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Bates, Primack, Duarte & PAN-Environment Working Group (in press) Global COVID-19 lockdown highlights
humans as both threats and custodians of the environment. Biological Conservation
Global COVID-19 lockdown highlights humans as both threats and custodians of the
environment
Amanda E. Bates1, Richard B. Primack2, PAN-Environment Working Group3
(https://docs.google.com/spreadsheets/d/1ltnPMOip-ffk-
vLsXNNOw3jmj3CGPm9Qk1WrkaM4E1o/edit#gid=1238906101) and Carlos M. Duarte4,5
1Department of Ocean Sciences, Memorial University of Newfoundland, St. John's, NL A1C 5S7, Canada.
2Biology Department, Boston University, 5 Cummington Mall, Boston, MA 02215, USA.
3PAN-Environment Working Group
4Red Sea Research Center (RSRC) and Computational Biosciences Research Center (CBRC),
5King Abdullah University of Science and Technology (KAUST), Thuwal, Kingdom of Saudi Arabia
*Correspondence to: bates.amanda@gmail.com
Highlights
• The global COVID-19 lockdown has impacted nature and conservation programs
• Immediate effects are documented across the world and in all ecosystems
• Initial responses are biased towards established monitoring programs and networks
• Complex positive and negative effects were detected, some with cascading impacts
• Humans are important custodians of species and ecosystems
Abstract
The global lockdown to mitigate COVID-19 pandemic health risks has altered human
interactions with nature. Here, we report immediate impacts of changes in human activities on
wildlife and environmental threats during the early lockdown months of 2020, based on 877
qualitative reports and 332 quantitative assessments from 89 different studies. Hundreds of
reports of unusual species observations from around the world suggest that animals quickly
responded to the reductions in human presence. However, negative effects of lockdown on
conservation also emerged, as confinement resulted in some park officials being unable to
perform conservation, restoration and enforcement tasks, resulting in local increases in illegal
activities such as hunting. Overall, there is a complex mixture of positive and negative effects of
the pandemic lockdown on nature, all of which have the potential to lead to cascading responses
which in turn impact wildlife and nature conservation. While the net effect of the lockdown will
need to be assessed over years as data becomes available and persistent effects emerge,
immediate responses were detected across the world. Thus initial qualitative and quantitative
data arising from this serendipitous global quasi-experimental perturbation highlights the dual
role that humans play in threatening and protecting species and ecosystems. Pathways to
favorably tilt this delicate balance include reducing impacts and increasing conservation
effectiveness.
1.0 Introduction
Human-driven alterations of atmospheric
conditions, elemental cycles and biodiversity
suggest that the Earth has entered a new epoch,
the Anthropocene (Crutzen, 2002; Steffen et al.,
2007). Negative impacts associated with human
activities include a much warmer Earth state,
marked expansion of urbanization, and
accelerating species extinctions (Schipper et al.,
2008). The perspective that the main role of
Bates, Primack, Duarte &. PAN-Environment Working Group (in press) Global COVID-19 lockdown highlights
humans as both threats and custodians of the environment. Biological Conservation
humans is a source of threats on species and
ecosystems leads to the prediction that the
global human lockdown to mitigate COVID-19
health risks may alleviate human impacts, with
resulting positive environmental responses
(Derryberry et al., 2020; Rutz et al., 2020).
Indeed, early reports indicate that restrictions
led to immediate decreases in air, land and
water travel, with similar declines in industry,
commercial exploitation of natural resources
and manufacturing, and lower levels of PM10,
NO2, CO2, SO2 and noise pollution (Bao and
Zhang, 2020; March et al., 2021; Millefiori et
al., 2021; Otmani et al., 2020; Santamaria et al.,
2020; Thomson et al., 2020; Terry et al., 2021
[this issue]; Ulloa et al., 2021 [this issue]).
Yet a more comprehensive consideration of the
links between human activities and species and
ecosystems also acknowledges the role of
humans as custodians of nature, who engage in
conservation research, biodiversity monitoring,
restoration of damaged habitats, and
enforcement activities associated with wildlife
protection (Bates et al., 2020; Corlett et al.,
2020; Evans et al., 2020; Manenti et al., 2020;
Rondeau et al., 2020; Zambrano-Monserrate et
al., 2020; Kishimoto et al., 2021 [this issue];
Miller-Rushing et al., 2021 [this issue]; Vale et
al., 2021 [this issue]; Sumasgutner et al., 2021
[this issue]). Indeed, the global COVID-19
human confinement has disrupted conservation
enforcement, research activities and policy
processes to improve the global environment
and biodiversity (Corlett et al., 2020; Evans et
al., 2020; Zambrano-Monserrate et al., 2020;
Quesada-Rodriguez et al., 2021 [this issue]).
The lockdown has also created economic
insecurity in rural areas, which may pose
biodiversity threats as humans seek to support
themselves through unregulated and illegal
hunting and fishing, and conservation spending
is reduced. In particular, declines in ecotourism
in and around national parks and other
protected areas lowered local revenue, park
staffing, and funding to enforce hunting
restrictions and invasive species management
programs (Spenceley et al., 2021; Waithaka et
al., 2021). In many areas, restoration projects
have been postponed or even cancelled (Bates
et al., 2020; Corlett et al., 2020; Manenti et al.,
2020).
Here, we consider the global COVID-19
lockdown to be a unique, quasi-experimental
opportunity to test the role of human activities
in both harming and benefiting nature (Bates et
al., 2020). If the negative roles of humans on
species and ecosystems predominate, we would
expect overwhelmingly positive reports of
responses of nature to human lockdown. We
integrate 30 diverse observations from before
and during the peak lockdown period to
examine how shifts in human behavior impact
wildlife, biodiversity threats, and conservation.
