Maximizing the rigor and reproducibility of citizen science in ecological research

PLOS ONE is organizing a Twitter chat on citizen science methodologies on 2nd April- see details below

Citizen science (CS) encompasses a broad range of research methodologies that involve public participation for data collection, transcription or analysis. Applications of CS have been found in many disciplines, but ecology has consistently been at the forefront. While some CS-based ecological monitoring schemes- such as the UK Butterfly Monitoring Scheme, established in 1976- have been running for decades, the popularity of CS has grown rapidly in more recent years. A wide range of projects based on CS methodologies are now being undertaken around the world, at local, national and international scales. The value of volunteer participation in activities ranging from transect-based species monitoring (Wepprich et al., 2019) and collection of biological specimens for lab-based analysis (Larson et al., 2020; Rasmussen et al., 2020) to crowdsourcing of creative thinking for study design (Can et al., 2017), has been repeatedly demonstrated.  Studies have also highlighted the particular utility of CS methodologies in supporting long-term ecological monitoring in resource-limited contexts, including in economically developing countries (Gouraguine et al., 2019). Meanwhile, examples of the real-world impact of CS research are abundant, both in specific ecological interventions and the wider political discourse. For instance, the influential UK State of Nature 2019 report, likely to be a key source of evidence for future environmental legislation, cites the outcomes of a wealth of CS projects.

With the expansion of CS research, there is lively debate about how to maximise rigor and reproducibility in different types of CS methodologies. One of the crucial aspects of a successful CS study is an appropriately designed protocol, which features a realistic degree of complexity and accounts for the specific challenges of handling CS-derived data. An example of this is provided by a recent comprehensive report of the design, launch and assessment of the UK National Plant Monitoring Scheme (Pescott et al., 2019). Pre-testing of protocols prior to project launch can provide confidence in the robustness of the study design. When designing a CS study, it is also important to understand volunteer motivation and ensure that this is appropriately matched with the nature of the task to be performed (Lyons & Zhang, 2019). Some CS studies utilize narrower demographic groups to meet the required level of motivation and understanding, such as amateur naturalists (Hallmann et al., 2017) or students who are following a course in a related topic (Chiovitti et al., 2019). Depending on the type of study, researchers may also plan to support CS volunteers with training or technological aids, increasingly in the form of mobile apps (Ožana et al., 2019; Appenfeller et al., 2020).



A certain amount of error, either random or systematic, is likely to be introduced by the collection of data by CS volunteers, and study designs must account for this. The level of error can be reduced by allowing volunteers to provide clarifying metadata or to register uncertainty (Torre et al., 2019), or using incentives to reduce sampling bias (Callaghan et al., 2019), but researchers should also ensure that they have means to assess the accuracy of contributed data (Falk et al., 2019; Gibson et al., 2019). Much ecological research is based on large public databases of volunteer-contributed records of species distributions, phenological events and other observational data (e.g. Siljamo et al., 2020). There is an active discussion in the ecological research community about how to maximize the reliability and utility of such data (Ball-Damerow et al., 2019).

The particular considerations that have to be made in the design, execution and evaluation of CS studies has led to calls for dedicated standards and guidelines for CS research. Of course, any such tools must strike the balance between promoting appropriate levels of standardization and allowing the flexibility required for applications of CS methodologies across diverse settings and research questions. Whilst some progress has been made towards this goal, maintaining an open and constructive dialogue among CS practitioners and other stakeholders remains critical to ensure that researchers, volunteers and society are able to realize the full potential of CS.

To foster discussion of these important issues, PLOS ONE (@plosone) will be moderating a Twitter chat on citizen science methodologies on Thursday 2nd April starting at 4pm BST (8am PDT, 11am EDT, 5pm CET). This is a chance for the CS community to share perspectives, experiences and suggestions for best practice. We’ll aim to cover the following questions (and more!):

  • How far can methods in CS projects be standardized?
  • What steps should be taken to maximize CS data quality?
  • Is there a need for clearer guidelines for the design and execution of CS studies?
  • How should credit for data collection be apportioned?

You can take part by using the hashtag #citscichat– we hope to see you there!



Appenfeller LR, Lloyd S, Szendrei Z (2020) Citizen science improves our understanding of the impact of soil management on wild pollinator abundance in agroecosystems. PLoS ONE 15(3): e0230007.

