The Condor921421-443 0 The Cooper Ornithological Society 1990

HABITAT SPECIALIZATION AND FORAGING BEHAVIOR BY OF AMAZONIAN RIVER ISLANDS IN NORTHEASTERN ’

GARY H. ROSENBERG~ Louisiana State UniversityMuseum of Natural Science,Baton Rouge, LA 70803

Abstract. Roughly 15% of the rich Amazonian avifauna has been shown to be dependent on riverine habitats, particularly islands that form in the channels of the and its largesttributaries. In northeasternPeru and southeasternColombia, over 230 species have occurredon river islands, about 19 of which appear to be restricted to habitats found almost exclusively on islands, such as -scruband large tracts of Cecropia forest. Habitat specializationand foragingbehavior were studied quantitatively for 3 1 species that used only terrestrial habitats on two study islands on the Napo River in northeastern Peru. Density estimates for residents on a small, Tessaria-dominatedisland, exceeded 160 birds/ha, a figure an order of magnitude greater than bird densities previously reported for forest habitats in the Neotropics. Obligate river island speciesshowed a higher degree of microhabitat specialization than did nonobligate island species. Several of the most spe- cialized specieswere found mainly in the Tessariascrub or the understory of the Cecropia forest. Most of the specieswere primarily insectivorous,but several also took advantageof the abundant Cecropiafruit and were at least partially fiugivorous. Little difference in the degreeof foragingspecialization was found between obligate and nonobligateisland species, however, both groupswere specializedwith respectto foragingtechnique and substrateuse. Water fluctuation of up to 20 m between seasons,completely flooding the young islands and the understory of the older islands, createsthe need for speciesto be good colonizers, as doesthe natural, rapid, successionof vegetationon the islandsfrom Tessaria,to Cecropia, to an older, more complex vegetation. Conservation plans for the should take into account the high dependencyof specieson riverine habitats, particularly islands. Key words: Amazonia; habitat specialization;river islands;Napo River;foragingbehavior; Peru; Tessaria scrub;Cecropia forest.

INTRODUCTION occurs only in riverine habitats (Remsen and Among the many factors thought to contribute Parker 1983). to the high bird species richness in the Neotropics Islands that form in the Amazon River and its is the high diversity of habitat and microhabitat larger tributaries, which are covered by early types, some of which are unique to tropical re- successionalvegetation, constitute a large pro- gions (Orians 1969, Karr 1976, Terborgh 1980b). portion of the total riverine habitat in Amazonia. Even more important is the increased degree of After formation, these islands travel down- specialization on specific microhabitats, such as stream, in a sense, by constant erosion of the bamboo (Parker and Parker 1982, Remsen 1985) older, upstream portions, and the constant in- and foraging substrates, such as suspended dead creasein size by the deposition of sand and silt leaves (Remsen and Parker 1984). Although bird on the downstream ends. This constant change species richness reaches its peak in terra jirme createsan array of early successionalhabitats on forest, it is the contribution by habitats other the islands. The use of and specialization on such than primary forest that elevates the richness to habitats by Amazonian birds has remained poor- such high levels in western Amazonia. For ex- ly known (see Remsen and Parker 1983, Hilty ample, it has been shown that more than 14% and Brown 1986). of the nonaquatic avifauna of the Amazon basin Exploratory visits to islands in the Napo River in northeastern Peru in 1982 with the Louisiana State University Museum of Natural Science (LSUMNS) revealed that the assemblageofland- 1Received 4 September 1989. Final acceptance26 December 1989. bird species on these islands was almost com- * Present address: 5441 N. Swan Road, apt. 313, pletely different from that found in terra jirme Tucson, AZ 85718. forest on the “mainland” only l-2 km away.

