Export selection as
Taxonomic name
- (-) Remove Aves filter Aves
- Animalia (42) Apply Animalia filter
- Arthropoda (42) Apply Arthropoda filter
- Insecta (42) Apply Insecta filter
- Phthiraptera (42) Apply Phthiraptera filter
- Ischnocera (21) Apply Ischnocera filter
- Philopteridae (21) Apply Philopteridae filter
- Passeriformes (16) Apply Passeriformes filter
- Columbiformes (14) Apply Columbiformes filter
- Amblycera (12) Apply Amblycera filter
- Menoponidae (12) Apply Menoponidae filter
- Myrsidea (10) Apply Myrsidea filter
- Columbidae (9) Apply Columbidae filter
- Galliformes (6) Apply Galliformes filter
- Columbicola (5) Apply Columbicola filter
- Physconelloides (5) Apply Physconelloides filter
- Anseriformes (3) Apply Anseriformes filter
- Goniodes (3) Apply Goniodes filter
- Anas (2) Apply Anas filter
- Anatidae (2) Apply Anatidae filter
- Apodiformes (2) Apply Apodiformes filter
- Brueelia (2) Apply Brueelia filter
- Campanulotes (2) Apply Campanulotes filter
- Coloceras (2) Apply Coloceras filter
- Columba (2) Apply Columba filter
- Columba livia (2) Apply Columba livia filter
- Emberizidae (2) Apply Emberizidae filter
- Falconiformes (2) Apply Falconiformes filter
- Mammalia (2) Apply Mammalia filter
- Penenirmus (2) Apply Penenirmus filter
- Phasianidae (2) Apply Phasianidae filter
- Piciformes (2) Apply Piciformes filter
- Psittacidae (2) Apply Psittacidae filter
- Psittaciformes (2) Apply Psittaciformes filter
- Ricinidae (2) Apply Ricinidae filter
- Zenaida (2) Apply Zenaida filter
- Accipitridae (1) Apply Accipitridae filter
- Alcedinidae (1) Apply Alcedinidae filter
- Alcedoecus (1) Apply Alcedoecus filter
- Alcedoffula (1) Apply Alcedoffula filter
- Amazonetta (1) Apply Amazonetta filter
- Anas formosa (1) Apply Anas formosa filter
- Apodidae (1) Apply Apodidae filter
- Aprosmictus (1) Apply Aprosmictus filter
- Aprosmictus erythropterus (1) Apply Aprosmictus erythropterus filter
- Apterygidae (1) Apply Apterygidae filter
- Apterygiformes (1) Apply Apterygiformes filter
- Artiodactyla (1) Apply Artiodactyla filter
- Artiodactyla (1) Apply Artiodactyla filter
- Auricotes (1) Apply Auricotes filter
- Boopiidae (1) Apply Boopiidae filter
- Bovicola (1) Apply Bovicola filter
- Bovidae (1) Apply Bovidae filter
- Bovidae (1) Apply Bovidae filter
- Brueelia nebulosa (1) Apply Brueelia nebulosa filter
- Buteo (1) Apply Buteo filter
- Buteo galapagoensis (1) Apply Buteo galapagoensis filter
- Caenolestidae (1) Apply Caenolestidae filter
- Caenolestidae (1) Apply Caenolestidae filter
- Campanulotes compar (1) Apply Campanulotes compar filter
- Canidae (1) Apply Canidae filter
- Canis (1) Apply Canis filter
- Canis lupus (1) Apply Canis lupus filter
- Capra (1) Apply Capra filter
- Capra (1) Apply Capra filter
- Capra hircus (1) Apply Capra hircus filter
- Capra hircus (1) Apply Capra hircus filter
- Caprimulgiformes (1) Apply Caprimulgiformes filter
- Caprinae (1) Apply Caprinae filter
- Carnivora (1) Apply Carnivora filter
- Casuariiformes (1) Apply Casuariiformes filter
- Catharus (1) Apply Catharus filter
- Catharus minimus (1) Apply Catharus minimus filter
- Catharus ustulatus (1) Apply Catharus ustulatus filter
- Chelopistes (1) Apply Chelopistes filter
- Ciconiiformes (1) Apply Ciconiiformes filter
- Collodennyus (1) Apply Collodennyus filter
- Columbicola columbae (1) Apply Columbicola columbae filter
- Columbicola longiceps (1) Apply Columbicola longiceps filter