Ball-Damerow JE, Brenskelle L, Barve N, Soltis PS, Sierwald P, Bieler R, et al. (2019) Research applications of primary biodiversity databases in the digital age. PLoS ONE 14(9): e0215794.

Callaghan CT, Rowley JJL, Cornwell WK, Poore AGB, Major RE (2019) Improving big citizen science data: Moving beyond haphazard sampling. PLoS Biol 17(6): e3000357.

Can ÖE, D’Cruze N, Balaskas M, Macdonald DW (2017) Scientific crowdsourcing in wildlife research and conservation: Tigers (Panthera tigris) as a case study. PLoS Biol 15(3): e2001001.

Chiovitti A, Thorpe F, Gorman C, Cuxson JL, Robevska G, Szwed C, et al. (2019) A citizen science model for implementing statewide educational DNA barcoding. PLoS ONE 14(1): e0208604.

Falk S, Foster G, Comont R, Conroy J, Bostock H, Salisbury A, et al. (2019) Evaluating the ability of citizen scientists to identify bumblebee (Bombus) species. PLoS ONE 14(6): e0218614.

Gibson KJ, Streich MK, Topping TS, Stunz GW (2019) Utility of citizen science data: A case study in land-based shark fishing. PLoS ONE 14(12): e0226782.

Gouraguine A, Moranta J, Ruiz-Frau A, Hinz H, Reñones O, Ferse SCA, et al. (2019) Citizen science in data and resource-limited areas: A tool to detect long-term ecosystem changes. PLoS ONE 14(1): e0210007.

Hallmann CA, Sorg M, Jongejans E, Siepel H, Hofland N, Schwan H, et al. (2017) More than 75 percent decline over 27 years in total flying insect biomass in protected areas. PLoS ONE 12(10): e0185809.

Larson RN, Brown JL, Karels T, Riley SPD (2020) Effects of urbanization on resource use and individual specialization in coyotes (Canis latrans) in southern California. PLoS ONE 15(2): e0228881.

Lyons E, Zhang L (2019) Trade-offs in motivating volunteer effort: Experimental evidence on voluntary contributions to science. PLoS ONE 14(11): e0224946.

Ožana S, Burda M, Hykel M, Malina M, Prášek M, Bárta D, et al. (2019) Dragonfly Hunter CZ: Mobile application for biological species recognition in citizen science. PLoS ONE 14(1): e0210370.

Pescott OL, Walker KJ, Harris F, New H, Cheffings CM, Newton N, et al. (2019) The design, launch and assessment of a new volunteer-based plant monitoring scheme for the United Kingdom. PLoS ONE 14(4): e0215891.

Rasmussen SL, Nielsen JL, Jones OR, Berg TB, Pertoldi C (2020) Genetic structure of the European hedgehog (Erinaceus europaeus) in Denmark. PLoS ONE 15(1): e0227205.

Siljamo P, Ashbrook K, Comont RF, Skjøth CA (2020) Do atmospheric events explain the arrival of an invasive ladybird (Harmonia axyridis) in the UK? PLoS ONE 15(1): e0219335.

Torre M, Nakayama S, Tolbert TJ, Porfiri M (2019) Producing knowledge by admitting ignorance: Enhancing data quality through an “I don’t know” option in citizen science. PLoS ONE 14(2): e0211907.

Wepprich T, Adrion JR, Ries L, Wiedmann J, Haddad NM (2019) Butterfly abundance declines over 20 years of systematic monitoring in Ohio, USA. PLoS ONE 14(7): e0216270.


All images used under Pixabay licence.

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Urban Ecology: where the wild meets the city

Urban ecosystems are expanding around the world as people migrate to cities and the human population continues to grow. What happens to other species as these urban ecosystems expand, and how species live and interact

Summertime Fun in the Sun

99-Bar Harbor

We are well into the summer months so discard those winter doldrums and get active! To help you get in the mood, we’ve assembled a variety of outdoorsy studies from around the world:

With the advent of digital cameras and camera phones, we have all become amateur photographers. Picturesque peaks and beautiful beaches can be captured with the press of a button, tagged, and shared with others instantly via social media. Researchers, like the ones in a recent PLOS ONE study, can now use this user-generated data—these geo-tagged photographs—to find striking vistas and examine how they correlate with environmental factors, such as soil carbon and farming. These researchers used photos of Cornwall, England, uploaded to Panaramio and plotted them on a map to see where users were taking pictures. Photographs that were clustered together indicated that the area was valued for its aesthetic or visual beauty. As you might think, most clusters were found in beaches and sparsely populated coastal towns. Their findings also suggest that agricultural areas were negatively correlated with aesthetic value.