WI 428 GARY H. ROSENBERG

Some species encountered on the islands were from one end to the other (the down-river end river-edge and second-growth speciesthat were being younger) and potentially have vegetation common on the mainland, but several appeared characteristicsof all three island types. unique to the islands. Since 1982, extensive sur- River islands are formed during the low-water veys of river-island and mainland habitats in season (June-October), when sandbars are ex- northeastern Peru by the LSUMNS and Phila- posedand enlargedby the deposition of silt. Dur- delphia Academy of Sciences suggestedthat as ing low water, vegetation grows rapidly on the many as 19 bird species may be restricted to exposedsandbars. At first, grass(Paspalum) cov- islands in this region ofAmazonia. These surveys ers the ground; this is later replaced by the com- have added significantly to the growing knowl- posite shrub Tessaria integrifolia and a willow edge of the distribution and natural history of Salix humboltiana (Remsen and Parker 1983). these apparent obligate island species,some of These young islands may be completely covered which were known from only a few museum by water during portions of the high-water season specimens and occasional sightings. (November-May). As an island grows in age and I returned to the Napo River in 1983 to study size, it becomesdominated by monotypic stands the birds found on river islands,particularly those of Cecropia forest. Although Cecropia sp. is a speciesapparently restricted to the islands. My common tree of disturbed area throughout the primary goals in this study were to: (1) enu- Neotropics, standsof suchlarge size are not char- merate the bird species using islands in upper acteristic of disturbed areas on the mainland. Amazonia; (2) describefor the first time the hab- During the high-water season,the entire under- itat use and foraging behavior of some river- story of the forest on middle-aged and old islands island birds; (3) evaluate the degreeof ecological may be under water. Old islands are character- specialization among river-island birds; and (4) ized by .largersize and vegetation that resembles discusshow this unique bird assemblagepersists in complexity the varzea forest (seasonally in- in such a dynamic, ephemeral environment. undated forest and permanently swampy forest usually bordering rivers; as described in Parker STUDY AREAS AND METHODS and Parker 1982) of the mainland. Preliminary observations indicated that most ISLAND FORMATION AND HABITATS of the poorly known island specieswere found Amazonian river islands are part of a continuous primarily in two major habitat types: Cecropia chain of islands that extends from eastern (river-edge) forest, and Tessaria sandbar scrub, up the Amazon River and most of its larger trib- as described by Remsen and Parker (1983). My utaries as far as and Peru. The islands study focusedon one middle-aged and one young studied here are “sandbar islands” that form in island in the Napo River that contained both the river, as opposed to “‘oxbow islands” that habitat types. My primary study site, visited dai- form when the river channel changesits course ly between 2 June and 31 July 1983, was Ron- and isolates a portion of mainland forest. These socoIsland, located opposite the small village of two island types differ in vegetation complexity, Libertad, approximately 1 km east of the village but a very old sandbar island will eventually vi- of Negro Urco, 80 km north of Iquitos. Accord- sually resemblean oxbow island in terms of vege- ing to local residents,Ronsoco was about 16 years tation complexity. old. Approximately 1 km by 0.25 km in size, this Water levels on the Amazon and Napo rivers island was about equidistant between the two in northeastern Peru fluctuate as much as 20 m banks of the Napo (which was about 1.5 km wide between seasonsdue to runoff from the at that point). Monotypic stands of Cecropia (Gentry and Lopez-Parodi 1980; Peter Jenson, ranging from 5 to 13 m tall were prevalent on pers. comm.), and as a result of the dynamic the island, with an occasional emergent Mimosa nature of this system, river islands vary substan- sp. A distinct middle-story layer consisted of a tially in age and size. Three age classesof islands “broad-leafed” tree (identification unknown) that may be recognized(young, middle-aged, and old, ranged from 4 to 7 m in height. The understory as describedbelow). Some islands are even-aged was dominated by Heliconia sp. thickets and a throughout and easyto classifyas one ofthe three vine (Zpomea sp.). Shorter Cecropia forest was types, whereas others vary considerably in age also present on Ronsoco and was characterized BIRDS OF AMAZONIAN RIVER ISLANDS 429

high rater

Tess8ri8 Short Cecrupi8 T a 11 Cmzropi8 Sandbar Scrub - River Edge Forest 2

RIVER - ISLAND HABITATS FIGURE 1. A diagrammatic sketchof river-island microhabitats:(1) canopy of tall Cecropiaforest; (2) canopy of short Cecropia forest; (3) middle story of tall Cecropiu forest; (4) understory of tall Cecropia forest; (5) understoryof short Cecropiuforest; (6) early successionalTessuriu scrub. Note the high-water line that indicates f which habitats are completely covered during high water.

