INDEX TO VOLUME 9, 1998

ORNITOLOGIA NEOTROPICAL UNA REVIATA INTERNACIONAL DE ORNITOLOGIA NEOTROPICAL UMA REVISTA INTERNACIONAL DE ORNITOLOGIA NEOTROPICAL AN INTERNATIONAL JOURNAL OF NEOTROPICAL ORNITHOLOGY MANAGING EDITOR RAYMOND McNEIL INDEX TO VOLUME 9, 1998 (Authors, key words, families, latin names) PUBLISHED BY THE NEOTROPICAL ORNITHOLOGICAL SOCIETY

INDEX, VOL. 9. 1998 Abundance, 161 176 Abundancia, 161 176 Accipitridae, 163, 172, 225 226 Alarm calls, 31 40 Alcedinidae, 64 Alimentação, 213 217 Alimentación, 213 217 Alvarez, Eugenia V., 31 40 Amazilia amabilis, 46 Amazilia fimbriata, 64, 173 Amazilia leucogaster, 51, 55, 57, 59 61, 64 Amazilia tobaci, 169, 173 Amazilia tzacatl, 46 Amazona aestiva, 37 Anas, 20 Anas specularoides, 13 14 Andes, 185 191 Androdon aequatorialis, 46 Anthracorax nigricollis, 61, 64 Anthracothorax viridigula, 64 Antrostomus, 2 Anthrostomus eckmani, 1 Antrostomus cubanensis, 1 Antunes, Alexsander Z., 71 76 Aphantochroa cirrhochloris, 78 Apodidae, 173 Aramburú, Rosana M., 95 98 Aratinga, 99 Aratinga acuticaudata, 31 40 Aratinga pertinax, 99 100, 173 Aremon taciturnus, 69 Argentina, 13 22, 31 40, 193 199 Arremonops conirostris, 176 Artrópodos, 41 50 Atalotriccus pilaris, 174 Atlapetes, 206 Attila cinnamomeus, 68 Attila rufus, 48, 147 Attila spadiceus, 68 Automolus, 136 Automolus infuscatus, 65 Automolus leucophthalmus, 134 Automolus rubiginosus, 65 Aves marinas, 193 199 Avifauna, 161 176 Azure Jay, 213 217 Basileuterus flaveolus, 176 Basileuterus rivularis, 68 Behavior, 31 40, 111 119 Biodiversity, 13 22 Black Swift, 219 221 Bolivia, 185 191 Bornschein, Marcos Ricardo, 213 217 Bosque, Carlos, 87 92 Brasil, 81 86, 213 217 Breeding, 209 212, 219 221 Bucconidae, 64, 163, 173 Busarellus nigricollis, 90 Buteo magnirostris, 140, 157, 165, 167 168, 170, 172 Buteogallus urubitinga, 172 Cache, 81 86 Cacicus cela, 90 Calidris fuscicollis, 18 Calothorax, 223 224 Calothorax lucifer, 224 Camptostoma obsoletum, 100, 174 Campylopterus largipennis, 57, 64 Campylorhamphus trochilirostris, 65, 174 Caprimulgidae, 1 12, 63, 173 Caprimulgus badius, 3, 10 Caprimulgus carolinensis, 3, 6, 63 Caprimulgus cubanensis cubanensis, 11 Caprimulgus cubanensis insulaepinorum, 2, 6, 11 Caprimulgus eckmani, 1, 4, 10 Caprimulgus europeus, 7 Caprimulgus noctitherus, 6 Caprimulgus otiosus, 6, 10 Caprimulgus ridgwayi, 10 Caprimulgus rufus, 6, 10 Caprimulgus salvini, 3, 6, 10 Caprimulgus vociferus, 6 Capsiempis flaveola, 151 152 Cardinalinae, 176 Carlos Verea, 161 176 Catharacta, 19 Catharacta antarctica, 13 14 Catharacta chilensis, 13 14 Cathartes aura, 35, 172 Cathartidae, 172 II