- Columbicola wolffhuegeli (1) Apply Columbicola wolffhuegeli filter
- Coraciiformes (1) Apply Coraciiformes filter
- Corvidae (1) Apply Corvidae filter
- Criniger (1) Apply Criniger filter
- Cummingsia (1) Apply Cummingsia filter
- Cummingsia Cummingsia maculata (1) Apply Cummingsia Cummingsia maculata filter
- Cuniculidae (1) Apply Cuniculidae filter
- Cuniculus (1) Apply Cuniculus filter
- Cuniculus paca (1) Apply Cuniculus paca filter
- Degeeriella (1) Apply Degeeriella filter
- Dennyus (1) Apply Dennyus filter
- Dromaiidae (1) Apply Dromaiidae filter
- Ducula (1) Apply Ducula filter
- Ducula bicolor (1) Apply Ducula bicolor filter
- Echinophilopterus (1) Apply Echinophilopterus filter
- Ectopistes (1) Apply Ectopistes filter
- Ectopistes migratorius (1) Apply Ectopistes migratorius filter
- Emersoniella (1) Apply Emersoniella filter
- Eucometis (1) Apply Eucometis filter
- Eucometis penicillata (1) Apply Eucometis penicillata filter
- Euphonia (1) Apply Euphonia filter
- Eurylaimidae (1) Apply Eurylaimidae filter
- Falco (1) Apply Falco filter
- Falco longipennis (1) Apply Falco longipennis filter
- Falconidae (1) Apply Falconidae filter
- Forficuloecus (1) Apply Forficuloecus filter
- Formicariidae (1) Apply Formicariidae filter
- Gallus (1) Apply Gallus filter
- Gallus gallus (1) Apply Gallus gallus filter
- Goniocotes (1) Apply Goniocotes filter
- Gymnopithys (1) Apply Gymnopithys filter
- Gyropidae (1) Apply Gyropidae filter
- Heterodoxus (1) Apply Heterodoxus filter
- Heterodoxus spiniger (1) Apply Heterodoxus spiniger filter
- Icteridae (1) Apply Icteridae filter
- Kodocephalon (1) Apply Kodocephalon filter
- Laemobothriidae (1) Apply Laemobothriidae filter
- Laemobothrion (1) Apply Laemobothrion filter
- Laemobothrion Laemobothrion tinnunculi (1) Apply Laemobothrion Laemobothrion tinnunculi filter
- Lagopoecus (1) Apply Lagopoecus filter
- Lestoros (1) Apply Lestoros filter
- Lestoros (1) Apply Lestoros filter
- Lestoros inca (1) Apply Lestoros inca filter
- Lestoros inca (1) Apply Lestoros inca filter
- Macrogyropus (1) Apply Macrogyropus filter
- Macrogyropus costalimai (1) Apply Macrogyropus costalimai filter
- Mammalia (1) Apply Mammalia filter
- Mammals (1) Apply Mammals filter
- Menopon (1) Apply Menopon filter
- Molothrus (1) Apply Molothrus filter
- Molothrus ater (1) Apply Molothrus ater filter
- Molothrus ater (1) Apply Molothrus ater filter
- Myrsidea minuscula (1) Apply Myrsidea minuscula filter
- Myrsidea seminuda (1) Apply Myrsidea seminuda filter
- Myrsidea troglodyti (1) Apply Myrsidea troglodyti filter
- Neopsittaconirmus (1) Apply Neopsittaconirmus filter
- Nitzschiella (1) Apply Nitzschiella filter
- Nitzschielloides (1) Apply Nitzschielloides filter
- Osborniella (1) Apply Osborniella filter
- Osborniella crotophagae (1) Apply Osborniella crotophagae filter
- Oxylipeurus (1) Apply Oxylipeurus filter
- Paucituberculata (1) Apply Paucituberculata filter
- Paucituberculata (1) Apply Paucituberculata filter
- Pectinopygus (1) Apply Pectinopygus filter
- Pelecaniformes (1) Apply Pelecaniformes filter
- Philepitta (1) Apply Philepitta filter
- Philepittidae (1) Apply Philepittidae filter
- Philopterus (1) Apply Philopterus filter
- Philopterus citrinellae (1) Apply Philopterus citrinellae filter
- Philopterus urocissae (1) Apply Philopterus urocissae filter
- Phoenicopteridae (1) Apply Phoenicopteridae filter