by even-aged trees 5 to 7 m tall, the lack of a was visited on 10 days, on five of which complete distinct middle-story, and an understory of vines censusesof speciesand individuals were taken. and grass,with few Heliconia. Basedon the structure of the vegetation on the The second study site was Tuhuayo Island, two islands, I divided the two macrohabitats only 130 m by 30 m, which was equidistant be- (river-edge and sandbar scrub) into six micro- tween Ronsoco Island and Negro Urco on the habitats that might be recognized by birds (Fig. mainland. Tuhuayo, only 2 years old according 1): (1) canopy of tall Cecropia forest; (2) canopy to local residents (in 1982 it was a grass-covered of short Cecropia forest; (3) middle-story of tall sandbar), was typical of a young island in an early Cecropia forest; (4) understory of tall Cecropia successionalstage. Vegetation structure was sim- forest; (5) understory of short Cecropia forest; ple on this island compared with that of older and (6) Tessaria scrub. Ronsoco was a mosaic islands, with the dominant speciesTessaria of tall and short Cecropia forest, as well as small integrijidia, which attained a maximum height patchesof Tessaria scrub. Tuhuayo was covered of 3 m. A lesser amount of Salix humboltiana entirely by Tessaria scrub. was common along the edge of the riverbank, with some individuals reaching a height of 5 m. AVIAN HABITAT USE AND FORAGING Bacharis sp. was also prevalent on the down- To establish the status of river-island speciesin stream end of the island, as were many sapling mainland habitats, and to determine which Cecropia scatteredamong the Tessaria. Tuhuayo specieswere restricted to islands in this region 430 GARY H. ROSENBERG

TABLE 1. List of obligate river-island speciesfound study sitesand other river islands on the Amazon in western Amazonia. Some of the specieslisted here River were deposited at the LSUMNS. were encounteredtoo infrequently to be included in To evaluate specialization by obligate and the quantitative portion of this paper. nonobligate island specieswith respectto habitat and foraging parameters, I first examined fre- Blue-rumped Parrotlet Forpusxanthopterygius Olive-spotted Hum- Leucippuschlorocercus quency distributions of observations for each mingbird variable. I then arbitrarily chosea value of 75% Pale-billed Homer0 Furnarius torridus or greater use of an ecological category to rep- Lesser Homer0 F. minor resent “specialization” on that category. In ad- White-bellied Spinetail Synallaxis propinqua dition, niche breadths were calculated using the Red-backed Spinetail Cranioleuca vulpina Red-and-white Spinetail Certhaixis mustelina formula B = l/[np,2] where pi is the proportion Castlenau’s Antshrike Thamnophiluscryptoleu- in category i, and n is the total number of cate- goriesfor the variable under consideration (Lev- Leaden Antwren M~~motherula assimilis ins 1968) for each of the following variables: Ash-breasted Myrmoborus lugubris Black-and-white - Myrmochaneshemileucus plant species; foraging height; foraging tech- bird nique; and foraging substrate. Brown Elaenia Elaenia pelzelni River Tyrannulet Serpophagahypoleuca RESULTS Lesser Wagtail-Tyrant Stigmatura napensis FuscousF ’lvcatcher Cnemotriccusfuscatus COMPOSITION OF RIVER-ISLAND AVIFAUNA Riverside Tyrant Knipolegusokocensis Conirostrumbicolor In this part of Amazonia, at least 18 species Pearly-breastedConebill C. margaritae seemed to be restricted to river islands (hereafter obligate island species; see Table 1). Of these, 14 were included in the quantitative portion of my study. During more than 8 months of fieldwork of Amazonia, I used data from three field ex- along the Napo and Amazon rivers in north- peditions to northeastern Peru by the LSUMNS, eastern Peru by the LSUMNS that included ex- an unpublished specieslist for a tourist lodge on tensive collecting in all habitats, not one indi- the Napo River (Explomapo Lodge) compiled vidual ofany obligate island specieswas recorded by Theodore A. Parker, III, unpublished field off islands. notes of J. V. Remsen, Jr. from Monkey Island About 23 1 specieshave been recordedon river and adjacent vurzea forest, near Leticia Colom- islands in northeastern Peru and southern Co- bia, from 1974-1975, and my own experience lombia (Appendix). Of these, only 3% have been from fieldwork on the Napo and Amazon rivers recorded in terra jirme forest on the mainland spanning 4 years. This included visits to more (Table 2). A far greaterproportion of river-island than 10 islands representing all age classes.Any specieswas found in other mainland habitats; speciesrecorded solely from river islands during 33% of the species also occurred in secondary these periods of observation is considered here woodland or second-growth, 25% occurred in to be an obligate island species. varzea (seasonally flooded forest), 40% occurred During my own visits to the two main study in water-dependent (riverine) habitats that in- islands, at the initial point of observation of each eluded river, lake, and stream margins, sandbars, bird, I recorded the following: bird species;tree and marsh; and at least 14% were seen as aerial species;tree height; distance from ground; and transients, that included both foraging and non- distance from canopy. If an individual was seen foragingbirds that flew over the islands. Virtually foraging,I alsorecorded foraging technique (glean, all of the speciesrecorded on river islands be- sally, hover, lunge, hang, or hammer) and for- tween May and August were residents in this aging substrate (leaf, bark, fruit, flower, grass, region of Amazonia, with the exception of the ground, or air). Data were not (knowingly) col- occurrence of several “austral” migrants (i.e., lected on the same individual during the same three speciesof Elaenia; see Appendix). Between day. For each observation, I placed the individ- August and April, severalNorth American species ual into one of the six microhabitats base upon may use river islands, particularly shorebirdsthat its location within the vegetation strata. Voucher probably use the rivers as migratory pathways specimens for all study speciescollected on my (Appendix). BIRDS OF AMAZONIAN RIVER ISLANDS 431

