About the Authors

Fiona Maisels

Contributed equally to this work with: Fiona Maisels, Samantha Strindberg

fmaisels@wcs.org

Affiliations Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America, School of Natural Sciences, University of Stirling, Stirling, Scotland, United Kingdom

Samantha Strindberg

Contributed equally to this work with: Fiona Maisels, Samantha Strindberg

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Stephen Blake

Current address: Max Planck Institute for Ornithology, Vogelwarte Radolfzell, Radolfzell, Germany

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

George Wittemyer

Affiliations Department of Fish, Wildlife, and Conservation Biology, Colorado State University, Fort Collins, United States of America, Save The Elephants, Karen, Nairobi, Kenya

John Hart

Current address: Lukuru Wildlife Research Foundation, Gombe, Kinshasa, Democratic Republic of Congo

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Elizabeth A. Williamson

Affiliation School of Natural Sciences, University of Stirling, Stirling, Scotland, United Kingdom

Rostand Aba’a

Current address: Agence Nationale des parcs Nationaux, Libreville, Gabon

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Gaspard Abitsi

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Ruffin D. Ambahe

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Fidèl Amsini

Current address: Frankfurt Zoological Society, Frankfurt, Germany

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Parfait C. Bakabana

Current address: International Union for Conservation of Nature, Kabo, Republic of Congo

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Thurston Cleveland Hicks

Current address: Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany

Affiliation The Institute of Biodiversity and Ecosystem Dynamics, University of Amsterdam, Amsterdam, The Netherlands

Rosine E. Bayogo

Affiliation Ministère des Eaux, Forêts, Chasse et Pêche, Bangui, Central African Republic

Martha Bechem

Current address: MIKE Subregional Office, Yaoundé, Cameroon

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Rene L. Beyers

Affiliation Beatty Biodiversity Centre, University of British Columbia, Vancouver, British Columbia, Canada

Anicet N. Bezangoye

Affiliation Direction de la Gestion de la Faune et de la Chasse, Ministère des Eaux et Forêts, Libreville, Gabon

Patrick Boundja

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Nicolas Bout

Current address: The Aspinall Foundation, Franceville, Gabon

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Marc Ella Akou

Current address: Central Africa Regional Programme Office, World Wildlife Fund, Yaoundé, Cameroon

Affiliation Direction de la Gestion de la Faune et de la Chasse, Ministère des Eaux et Forêts, Libreville, Gabon

Lambert Bene Bene

Deceased.

Affiliation Central Africa Regional Programme Office, World Wildlife Fund, Yaoundé, Cameroon

Bernard Fosso

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Elizabeth Greengrass

Current address: Bradford on Avon, Wiltshire, United Kingdom

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Falk Grossmann

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Clement Ikamba-Nkulu

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Omari Ilambu

Current address: Central Africa Regional Programme Office, World Wildlife Fund, Yaoundé, Cameroon

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Bila-Isia Inogwabini

Current address: Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Fortune Iyenguet

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Franck Kiminou

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Max Kokangoye

Deceased.

Affiliations Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America, Direction de la Gestion de la Faune et de la Chasse, Ministère des Eaux et Forêts, Libreville, Gabon

Deo Kujirakwinja

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Stephanie Latour

Current address: Vaucresson, France

Affiliations Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America, The Jane Goodall Institute, Arlington, Virginia, United States of America

Innocent Liengola

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Quevain Mackaya

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Jacob Madidi

Current address: Societé Générale de Surveillance, Bunia, Oriental Province, Democratic Republic of Congo

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Bola Madzoke

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Calixte Makoumbou

Current address: Mokabi Société anonyme (Rougier Group), Brazzaville, Republic of Congo

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Guy-Aimé Malanda

Current address: Odzala-Kokoua National Park, African Parks, Brazzaville, Republic of Congo

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Richard Malonga

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Olivier Mbani

Current address: Environment Department, Association Sylvatrop, Conakry, Guinea

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Valentin A. Mbendzo

Current address: Programme d’Appui à la Conservation des Ecosystèmes du Bassin du Congo, Yaoundé, Cameroon

Affiliations Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America, Central Africa Regional Programme Office, World Wildlife Fund, Yaoundé, Cameroon

Edgar Ambassa

Current address: Ministry of Forestry and Wildlife, Yaoundé, Cameroon

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Albert Ekinde

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Yves Mihindou

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Bethan J. Morgan

Affiliations School of Natural Sciences, University of Stirling, Stirling, Scotland, United Kingdom, Central Africa Program, Zoological Society of San Diego, Yaoundé, Cameroon

Prosper Motsaba

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Gabin Moukala

Current address: Environment Department, Association Sylvatrop, Conakry, Guinea

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Anselme Mounguengui

Affiliation Central Africa Regional Programme Office, World Wildlife Fund, Yaoundé, Cameroon

Brice S. Mowawa

Current address: Ministère de l’Economie Forestière, Brazzaville, Republic of Congo

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Christian Ndzai

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Stuart Nixon

Current address: Fauna & Flora International, Cambridge, United Kingdom

Affiliation Zoological Society of London, Regents Park, London, United Kingdom

Pele Nkumu

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Fabian Nzolani

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Lilian Pintea

Affiliation The Jane Goodall Institute, Arlington, Virginia, United States of America

Andrew Plumptre

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Hugo Rainey

Current address: The Biodiversity Consultancy Ltd, Cambridge, United Kingdom

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Bruno Bokoto de Semboli

Affiliation Ministère des Eaux, Forêts, Chasse et Pêche, Bangui, Central African Republic

Adeline Serckx

Affiliation Behavioral Biology Unit, University of Liege, Liege, Belgium

Emma Stokes

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Andrea Turkalo

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Hilde Vanleeuwe

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Ashley Vosper

Current address: Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Affiliations Lukuru Wildlife Research Foundation, Gombe, Kinshasa, Democratic Republic of Congo, African Wildlife Foundation, Gombe, Kinshasa, Democratic Republic of Congo

Ymke Warren

Deceased.

Affiliation Global Conservation Program, Wildlife Conservation Society, Bronx, New York, United States of America

Competing Interests

The authors have the following interest: This study was in part supported by the following: Busch Gardens and TOTAL Gabon. CIB (Congolaise Industrielle du Bois) provided some logistical help for the 2006 and 2010–11 surveys in the following northern Congo sites (Pokola, Kabo, Loundougou. This does not alter the authors’ adherence to all the PLOS ONE policies on sharing data and materials, as detailed online in the guide for authors.

Author Contributions

Commented on the MS and organised fieldwork: AB AE AP AS AT AV BBds BF B-II BJM BM BSM TCH CI-N CM CN DK EA EAW EG ES FA FG FI FK FM FN GA G-AM GM GW HR HV IL JH JM LP MA MB MK NB OI OM PB PCB PM PN QM RA RLB REB RDA RM SB SL SN SS VAM YM. Conceived and designed the experiments: AP AS AV BJM TCH DK ES FA FG FI FM G-AM HR HV JH RA SB SL SN SS YW. Performed the experiments: AB AE AM AP AS AV BBds B-II BJM BM BSM TCH CI-N CM CN DK EA EAW EG FA FG FI FK FM FN GA G-AM GM HV JH JM LB MA MB MK NB OI OM PB PCB PM PN QM RA REB RDA SB SL SN VAM YM YW. Analyzed the data: SS FM GW. Wrote the paper: AP AT AV B-II BJM TCH EAW EG ES FI FM GW HR HV JH NB PB RLB RM SB SL SN SS.