- Phyllastrephus (1) Apply Phyllastrephus filter
- Physconelloides galapagensis (1) Apply Physconelloides galapagensis filter
- Picicola (1) Apply Picicola filter
- Picicola quadripustulosus (1) Apply Picicola quadripustulosus filter
- Picophilopterus (1) Apply Picophilopterus filter
- Pittidae (1) Apply Pittidae filter
- Platycercus (1) Apply Platycercus filter
- Psephotus (1) Apply Psephotus filter
- Pseudolipeurus (1) Apply Pseudolipeurus filter
- Pseudophilopterus (1) Apply Pseudophilopterus filter
- Pycnonotidae (1) Apply Pycnonotidae filter
- Rallicola (1) Apply Rallicola filter
- Ramphasticola (1) Apply Ramphasticola filter
- Ramphocelus (1) Apply Ramphocelus filter
- Rheiformes (1) Apply Rheiformes filter
- Ricinus (1) Apply Ricinus filter
- Rodentia (1) Apply Rodentia filter
- Saltator (1) Apply Saltator filter
- Strongylocotes (1) Apply Strongylocotes filter
- Struthioniformes (1) Apply Struthioniformes filter
- Sturnidae (1) Apply Sturnidae filter
- Sturnus (1) Apply Sturnus filter
- Sturnus vulgaris (1) Apply Sturnus vulgaris filter
- Tachyeres (1) Apply Tachyeres filter
- Tetrao (1) Apply Tetrao filter
- Thamnophilus (1) Apply Thamnophilus filter
- Thamnophilus doliatus (1) Apply Thamnophilus doliatus filter
- Tinamidae (1) Apply Tinamidae filter
- Tinamiformes (1) Apply Tinamiformes filter
- Tinamotaecola (1) Apply Tinamotaecola filter
- Trichodectidae (1) Apply Trichodectidae filter
- Trimenoponidae (1) Apply Trimenoponidae filter
- Troglodytidae (1) Apply Troglodytidae filter
- Turdidae (1) Apply Turdidae filter
- Urocissa (1) Apply Urocissa filter
- Urocissa erythrorhyncha (1) Apply Urocissa erythrorhyncha filter
- Zenaida asiatica (1) Apply Zenaida asiatica filter
- Zosteropidae (1) Apply Zosteropidae filter
- Zosterops (1) Apply Zosterops filter
Author
- (-) Remove Johnson, KP. filter Johnson, KP.
- Adams, RJ. (2) Apply Adams, RJ. filter
- Alickovic, L (1) Apply Alickovic, L filter
- Allen, JM. (6) Apply Allen, JM. filter
- Altuna, JC. (1) Apply Altuna, JC. filter
- Avendaño, JEnrique (1) Apply Avendaño, JEnrique filter
- Baker, AJ. (1) Apply Baker, AJ. filter
- Bates, JM. (1) Apply Bates, JM. filter
- Beach, AB. (1) Apply Beach, AB. filter
- Boyd, BM. (2) Apply Boyd, BM. filter
- Browne, DR. (1) Apply Browne, DR. filter
- Bueter, C (1) Apply Bueter, C filter
- Bush, SE. (5) Apply Bush, SE. filter
- Cacioppo, JA. (1) Apply Cacioppo, JA. filter
- Cameron, SL. (3) Apply Cameron, SL. filter
- Cao, Y (1) Apply Cao, Y filter
- Catanach, TA. (2) Apply Catanach, TA. filter
- Clayton, DH. (14) Apply Clayton, DH. filter
- Cook, AT. (1) Apply Cook, AT. filter
- Dalgleish, R (3) Apply Dalgleish, R filter
- de_Moya, RS. (2) Apply de_Moya, RS. filter
- DiBlasi, E (2) Apply DiBlasi, E filter
- Doña, J (1) Apply Doña, J filter
- Drown, DM. (1) Apply Drown, DM. filter
- Dumbacher, JP. (1) Apply Dumbacher, JP. filter
- Faucett, RC. (1) Apply Faucett, RC. filter
- Fleischer, RC. (1) Apply Fleischer, RC. filter
- Galloway, TD. (1) Apply Galloway, TD. filter
- Gordon, CE. (1) Apply Gordon, CE. filter
- Gustafsson, DR (1) Apply Gustafsson, DR filter
- Hansen, AN. (1) Apply Hansen, AN. filter
- Hernandez, AG. (1) Apply Hernandez, AG. filter
- Hughes, J (1) Apply Hughes, J filter
- Jamkowski, JE. (1) Apply Jamkowski, JE. filter
- Kennedy, M (2) Apply Kennedy, M filter
- KOLENCIK, S (1) Apply KOLENCIK, S filter
- Londoño, GA (1) Apply Londoño, GA filter