INDEX, VOL. 9, 1998 Cave Swallow, 209 212 Censos, 193 199 Census, 193 199 Centropus phasianinus, 89 Chachalaca, 177 184 Chalybura buffoni, 173 Chalybura urochrysia, 46 Chamaeza, 142 Charadriidae, 172 Charadrius falklandicus, 18 Chionis alba, 18 Chiroxiphia caudata, 134, 145, 146, 151 Chiroxiphia lanceolata, 169,175 Chlorestes notatus, 57, 64 Chloroceryle aena, 55, 57, 59, 61, 64 Chlorochrysa, 206 Chlorophonia, 206 Chlorospingus, 206 Chlorostilbon aureoventris, 71 76 Chlorostilbon mellisugus, 64, 173 Chrysolampis mosquitus, 57, 64 Cinnamon vented Piha, 129 159 Clark, John, 205 207 Cnemotriccus fuscatus, 67, 167, 174 Coccyzus americanus, 173 Coereba flaveola, 68, 175 Coerebinae, 175 Colibri thalassinus, 41 50 Colibries, 41 50 Collecting birds, 201 203 Collection, 201 203 Columbidae, 58, 63, 163, 172 Columbina passerina, 57, 63, 172 Columbina talpacoti, 172 Comparative method, 23 30 Comunidad, 161 176 Community, 161 176 Conirostrum bicolor, 55, 57, 69 Conopophaga aurita, 66 Conopophagidae, 66 Conservation 13 22, 111 119, 121 128 Coragyps atratus, 172 Corapipo gutturalis, 67 Corvidae, 175, 213 217 Coryphospingus pileatus, 164, 167, 169, 176 Corythopis torquata, 67 Costa Rica, 99 102, 219 221 Cotingidae, 66 Cotinginae, 129 159 Cracidae, 172, 177 184 Crax, 177 Crotophaga major, 87 92 Crypturellus erythropus, 172 Cuba, 1 12, 209 212 Cuculidae, 63, 173 Curry, Robert L., 103 110 Cyanerpes caeruleus, 69 Cyanerpes cyaneus, 69 Cyanocompsa cyanea, 176 Cyanocompsa cyanoides, 69 Cyanocorax caeruleus, 213 217 Cyanocorax chrysops, 213 217 Cyanocorax ynca, 175 Cyclarhis gujanensis, 167, 174 Cyphorhinus aradus, 68 Cypseloides niger, 219 221 Dacnis cayana, 69 Daption capense, 196, 198 Deciduous forest, 161 176 Deconychura longicauda, 65 Deconychura stictolaema, 65 Dencrocolaptes certhia, 65 Dendrocincla, 151 Dendrocincla fuliginosa, 57, 65, 174 Dendrocincla merula, 65 Dendrocincla turdina, 153 Dendrocolaptidae, 65, 130, 163, 174 Dendroica discolor, 114 Dendroica petechia, 68 Diomedea exulans, 196 Diomedea melanophris, 18, 193 194, 196, 198 Distribution, 121 128, 193 199, 223 226 Distributional records, 99 102 Dives, 99 Dives dives, 99 100 Dominican Republic, 1 12 Doricha eliza, 223 224 Dysithamnus mentalis, 174 Ecuador, 205 207 Edge effects, 129 159 III

INDEX, VOL. 9. 1998 Egg, 205 207, 209 212 Elaenia flavogaster, 67 Elaenia parvirostris, 67 Emberizidae, 58, 68, 163, 164, 175 Emberizinae, 164, 176, 206 Empidonomus, 149 Estrategias de forrajeo, 41 50 Eucometis penicillata, 176 Eucometis, 206 Eudyptes chrysocome chrysocome, 13 14, 17 Eulampis jugularis, 46 Euphonia, 206 Euphonia xanthogaster, 16 Evolution, 185 191 Factores de mortalidad, 95 98 Falconidae, 63, 172 Fernández-Juricic, Esteban, 31 40 Fjeldså, Jon, 185 191 Floater, 111 119 Floating, 111 119 Flores Ceballos, Edmundo, 223 224 Florisuga mellivora, 46, 64 Food, 213 217 Formicariidae, 66, 163, 174 Formicarius colma, 66 Formicivora grisea, 55, 57, 66, 167, 174 Formicivora melanogaster, 190 Forpus passerinus, 83, 168, 173 French Guyana, 51 70 Frere, Esteban, 13 22 Friggens, Michael T., 185 191 Fulmarus glacialoides, 18, 198 Furnariidae, 64, 163, 174 Galbula albirostris, 59, 64 Galbula galbula, 51, 57, 59, 61, 64 Galbula ruficauda, 173 Galbulidae, 64, 163, 173 