Actions taken against the COVID-19 pandemic have dramatically affected many aspects of human activity, giving us a unique opportunity to study how wildlife responds to the human-induced rapid environmental changes. The wearing of face masks, widely adopted to prevent pathogen transmission, represents a novel element in many parts of the world where wearing a face mask was rare before the COVID-19 outbreak. During September 2020-March 2021, we conducted large-scale multi-species field experiments to evaluate whether face mask-use in public places elicits a behavioural response in birds by comparing their escape and alert responses when approached by a researcher with or without a face mask in four European countries (Czech Republic, Finland, Hungary, and Poland) and Israel. We also tested whether these patterns differed between urban and rural sites. We employed Bayesian generalized linear mixed models (with phylogeny and site as random factors) controlling for a suite of covariates and found no association between the face mask-wear and flight initiation distance, alert distance, and fly-away distance, respectively, neither in urban nor in rural birds. However, we found that all three distances were strongly and consistently associated with habitat type and starting distance, with birds showing earlier escape and alert behaviour and longer distances fled when approached in rural than in urban habitats and from longer initial distances. Our results indicate that wearing face masks did not trigger observable changes in antipredator behaviour across the Western Palearctic birds, and our data did not support the role of habituation in explaining this pattern.

Arctic Centre University of Lapland PO Box 122 96101 Rovaniemi Finland

Behavioural Ecology Group Department of Systematic Zoology and Ecology ELTE Eötvös Loránd University Pázmány Péter sétány 1 C 1117 Budapest Hungary; Department of Plant Pathology Institute of Plant Protection Hungarian University of Agriculture and Life Sciences Ménesi út 44 1118 Budapest Hungary

Ben Gurion University of the Negev Eilat Campus P O Box 272 Eilat 88000 Israel

Department of Ecology Institute of Biology University of Veterinary Medicine Budapest Rottenbiller u 50 Budapest H 1077 Hungary

Ecologie Systématique Evolution Université Paris Sud CNRS AgroParisTech Université Paris Saclay Orsay Cedex F 91405 France; Ministry of Education Key Laboratory for Biodiversity Sciences and Ecological Engineering College of Life Sciences Beijing Normal University Beijing 100875 China

Faculty of Environmental Sciences Czech University of Life Sciences Prague Kamýcká 129 165 00 Praha 6 Czech Republic; Department of Zoology Poznań University of Life Sciences Wojska Polskiego 71C 60 625 Poznań Poland

Faculty of Environmental Sciences Czech University of Life Sciences Prague Kamýcká 129 165 00 Praha 6 Czech Republic; Faculty of Biological Sciences University of Zielona Góra Prof Z Szafrana St 1 PL 65 516 Zielona Góra Poland

Institute of Vertebrate Biology Czech Academy of Sciences Květná 8 603 65 Brno Czech Republic

Institute of Vertebrate Biology Czech Academy of Sciences Květná 8 603 65 Brno Czech Republic; Department of Zoology Faculty of Science Charles University Viničná 7 Praha 12844 Czech Republic

See more in PubMed

Aravindakshan A., Boehnke J., Gholami E., Nayak A. Mask-wearing during the COVID-19 pandemic. medRxiv. 2020 doi: 10.1101/2020.09.11.20192971. DOI

Ban J., Zhou L., Zhang Y., Brooke Anderson G., Li T. The health policy implications of individual adaptive behavior responses to smog pollution in urban China. Environ. Int. 2017;106:144–152. doi: 10.1016/j.envint.2017.06.010. PubMed DOI

Bateman P.W., Fleming P.A. Who are you looking at? Hadeda ibises use direction of gaze, head orientation and approach speed in their risk assessment of a potential predator. J. Zool. 2011;285:316–323. doi: 10.1111/j.1469-7998.2011.00846.x. DOI

Bates D., Mächler M., Bolker B., Walker S. Fitting linear mixed-effects models using lme4. J. Stat. Softw. 2015;67:1–48.

