The role of dispersal in range change by birds

Lead Research Organisation: University of York
Department Name: Biology


Dispersal is arguably the poorest understood component of demography, yet understanding it is key to answering important ecological questions: how fast will species respond to changing climates? How well are sub-populations connected? How long will invasive species take to reach a new site? This project makes use of one of the most comprehensive datasets on animal movement available to develop a new understanding of dispersal processes in the UK's fragmented landscape.

This project will use Reed warblers, a common migrant bird species found in reed beds across southern and central England. The British Trust for Ornithology (CASE partner on this project) has large dataset of movement between breeding seasons (c. 3000 individual movements) generated from citizen science. Using the extensive reed warbler dataset, combined with fieldwork on fine-scale movements currently undertaken by the CASE partner, the student will develop and test statistical methods to characterise dispersal that can then be applied to a wide range of species with more limited recovery datasets. The project has three components:

(1) a spatio-temporally explicit demographic model of reed warbler range change. This component will apply state of the art statistical and theoretical models to the existing BTO datasets to explore whether recent range change is driven by changes in dispersal or by changes in breeding success of survival.

(2) Fieldwork will be undertaken as part of ongoing research by BTO. A population of individually marked reed warblers has been established and the fine-scale movements of marked birds between breeding season is being monitored within a large reed bed. This studentship will enable expansion of the fieldwork to neighbouring breeding areas, with fieldwork focussing on mapping all reed warbler territories within 20km of the primary field site and identifying all individually marked birds outside the core area. These data will be combined with the larger scale existing data to ensure the student has a full understanding of dispersal at a range of spatial scales: it is just as important to know how many individuals move nowhere as how many move long distances.

(3) The final stage of the project will involve broadening the scope to multiple species. Using the insights gained from parts one and two, appropriate dispersal models will be selected and applied to the wider BTO ringing dataset. This component of the project will not only enable more species to be incorporated, but will allow the student to assess whether dispersal behaviour in changing in many species may be seen as a consequence of global change.

The information gathered during this project will be useful to governmental and non-governmental organisations working to develop spatial conservation plans for England, as well as proving useful information about where new nature areas (such as those created by biodiversity offsetting) may be most effectively sited to ensure species can move and colonise them,


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Description Species' geographical distributions are changing under global environmental change. To be able to adequately conserve biodiversity, we need to be able to understand, and even predict, how species will change their ranges in the future. I sought to understand, for a species with very rich data, the mechanisms underlying its recent range expansion in Britain. My study species (reed warbler, a small passerine bird) did not keep pace with its climate space during the range expansion, because young individuals did not disperse far enough. This is surprising for an apparently highly dispersive species in a region where climate change is progressing relatively slowly. Additionally, reed warbler occupancy at a location was better predicted by the temperature of the current year than of the previous year. This suggests that when environmental change is rapid the range limit is set up by dispersal limitation, and when environmental change is slow the range limit is set up by a decision not to settle where the temperature is too low. This demonstrates that we should expect species' range limits to be dynamically generated by multiple causes over time. I found no evidence that the range limit was caused by deaths exceeding births outside of the range, but it was not possible to estimate all aspects of reed warbler's productivity. An element of productivity increased during the range expansion, particularly in the newly colonised area, and was positively related to temperature. Therefore although the range expansion is explicable by reed warbler occupying newly climatically available range, the rate of range expansion itself may have additionally been boosted by climate change.
Exploitation Route I was able to describe in unusual detail the causes of range limitation and expansion in one species. By applying the modelling framework I used to a variety of species, it may be possible to ascertain generalities about causes of range dynamics across species. This might assist in improving predictive models of range expansion.
Sectors Environment

Description Talk (Skomer) 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact 30 min talk given generating questions and discussion afterwards.
Year(s) Of Engagement Activity 2019