TABLE 2. Bird speciescomposition among three age represented taxa were flycatchers (Tyrannidae; classesof Amazonian river islands.Numbers represent 38 of 72 species) and icterids (Icterinae; 11 of the percentageof speciesfound on a particular classof 15 species). island (let?hand column) and also found on the other two island classes(across the top). Note that some Bird species composition on young islands was speciesare found on more than one age classof island. more similar to middle-aged islands than to old islands (Table 2). A higher percentageof species Island age found on middle-aged islands were also found NO. Middle- on old islands, as opposed to young islands. A Island age species YOlUg aged Old similarly.high percentageof speciesfound on old Young 62 - 83% 37% islands were also found on middle-aged islands, Middle-aged 31% - 143 63% with very few having been recorded on young Old 166 13% 59% - islands (Table 2). More striking is the comparison between the number of bird speciesfound on the three age Most of the obligate island species are repre- classesof islands and the various mainland hab- sentatives of genera typically found in open hab- itats (Table 3). Of the 62 speciesrecorded from itats. Those found in open shrubby habitats in- young islands, most were found either in sec- cluded: Leucippus (Trochillidae), Furnarius and ondary habitats or riverine habitats on the main- Certhiaxis (Furnariidae), and Elaenia, Stigma- land, whereasnone was found in terrafirme for- tura, and (Tyrannidae), whereas, est, and only one was found in varzea. As on others that were found in a mixture of forest and young islands, a high percentageof speciesthat open habitats included Synallaxis and Crani- occurredon middle-aged islands were also found oleuca (Fumariidae), (Formica- in secondaryhabitats on the mainland, but more riidae), Cnemotriccus (Tyrannidae), and Coni- specieswere also found in varzea. The forest on rostrum (Coerebidae). Only Myrmotherula and old islands visually resembled mainland varzea Myrmoborus (both Formicariidae) can be con- forest, and a much higher percentageof the old sidered mostly forest genera. island speciesalso occurredin varzea. In general, Several families or subfamilies of forest birds the bird-species composition on islands resem- were absent or poorly represented on river is- bled the composition in the riverine habitats lands including quail (Odontophorinae), trum- (river, lake, and stream margins, sandbars, etc.) peters (Psophiidae), motmots (Momotidae), tro- on the mainland with at least 40% of the island gons (Trogonidae), tapaculos (Rhinocryptidae), speciesoccurring there. and gnatcatchers (Polioptilinae). Equally striking During June and July 1983, I found 110 species is that only one of seven toucans (Ramphasti- on the two study islands. Ofthese, sufficient sam- dae), three of 16 woodcreepers (Dendrocolapti- ple sizes of observations of 31 specieswere ob- dae), seven of 56 (Formicariidae), one tained for quantitative analysis (Table 4). Many of 11 manakins (Pipridae), and nine of 27 tan- additional nonpasserinesthat visited the islands agers (Thraupidae), found in this region of Ama- were eliminated from the study becausethey in- zonia were found on islands. Among the better- frequently used the terrestrial habitats, or were