We first analyze the mobility of humans on land
and waterways, and in the air, to quantify the
change in human activities. Second, we
compile qualitative reports from social media,
news articles, scientists, and published
manuscripts, describing seemingly lockdown-
related responses of nature, encompassing 406
media reports and 471 observations from 67
countries. Third, we map the direction and
magnitude of responses from wildlife, the
environment and environmental programs,
using data collected before and during
lockdown provided by scientists, representing
replicated observations across large geographic
areas. We collated data from 84 research teams
that maintained or accessed existing monitoring
programs during the lockdown period,
reporting 326 responses analyzed using a
standardized analytical framework. We
accounted for factors including autocorrelation
and observation bias using mixed effects
statistical models, and selected the most robust
available baselines for each study to report
lockdown-specific effect sizes (see methods).
We empirically describe the type, magnitude,
and direction of responses for those linked with
confidence to the lockdown, and offer
Bates, Primack, Duarte &. PAN-Environment Working Group (in press) Global COVID-19 lockdown highlights
humans as both threats and custodians of the environment. Biological Conservation
integrated outcomes supported by examples
drawn from our results. Finally, we use these
results to provide recommendations to increase
the effectiveness of conservation strategies.
2.0 Materials and Methods
Here we interpret data and qualitative
observations that represent a non-random
sample of available information comprising
diverse response variables. Thus, we make
inferences about the geographic scope of
observations and focus on what integrated
understanding can be gained from considering
the evidence of both positive and negative
effects of the lockdown and their linkages.
From diverse data sources and analyses, we
compiled a high-level view of how the
lockdown influenced four major categories of
responses of shifts in (1) human mobility and
activity, (2) biodiversity threats, (3) wildlife
responses, and the (3) social structures and
systems that influence nature and conservation
(described in further detail in Appendix 1,
Table A1). In brief, human mobility and
activities included recreational activities such
as park visits and boating, commuting, and
activities related to industry, such as shipping.
Biodiversity threats included categories which
were linked directly to a possible negative
wildlife response, such as hunting, fishing,
mining, vehicle strikes, wildlife trade,
environmental pollution, and deforestation.
Wildlife responses represented observations
related to biodiversity and species, such as
community structure, animal performance (e.g.,
reproduction, health, foraging) and habitat use
(i.e., abundance and distribution).
Environmental monitoring, restoration
programs, conservation, and enforcement were
grouped as representing social systems and
structures that influence and support
conservation.
2.1 Human Mobility Data
Data on government responses to COVID-19
across countries and time were retrieved from
the Oxford COVID-19 Government Response
Tracker (Hale et al., 2021), which also reports
where the restrictions on internal movement
apply to the whole or part of the country. The
global population under confinement of internal
movement was calculated by adding up the
population of countries where the restriction is
general, and 20% of the population of countries
where the restriction is targeted, as an estimate
of the fraction of the population affected.
Population data by country corresponding to
year 2020 have been obtained from the
Population Division of the Department of
Economic and Social Affairs of the United
Nations (United Nations, 2018). Note that the
data about restrictions contain missing
information for some countries and dates.
Therefore, the calculated number of human
confinement does not take into account the
population of countries with missing
information and may thus underestimate the
actual number of humans under restriction.
Changes in human mobility data were recorded
by a number of agencies globally, and
combined, describe how the lockdown affected
movements on land, at sea and in the air. Data
on the restriction of individuals in residential
areas and to parks were derived from Google
Community Mobility Reports
(https://www.google.com/covid19/mobility/).
Data on driving were obtained from the Apple
Maps Mobility Trends Report
(https://www.apple.com/covid19/mobility).
Marine traffic and air traffic data were derived
from exactEarth Ltd.
(http://www.exactearth.com/), and OpenSky
Network (https://openskynetwork.org/)
respectively. Google Community Mobility
Report data are based on anonymized data on
how long users stay in different types of
localities and are available aggregated to
regional scales (usually country). Each regional
mobility report reflects a percentage change
Bates, Primack, Duarte &. PAN-Environment Working Group (in press) Global COVID-19 lockdown highlights
humans as both threats and custodians of the environment. Biological Conservation
over time compared to a 5-week baseline (Jan.
3 to Feb. 6, 2020). Similarly, Apple Maps
Mobility Trends Reports are based on Apple
maps user data and aggregated by region to
reflect the percent change in time Apple maps
users spent driving relative to a baseline (Jan.
12, 2020). The percent change in the responses
of human mobility through time allows
identification of extreme inflections related to
human behavior. For Google and Apple data,
we extracted the overall mobility trends for
each country until May 1st, which was selected
from a sensitivity test and before relaxation of
confinement measures were introduced in most
countries. We further excluded within-country
variations in mobility, and removed all
countries with extensive data gaps and
countries that did not show a response to
lockdown.
The first step to quantifying the effect due to the
lockdown on community mobility (residential
and parks) and driving data identified the date
of greatest change in each time-series (data and
script files are here:
https://github.com/rjcommand/PAN-
Environment). Because each country had
differing lockdown dates and multiple types of
lockdown, we identified critical transition dates
which best explained the change in mobility for
each country. To do so, we used Generalized
Additive Models (GAM (Wood, 2011)) on
daily mobility levels in each country, using the
Oxford Covid-19 Government Response
Tracker database of country-level containment
policies (C1-C7) to define a variable for the
before and after lockdown periods, running up
to 15 models per country depending on the
number of different kinds of lockdown
measures imposed. From these models, we
selected the lockdown date that explained the
greatest amount of change. We manually
identified the confinement dates in cases where
the models did not converge or when multiple
unexplained inflection points were detected (N
= 10 countries). Percent change was calculated
as the mean percentages after implementation
of the confinement measure selected from the
models.
