Post provided by Yves P. Klinger (he/him)

Photos collected by citizen scientists are a rich source of information that is still relatively unexplored. Phenology, the study of recurring biological events, could make use of photos taken by citizen scientists at different times, but accessing and preparing the plethora of publicly available data is challenging. In this post, Yves P. Klinger describes the motivation behind developing a workflow for using citizen science photos for phenological research, as featured in the paper “iPhenology – using open-access citizen science photos to track phenology at continental scale”.

What is phenology?

Phenology explores the timing of recurring biological events, such as the emergence of insects or flowering in plants. It is, arguably, one of the oldest fields of science, as the first phenological records date back millennia. For example, written records on the phenology of olive trees in the Mediterranean can be found dating back to times of ancient Greece. In Japan, written observations on the timing of cherry tree blossoms date back to the 9th century.

It was, and still is, highly relevant for humans to track seasonal shifts. Tracking seasonal shifts helps determine when edible plants will become available or when to sow and harvest crops. This is why I was surprised when I first learned how scarce detailed information is for the phenology (and its drivers) of many species.

The challenge of studying phenology

The idea for this paper was first sparked during fieldwork tracking an invasive legume. We collaborated with other scientists located along a latitudinal gradient in Europe to track the phenology of the species. It became obvious how laborious it was to perform detailed phenological observations and how challenging it is to organize such a large collaborative study – mainly because large-scale phenological studies require frequent observations across large areas.

Phenology explores the timing of recurrent biological events. For plants, this includes the timing of development of buds (left), flowering (mid), or seed production (right). Photos by Yves P. Klinger.

I was excited to learn about the amount of photos accessible through public databases such as iNaturalist or GBIF. Our group quickly started exploring how we could make use of the available photo observations to complement existing phenological studies.

As I am interested in non-native species, we started looking at photo observations of different alien plants in Europe. This turned out to be a good starting point, as many invasive plants were introduced for ornamental use and thus attract people with cameras. Additionally, many of the non-native species we studied do not look similar to any of the native species in the invaded range. This makes checking images for correct identification much easier and more reliable.

Working with citizen science photos

One great advantage of working with photos is that researchers can see the world through the eyes of the citizen scientist. It can be easier to evaluate the quality of observations concerning correct species identification, as well as assessing other information such as the state and habitat in which a specimen was found. However, as with all citizen science data, photo observations may comprise very heterogeneous datasets that can be challenging to deal with.

For example, observations may be spatially clumped in urbanized areas and are mostly collected during summer, when people spend recreational time outdoors. Images provided by citizen scientists vary greatly concerning image quality, distance between photographer and specimen, and the number of individuals found in the photo. Sometimes, it may even be hard to determine the phenological stage of single individuals.

From early-stage flowers to fruits, this specimen of the garden lupine covers several phenological stages at once. Photo by Eduard Garin (CC-BY-NC),

The workflow provided with the paper is intended to give researchers interested in performing phenological studies an entry point to harnessing publicly available citizen science photos. While the suggested workflow covers all steps, from data acquisition and phenological classification to analyzing spatiotemporal patterns, it can (and should) be adapted and extended to suit the researcher’s needs. We are curious to see how ideas will develop!

You can read more in the full article:

iPhenology – using open-access citizen science photos to track phenology at continental scale