Biondi L.M., Fuentes G.M., Córdoba R.S., Bó M.S., Cavalli M., Paterlini C.A., Castano M.V., García G.O. Variation in boldness and novelty response between rural and urban predatory birds: the Chimango Caracara, Milvago chimango as study case. Behav. Process. 2020;173:104064. doi: 10.1016/j.beproc.2020.104064. PubMed DOI

Blumstein D.T. Developing an evolutionary ecology of fear: how life history and natural history traits affect disturbance tolerance in birds. Anim. Behav. 2006;71:389–399. doi: 10.1016/j.anbehav.2005.05.010. DOI

Blumstein D.T., Fernández-Juricic E., Zollner P.A., Garity S.C. Inter-specific variation in avian responses to human disturbance. J. Appl. Ecol. 2005;42:943–953. doi: 10.1111/j.1365-2664.2005.01071.x. DOI

Braimoh B., Iwajomo S., Wilson M., Chaskda A., Ajang A., Cresswell W. Managing human disturbance: factors influencing flight-initiation distance of birds in a West African nature reserve. Ostrich. 2018;89:59–69. doi: 10.2989/00306525.2017.1388300. DOI

Brunton J. Guardian; 2020. “Nature is taking back Venice”: wildlife returns to tourist-free city. https://www.theguardian.com/environment/2020/mar/20/nature-is-taking-back-venice-wildlife-returns-to-tourist-free-city

Castellano-Navarro A., Macanás-Martínez E., Xu Z., Guillén-Salazar F., MacIntosh A.J.J., Amici F., Albiach-Serrano A. Japanese Macaques’ (Macaca fuscata) sensitivity to human gaze and visual perspective in contexts of threat, cooperation, and competition. Sci. Rep. 2021;11:5264. doi: 10.1038/s41598-021-84250-5. PubMed DOI PMC

Cavalli M., Baladrón A.V., Isacch J.P., Biondi L.M., Bó M.S. Differential risk perception of rural and urban Burrowing Owls exposed to humans and dogs. Behav. Process. 2016;124:60–65. doi: 10.1016/j.beproc.2015.12.006. PubMed DOI

Clucas B., Marzluff J.M., Mackovjak D., Palmquist I. Do American crows pay attention to human gaze and facial expressions? Ethology. 2013;119:296–302. doi: 10.1111/eth.12064. DOI

Davidson G.L., Clayton N.S., Thornton A. Wild jackdaws, Corvus monedula, recognize individual humans and may respond to gaze direction with defensive behaviour. Anim. Behav. 2015;108:17–24. doi: 10.1016/j.anbehav.2015.07.010. DOI

Derryberry E.P., Phillips J.N., Derryberry G.E., Blum M.J., Luther D. Singing in a silent spring: birds respond to a half-century soundscape reversion during the COVID-19 shutdown. Science. 2020;370:575–579. doi: 10.1126/SCIENCE.ABD5777. PubMed DOI

Díaz M., Møller A.P., Flensted-Jensen E., Grim T., Ibáñez-Álamo J.D., Jokimäki J., Markó G., Tryjanowski P. The geography of fear: a latitudinal gradient in anti-predator escape distances of birds across Europe. PLoS One. 2013;8 doi: 10.1371/journal.pone.0064634. PubMed DOI PMC

Dormann C.F., Elith J., Bacher S., Buchmann C., Carl G., Carré G., Marquéz J.R.G., Gruber B., Lafourcade B., Leitão P.J., Münkemüller T., Mcclean C., Osborne P.E., Reineking B., Schröder B., Skidmore A.K., Zurell D., Lautenbach S. Collinearity: a review of methods to deal with it and a simulation study evaluating their performance. Ecography. 2013;36:27–46. doi: 10.1111/j.1600-0587.2012.07348.x. DOI

Ducatez S., Audet J.N., Rodriguez J.R., Kayello L., Lefebvre L. Innovativeness and the effects of urbanization on risk-taking behaviors in wild Barbados birds. Anim. Cogn. 2017;20:33–42. doi: 10.1007/s10071-016-1007-0. PubMed DOI

Dunning J.B. CRC Press; Boca Raton: 2008. CRC Handbook of Avian Body Masses.