For marine traffic mobility, satellite AIS (S-
AIS) data for April 2019 and 2020 were
obtained from exactEarth Ltd.
(http://www.exactearth.com/), a space-based
data service provider which operates a
constellation of 65 satellites to provide global
AIS coverage at a high-frequency rate (< 5 min
average update rate). The latest upgrade in the
constellation entered into production in
February 2019 and S-AIS coverage was
equivalent for both periods (exactEarth Ltd.,
pers comm.). Values represented the monthly
number of unique vessels within grid cells of
0.25 x 0.25 degrees. We calculated the vessel
density as the number of vessels per unit area,
considering the difference of cell size across the
latitudinal gradient (March et al., 2021). Grid
cells from the Caspian Sea and with <10%
ocean area were removed from the analysis,
based on the GADM Database of Global
Administrative Areas (version 3.6,
https://gadm.org/). Further quality control
procedures were provided in more detail in a
complementary publication. We calculated the
percentage change in marine traffic density
between April 2019 and April 2020 per country
and Exclusive Economic Zones (EEZ, Figs. S6
& S7) using a Generalized Linear Model (GLM
(R Core Team, 2020; Pinheiro et al., 2021)).
For air traffic mobility, data were downloaded
from the OpenSky network
(https://openskynetwork.org). OpenSky uses
open-source, community-based receivers to
receive air traffic data from around the world
and makes these data available in an online
repository. The online database consists of
latitude and longitude of departure and landing
for all flights detected where receivers are
available. Data are limited in some areas,
including Africa and parts of Asia. We
downloaded daily data for 129 countries where
Bates, Primack, Duarte &. PAN-Environment Working Group (in press) Global COVID-19 lockdown highlights
humans as both threats and custodians of the environment. Biological Conservation
data were available in April 2019 (1,302,282
flights) and the same period in April 2020
(316,609 flights, when most countries included
in the analysis had imposed international travel
restrictions) to compare the total volume of
traffic departing from, or arriving to, all
countries where data were available for both
years. We aggregated these flights by country,
then ran a GLM on the daily number of 5 flights
in each country, accounting for the day of the
week and comparing 2020 (countries in
lockdown) to 2019. We used this model to
calculate a t-statistic for the lockdown effect in
each country, and then calculated a percentage
change in flight volume based on numbers of
flights per country in April 2019 versus the
lockdown period in April 2020.
2.2 Qualitative Observations
Observational evidence of the impact of the
first four months of the COVID-19 lockdown
on society, the environment and biodiversity
was collected and collated through: (1) internet
searches with the keywords nature,
conservation, environment and COVID-19; (2)
calls on social media for personal observations
and for volunteers to contribute from our
networks; (3) Web of Science general search
for papers (terms: nature, conservation,
environment, COVID-19) released released
between May to August 2020 that also used
qualitative evidence to investigate the
lockdown effect, and (4) through volunteer
contributions from our global PAN-
Environment working group of over 100
scientists. Each qualitative observation (N =
877 observations) was assigned a geographic
location (latitude and longitude) and classified
by observation type (described in Appendix 1,
Table A1), including a description and details
on the species impacted (where relevant).
Reports that listed several impacts (e.g.,
independent observations, species, or locations)
were entered as multiple lines. Following entry
to our dataset, each observation was assigned an
effect score from 0-10 (as described in
Appendix 1, Table A2) to distinguish between
observations with ephemeral effects with
unknown impacts from those that will have
widespread or persistent outcomes with strong
effects in positive or negative directions.
Qualitative data were recorded for all
continents, except Antarctica, representing 67
countries. Non country-specific observations
were also included, representing 20% of all
anecdotes. The majority of countries were
represented by less than five observations (51
countries), while South Africa submitted
approximately one third of the total
observations (total = 297). This high
representation in South Africa was a known
bias due to the use of African birding forums to
collect citizen science data which were
organized to communicate and engage widely
as lockdown measures were implemented.
Similarly, other known biases included high
relative representation of charismatic species
and those that were easily observed during
lockdown by humans (e.g., giant pandas and
garden birds). Most reports were gathered from
English sources, however, over 100
observations were translated from Italian, and
another 50 and 10 were from Spanish and
Afrikaans, respectively. We interpreted our
results in this context by focusing on the
inferences that can be made in spite of these
biases, and in combination with the empirical
data. See Appendix 3 (Table S3) for the full
dataset.
2.3 Empirical Data
We further assembled a global network of
scientists and managers to download, interpret,
and analyze quantitative information
investigating the negative, neutral and positive
effects resulting from the lockdown. We made
use of ongoing monitoring programs for
comparisons before, during and after the
lockdown confinement period, or in similar
time windows in previous unaffected years.
Seven example scripts were provided to
represent different types of considerations for
Bates, Primack, Duarte &. PAN-Environment Working Group (in press) Global COVID-19 lockdown highlights
humans as both threats and custodians of the environment. Biological Conservation
analyses for each team to match with the types
of response data, biases, references, study
durations and complexity (covariates, spatial
and temporal autocorrelation, and random
effects) (available in Appendix 2). The core
author team further consulted on the analysis of
each dataset to ensure consistency across
studies. The original authors reviewed and
edited their data following transcription.