TABLE 3. Number of bird speciesfound on three ageclasses of river islandsand also found in various mainland habitats. Terrufirme refers to upland forest that is never flooded. Vurzeu refers to seasonallyflooded forest. Secondaryhabitats are influencedby man, suchas second-growthand older secondarywoodland. Rivetine habitats include river, lake, and stream margins, open river, sandbars,and marsh. Aerial refers to speciesthat were seen flying over islands(foraging and nonforaging).Numbers in parenthesesare percentagesof specieson that particular age classof island. Rows add up to greater than 100% becausesome speciesoccupy more than one habitat.

Mainland habitats Island age No. species Terra jirme VUrZL?U Secondary habitats Riverim habitats A&?1

Young 62 0 (0%) 1 (lo/o) 23 (29%) 48 (60%) 10 (12%) Middle-aged 143 4 (3%) 25 (17%) 63 (44%) 47 (33%) 11 (8%) Old 166 7 (4%) 51 (31%) 53 (32%) 77 (46%) 17 (10%) Total 231 8 (3%) 58 (25%) 76 (33%) 92 (40%) 33 (14%) 432 GARY H. ROSENBERG

TABLE 4. Frequency of observations within microhabitats: (1) canopy of tall Cecropiaforest; (2) canopy of short Cecropiaforest; (3) middle story of tall Cecropiuforest; (4) understoryof tall Cecropiaforest; (5) understory of short Cecropiaforest; and (6) Tessariascrub. Also, frequency of observationsin various plant species:CP = Cecropia;M = Mimosa; BL = broad-leafed; T = Tessaria;S = Sal& P = Paspalum; V = vines (Ippomoea); 0 = other. n = sample size.

Microhabitat Plant species Bird species n I 2 3 4 5 6 CP M BL T S P V 0

Obligate island species Leucippuschlorocercus 36 6 17 14 25 8 31 6 3 14 19 31 28 Furnarius minor 30 47 10 43 17 7 30 3 10 33 Synallaxis propinqua 34 9 91 3 56 9 24 9 Cranioleucavulpina 41 7 17 7 10 12 46 17 10 20 20 20 13 Thamnophiluscryptoleucus 47 4 15 21 23 21 15 26 9 43 4 15 3 Myrmotherula assimilis 12 17 33 50 75 17 8 Myrmoborus lugubris 22 86 14 55 23 22 Myrmochaneshemileucus 3 7 31 17 43 1 9 13 5 63 8 Elaenia pelzelni :z 81 14 5 61 36 3 Stigmatura napensis 19 11 5 84 11 79 10 Serpophagahypoleuca 15 100 20 80 Cnemotriccusficatus 45 7 4 11 33 29 16 9 7 27 13 2 20 23 Conirostrumbicolor 44 86 14 61 36 2 Conirostrummargaritae 10 90 10 100 Nonobligate island species Chrysoptiluspunctigula 21 29 19 24 5 10 14 33 43 24 Veniliornispasserinus 14 21 7 36 21 14 43 36 7 14 Synallaxis gujanensis 22 68 32 36 5 45 14 Synallaxis albigularis 29 3 3 17 24 52 10 10 45 38 7 Thamnophilusdoliatus 11 18 9 9 27 36 27 36 18 19 Todirostrummaculatum 47 36 21 15 2 6 19 42 28 7 21 2 Myiarchusferox 13 62 15 23 46 31 15 8 Myiodynastesmaculatus 23 43 35 13 9 70 17 13 Tyrannus melancholicus 19 42 42 21 37 5 32 Tyrannus albogularis 21 52 24 :: 29 48 14 ; Turdus ignobilis 39 69 18 5 8 82 8 5 5 Thraupis episcopus 41 78 20 2 71 22 7 Thlypopsissordida 36 22 28 8 9 3 28 39 8 11 17 8 8 9 Ramphoceluscarbo 14 29 64 7 79 14 7 Sporophilacastaneiventris 39 23 31 3 44 54 3 18 5 15 5 Saltator coerulescens 39 54 15 10 13 8 59 10 8 3 13 7 Ammodramus aurtfrons 9 22 79 22 33 22 22