Fang H., Wang L., Yang Y. Human mobility restrictions and the spread of the Novel Coronavirus (2019-nCoV) in China. J. Public Econ. 2020;191:104272. doi: 10.1016/j.jpubeco.2020.104272. PubMed DOI PMC

Felter C., Bussemaker N. Counc. Foreign Relations; 2020. Which countries are requiring face masks? https://www.cfr.org/in-brief/which-countries-are-requiring-face-masks

Fernández-Juricic E., Jimenez M.D., Lucas E. Alert distance as an alternative measure of bird tolerance to human disturbance: implications for park design. Environ. Conserv. 2001;28:263–269. doi: 10.1017/S0376892901000273. DOI

Fox J., Weisberg S., Price B., Adler D., Bates D., Baud-Bovy G., Bolker B., Ellison S., Firth D., Friendly M., Gorjanc G., Graves S., Heiberger R., Krivitsky P., Laboissiere R., Maechler M., Monette G., Murdoch D., Nilsson H., Ogle D., Ripley B., Venables W., Walker S., Winsemius D., Zeileis A. Package “car”. 2020. http://cran.r-project.org/web/packages/car/car.pdf

Gatto M., Bertuzzo E., Mari L., Miccoli S., Carraro L., Casagrandi R., Rinaldo A. Spread and dynamics of the COVID-19 epidemic in Italy: effects of emergency containment measures. Proc. Natl. Acad. Sci. U. S. A. 2020;117:10484–10491. doi: 10.1073/pnas.2004978117. PubMed DOI PMC

Gordo O., Brotons L., Herrando S., Gargallo G. Rapid behavioural response of urban birds to COVID-19 lockdown. Proc. R. Soc. B Biol. Sci. 2021;288:20202513. doi: 10.1098/rspb.2020.2513. PubMed DOI PMC

Gould M.L., Green L., Altenau B., Blumstein D.T. A study of the species-confidence hypothesis with Spiny-cheeked Honeyeaters (Acanthagenys rufogularis) Emu. 2004;104:267–271. doi: 10.1071/mu03033. DOI

Greenhalgh T., Schmid M.B., Czypionka T., Bassler D., Gruer L. Face masks for the public during the covid-19 crisis. BMJ. 2020;369:m1435. doi: 10.1136/bmj.m1435. PubMed DOI

Griffin A.S., Netto K., Peneaux C. Neophilia, innovation and learning in an urbanized world: a critical evaluation of mixed findings. Curr. Opin. Behav. Sci. 2017;16:15–22. doi: 10.1016/j.cobeha.2017.01.004. DOI

Gutzwiller K.J., Marcum H.A. Avian responses to observer clothing color: caveats from winter point counts. Wilson Bull. 1993;105:628–636.

He E., Laurent L. Blomberg; 2020. The world is masking up, some are opting out. https://www.bloomberg.com/graphics/2020-opinion-coronavirus-global-face-mask-adoption/

Hentati-Sundberg J., Berglund P.A., Hejdström A., Olsson O. COVID-19 lockdown reveals tourists as seabird guardians. Biol. Conserv. 2021;254:108950. doi: 10.1016/j.biocon.2021.108950. PubMed DOI PMC

Huang X., Li Z., Jiang Y., Li X., Porter D. Twitter reveals human mobility dynamics during the COVID-19 pandemic. PLoS One. 2020;15 doi: 10.1371/journal.pone.0241957. PubMed DOI PMC

Huber L., Racca A., Scaf B., Virányi Z., Range F. Discrimination of familiar human faces in dogs (Canis familiaris) Learn. Motiv. 2013;44:258–269. doi: 10.1016/j.lmot.2013.04.005. PubMed DOI PMC

Imperial College London, YouGov Covid-19 behaviour tracker. 2021. https://ichpanalytics.imperialcollegehealthpartners.com/