With this overall approach, we were able to
provide insights on the immediate changes
likely due to the lockdown (69 studies used a
historical reference period including the
lockdown months in previous years; studies
compared the strict lockdown period to the
same months in pre-lockdown years, described
in detail for each study in Appendix 4, Table
A4). In other cases, the reference was an area
representing a reference state (i.e., remote areas
or large, well-governed protected areas did not
undergo a difference in human activities due to
lockdown measures). If observations were
unavailable prior to the start of the pandemic
lockdown or for reference year(s), comparisons
were made (if sensible) during and after the
lockdown, i.e., the reference was the post-
confinement period (8 studies). For instance,
litter accumulation at two locations was
measured from the strict lockdown in April
2020, and over two months as restrictions
eased. Spatial comparisons between areas
impacted by the lockdown with unaffected sites
were also included to detect lockdown related
effects. These unaffected sites were considered
as reference areas after evaluation by the
relevant research teams who contributed the
data (2 studies). The rationale for each study
design and selection of the baseline period is
reported in Table A4 and A5 (Appendix 4 and
5), and was reviewed by the core analysis team
to ensure the baseline period comprised a
suitable reference for the given response of
interest. Total percent changes were
calculated as the difference between the
response coefficient (attributed to the
lockdown) relative to the reference coefficient.
For instance, if we observed a 400% increase in
a response during the lockdown, this translates
to an effect which was 4 times greater. We used
Generalized Linear, Additive Mixed (GAMM
(Wood, 2004)) or Linear Mixed-Effects (LME
(Pinheiro et al., 2021)) models, as best suited
for each data type. Suitability was based on the
distribution of the response data, fit of the
statistical data and the covariates that needed to
be accounted for to estimate the appropriate
coefficients. In brief, for each dataset, we
quantified percentage change from expected or
typical values, as well as an effect size in the
form of a t-statistic standardized by sample size
(Bradley et al., 2019). Datasets and results
summary tables for each analysis of human
mobility and empirical datasets are deposited in
a GitHub repository, filed under each
contributing author’s name:
https://github.com/rjcommand/PAN-
Environment. The independent data availability
statement for each study is reported in Table A5
(Appendix 5).
Different datasets were analyzed using
statistical models with parameters dependent on
the type, duration and complexity of each
response and study design. Table S5 (Appendix
5) provides a summary of the information that
was collected from the authors who contributed
each study, a description of the methods and
relevant references, analysis type, spatial scale,
details on the temporal or spatial baselines and
how they were accounted for or interpreted,
reports of any confounding factors (included as
covariates), model results summary table links
to GitHub, interpretation, and confidence score
that the observed effect was indeed due to the
lockdown (with a rationale for this selection).
The relevant information for interpretation
across studies was subsequently transcribed to
Table S4 (Appendix 4).
Bates, Primack, Duarte & PAN-Environment Working Group (in press) Global COVID-19 lockdown highlights
humans as both threats and custodians of the environment. Biological Conservation
3.0 Results
3.1 Human mobility on land, in the air and on water
Fig. 1. Total humans under COVID-19 mobility restrictions. Time series of the number of humans under lockdown
across the global population under the 2020 COVID-19 mitigation policies. This assumes that in countries with
targeted restrictions, a fraction of 20% of the population was under lockdown. Assuming different fractions, similar
time patterns but different magnitudes of populations under lockdown are obtained. For example, assuming fractions
of 20% and 30%, April 5th was the day with the maximum population under lockdown equal to 57% and 61% of the
global population, respectively. Assuming fractions of 5% and 10%, April 26th was the day with the maximum
population under lockdown equal to 53% and 54% of the population, respectively.
The global peak of lockdown occurred on April
5th, 2020, at which time 4.4 billion people were
impacted (Fig. 1), representing 57% of the
world’s population. In the weeks before and
after this lockdown peak, residents of most
countries spent much more time at home (Fig.
2). Country specific critical transition dates
(which occurred primarily in late March leading
up to the April peak) were used to assess the
total change in mobility until May 1st. During
this period, driving decreased by 41%, there
was a 20% overall reduction in park visits,
particularly in Central and South American
countries, although Nordic countries were an
exception (Figs. S1 & S2). The April 2020
period also saw major disruptions in
community, food transport, and supply chains,
with a 9% decrease in marine traffic globally
and a 75% total reduction in air traffic (both
relative to April 2019, Figs. A3-A5). Thus, the
COVID-19 lockdown has led to a significant
global reduction in human mobility, notably
travel, causing an “anthropause” (Rutz et al.,
2020).
3.2 Effects on wildlife around the world
As humans retreated, animals quickly moved to
fill vacated spaces (Fig. 3) (Derryberry et al.,
2020; Zellmer et al., 2020). In our dataset,
approximately half of the qualitative
observations and more than one third of all
measured quantitative species responses that
were linked with some confidence to the
lockdown related to unusual animal sightings in
urban areas (both land and waterways), and to
species occurring in different abundances
compared to pre-perturbation baseline
estimates (Figs. 4 and 5). Many initial
observations painted a rosy picture of wildlife
“rebounding”; indeed, our qualitative
observations of wildlife responses are
predominantly positive, likely reflecting
reporting biases (Fig. 4). Reports include
changes in behavior, reproductive success,
health, and reductions in mortality, apparently
in response to altered levels of human activity
(Fig. 4)
Bates, Primack, Duarte & PAN-Environment Working Group (in press) Global COVID-19 lockdown highlights
humans as both threats and custodians of the environment. Biological Conservation
Fig. 2. Change in mobility. Percent change in time spent within home residences (residential) following
implementation of confinement measures in each country.
Bates, Primack, Duarte & PAN-Environment Working Group (in press) Global COVID-19 lockdown highlights
humans as both threats and custodians of the environment. Biological Conservation
Our quantitative assessments suggest a mixed
role of human confinement in positively and
negatively influencing wildlife (Fig. 5). Some
species changed their behavior (e.g., daily
activity patterns) and relocated to entirely new
areas, including seeking new food sources and
roaming to unusual areas. This included air
space, such as when critically endangered
Griffon vultures in Israel flew further afield in
2020, apparently due to reduced military
training during the lockdown (Appendix 4,
Table A4, StudyID 55). Some animals also
moved to human settlements from rural
locations (e.g., golden jackals: Appendix 4,
Table A4, StudyID 28), while other species
showed very little changes (Fig. 5 showing
distribution of wildlife responses as effect sizes
which center on zero).