Gandini, Patricia Alejandra, 13 22 Garrido, Orlando H., 1 12 Geospiza, 107 Geotrygon montana, 63 Glaucis hirsuta, 55, 59, 63, 169, 173 Glyphorynchus spirurus, 51, 55, 57 58, 61, 65 Gralha-azul, 213 217 Grallaria varia, 136, 142 Grallaria, 136 Greater Antillean Nightjar, 1 12 Green-cheecked Parakeet, 185 191 Greeney, Harold F., 205 207 Group size, 177 184 Guacharaca, 177 184 Guadeloupe, 121 128 Guilds, 51 70 Guira guira, 97 Gymnopithys rufigula, 55, 57 58, 66 Habia, 206 Habitat selection, 111 119 Haematopus ater, 13 14, 19 Haematopus leucopodus, 18 Haematopus palliatus, 18 Haiti, 1 12 Harpagus diodon, 134, 143 Harpia harpyja, 225 226 Harpy Eagle, 225 226 Hayes, Floyd E., 93 94 Heliothryx barroti, 46 Herpetotheres cachinnans, 84 Herzog, Sebastian K., 185 191 Hirundinidae, 163, 175 Hirundo fulva, 209 212 Hirundo ruficollis, 209 Hylocharis sapphirina, 64 Hylocichla mustelina, 113 Hylophilus aurantiifrons, 174 Hylophilus flavipes, 170, 174 Hylophilus ochraceiceps, 57, 68 Hylophilus pectoralis, 68 Hylophylax naevia, 61, 66 Hylophylax poecilonota, 55, 57 58, 66 Hypnelus ruficollis, 173 Hypocnemis cantator, 66 Hypocnemoides melanopogon, 57, 66 Icteridae, 68 Icterinae, 176 Icterus nigrogularis, 68, 176 Incubation, 77 80 Inezia subflava, 57, 67 Iodopleura pipra, 133, 157 Iodopleura, 140 Jalisco, 41 50 IV

INDEX, VOL. 9, 1998 Kessler, Michael, 185 191 Klais guimeti, 169, 173 Kleptoparasitism, 93 94 Lagopus lagopus lagopus, 117 Lampornis amethystinus, 41 50 Laniisoma elegans, 147 Laniocera hypopyrrha, 68 Lara, Carlos, 41 50 Larus dominicanus, 13 14, 19, 196 Larus maculipenni, 18, Larus scoresbei, 13 14, 19 Lau, Pablo, 87 92 Lepidocolaptes souleyetii, 174 Leptotila, 59 Leptotila rufaxilla, 63 Leptotila verreauxi, 63, 168, 173 Lesser Antilles, 121 128 Ligaugus unirufus, 149 Lipaugus lanioides, 129 159 Lipaugus streptophorus, 155 Lipaugus vociferans, 131, 156 Llanes, A., 209 212 Lophornis, 77 Lophornis magnifica, 77 80 Lophotriccus galeatus, 67 Lysinger, Mitch, 205 207 Macronectes giganteus, 18, 195 197 Macronectes halli, 196 197 Maijer, Sjoerd, 185 191 Malacoptila fusca, 64 Manacus manacus, 51, 55, 57, 61, 67 Marín, Manuel, 219 221 Martella, Mónica B., 31 40 Martínez-Gómez, Juan E., 103 110 Measurements, 23 30 Megarhynchus pitangua, 93, 167, 169, 174 Melanerpes cactorum, 81 Melanerpes carolinus, 81 Melanerpes erythrocephalus, 81 Melanerpes flavifrons, 81 86 Melanerpes formicivorus, 81 Melanerpes herminieri, 121 128 Melanerpes lewis, 81 Melanerpes rubricapillus, 81, 167, 173 Melopsittacus undulatus, 37 Methodology, 23 30 Mexican Sheartail, 223 224 México, 41 50, 103 110, 223 226 Micrastur gilvicollis, 59, 63 Micrastur ruficollis, 134 Microbates collaris, 68 Microcerculua bambla, 68 Microspingus, 206 Milvago chimachima, 172 Mimidae, 175 Mimodes graysoni, 103 110 Mimus gilvus, 105, 175 Mimus polyglottos, 105 Mionectes macconnelli, 57 58, 67 Mionectes oleaginea, 55, 57 58, 61, 67 Mionectes, 130 Mitu, 177 