Jetz W., Thomas G.H., Joy J.B., Hartmann K., Mooers A.O. The global diversity of birds in space and time. Nature. 2012;491:444–448. doi: 10.1038/nature11631. PubMed DOI

Jiang X., Liu J., Zhang C., Liang W. Face masks matter: Eurasian tree sparrows show reduced fear responses to people wearing face masks during the COVID-19 pandemic. Glob. Ecol. Conserv. 2020;24 doi: 10.1016/j.gecco.2020.e01277. PubMed DOI PMC

Kraemer M.U.G., Yang C.H., Gutierrez B., Wu C.H., Klein B., Pigott D.M., du Plessis L., Faria N.R., Li R., Hanage W.P., Brownstein J.S., Layan M., Vespignani A., Tian H., Dye C., Pybus O.G., Scarpino S.V. The effect of human mobility and control measures on the COVID-19 epidemic in China. Science. 2020;368:493–497. doi: 10.1126/science.abb4218. PubMed DOI PMC

Lavee D., Safriel U.N., Meilijson I. For how long do trans-Saharan migrants stop over at an oasis? Ornis Scand. 1991;22:33–44. doi: 10.2307/3676619. DOI

Lecocq T., Hicks S.P., van Noten K., van Wijk K., Koelemeijer P., de Plaen R.S.M., Massin F., Hillers G., Anthony R.E., Apoloner M.T., Arroyo-Solórzano M., Assink J.D., Büyükakpınar P., Cannata A., Cannavo F., Carrasco S., Caudron C., Chaves E.J., Cornwell D.G., Craig D., den Ouden O.F.C., Diaz J., Donner S., Evangelidis C.P., Evers L., Fauville B., Fernandez G.A., Giannopoulos D., Gibbons S.J., Girona T., Grecu B., Grunberg M., Hetényi G., Horleston A., Inza A., Irving J.C.E., Jamalreyhani M., Kafka A., Koymans M.R., Labedz C.R., Larose E., Lindsey N.J., McKinnon M., Megies T., Miller M.S., Minarik W., Moresi L., Márquez-Ramírez V.H., Möllhoff M., Nesbitt I.M., Niyogi S., Ojeda J., Oth A., Proud S., Pulli J., Retailleau L., Rintamäki A.E., Satriano C., Savage M.K., Shani-Kadmiel S., Sleeman R., Sokos E., Stammler K., Stott A.E., Subedi S., Sørensen M.B., Taira T., Tapia M., Turhan F., van der Pluijm B., Vanstone M., Vergne J., Vuorinen T.A.T., Warren T., Wassermann J., Xiao H. Global quieting of high-frequency seismic noise due to COVID-19 pandemic lockdown measures. Science. 2020;369:1338–1343. doi: 10.1126/science.abd2438. PubMed DOI

Lee W.Y., Lee S. Im, Choe J.C., Jablonski P.G. Wild birds recognize individual humans: experiments on magpies, Pica pica. Anim. Cogn. 2011;14:817–825. doi: 10.1007/s10071-011-0415-4. PubMed DOI

Levey D.J., Londoño G.A., Ungvari-Martin J., Hiersoux M.R., Jankowski J.E., Poulsen J.R., Stracey C.M., Robinson S.K. Urban mockingbirds quickly learn to identify individual humans. Proc. Natl. Acad. Sci. U. S. A. 2009;106:8959–8962. doi: 10.1073/pnas.0811422106. PubMed DOI PMC

Li D., Dinnage R., Nell L.A., Helmus M.R., Ives A.R. phyr: an r package for phylogenetic species-distribution modelling in ecological communities. Methods Ecol. Evol. 2020;11:1455–1463. doi: 10.1111/2041-210X.13471. DOI

Lima S.L., Dill L.M. Behavioral decisions made under the risk of predation: a review and prospectus. Can. J. Zool. 1990;68:619–640. doi: 10.1139/z90-092. DOI

Macdonald H. New York Times; 2020. Animals are rewilding our cities. On YouTube, at least. https://www.nytimes.com/2020/04/15/magazine/quarantine-animal-videos-coronavirus.html