There was also qualitative evidence of
increased human-wildlife conflicts (described
in Appendix 3, Table A3 under the categories:
Biodiversity threat, Human-wildlife
interaction, Aggression). Four non-fatal shark
attacks on humans occurred over a span of five
weeks in French Polynesia, a number typically
observed over a whole year, and an unusually
high number of fatal shark attacks has been
reported for Australia. On land, monkeys that
normally live closely and peacefully with
humans near a pilgrim center in Uttar Pradesh,
in northern India, attacked residents – atypical
behavior that may be related to starvation and
corresponding aggression.
Fig. 3. Reports of 275 species that occupied an unusual area (distribution change), or shifted in number (abundance
change) were attributed to a reduction in human activities. Changes in species distributions were observed around
the world as qualitative observations (Appendix 3, Table A3, albeit with biases in effort such as greater coverage in
the Northern Hemisphere and South Africa), and based on empirical data of time series surveys and bio logging data
using statistical modeling to quantify change. Only changes that were attributed to the lockdown with high
confidence are included here (Appendix 4, Table A4). Bubble size represents data density (the largest bubble
represents 41-60 observations and the smallest is 1-20).
Bates, Primack, Duarte & PAN-Environment Working Group (in press) Global COVID-19 lockdown highlights
humans as both threats and custodians of the environment. Biological Conservation
3.3 Changes in biodiversity threats
The pandemic lockdown generally highlighted
the enormous and wide-ranging impacts that
humans have on the environment and wildlife.
For instance, in a remote forest area in Spain, a
45% reduction in NO2 and SO2 lead to reduced
atmospheric deposition of NO3- and SO42-, and
limited the input of N and S to soil ecosystems
(Appendix 4, Table A4, StudyID 84). Ocean
fishing was also reduced by 12% based on our
analysis of 68,555 vessels representing 145
national flags and 14 gear types (including
drifting longlines and nets, purse seines and
trawlers, Appendix 4, Table A4, StudyID 5).
Animal deaths from vehicle strikes on roads
and vessel strikes in the water during peak
lockdown were dramatically lower than
baseline periods in two data sets (e.g., 19%
reduction: South Korea, 42% reduction: USA,
Appendix 4, Table A4, StudyIDs 7 & 27).
There was also a marked reduction in ocean
noise, which can negatively impact a wide
range of marine organisms, as reported from
several locations. For example, lockdown-
related reductions in ferry traffic, seaplane
activity, and recreational boating activity near
the transport hub of Nanaimo Harbour, Canada,
combined to reduce the sound pressure levels
by 86% (Appendix 4, Table A4, StudyID 23).
In urban parks in Boston, noise from road
traffic dropped by as much as 50% as traffic
volumes decreased (Appendix 4, Table A4,
StudyID 52; Terry et al., 2021 [this issue]). On
roadways, parks and beaches around the world,
direct pollution from humans was also reduced
during the lockdown. For example, surveys of
15 beaches in Colombia and Cuba found
negligible evidence of noise, human waste, and
litter during the strict lockdown period, in
contrast to pervasive human impact before the
lockdown (Appendix 3, Table A3, Lines 742-
748).
While some biodiversity threats were
alleviated, as discussed above, responses were
highly variable. For example, marine traffic
increased slightly in some regions (Appendix 4
and 5, Fig. A4 and A5) including shifts of
fishing fleets to near-shore coastlines. In some
regions, fishing activities intensified rather than
declined (e.g., some recreational fisheries and
commercial fisheries) (Fig. 5). Other impacts
escalated, including massive increases in
plastic waste due to discarded personal
protective equipment to prevent COVID-19
transmission, and abnormally large crowds of
visitors to parks for recreation in countries
where outdoor activities were permitted (e.g., a
47% visitation increase in the Swiss National
Park, Appendix 4, Table A4, StudyID 57). In
many parks, hikers were observed expanding
trails, destroying or changing local habitats, and
even trampling endangered orchid species
(Appendix 3, Table A3).
The lockdown also interrupted conservation
enforcement activities with dire consequences
including increased illegal activities, such as
hunting, deforestation, and the dumping of
waste (Figs. 4 and 5). For instance, pangolins,
which are amongst the world’s most trafficked
mammals (for food and traditional medicine),
seem to have come under even greater pressure;
trade seizures increased in India by >500% (i.e.,
a 5-fold increase) during the lockdown period
(Appendix 4, Table A4, StudyID 62). Indeed, a
spike in exploitation of many animal species for
food and trade was reported from around the
world (e.g., China, Kenya, India, Peru, South
Africa, Sri Lanka, UK), often for national parks
and protected areas. For example, in the
protected Bugoma Forest reserve in Uganda
(Appendix 4, Table A4, StudyID 19), increased
use of animal snares during the pandemic was
detected, which can injure and kill non-target
animals, including endangered species such as
chimpanzees. Likewise, during the lockdown,
the conch fishery in the Bahamas shifted to
smaller illegal-sized juvenile animals from a
nursery area (Appendix 4, Table A4, StudyID
47).