difficult to observe (e.g., speciesin the Ardeidae, idents” included several species that represented Cathartidae, Accipitridae, Rallidae, Charadri- obvious wanderers from older islands (e.g., Pale- idae, Columbidae, , Caprimulgidae, vented Pigeon, Columba cayennensis,Swallow- and Alcedinidae). Fourteen of these 110 species winged Puffbird, Chelidoptera tenebrosa,Great were determined to be obligate island species. Kiskadee, Pitangussulphuratus,Bicolored Cone- Five complete censuseson Tuhuayo yielded a bill, bicolor, and Blue-gray Tana- total of 44 species(see Appendix for complete ger, Thraupis episcopus).Counts of individuals river-island specieslist), averaging 22.5 species averaged 108 (SD = 5.7) per visit. The 16 species (SD = 1.8) per visit. That only half the total presentduring all five censusestogether exceeded number of specieswere detected per censussug- 160 birds/ha. This amazingly high density is an gest a high day to day turnover of migrating or order of magnitude greater than any published roosting birds; this is consistent with other Tes- density figures for mature forest or secondary saria-dominated habitats in southeastern Peru habitats in the tropics (Karr 1976), and illustrates (Scott Robinson, pers. comm.). These “nonres- how abundant birds on river islands can be. The BIRDS OF AMAZONIAN RIVER ISLANDS 433

FIGURE 2. Niche breadthsfor microhabitatand plant FIGURE 3. Mean foraging heights of river-island speciesusage on the two study islands. The six cate- birds and niche breadths for foraging heights. Niche goriesfor microhabitat are presentedin Figure 1. The breadths are presented as a proportion of the total eight categoriesfor plant speciesare listed in Table 4. number of foraging heights (categories) available. Breadth values are presented as a proportion of the Shaded circles represent obligate island species and total number of categoriesfor each variable (e.g., [ac- open circles represent nonobligate island species.See tual breadth value/61 = value presentedfor breadth of Table 5 for speciesabbreviations. microhabitat as there are six microhabitat categories). Shaded circles represent obligate island species and open circles represent nonobligate island species.See Table 5 for speciesabbreviations. The Black-and-white Antbird was largely re- stricted to vine tangles, where it occasionally as- cended along tree trunks into the middle story. most common resident on Tuhuayo was the The Leaden Antwren foragedmostly in the lower White-bellied Spinetail (Synalluxis propinqua) branches of the “broad-leafed” trees that grew with density estimates averaging about 20 indi- primarily in the tall Cecropia forest. The Lesser viduals/visit (or about 47 birds/ha!). Homer0 foraged primarily on the ground in any habitat, and would occasionally be found off the HABITAT AND MICROHABITAT USE ground on exposed roots or low branches. Seven of the 14 obligate island species that I In contrast, only two of the 17 nonobligate studied were specialized on a particular micro- island species studied here were microhabitat habitat (> 75% of observations, Table 4). Of these specialists.Both are widespread tropical species; Brown Elaenia, Elaenia pelzelni, and the two the Blue-gray , a canopy species,and the conebills, Conirostrum bicolor and C. margari- Yellow-browed Sparrow, Ammodramus auri- tae, were restricted to the canopy of tall Cecropia frons, a speciesof open, grassy,habitats both on forest. Pearly-breasted Conebill, C. margaritae, and off islands. Four flycatchers,the Short-crest- perhaps the least-known species in my study, was ed Flycatcher, Myiarchusferox, the StreakedFly- observed only near the tops of Cecropia,whereas catcher, Myiodynastes maculatus, the Tropical the other two canopy species used Mimosa fre- Kingbird, Tyrannus melancholicus, and the quently. Three other specialists were restricted White-throated Kingbird, T. albogularis, as well largely to sandbar scrub. White-bellied Spinetails as the Black-billed Thrush, Turdus ignobilis,and and Lesser Wagtail-Tyrants, Stigmatura napen- the Silver-beaked Tanager, Ramphoceluscarbo, sis, used Tessaria most heavily within the hab- were all canopy specialists(when microhabitats itat, but the River Tyrannulet, Serpophaguhy- 1 and 2 were combined); the two kingbird species poleucu,seemed to prefer the taller willows (Sulix) also perched in the tops of willows in sandbar when it foragedin the Tessaria-dominated scrub scrub habitat and occasionally flew between the habitat. The Ash-breastedAntbird, Myrmoborus two islands. lugubris, was restricted to the understory of tall To summarize, a majority of the most spe- Cecropia forest. cialized species,as illustrated by the breadth of The remaining obligate island specieswere not microhabitat and tree-speciesuse (Fig. 2) were specialists;they occurred in more than one mi- obligate island species.Most of thesewere found crohabitat. The Lesser Hornero, Furnarius mi- almost exclusively in either Cecropiaor Tessaria nor, Leaden Antwren, Myrmotherula assimilis, trees, and were either sandbar scrub or Cecropia and Black-and-white Antbird, Myrmochanes forest specialists. However, some of the most hemileucus,were primarily understory species. generalized specieswith regard to these habitat 434 GARY H. ROSENBERG