Manenti R., Mori E., Di Canio V., Mercurio S., Picone M., Caffi M., Brambilla M., Ficetola G.F., Rubolini D. The good, the bad and the ugly of COVID-19 lockdown effects on wildlife conservation: insights from the first European locked down country. Biol. Conserv. 2020;249:108728. doi: 10.1016/j.biocon.2020.108728. PubMed DOI PMC

Marzluff J.M., Bowman R., Donnelly R. In: Avian Ecology and Conservation in an Urbanizing World. Marzluff J.M., Bowman R., Donnelly R., editors. Kluwer; New York: 2001. A historical perspective on urban bird research: trend, terms, and approaches; pp. 20–47.

Marzluff J.M., Walls J., Cornell H.N., Withey J.C., Craig D.P. Lasting recognition of threatening people by wild American crows. Anim. Behav. 2010;79:699–707. doi: 10.1016/j.anbehav.2009.12.022. DOI

Mikula P. Pedestrian density influences flight distances of urban birds. Ardea. 2014;102:53–60. doi: 10.5253/078.102.0105. DOI

Mikula P., Díaz M., Albrecht T., Jokimäki J., Kaisanlahti-Jokimäki M.-L., Kroitero G., Møller A.P., Tryjanowski P., Yosef R., Hromada M. Adjusting risk-taking to the annual cycle of long-distance migratory birds. Sci. Rep. 2018;8:13989. doi: 10.1038/s41598-018-32252-1. PubMed DOI PMC

Mikula P., Jokimäki J., Kaisanlahti-Jokimäki M.-L., Markó G., Morelli F., Møller A.P., Szakony S., Yosef R., Albrecht T., Tryjanowski P. Primary data for “Face mask-wear did not affect large-scale patterns in escape and alertness of urban and rural birds during the COVID-19 pandemic”. Mendeley Data. 2021 doi: 10.17632/mcmzzct9m9.1. PubMed DOI PMC

Møller A.P., Liang W. Tropical birds take small risks. Behav. Ecol. 2013;24:267–272. doi: 10.1093/beheco/ars163. DOI

Møller A.P., Tryjanowski P. Direction of approach by predators and flight initiation distance of urban and rural populations of birds. Behav. Ecol. 2014;25:960–966. doi: 10.1093/beheco/aru073. DOI

Morelli F., Mikula P., Benedetti Y., Bussière R., Jerzak L., Tryjanowski P. Escape behaviour of birds in urban parks and cemeteries across Europe: evidence of behavioural adaptation to human activity. Sci. Total Environ. 2018;631–632:803–810. doi: 10.1016/j.scitotenv.2018.03.118. PubMed DOI

Morelli F., Benedetti Y., Díaz M., Grim T., Ibáñez-Álamo J.D., Jokimäki J., Kaisanlahti-Jokimäki M., Tätte K., Markó G., Jiang Y., Tryjanowski P., Møller A.P. Contagious fear: escape behavior increases with flock size in European gregarious birds. Ecol. Evol. 2019;9:6096–6104. doi: 10.1002/ece3.5193. PubMed DOI PMC

Nagasawa M., Murai K., Mogi K., Kikusui T. Dogs can discriminate human smiling faces from blank expressions. Anim. Cogn. 2011;14:525–533. doi: 10.1007/s10071-011-0386-5. PubMed DOI

Nunes J.A.C.C., Costa Y., Blumstein D.T., Leduc A.O.H.C., Dorea A.C., Benevides L.J., Sampaio C.L.S., Barros F. Global trends on reef fishes’ ecology of fear: flight initiation distance for conservation. Mar. Environ. Res. 2018;136:153–157. doi: 10.1016/j.marenvres.2018.02.011. PubMed DOI

Pradel R., Rioux N., Tamisier A., Lebreton J.-D. Individual turnover among wintering Teal in Camargue: a mark-recapture study. J. Wildl. Manag. 1997;61:816–821. doi: 10.2307/3802189. DOI