Bates, Primack, Duarte & PAN-Environment Working Group (in press) Global COVID-19 lockdown highlights
humans as both threats and custodians of the environment. Biological Conservation
Fig. 4. Qualitative negative and positive effects observed which were relative to the response observed (Appendix 4,
Table A4). Negative effects indicate a dampening in the responses which were grouped into categories representing
“Human Mobility & Activities”, Biodiversity Threats”, “Wildlife Responses” and “Social Systems & Structures”,
while positive effects indicate an increase. The effect score is based on the criteria outlined in Appendix 1, Table
A2, and considered the duration, spatial extent and total impact of the effect on the response. A negative or positive
effect direction is relative to each category is based on the observed effect, rather than an interpreted impact. For
instance, a negative effect on noise is a decrease in noise (which may have had positive wildlife impacts). a)
Distribution of effects showing the direction and magnitude. The dotted line is the intercept, and the colored line
indicates the median effect score. b) The mean effect score for categories falling within effects on human activities
(blue), biodiversity threats (orange), biodiversity (green) and social systems (purple). Bars are the mean across
reports pooled for positive and negative effects on the y-axis category, and white numbers are the number of
observations upon which the mean is based.
Bates, Primack, Duarte & PAN-Environment Working Group (in press) Global COVID-19 lockdown highlights
humans as both threats and custodians of the environment. Biological Conservation
3.4 Responses of social systems which
support biological conservation
We found that management and conservation
systems were initially weakened and even
ceased in many areas of the world (the median
effect size was negative in both the qualitative
and quantitative data sets: Figs. 4b and 5b). In
one region of the Amazon, Brazil, the
deforested area relative to historical years
increased by 168% (i.e., a 1.68-fold change)
during the lockdown, and a similar response
was seen for the eruption of fire hotspots in
Colombia, both attributed to a lack of
enforcement (Appendix 4, Table A4, StudyID
35). Environmental monitoring and
community-based programs to restore habitats
or remove waste from beaches have also been
severely restricted. Anecdotes highlight that
pest management programs have not been able
to recruit community volunteers to trap rats and
mobilize personnel to combat locust outbreaks.
In one dramatic example, failure to remove
non-native mice from remote seabird islands is
expected to lead to the loss of two million
seabird chicks in 2020 (Appendix 3, Table A3,
Line 265).
The number of observers contributing to
community science efforts has also
immediately declined for many programs (e.g.,
eBird Colombia, eButterfly, Nature’s Notebook
and the LEO Network; Crimmins et al., 2021
[this issue]), although growth was also noted in
some US programs in particular cities and
regions (eBird and iNaturalist, Appendix 4,
Table A4; Crimmins et al., 2021 [this issue];
Hochachka et al., 2021 [this issue]). A lack of
reporting can be a major conservation concern,
such as when the number of whale observers
declined by 50% along the Pacific Northwest
during the lockdown, leading to a reduced
ability of ships to avoid striking whales
(Appendix 3, Table A3, Line 272).
4.0 Discussion
The COVID-19 lockdown provided an
unprecedented, serendipitous opportunity to
examine the multi-faceted links between human
activity and the environment, providing
invaluable insights that can inform
conservation strategies and policy making.
Specifically, this lockdown has created a period
during which global human activity, especially
travel, was drastically reduced, enabling quasi-
experimental investigation of effects across a
large number of ‘replicates’ (Bates et al., 2020).
Overall, we found that both positive and
negative responses of human activity on species
and ecosystems are prevalent – results that are
inconsistent with the prevailing view of humans
as primarily harming biodiversity. Indeed,
while the qualitative observations presented
here provide evidence of interpretation bias,
viewing unusual behaviours in wildlife as
positive (Fig. 4), our quantitative assessments
were balanced between negative and positive
responses (Fig. 5). Even if our dataset does not
represent a random sampling design, the reports
collated are a comprehensive inventory of
information across the globe. Emerging from
this initial dataset is support for both negative
and positive responses of wildlife to human
activity and the systems in place to monitor and
protect nature. Thus, the lockdown provides a
striking illustration of the positive role humans
can play as custodians of biodiversity. While
negative impacts were expected, the potential
for humans to positively influence biological
conservation through scientific research,
environmental monitoring, opportunistic
citizen reporting, conservation management,
restoration and enforcement activities was
strong in our datasets. Combined, these
activities jointly deliver conservation benefits.
Bates, Primack, Duarte &. PAN-Environment Working Group (in press) Global COVID-19 lockdown highlights
humans as both threats and custodians of the environment. Biological Conservation
Fig. 5. Responses during the lockdown based on our empirical data (Appendix 5, Table A5) where positive and
negative effects represent the observed direction of change for the different response categories. 71 studies which
attributed the observed effect to the lockdown with high confidence are included (i.e., a qualitative confidence score
of 3 or greater out of a maximum of 5). Frequency histograms (panels a-d) show bars representing data density and a
curve representing a smoothed distribution of effect sizes and direction. The dotted line is zero, and the solid colored
line is the median. Only responses that were attributed to the lockdown with high confidence are included. a)
Human activities and mobility (blue) includes measured responses in human activities and mobility, such as related
to commuting and recreational activities (categories are described in Appendix 1, Table A1). b) Biodiversity threats
(orange) include categories that harm wildlife and natural systems, such as hunting, fishing, mining, vehicle strikes,
wildlife trade, environmental pollution, and deforestation. c) Wildlife responses (green) incorporate observations of
animals and plants related to performance (e.g., reproduction, health, foraging) and habitat use (abundance and
distribution) and community change (species richness). d) Social systems (purple) include environmental
monitoring, restoration, conservation, and enforcement. The chord diagrams highlighted the observed positive and
negative effects which were attributed to different lockdown-related drivers as identified by each study (black), and
linked to what was measured by each study where responses grouped into the four categories: human activities and
mobility, biodiversity threats, wildlife responses, and social systems and structures. One chord represents one
measured response.