Momotidae, 64 Momotus momota, 59, 64 Monogamy, 129 159 Montalti, Diego, 193 199 Morales-Pérez, José Eduardo, 225 226 Morphometrics, 23 30 Muscicapidae, 163, 175 Muscivora tyrannus, 174 Myiarchus, 149 Myiarchus ferox, 68 Myiarchus tyrannulus, 68, 170, 174 Myiarchus venezuelensis, 168, 174 Myiobius, 130, 153 154 Myiobius barbatus, 57, 67 Myiodynastes, 149 Myiodynastes maculatus, 147 151, 167 169, 174 Myiopagis flavivertex, 67 Myiopagis viridicata, 168, 174 Myiophobus fasciatus, 67, 174 Myiopsitta monachus catita, 96 Myiopsitta monachus monachus, 95 98 Myiopsitta monachus, 37, 95 98 Myiozetetes anensis, 68 Myiozetetes cayanensis, 175 Myiozetetes similis, 168 169, 175 Myrmeciza atrothorax, 66 Myrmeciza ferruginea, 57, 66 Myrmeciza longipes, 167, 174 V

INDEX, VOL. 9. 1998 Myrmornis torquata, 66 Myrmotherula axillaris, 57 58, 61, 66 Myrmotherula brachyura, 66 Myrmotherula guttata, 57, 61, 66 Myrmotherula gutturalis, 66 Myrmotherula longipennis, 57 58, 66 Myrmotherula menetriesii,, 6166 Naoki, Kazuya, 99 102 Need of collection, 201 203 Neotropics, 201 203 Nesomimus, 105 Nest, 71 76, 81 86, 205 207, 209 212, 223 224 Nest-building, 77 80 Nesting biology, 205 207 Nesting site, 87 92 Nesting success, 87 92 Nesting, 81 86, 129 159, 177 184, 205 207 Nestling, 71 76, 81 86 New records, 99 102 Nido, 223 224 Nothocrax, 177 Nycticorax nycticorax, 13 14, 20 Nycticorax violaceus, 89 90 Nyctidromus albicollis, 82, 173 Oceanites oceanicus, 196 Oniki, Yoshika, 71 76, 77 80, 81 86, 129 159 Onychorhynchus coronatus, 67 Opisthocomus hoazin, 89 Oreopholus ruficollis, 18 Oreothraupis arremonops, 205 207 Orgeira, José L., 193 199 Ornelas, Juan Francisco, 41 50 Ortalis cinereiceps, 183 Ortalis leucogastra, 182 Ortalis ruficauda, 172, 177 184 Ortalis veluta, 178 Ortalis, 177 184 Ortiz Pulido, Rubén, 223 224 Ortiz-Pulido, Raúl, 223 224 Oryzoborus angolensis, 69 Otididae, 131 Oxyruncus cristatus, 153 Pachyptila, 193 194, 196, 198 Pachyramphus cinnamomeus, 167 169, 175 Pachyramphus polychopterus, 68 Pagatonia, 13 22 Paradisaeidae, 130 Parulidae, 68 Parulinae, 176 Parus, 37 Parus major, 114 Patagonia, 193 199 Pauxi, 177 Percnostola leucostigma, 66 Percnostola rufifrons, 57, 66 Periporphyrus erythromelas, 69 Peris, Salvador, 209 212 Petites Antilles, 121 128 Phacellodomus rufifrons, 167, 174 Phaeomyias, 99 Phaeomyias murina, 55, 57, 67, 100, 175 Phaethornis anthophilus, 169, 173 Phaethornis bourcieri, 57, 64 Phaethornis longuemareus, 64, 169, 173 Phaethornis malaris, 63 Phaethornis superciliosus, 57, 59, 63 Phalacrocorax albiventer, 17 Phalacrocorax atriceps, 13, 17 Phalacrocorax brasilianus, 13 14, 18 Phalacrocorax gaimardi, 13 14, 18 Phalacrocorax magellanicus, 13 14, 17 Phalaenoptilus nutallii, 7 Philydor erythrocercus, 65 Philydor pyrrhodes, 65 Philydor ruficaudatus, 59, 61, 65 Phoenicircus carnifex, 66 Phylloscartes virescens, 67 Piaya cayana, 173 Piaya minuta, 63 Pichones, 95 98 Picidae, 60, 64, 81 86, 163, 173 Picumnus exilis, 64 Picumnus spilogaster, 64 Picumnus squamulatus, 173 Pionus maximiliani, 132 Pipra aureola, 51, 55, 57 58, 61, 67 Pipra erythrocephala, 57, 61, 66, 175 Pipra pipra, 55 57 58, 66 VI