When looking for your next vacation destination, find somewhere picturesque with clean water. In the US, researchers have studied the effect that water quality may have on recreational activities in the Puget Sound. To do so, they used data from the Washington State Parks to determine how many people entered, camped, or moored in the Puget Sound, starting from the late 1980s to the present day. They then plotted this against fluctuations in Enterococcus, a type of bacteria associated with urinary tract infections and meningitis, in the water. Their findings indicate that an increase of Enterococcus corresponded to a recorded decrease in visitation rates.

Feel like getting involved in the scientific process? You can spend your summer taking part in the citizen science movement and enjoy the great outdoors at the same time. Your contributions may help someone with their research! For example, take this recent PLOS ONE study that uses observational data collected by a Turkish ornithological society. The researchers took recorded sightings of 29 songbird species and combined it with climate data (rainfall and temperature) to develop a model predicting how songbirds may be affected by climate change. The model helped them predict the birds’ distribution in 2020, 2050, and 2080.

Fun can also be found closer to home. For those of you with little ones, there is research to indicate that children’s sedentary behavior can be reduced using a few simple methods. The researchers of this study suggest decreasing the amount of time parents watch TV on the weekend, and instead recommend participating in boys’ sports and encouraging girls to play outside. Their suggestions are based on data collected from participants’ accelerometers over the course of a year. Learn more about this study here.


Casalegno S, Inger R, DeSilvey C, Gaston KJ (2013) Spatial Covariance between Aesthetic Value & Other Ecosystem Services. PLoS ONE 8(6): e68437. doi:10.1371/journal.pone.0068437

Kreitler J, Papenfus M, Byrd K, Labiosa W (2013) Interacting Coastal Based Ecosystem Services: Recreation and Water Quality in Puget Sound, WA. PLoS ONE 8(2): e56670. doi:10.1371/journal.pone.0056670

Abolafya M, Onmu? O, ?ekercio?lu ÇH, Bilgin R (2013) Using Citizen Science Data to Model the Distributions of Common Songbirds of Turkey Under Different Global Climatic Change Scenarios. PLoS ONE 8(7): e68037. doi:10.1371/journal.pone.0068037

Atkin AJ, Corder K, Ekelund U, Wijndaele K, Griffin SJ, et al. (2013) Determinants of Change in Children’s Sedentary Time. PLoS ONE 8(6): e67627. doi:10.1371/journal.pone.0067627

Image:  99-Bar Harbor by Robert & Pam.

It’s for the birds: Citizen science reveals shift in winter bird homes

western grebe 2

Just in time for summer solstice (the longest day of the year!), we bring you the heartwarming tale of a study that analyzed data collected about our feathery friends in the middle of winter. The Audobon Christmas Bird Count, a yearly bird census originating back in 1900, is conducted by bird-loving volunteers all over the Western Hemisphere who spot birds and record their sightings. It is also an example of what some call “citizen” or “crowd-sourced” science, and a newly published PLOS ONE article demonstrates how this scientific data, collected by the general public, can help researchers assess the conservation needs of an at-risk migratory bird, the western grebe.

Canadian researchers wanted to take a closer look at the bird population patterns of the grebe, a marine water bird that had recently been showing a worrying trend of drastic population declines in its winter home, ranging from the Pacific coast to California. In “Citizen Science Reveals an Extensive Shift in the Winter Distribution of Migratory Western Grebes,” researchers modeled a whoppin’ 36 years of collected bird count data from 163 “circles,” or designated diameters of land, mounting to a total of 2.5 million grebe observations.

So, what did they—and we, in this case—find? Thanks to decades of data collected by birdwatchers (1975-2010), researchers were able to show that western grebe populations along the northern Pacific coastal region decreased by about 95% over 36 years, but increased by over 300% in coastal California. Similar trends were observed for related bird species, suggesting that the winter habitat of the grebe has shifted south by ~ 900 km, to California, between 1980 and 2010.

western grebe 3

This is much better news than finding a concerning population decline that might prompt time-consuming and expensive conservation efforts. The researchers state that they aren’t yet sure of the reasons for this shift, but they suspect that the types of fish prey the grebes feed on may have also shifted in abundance between the two locations. All in all, this study demonstrates that wildlife data gathered by the general public (in any season, really) can result in meaningful, published scientific research that is useful to ecologists and conservationists alike.