Bates, Primack, Duarte &. PAN-Environment Working Group (in press) Global COVID-19 lockdown highlights
humans as both threats and custodians of the environment. Biological Conservation
Another major take-home from this synthesis
effort is that humans and their activities have
measurable impacts on food availability for
animals from both land and marine habitats,
including that of top predators and scavengers.
The role of human-sourced food is an important
driver of wildlife occurrence and condition. For
instance, in Singapore, feral pigeons shifted
their diets from human foods to more natural
food sources and their numbers declined
(Appendix 4, Table A4, StudyID 75, Soh et al.,
2021 [this issue]). At a university campus in
South Africa, red-winged starlings lost body
mass, presumably because their typical
foraging grounds were bare of waste food
(Appendix 4, Table A4, StudyID 58).
Scavenging crows also spread to coastal
beaches in Australia when human food was no
longer available (Gilby et al., 2021 [this issue]).
Many species that are routinely fed during
wildlife tours (e.g., sharks (Gallagher and
Huveneers, 2018)) have not had access to this
supplementary food due to drastically reduced
tourism. This appeared to drive a change in the
abundance and types of species that were
detected at sites in the Bahamas during the
lockdown period (Appendix 4, Table A4,
StudyID 67). In addition to food, animal use of
nutritional supplements was also influenced by
human activities. For instance, in response to
reduced traffic on highways in the Canadian
Rockies, mountain goats spent more time at
mineral licks, interpreted as a wildlife benefit
(Appendix 4, Table A4, StudyID 37).
Another major take-home from this synthesis
effort is that many wildlife and ecosystem
responses were unexpected. A classic example
is from the Baltic Sea, where due to the
lockdown, only researchers and a park warden
were present on a seabird island during 2020.
The number of people on the island was thus
reduced by 92%, by contrast to normal years
where summer visitors enjoy the island. The
reduction in human presence corresponded with
the unexpected arrival of 33 white-tailed eagles
where no more than three had been observed in
each year for several decades (white-tailed
eagle: Fig. 3). By regularly flying near a murre
colony, the eagles flushed incubating birds at
disturbance rates 700% greater (7-fold
increase) than historical rates, resulting in
abandoned ledges where the birds lay their
eggs, and subsequent increased egg predation
by gulls and crows (Appendix 4, Table A4,
StudyID 31; Hentati-Sundberg et al., 2021 [this
issue]). The absence of humans in this case
seems to have negatively impacted a species of
conservation concern, through changing the
distribution of a species which evoked a
predator avoidance response.
Hunting also increased across many countries,
including in parks, to supplement incomes. A
classic example is the increase in pangolin
hunting which was likely due to a combination
of reduced protection from forest departments,
increased sales of hunting permits, and greater
illegal hunting. This is surprising considering
the possible role of pangolins as intermediary
hosts of SARS-COV-2, and calls to halt the
consumption of wildlife to avoid future
zoonoses (Zhang et al., 2020). Furthermore, it
is clear that resilient socio-ecological systems
are fundamental to supporting nature
conservation.
We further find that impacts of the lockdown on
human hunting activity have created not only
direct but cascading ecological impacts. For
instance, in North America the large greater
snow goose population is considered a pest due
to grazing on crops. Goose numbers are
controlled during their migration to the High
Arctic by allowing spring hunting. Yet, hunting
pressure decreased by up to 54% in 2020 in
comparison with 2019, and geese benefitted
from undisturbed foraging, resulting in rapid
weight gain to fuel their northward migration
(Appendix 4, Table A4, StudyID 25;
Bates, Primack, Duarte &. PAN-Environment Working Group (in press) Global COVID-19 lockdown highlights
humans as both threats and custodians of the environment. Biological Conservation
LeTourneux et al., 2021 [this issue]). Indeed,
hunters from Mittimatalik (Nunavut) reported
that those birds arriving in the Arctic this year
were unusually large and healthy. This year’s
cohort of geese, which graze the fragile arctic
tundra and degrade the habitat for other species,
will potentially drive future population growth
and environmental impacts (Snow Goose, Fig.
3).
The magnitudes of some effects were also more
dramatic than anticipated, such as in cases
where the lockdown coincided with
reproductive activity. For example, in
Colombia, a hotspot of bird diversity, species
richness in residential urban areas in Cali
increased on average by 37% when human
activity was lowest during the lockdown, which
coincided with the beginning of the breeding
season. Similarly, various species of sea turtles
benefited from nesting on undisturbed beaches
during the lockdown period. In Florida, for
instance, lockdown-related beach closures in a
conservation area were linked to a surprising
39% increase in nesting success in loggerhead
turtles, attributed to a lack of disturbances from
fishers and tourists with flashlights, and lack of
obstructions such as sandcastles (Appendix 4,
Table A4, StudyID 74).
4.1 Management implications
The global human lockdown experiment has
revealed the strong potential for humans as
custodians of the environment. The wealth of
observations collated here provides compelling,
near-experimental evidence for the role of
humans as a source of threats to species
ecosystems, illustrated by a range of increases
in biodiversity threats with release from human
disturbance during lockdown. Increases in
biodiversity threats are consistent with the
assumed role of human activity as a source of
negative impacts on the environment. These
observations help identify ways in which
human disturbance may play stronger roles in
impeding conservation efforts than previously
recognized, even for well-studied species such
as sea turtles. Our data also reveal contexts
where one simple change in human activity
could lead to multiple benefits. For instance, in
one park near Boston, noise did not decrease as
traffic volumes declined – surprisingly, noise
levels increased, likely because cars were
moving faster (Appendix 4, Table A4, StudyID
52). At the same time, greater traffic speed near
parks can increase the probability of vehicle
strikes (Nyhus, 2016), impacting both wildlife
and humans. Thus, rather than reducing traffic
volume, reducing traffic speed would lead to
less noise pollution and protect both wildlife
and human safety.