Reynolds C., Henry D.A.W., Tye D.R.C., Tye N.D. Defining separation zones for coastal birds at a wetland of global importance. Wildl. Res. 2020;48:134–141. doi: 10.1071/wr20098. DOI

Runyan A.M., Blumstein D.T. Do individual differences influence flight initiation distance? J. Wildl. Manag. 2004;68(4):1124–1129. doi: 10.2193/0022-541X(2004)068[1124:DIDIFI]2.0.CO;2. DOI

Rutz C., Loretto M.C., Bates A.E., Davidson S.C., Duarte C.M., Jetz W., Johnson M., Kato A., Kays R., Mueller T., Primack R.B., Ropert-Coudert Y., Tucker M.A., Wikelski M., Cagnacci F. COVID-19 lockdown allows researchers to quantify the effects of human activity on wildlife. Nat. Ecol. Evol. 2020;4:1156–1159. doi: 10.1038/s41559-020-1237-z. PubMed DOI

Samia D.S.M., Møller A.P., Blumstein D.T. Brain size as a driver of avian escape strategy. Sci. Rep. 2015;5:11913. doi: 10.1038/srep11913. PubMed DOI PMC

Samia D.S.M., Nakagawa S., Nomura F., Rangel T.F., Blumstein D.T. Increased tolerance to humans among disturbed wildlife. Nat. Commun. 2015;6:8877. doi: 10.1038/ncomms9877. PubMed DOI PMC

Schliep K.P. phangorn: phylogenetic analysis in R. Bioinformatics. 2011;27:592–593. doi: 10.1093/bioinformatics/btq706. PubMed DOI PMC

Simpson D., Rue H., Riebler A., Martins T.G., Sørbye S.H. Penalising model component complexity: a principled, practical approach to constructing priors. Stat. Sci. 2017;32:1–28. doi: 10.1214/16-STS576. DOI

Snell-Rood E.C. An overview of the evolutionary causes and consequences of behavioural plasticity. Anim. Behav. 2013;85:1004–1011. doi: 10.1016/j.anbehav.2012.12.031. DOI

Soga M., Evans M.J., Cox D.T.C., Gaston K.J. Impacts of the COVID-19 pandemic on human–nature interactions: pathways, evidence and implications. People Nat. 2021;3:518–527. doi: 10.1002/pan3.10201. PubMed DOI PMC

Sol D., Duncan R.P., Blackburn T.M., Cassey P., Lefebvre L. Big brains, enhanced cognition, and response of birds to novel environments. Proc. Natl. Acad. Sci. U. S. A. 2005;102:5460–5465. doi: 10.1073/pnas.0408145102. PubMed DOI PMC

Sol D., Lapiedra O., González-Lagos C. Behavioural adjustments for a life in the city. Anim. Behav. 2013;85:1101–1112. doi: 10.1016/J.ANBEHAV.2013.01.023. DOI

Stankowich T., Blumstein D.T. Fear in animals: a meta-analysis and review of risk assessment. Proc. R. Soc. Lond. B Biol. Sci. 2005;272:2627–2634. doi: 10.1098/rspb.2005.3251. PubMed DOI PMC

Tang C.S.K., Wong C.Y. Factors influencing the wearing of facemasks to prevent the severe acute respiratory syndrome among adult Chinese in Hong Kong. Prev. Med. 2004;39:1187–1193. doi: 10.1016/j.ypmed.2004.04.032. PubMed DOI PMC

Tätte K., Møller A.P., Mänd R. Towards an integrated view of escape decisions in birds: relation between flight initiation distance and distance fled. Anim. Behav. 2018;136:75–86. doi: 10.1016/j.anbehav.2017.12.008. DOI

Tryjanowski P., Møller A.P., Morelli F., Biaduń W., Brauze T., Ciach M., Czechowski P., Czyz S., Dulisz B., Golawski A., Hetmański T., Indykiewicz P., Mitrus C., Myczko L., Nowakowski J.J., Polakowski M., Takacs V., Wysocki D., Zduniak P. Urbanization affects neophilia and risk-taking at bird-feeders. Sci. Rep. 2016;6:1–7. doi: 10.1038/srep28575. PubMed DOI PMC

