatial and temporal scales. Specifically, I estimated the impact of lowland wet grassland reserves on breeding trends of wading birds in the United Kingdom by creating counterfactual reserve trends from national monitoring records collected by volunteers. This demonstrates that lowland wet grassland reserves have a positive impact on targeted species of wading birds.

To understand the drivers of breeding abundance within these reserves, I combined local management records with climatic variables and breeding counts and use a Bayesian mixed modelling framework to estimate the association between conservation actions, site-specific conditions and annual breeding abundance for four wading bird species. The resulting estimates show that breeding abundance associates with different factors for the four species and provides new information on conservation effectiveness that can be used to inform local reserve management.

Last, I explored the impact of conservation actions on trends in vertebrate populations worldwide. I categorized conservation actions for more than 26,000 populations, create counterfactual population indices representing how populations may have developed in the absence of conservation, calculate the impact of conservation on a global population index, and estimate how specific conservation actions relate to population changes. I showed that conservation benefits targeted vertebrate populations, that in the absence of conservation, a global index of vertebrate abundance could have declined in addition to what is currently observed and that, in particular, conservation through species and land & water management has a positive impact on targeted populations.

The methods developed and applied in this thesis demonstrate how to estimate the impact of conservation actions on species’ populations. This work also highlights the potential of longitudinal abundance records for evaluating conservation impact and emphasizes the importance of large-scale monitoring programmes.


Jellesmark, S., Ausden, M., Blackburn, T.M., Gregory, R.D., Hoffmann, M., Massemino, D., McRae, L., Visconti, P. (2021) A counterfactual approach to measure the impact of wet grassland conservation on UK breeding bird populations. Conservation Biology 35, 1575-1585. Access Repository

Jellesmark, S., Ausden, M., Blackburn, T.M., Hoffmann, M., McRae, L., Visconti P. & Gregory, R.D. (2023) The effect of conservation interventions on the abundance of breeding waders within nature reserves in the United Kingdom. Ibis, 165, 69-81. Access repository

Jellesmark, S. (2022) Measuring the impact of conservation on species’ populations. PhD Thesis. University College of London, London, UK. → Open Access Repository

Academic Host

University College London
London, UK
Tim Blackburn
Richard Gregory


Zoological Society of London
London, UK
Mike Hoffmann
Robin Freeman
Louise McRae
Piero Visconti Collaborator