Considering how wildlife and humans have
responded during the lockdown offers the
potential to improve conservation strategies. In
particular, restrictions and enforcement
mechanisms to control human activities in
conservation areas and parks seem critical to
their effective functioning. Adaptive
conservation management during reproductive
seasons, such as during the nesting season of
birds and sea turtles, may also have much
stronger positive impacts than previously
recognized. The pandemic also highlights the
value of parks near urban centers that protect
species and the environment, and offer
opportunities for humans to conveniently enjoy
nature without traveling long distances (Airoldi
et al., 2021). The role of humans in supplying
food for some animal species is also apparent,
and suggests that this interaction can be
managed to improve conservation outcomes,
and avoid risks such as wildlife-human
conflicts. Regulation of marine shipping traffic
speed and volume can also have a major
contribution to conservation, which would
require, similar to the case of terrestrial
systems, the identification and regulation of
hotspots where strikes are frequent and noise
levels are elevated; the analysis of detailed
animal tracking data could further inform such
interventions (Rutz et al., 2020). Our results
Bates, Primack, Duarte &. PAN-Environment Working Group (in press) Global COVID-19 lockdown highlights
humans as both threats and custodians of the environment. Biological Conservation
also provide compelling evidence for the
benefits of reducing noise levels, particularly at
sea, and give additional impetus to policies that
incentivize the development of noise reduction
technologies (Duarte et al., 2021).
While many changes were linked to the
lockdown, we failed to link effects to the
lockdown in 18 different studies which
represent a wide range of systems and contexts.
Even so, what was interesting is that 15 of these
studies focussed on wildlife responses. This
includes where wildlife observations were in
remote areas or under effective management
and protection from human activities, or on
species that are unresponsive to humans. For
instance, we found that reduced wildlife
tourism in 2020 at the Neptune Islands Group
Marine Park, Australia, had no effects on white
shark residency (Appendix 4, Table A4,
StudyID 17; Huveneers et al., 2021 [this issue]).
This is likely due to current regulations
minimizing the impact of shark-diving tourism
when it occurs, suggesting effectiveness of
prior efforts to decrease animal harassment.
Likewise, the distribution of hawksbill turtles
(Chagos Archipelago, Indian Ocean), in an
infrequently visited area that is effectively
protected, was indistinguishable from previous
years (Appendix 4, Table A4, StudyID 76). In
remote northern Queensland, Australia, tagged
estuarine crocodiles exhibited similar habitat
use patterns despite restrictions on the number
of people allowed into the area (Appendix 4,
Table A4, StudyID 54). We also found strong
changes that were attributed to other factors,
such as the use of the Kerguelen toothfish
fishing grounds (Australia) by seals in 2020
(Appendix 4, Table A4, StudyID 40). The seals’
observed distribution changes during the
lockdown period likely represent responses to
other environmental factors, rather than
changes in fishing effort.
It is unclear if any of the changes in animal
distribution, abundance, behavior and sources
of food will persist once the lockdown
restrictions cease. Many of the responses
observed may be transient. For example,
animals roaming in areas typically supporting
intense human activity may retreat back to
smaller ranges once human activity resumes
full-scale. However, negative impacts resulting
from the interruption of conservation efforts
may be long-lasting and reverse years and
decades of such efforts. It is likely that long-
term impacts of hunting will be apparent into
the future in the abundance of this species
(Appendix 4, Table A4, StudyID 47), and in
most other cases where illegal activities have
injured or removed animals. On the positive
side, strong recruitment success of endangered
species in areas where disturbance declined
may have long-lasting positive effects,
particularly where the beneficiary species, such
as sea turtles, have long life spans. Long-term
studies should track the cohorts of the 2020
wildlife generation over years and decades to
integrate the positive and negative conservation
impacts of the human lockdown.
Our finding of both positive and negative
impacts of human confinement do not support
the view that biodiversity and the environment
will predominantly benefit from reduced
human activity during lockdown – a
perspective taken by some early media reports.
Positive impacts of lockdown on wildlife and
the environment stem largely from reduction of
pressures that are typically an unintended
consequence of human activity, such as ocean
noise. In contrast, the negative impacts of the
lockdown on biodiversity emerge from the
disruption of the deliberate work of humans to
conserve nature through research, restoration,
conservation interventions and enforcement. As
plans to re-start the economy progress, we
should strengthen the important role of people
as custodians of biodiversity, with benefits in
reducing the risks of future pandemics.
Bates, Primack, Duarte & PAN-Environment Working Group (in press) Global COVID-19 lockdown highlights
humans as both threats and custodians of the environment. Biological Conservation
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Supplementary materials (contact bates.amanda@gmail.com)
Appendix 1:
• Fig. A1. Change in time spent visiting nature.
• Fig. A2. Change in time spent driving.
• Fig. A3. Change in air traffic based on flight schedules.
• Fig. A4. Change in marine traffic based on AIS by country.
• Fig. A5. Change in marine traffic based on AIS by Overseas Territory.
• Table A1. Categories describing the type of effect related to human activities, biodiversity threats,
biodiversity and social systems.
• Table A2. Effect scoring scheme applied to anecdotal observations.
Appendix 2:
• Supplementary Methods. Statistical analysis methods.
Appendix 3:
• Table S3. Anecdotal observations. Excel file containing transcribed, categorized, and scored anecdotal
observations.
Appendix 4:
• Table S4. Transcribed empirical data. Excel file containing the empirical results transcribed from
Appendix 5:
• Table S5. Raw empirical results and study details. An excel file containing the raw author-submitted
empirical data analysis, results, results interpretation, meta-data, and a description of confounding variables
and how these were accounted for, author contributions, grants, and study-specific acknowledgements.