- Marks, BD. (1) Apply Marks, BD. filter
- McCracken, KG. (1) Apply McCracken, KG. filter
- McKinney, F (1) Apply McKinney, F filter
- Meyer, MJ. (2) Apply Meyer, MJ. filter
- Moyle, RG. (2) Apply Moyle, RG. filter
- Najer, T (1) Apply Najer, T filter
- Nguyen, N (1) Apply Nguyen, N filter
- Page, RD. M. (1) Apply Page, RD. M. filter
- Palma, RL. (3) Apply Palma, RL. filter
- Papoušek, I (1) Apply Papoušek, I filter
- Parker, PG. (1) Apply Parker, PG. filter
- Pereira, SL. (1) Apply Pereira, SL. filter
- Price, RD. (11) Apply Price, RD. filter
- Santiago-Alarcon, D (1) Apply Santiago-Alarcon, D filter
- Shapiro, MD. (2) Apply Shapiro, MD. filter
- Skeen, HR. (1) Apply Skeen, HR. filter
- Skinner, RK. (1) Apply Skinner, RK. filter
- Smith, VStuart (1) Apply Smith, VStuart filter
- Sonsthagen, SA. (1) Apply Sonsthagen, SA. filter
- Sorenson, MD. (2) Apply Sorenson, MD. filter
- Soto-Patiño, J (1) Apply Soto-Patiño, J filter
- Stringham, SA. (1) Apply Stringham, SA. filter
- Sweet, AD. (10) Apply Sweet, AD. filter
- Sychra, O (2) Apply Sychra, O filter
- Tan, M (1) Apply Tan, M filter
- Valim, MPaiva (2) Apply Valim, MPaiva filter
- Villa, SM. (1) Apply Villa, SM. filter
- Virrueta-Herrera, S (3) Apply Virrueta-Herrera, S filter
- Vo, KB. (1) Apply Vo, KB. filter
- Walden, KK. O. (2) Apply Walden, KK. O. filter
- Waterhouse, RM. (1) Apply Waterhouse, RM. filter
- Weckstein, JD. (11) Apply Weckstein, JD. filter
- Whiteman, NKerness (1) Apply Whiteman, NKerness filter
- Williams, BL. (1) Apply Williams, BL. filter
- Wilson, RE. (1) Apply Wilson, RE. filter
- Witt, CC. (1) Apply Witt, CC. filter
Publication year
- 1999 (2) Apply 1999 filter
- 2000 (2) Apply 2000 filter
- 2001 (3) Apply 2001 filter
- 2002 (1) Apply 2002 filter
- 2003 (1) Apply 2003 filter
- 2004 (1) Apply 2004 filter
- 2006 (5) Apply 2006 filter
- 2007 (3) Apply 2007 filter
- 2008 (5) Apply 2008 filter
- 2009 (2) Apply 2009 filter
- 2010 (1) Apply 2010 filter
- 2011 (2) Apply 2011 filter
- 2018 (4) Apply 2018 filter
- 2019 (3) Apply 2019 filter
- 2020 (2) Apply 2020 filter
- 2021 (4) Apply 2021 filter
- 2022 (2) Apply 2022 filter
- 2023 (1) Apply 2023 filter
Publication type
Journal keyword
- adaptation (2) Apply adaptation filter
- Africa (1) Apply Africa filter
- Alcedininae (1) Apply Alcedininae filter
- analysis (2) Apply analysis filter
- Anas (1) Apply Anas filter
- anatini (1) Apply anatini filter
- Ancient DNA (1) Apply Ancient DNA filter
- animals (1) Apply animals filter
- AT-bias (1) Apply AT-bias filter
- aves (2) Apply aves filter
- Avian lice (1) Apply Avian lice filter
- avian lice; coevolution; doves; phylogenomics; population genomics (1) Apply avian lice; coevolution; doves; phylogenomics; population genomics filter
- avian systematics (1) Apply avian systematics filter
- background-matching coloration (1) Apply background-matching coloration filter
- Base Sequence (1) Apply Base Sequence filter
- Biogeography (2) Apply Biogeography filter
- Bird parasites (1) Apply Bird parasites filter
- birds (1) Apply birds filter
- Brueelia (1) Apply Brueelia filter
- Brueelia complex (1) Apply Brueelia complex filter
- camouflage (1) Apply camouflage filter
- Cerylinae (1) Apply Cerylinae filter
- character (1) Apply character filter
- Chewing lice (4) Apply Chewing lice filter
- cladistic analysis (1) Apply cladistic analysis filter
- co-evolution (1) Apply co-evolution filter