INDEX, VOL. 9, 1998 Pipra serena, 55, 57 58, 66 Pipridae, 66, 163, 175 Piprinae, 130 Pitangus sulphuratus, 93, 165, 168 169, 175 Pithys albifrons, 51, 55 58, 66 Platyrinchus coronatus, 57, 67 Platyrinchus saturatus, 58, 67 Pluvialis dominica, 18 Podiceps major, 18, 196 197 Poecilotriccus fumifrons, 67 Poecilurus scutatus, 190 Polioptila plumbea, 175 Polyborus plancus, 172 Polytmus theresiae, 57, 64 Poospiza boliviana, 190 Population size, 121 128 Predation, 87 92, 129 159 Procellaria aequinoctialis, 193, 196, 198 Procnias, 131 Promiscuity, 129 159 Protonotaria citrea, 27 Psarocolius decumanus, 176 Psittacidae, 95 98, 163, 173, 185 191 Pteroglossus aracari, 83 Puerto Deseado, 13 22 Puffinus assimilis, 196 197 Puffinus gravis, 193 194, 196, 198 Puffinus griseus, 18 Puffinus puffinus, 193 194, 196 Pyrrhura frontalis, 148 Pyrrhura molinae flavoptera, 185 191 Pyrrhura molinae molinae, 185 191 Pyrrhura molinae, 185 191 Ramphastos vitellinus, 84 Ramphocaenus melanurus, 68, 175 Ramphocelus carbo, 55, 57, 59, 6169 Ramphotrigon ruficauda, 67 Reinert, Bianca Luiza, 213 217 Revillagigedo Archipelago, 103 110 Reynard, George B., 1 12 Reynaud, Pierre Adrien, 51 70 Rhodinocichla, 206 Rhodinocichla rosea, 176 Rhynchocynclus olivaceus, 67 Rhytipterna, 149 Richness, 161 176 Riqueza, 161 176 Rosthramus sociabilis, 90 Rousteau, Alain, 121 128 Rufous-vented Chachalaca, 177 184 Sakesphorus canadensis, 57, 65 Sakesphorus melanonotus, 174 Saltator, 206 Saltator albicollis, 165, 176 Saltator maximus, 69 Sánchez, Julio E., 99 102, 219 221 Sarcoramphus papa, 172 Scardafella squammata, 168, 173 Schiffornis turdinus, 57, 61, 67 Schmitz Ornés, 177 184 Sclerurus caudatus, 65 Sclerurus mexicanus, 65 Sclerurus rufigularis, 65 Scolopacidae, 131 Seabirds, 13 22, 193 199 Seasonal variations, 161 176 Seiurus aurocapillus, 168, 176 Seiurus noveboracensis, 68, 113, 168, 176 Selenidera maculirostris, 135, 154 Selva decidua, 161 176 Sericotes holosericeus, 46 Setochalcis, 2 Setophaga ruticilla, 113, 168, 176 Sexing, 103 110 Shorebirds, 13 22 Silviinae, 175 Sittasomus griseicapillus, 134, 147, 153, 167, 174 Socorro Island, 103 110 Solorzano, Alecio, 161 176 Sotobosque, 161 176 Spheniscus magellanicus, 13 14, 17, 37, 193 194, 196, 198 Sporophila castaneiventris, 69 Sporophila intermedia, 176 Sporophila lineola, 169, 176 Sporophila minuta, 176 Statistics, 23 30 Stelgydopteryx ruficollis, 168, 175 Stercorarius parasiticus, 18 Sterna, 19, 196 VII

