The city nature challenge: A global citizen science phenomenon contributing to biodiversity knowledge and informing local government practices

Abstract

The bioblitz phenomenon has recently branched into cities, presenting exciting opportunities for local governments to channel participants' efforts toward local issues. The City Nature Challenge (CNC) is one such initiative that has been quickly taken up by hundreds of municipalities worldwide. Despite high levels of participation, we still lack a framework for evaluating how the CNC contributes to local biodiversity knowledge and to inform local government practices. In the present article, we develop such a tool and present a case study that illustrates its applicability. We demonstrate that the collected records contributed to a better understanding of contemporary, local biodiversity patterns and provide a more realistic representation of understudied groups such as insects and fungi. Importantly, we show that the CNC presented local governments with a cost-effective tool to make informed, evidence-based management and policy decisions, improve education and engagement programs, foster cross-council collaborations, and support a stronger sense of environmental stewardship within the local community.

Keywords: bioblitz; codesigned research; community engagement; iNaturalist; urban environments.

Figure 1.

The number of countries (a) and participants (b) per year who took part in the City Nature Challenge from 2016 to 2021, along with the number of records contributed (c) and species found (d) per year for the same period.

Figure 2.

(a) The number of observations collected across countries that participated in the 2021 City Nature Challenge. (b) The number of participants for each country during the 2021 City Nature Challenge.

Figure 3.

Conceptual framework of the contribution of citizen science events to local biodiversity knowledge. (a) The biodiversity known to the area before citizen science activity (species with historical or recent records on biodiversity repositories). (b) Possibly extinct species (species with historical but no recent records on biodiversity repositories). (c) Extant species (species with recent records on biodiversity repositories, with or without historical records). (d) Extinct species (species for which records will not be found anymore because they have gone locally extinct). (e) Rediscovered species (species with historical, but no recent, records—thought to be possibly extinct—for which records have been found during citizen science activity). (f) Species found during citizen science activity. (g) Newly discovered species (species without neither historical nor recent records that were found during citizen science activity). (h) Rediscovered species (extant species, with recent records on biodiversity repositories, found during citizen science activity). (i) Not re-found species (extant species, with recent records on biodiversity repositories, missed during citizen science activity). (j) Updated biodiversity known to the area after citizen science activity.

Figure 4.

Contribution of the observations collected during the 2021 City Nature Challenge to local biodiversity knowledge from the Melbourne Eastern Metropolitan Area node. See supplemental table S4 for summaries of each taxonomic group.

Figure 5.

Participants’ contribution to the 2021 City Nature Challenge across the Melbourne Eastern Metropolitan Area node. (a) Number of records contributed by different types of participants (members of the general public versus CNC organizers). Black lines represent mean estimates and blue areas the associated 95% credible intervals. (b) Number of species contributed by different types of participants (members of the general public versus CNC organizers). Black lines represent mean estimates and blue areas the associated 95% credible intervals. (c) Accumulated number of records contributed by participants. Participants are ordered from largest to smallest contribution in number of records, with members of the general public (n = 267) shown in black and CNC organizers (n = 24) show in blue.

Figure 6.

(a) Greenspaces visited during the 2021 City Nature Challenge (in green) from all the available greenspaces (in grey) across the Melbourne Eastern Metropolitan Area node. (b) Probability of greenspace visitation across the eight city councils that formed the Melbourne Eastern Metropolitan Area node during the 2021 City Nature Challenge. Black lines represent mean estimates and blue areas the associated 95% credible intervals. (c) Effect of area on the probability of greenspace visitation. The black line represents the mean estimate, the blue area the associated 95% credible interval, and the grey dots the data used to fit the model.