Tryjanowski P., Kosicki J.Z., Hromada M., Mikula P. The emergence of tolerance of human disturbance in Neotropical birds. J. Trop. Ecol. 2020;36:1–5. doi: 10.1017/S0266467419000282. DOI

Venter Z.S., Aunan K., Chowdhury S., Lelieveld J. COVID-19 lockdowns cause global air pollution declines. Proc. Natl. Acad. Sci. U. S. A. 2020;117:18984–18990. doi: 10.1073/pnas.2006853117. PubMed DOI PMC

Vincze E., Papp S., Preiszner B., Seress G., Bókony V., Liker A. Habituation to human disturbance is faster in urban than rural house sparrows. Behav. Ecol. 2016;27:1304–1313. doi: 10.1093/beheco/arw047. DOI

Wada K., Oka-Ezoe K., Smith D.R. Wearing face masks in public during the influenza season may reflect other positive hygiene practices in Japan. BMC Public Health. 2012;12:1065. doi: 10.1186/1471-2458-12-1065. PubMed DOI PMC

Warnock N., Bishop M.A. Spring stopover ecology of migrant western sandpipers. Condor. 1998;100:456–467. doi: 10.2307/1369711. DOI

Weston M.A., McLeod E.M., Blumstein D.T., Guay P.-J. A review of flight-initiation distances and their application to managing disturbance to Australian birds. Emu. 2012;112:269–286. doi: 10.1071/MU12026. DOI

Wilman H., Belmaker J., Simpson J., de la Rosa C., Rivadeneira M.M., Jetz W. EltonTraits 1.0: species-level foraging attributes of the world’s birds and mammals. Ecology. 2014;95:2027. doi: 10.1890/13-1917.1. DOI

Wong B.B.M., Candolin U. Behavioral responses to changing environments. Behav. Ecol. 2015;26:665–673. doi: 10.1093/beheco/aru183. DOI

Wong C.Y., Tang C.S.K. Practice of habitual and volitional health behaviors to prevent severe acute respiratory syndrome among Chinese adolescents in Hong Kong. J. Adolesc. Health. 2005;36:193–200. doi: 10.1016/j.jadohealth.2004.02.024. PubMed DOI PMC

World Health Organization Mask use in the context of COVID-19. 2020. https://www.who.int/publications/i/item/advice-on-the-use-of-masks-in-the-community-during-home-care-and-in-healthcare-settings-in-the-context-of-the-novel-coronavirus-(2019-ncov)-outbreak

World Health Organization WHO coronavirus disease (COVID-19) dashboard. 2021. https://covid19.who.int/

Zambrano-Monserrate M.A., Ruano M.A., Sanchez-Alcalde L. Indirect effects of COVID-19 on the environment. Sci. Total Environ. 2020;728:138813. doi: 10.1016/j.scitotenv.2020.138813. PubMed DOI PMC

Zellmer A.J., Wood E.M., Surasinghe T., Putman B.J., Pauly G.B., Magle S.B., Lewis J.S., Kay C.A.M., Fidino M. What can we learn from wildlife sightings during the COVID-19 global shutdown? Ecosphere. 2020;11 doi: 10.1002/ecs2.3215. PubMed DOI PMC

Zhang J., Mu Q. Air pollution and defensive expenditures: evidence from particulate-filtering facemasks. J. Environ. Econ. Manag. 2018;92:517–536. doi: 10.1016/j.jeem.2017.07.006. DOI

Zhou B., Liang W. Avian escape responses to observers wearing clothing of different colors: a comparison of urban and rural populations. Glob. Ecol. Conserv. 2020;22 doi: 10.1016/j.gecco.2020.e00921. DOI

Urban birds' tolerance towards humans was largely unaffected by COVID-19 shutdown-induced variation in human presence

Bird tolerance to humans in open tropical ecosystems

Face mask-wear did not affect large-scale patterns in escape and alertness of urban and rural birds during the COVID-19 pandemic