- Coalescence (1) Apply Coalescence filter
- coevolution (7) Apply coevolution filter
- Columbidae (2) Apply Columbidae filter
- Columbiformes (3) Apply Columbiformes filter
- Community ecology (1) Apply Community ecology filter
- comparative (1) Apply comparative filter
- cophylogenetic analysis (1) Apply cophylogenetic analysis filter
- cospeciation (5) Apply cospeciation filter
- Crotophaga ani (1) Apply Crotophaga ani filter
- differentiation (1) Apply differentiation filter
- Diversification (1) Apply Diversification filter
- dna (1) Apply dna filter
- doves (1) Apply doves filter
- ducks (1) Apply ducks filter
- Ectomorph (1) Apply Ectomorph filter
- ectoparasite (3) Apply ectoparasite filter
- Ectoparasite. lice (1) Apply Ectoparasite. lice filter
- ectoparasites (2) Apply ectoparasites filter
- Ecuador (1) Apply Ecuador filter
- Endosymbiont (2) Apply Endosymbiont filter
- Evolution (6) Apply Evolution filter
- Feather lice (2) Apply Feather lice filter
- Galliformes (1) Apply Galliformes filter
- Galloanserae (1) Apply Galloanserae filter
- genes (1) Apply genes filter
- genetic (1) Apply genetic filter
- genetic divergence (1) Apply genetic divergence filter
- Genome reduction (1) Apply Genome reduction filter
- genome sequencing (1) Apply genome sequencing filter
- genomics (1) Apply genomics filter
- geography (1) Apply geography filter
- Goniodidae (1) Apply Goniodidae filter
- grebes (1) Apply grebes filter
- grouse (1) Apply grouse filter
- Halcyoninae (1) Apply Halcyoninae filter
- historical effective population size (1) Apply historical effective population size filter
- history (1) Apply history filter
- host (1) Apply host filter
- host parasite (1) Apply host parasite filter
- host switch (1) Apply host switch filter
- host-switching (2) Apply host-switching filter
- host–parasite interactions (2) Apply host–parasite interactions filter
- ILD (1) Apply ILD filter
- insects (1) Apply insects filter
- Ischnocera (1) Apply Ischnocera filter
- Keratin (1) Apply Keratin filter
- lice (5) Apply lice filter
- Lice/classification/genetics (1) Apply Lice/classification/genetics filter
- macroevolution (1) Apply macroevolution filter
- Madagascar (1) Apply Madagascar filter
- Metabolic complementation (1) Apply Metabolic complementation filter
- mitochondrial (1) Apply mitochondrial filter
- mitochondrial dna (1) Apply mitochondrial dna filter
- mitogenome (1) Apply mitogenome filter
- molecular (1) Apply molecular filter
- molecular data (1) Apply molecular data filter
- Molecular Sequence Data (1) Apply Molecular Sequence Data filter
- molecular systematics (1) Apply molecular systematics filter
- mtax (3) Apply mtax filter
- Myiothylpis luteoviridis (1) Apply Myiothylpis luteoviridis filter
- Myrsidea (1) Apply Myrsidea filter
- natural selection (1) Apply natural selection filter
- Neoaves (1) Apply Neoaves filter
- Organelle genomics (1) Apply Organelle genomics filter
- PacBio (1) Apply PacBio filter
- Palaeognathae (1) Apply Palaeognathae filter
- ParaFit (1) Apply ParaFit filter
- parasite (2) Apply parasite filter
- parasites (2) Apply parasites filter
- Parsimony (1) Apply Parsimony filter
- Passeriformes (1) Apply Passeriformes filter
- Pelecaniformes (1) Apply Pelecaniformes filter
- Philopteridae (1) Apply Philopteridae filter
- Philopteroides cucphuongensis (1) Apply Philopteroides cucphuongensis filter
- Philopteroides flavala (1) Apply Philopteroides flavala filter