Citation: Wilson S, Anderson EM, Wilson ASG, Bertram DF, Arcese P (2013) Citizen Science Reveals an Extensive Shift in the Winter Distribution of Migratory Western Grebes. PLoS ONE 8(6): e65408. doi:10.1371/journal.pone.0065408

Image Credits: Grebe photo by Mike Baird; map photo from article


A floral ‘map’ to nectar discourages bumblebee robbers

In the business of survival, the bright colors of blooming flowers mark a serious transaction. Their nectar, color and fragrances are all designed to attract pollinators to come hither and transfer pollen to help plants reproduce but occasionally, these plans go awry. Some bees choose to avoid the pollen and tunnel into flowers to steal nectar instead. A study published in PLOS ONE last week explains how plants deter these robbers by providing them a map to reach nectar more quickly. Author Anne Leonard explains their results:

How did you become interested in studying floral guide patterns? 

I think many people are intrigued by the fact that bees see the patterns on flowers differently than we do. I was studying color learning in bumble bees, and as I looked through the literature I realized there were still many unanswered questions about how these patterns affect bees’ behavior. Living in Tucson, I started to photograph the dazzling variety of nectar guides on Sonoran desert wildflowers, slowing down many a hike in the process. Between all the reading and photography, I clearly had nectar guides on the brain.

Why do flowers have nectar guide patterns?

The patterns of nectar guides appear to be very attractive to many bee species. Bright colors, high color contrasts and star-like outlines could simply help a plant increase visits from pollinators. It’s even been suggested that these visual features might have evolved to mimic rewards, for example bright yellows and oranges might resemble protein-rich pollen to the insects. Secondly, plants that produce distinctive and memorable patterns might also benefit because they provide an identifying feature for pollinators to learn, remember, and return to.

Third, a nectar guide may reduce the overall time the bee spends on the flower. If bees are sensitive to the time costs associated with visiting different flowers, then they should prefer to visit flowers they can handle quickly. Finally, our research suggests a novel benefit: the pattern can reduce a bee’s tendency to rob nectar. In this case, the pattern benefits the plant by incentivizing the bee to access nectar “legitimately,” in a way that is most likely to transfer pollen.

Can you explain what nectar robbing refers to and what a ‘legitimate’ way of getting nectar looks like?

If you take a moment and imagine a bee visiting a trumpet-shaped flower like a morning glory, what you’re picturing is most likely what we call a “legitimate” visit. The bee lands on a  petal, and walks forward to probe down to the nectar located in the tube-like part of the flower. In the process, she is likely to pick up pollen or transfer pollen from her body to the flower. This exchange of nectar for pollen transfer forms the basis of the relationship between plant and bee. We refer to this type of nectar for pollen transfer via the floral opening as a “legitimate” visit, from the plant’s perspective.

In  a second type of visit,  the bee lands on the flower but instead of going the legitimate route, it  bites a hole in the side of the flower to access nectar, without necessarily depositing pollen or picking up new pollen. Because the plant has lost nectar to the bee without gaining pollen transfer, this type of visit is termed ‘nectar robbing’.

Why do bees indulge in ‘nectar robbing’? Is this behavior seen with other insects and birds?

Although observations of bees nectar robbing date back to at least the 18th century writings of Sprengel, we are still studying why bees do it. Some species, like carpenter bees, have a reputation as frequent robbers. Others like honey bees and the bumble bee species I study, Bombus impatiens, are better known as opportunistic nectar robbers. They’ll rob some plant species but not others; propensity to rob seems to also vary somewhat across individuals. Some studies show that bees may be more likely to rob if a previous visitor has already created the access hole. Likewise, our research suggests that if the flower doesn’t have a nectar guide pattern to direct the bee to the floral opening, they are more likely to stray and encounter an access hole left by a previous robber.

In your paper, you found that when a flower had a guide pattern, bees were less likely to rob nectar. How did you test the bees’ behavior?

We use an array of specially designed artificial flowers that my co-author Josh Brent spent many hours trouble-shooting. These flowers had nectar available in two different ways. The bee could either land on the top of the flower and access nectar “legitimately” from a small central well, or she could land on the underside of the flower, and “rob” nectar from a small well located on the side of the floral tube.