INDEX, VOL. 9. 1998 Sterna eurygnatha, 13 14, 196 Sterna hirundinacea, 13 14, 196 Sterna maxima, 18 Strahl, Stuart D., 87 92 Streptoprocnes zonaris, 173 Sublegatus modestus, 175 Subspecies, 185 191 Supervivencia, 95 98 Sylviidae, 68 Synallaxis albescens, 167, 174 Synallaxis guyanensis, 59, 65 Tachyeres patachonicus, 13 14 Tachyphonus rufus, 61, 69, 167 168, 176 Tachyphonus surinamus, 57, 69 Tachyphonus, 206 Tanager Finch, 205 207 Tangara, 206 Tapera naevia, 173 Taxonomy, 1 11 Techniques, 23 30 Terenotriccus erythrurus, 67 Territorial systems, 111 119 Territoriality, 111 119 Tetraonidae, 131, 153, 156 Thalurania colombica, 46 Thalurania furcata, 55, 57, 59, 64, 78 Thamnomanes ardesiacus, 57, 61, 66 Thamnomanes caesius, 57, 66 Thamnophilidae, 65 Thamnophilus amazonicus, 65 Thamnophilus doliatus, 57, 65, 167, 175 Thamnophilus nigrocinereus, 65 Thamnophilus punctatus, 57, 61, 65 Thraupinae, 176, 206 Thraupis, 206 Thraupis episcopus, 69, 176 Thraupis palmarum, 69 Threnetes niger, 63 Thryothorus coraya, 68 Thryothorus rufalbus, 175 Tiaris bicolor, 167, 176 Tinamidae, 172 Todirostrum cinereum, 167, 175 Todirostrum maculatum, 67 Todirostrum sylvia, 167, 175 Tolmomyias assimilis, 67 Tolmomyias flaviventris, 175 Tolmomyias sulphurescens, 67 Tomios aserrados, 41 Triclaria malachitacea, 152 Trinidad, 93 94 Trochilidae, 131, 163, 173 Trochilidae, 63, 71 76, 77 80 Troglodytes aedon, 175 Troglodytidae, 68, 163, 175 Trogon, 134 Trogon collaris, 173 Trogon serrucura, 134 Trogon violaceus, 64 Trogonidae, 64, 173 Tropical forest, 51 70 Turdidae, 68 Turdinae, 175 Turdus albicollis, 57, 68 Turdus leucomelas, 68, 175 Turdus nudigenis, 68, 167, 175 Tyrannidae, 67, 93 94, 129 159, 163, 164, 174 Tyrannopsis sulphurea, 93 Tyrannulus elatus, 67 Tyrannus melancholicus, 168 169, 175 Understory avifauna, 51 70 Upucerthia harterti, 190 Vanellus, 99 Vanellus chilensis, 99, 172 Variaciones estacionales, 161 176 Venezuela, 87 92, 161 176, 177 184 Veniliornis cassini, 64 Veniliornis kirki, 173 Veniliornis passerinus, 64 Vermivora peregrina, 16 Villard, Pascal, 121 128 Vireo olivaceus, 68, 168, 174 Vireonidae, 68, 163, 174 Vocal repertoire, 31 40 Vocalizations, 1 9, 31 40 Volatina jacarina, 57, 69, 176 Vuilleumier, François, 201 203 Walla, Tom, 205 207 Willis, Edwin O., 77 80, 81 86, 129 159 VIII

INDEX, VOL. 9, 1998 Wilsonia citrina, 113 Winker, Kevin, 23 30, 111 119 Xenops minutus, 65, 167, 174 Xenops tenuirostris, 65 Xiphocolaptes albicollis, 135, 156 Xiphorhynchus guttatus, 65 Xiphorhynchus pardalotus, 61, 65 Xiphorhynchus picus, 65, 174 Zimmerius gracilipes, 67 Zonotrichia capensis, 74 Zook, Jim, 99 102 Reviewers for Ornitología Neotropical, Volume 9 Each manuscript submitted for publication in Ornitología Neotropical is generally reviewed by two specialists, often including a member of the editorial board, and frequently by a third one. The following individuals kindly reviewed one or more (*) manuscripts for Volume 9: Allison V. Andors*, Luis F. Baptista, Carlos Bosque, Enrique Bucher, Ernesto Enkerlin, Jaime Jimenez, Lloyd Kiff*, Gaëtan Lefebvre, Raymond McNeil*, Brigitte Poulin, John H. Rappole*, J. V. Remsen, Lester L. Short, Gary Stiles*, François Vuilleumier*, and James W. Wiley*, Edwin O. Willis. IX