- Philopterus gustafssoni (1) Apply Philopterus gustafssoni filter
- Phoenicopteridae (1) Apply Phoenicopteridae filter
- PHP (1) Apply PHP filter
- Phthiraptera (3) Apply Phthiraptera filter
- Phylogenetics (1) Apply Phylogenetics filter
- Phylogenomics (2) Apply Phylogenomics filter
- Phylogeny (4) Apply Phylogeny filter
- phylogeny. (1) Apply phylogeny. filter
- population genetics—empirical (1) Apply population genetics—empirical filter
- ptarmigan (1) Apply ptarmigan filter
- Research Support, Non-U.S. Gov't (1) Apply Research Support, Non-U.S. Gov't filter
- Research Support, U.S. Gov't, Non-P.H.S. (1) Apply Research Support, U.S. Gov't, Non-P.H.S. filter
- rhagoletis pomonella (1) Apply rhagoletis pomonella filter
- Rock Pigeon (1) Apply Rock Pigeon filter
- sequence (1) Apply sequence filter
- sexual dichromatism (1) Apply sexual dichromatism filter
- specialization. (1) Apply specialization. filter
- species interactions (1) Apply species interactions filter
- specificity (1) Apply specificity filter
- systematic (1) Apply systematic filter
- TELL-Seq (1) Apply TELL-Seq filter
- Tetraoninae (1) Apply Tetraoninae filter
- toucans (1) Apply toucans filter
- tree (1) Apply tree filter
- TreeFitter (1) Apply TreeFitter filter
- TreeMap. (1) Apply TreeMap. filter
- Tropical Forests (1) Apply Tropical Forests filter
- Tyranniphilopterus sp. (1) Apply Tyranniphilopterus sp. filter
Journal
- Auk (1) Apply Auk filter
- Biodiversity Data Journal (1) Apply Biodiversity Data Journal filter
- Biological Journal of the Linnean Society (1) Apply Biological Journal of the Linnean Society filter
- Biology Letters (1) Apply Biology Letters filter
- BMC Ecology and Evolution (1) Apply BMC Ecology and Evolution filter
- Communications Biology (1) Apply Communications Biology filter
- Condor (1) Apply Condor filter
- Ecology and Evolution (1) Apply Ecology and Evolution filter
- Evolution (1) Apply Evolution filter
- Evolution Letters (1) Apply Evolution Letters filter
- G3 Genes|Genomes|Genetics (1) Apply G3 Genes|Genomes|Genetics filter
- Gene (1) Apply Gene filter
- International Journal for Parasitology (2) Apply International Journal for Parasitology filter
- Journal of Medical Entomology (1) Apply Journal of Medical Entomology filter
- Journal of Parasitology (2) Apply Journal of Parasitology filter
- Journal of the Kansas Entomological Society (1) Apply Journal of the Kansas Entomological Society filter
- Molecular Ecology (3) Apply Molecular Ecology filter
- Molecular Phylogenetics and Evolution (3) Apply Molecular Phylogenetics and Evolution filter
- Parasitology (2) Apply Parasitology filter
- Proceedings of the Entomological Society of Washington (2) Apply Proceedings of the Entomological Society of Washington filter
- Proceedings of the Royal Society B (1) Apply Proceedings of the Royal Society B filter
- Proceedings of the Royal Society B: Biological Sciences (1) Apply Proceedings of the Royal Society B: Biological Sciences filter
- Proceedings of the Royal Society of London, Series B, Biological Sciences (1) Apply Proceedings of the Royal Society of London, Series B, Biological Sciences filter
- Systematic Biology (2) Apply Systematic Biology filter
- Systematic Entomology (2) Apply Systematic Entomology filter
- Trends in Ecology and Evolution (1) Apply Trends in Ecology and Evolution filter
- Zootaxa (8) Apply Zootaxa filter