We kept bee colonies in the lab so they were naïve with respect to experience with real flowers. We let bees into the arena one at a time, and recorded their visits to the flowers on the array. Half the bees were given blue flowers with yellow star-shaped guides, and the other half saw only plain blue flowers with no patterns. We noted whether the bee robbed or visited each flower legitimately, and we were also able to measure how quickly she located the nectar after landing in each case.

We found that bees robbed less frequently when the flowers had nectar guides and also landed more quickly on flowers with guides than those without them. This suggests the bees indeed found the nectar guide more attractive to land upon than the plain flower top, and that the  guide helped them find nectar faster.

Does this discovery have applications for bee-keepers or horticulturists?

We’d need a few more of the pieces of the puzzle before claiming that our research on floral patterns might yield better honey or healthier honeybees, but our research suggests that the stripes and dots that provide color patterns pleasing to the human eye can also affect the way the bee interacts with the flower.

Typically, varieties of nursery plants are bred for human aesthetics. Given a choice, planting a variety with a dramatic nectar guide pattern might allow an observant gardener the satisfaction of seeing more pollen transferred by bees. On the other hand, those gardeners eager to see nectar robbing in action might select a relatively plain variety. The committed backyard scientist might be inspired to plant varieties with different types of patterns, sit back, and watch what happens. Of course, flowers of different plants can also differ in many other aspects that might affect a bee’s propensity to rob nectar (such as floral scent or nectar chemistry) and keep in mind that some may have UV patterns that the human eye can’t see.

Citation and images: Leonard AS, Brent J, Papaj DR, Dornhaus A (2013) Floral Nectar Guide Patterns Discourage Nectar Robbing by Bumble Bees. PLoS ONE 8(2): e55914. doi:10.1371/journal.pone.0055914


Manta ray preferences revealed

Image credit: Fabrice Jaine, PLOS ONE (2012)

If the thought of a calm moonlit night out on a tropical island makes you want to be at the beach, you may have something in common with the reef manta ray. Researchers studying the habits of manta rays in the waters off an island in the Great Barrier Reef have found that the rays aggregate in larger numbers when wind speeds are low and tides are particularly high or low (because of a new or full moon). Published today in PLOS ONE, their findings may help understand how manta ray populations are affected by climate and ocean conditions, they say.

This type of insight is particularly important because reef manta rays are classified a ‘vulnerable’ species by the International Union for Conservation of Nature (IUCN), just one step away from being endangered. Though they have few natural predators, they are hunted for their supposed efficacy in traditional Chinese medicine and are frequently trapped accidentally in fisheries. In several regions around the world, their populations are thought to have declined by about 80%, and globally, the IUCN estimates a drop of approximately 30% in the last 75 years. Little is known, however, about what factors predict their behavior or abundance in a particular geographical area; such knowledge is critical to conservation efforts, particularly in the context of a changing climate.

To begin addressing this question, the authors of today’s paper recorded weather and water conditions around the island and correlated these to the population of rays around the island and the kinds of behaviors they displayed. To study the animals themselves, the researchers enlisted volunteer SCUBA divers and tour operators on the island to watch for rays and their behavior. Another paper recently published in PLOS ONE uses a similar approach to track the decline of baiji, a freshwater dolphin in the Yangtse River. The authors of this paper surveyed local fishing communities along the river to estimate the abundance and decline of large species in the ecosystem, tracking the river dolphin, finless porpoise and two large fish now considered critically endangered or possibly extinct. They found that plotting the decline in frequency of sightings reported by the locals could help establish the dynamics of species decline and extinction.

Protecting larger animals like dolphins and manta rays can help more than just a single species.  In addition to acting as attractive poster children for conservation efforts, these animals frequently act as indicator or umbrella species. As indicators, their presence (or absence) can be a marker to monitor environmental conditions known to impact other species in the area, and targeting conservation efforts towards these animals can help conserve the habitat of several other species. Information on whether manta rays can serve as indicator or umbrella species is sparse, but research such as this study should help to answer this question.


Jaine FRA, Couturier LIE, Weeks SJ, Townsend KA, Bennett MB, et al. (2012) When Giants Turn Up: Sighting Trends, Environmental Influences and Habitat Use of the Manta Ray Manta alfredi at a Coral Reef. PLoS ONE 7(10): e46170. doi:10.1371/journal.pone.0046170

Turvey ST, Risley CL, Barrett LA, Yujiang H, Ding W (2012) River Dolphins Can Act as Population Trend Indicators in Degraded Freshwater Systems. PLoS ONE 7(5): e37902. doi:10.1371/journal.pone.0037902