TABLE 5. Frequencyof observationsin variousforaging technique and substratecategories used by 3 1 bird specieson two river islands.n = samplesize. Substrates include: LF = leaf;BK = bark, FR = fruit; GR = grass; GD = ground;FL = flower;and AR = air. Techniquesinclude: CL = glean;SL = sally;HM = hammer;HV = hover;LG = lunge;and HG = hangingdown. Speciescodes are includedafter the name.

substrate Technique Bird species n LF BK FR GR GD FL AR GL SL HM HV LG HG Obligateisland species Leucippuschlorocercus LC 16 19 6 6 6 ;: 6 100 Furnarius minor FM 17 59 41 Synallaxis propinqua SP 25 20 72 4 4 100 Cranioleucavulpina CV 30 37 63 93 7 Thamnophiluscryptoleucus TC 21 52 48 76 10 14 Myrmotherula assimilisMA 9 67 33 89 11 Myrmoborus lugubrisML 8 25 62 13 88 12’ Myrmochaneshemileucus MH 35 54 37 9 100 Elaenia pelzelni EP 24 58 17 25 13 87 Stigmatura napensisSN 16 94 6 38 50 12 Serpophagahypoleuca SH 11 82 18 18 82 Cnemotriccusfuscatus CF 1984 5 11 100 Conirostrum&color CB 32 75 25 84 9 7 Conirostrummargaritae CM 8 88 12 87 13 Nonobligateisland species Chrysoptiluspunctigula CP 16 100 19 81 Veniliornispasserinks VP 11 100 100 Synallaxis gujanensisSG 7 71 14 15 100 Synallaxis albigularisSA 8 25 63 12 100 Thamnonhilusdoliatus TD 5 80 20 100 Todirosthm maculatum TM 39 97 3 5 95 Myiarchusferox MF 7 86 14 100 Myiodynastesmaculatus MM 14 79 7 14 100 Tyrannus melancholicusTZ 12 8 :: 100 Tyrannus albogularisTA 15 13 100 Turdus ignobilisTI 19 5 9: Thraupis episcopusTE 21 33 10 52 5 :; :4 5 Thlypopsissordida TS 26 92 4 4 92 8 Ramphoceluscarbo RC 7 29 29 42 57 29 14 Sporophilacastaneiventris SZ 10 10 30 10 50 100 Saltator caerulescensSC 17 12 12 71 59 35 6 Ammodramus aurtfions AA 5 20 20 6; 40 60

variables were also obligate island species.These mediate, with only four speciesfound primarily were all found in almost all the available micro- in the understory vegetation. In addition to this habitat on the islands. Most nonobligate island difference in mean foraging height, obligate is- speciesstudied had intermediate breadth values land speciesappeared to use a narrower range of for these measures. heights than nonobligate island speciesas illus- trated by their smaller niche breadths (Fig. 3). FORAGING BEHAVIOR In general, most river-island specieswere in- Little was known about the foraging behavior of sectivorous,although some were at least partially many speciesstudied here, particularly those re- frugivorous, taking advantage of the abundant stricted to river-island habitats. Among the 14 supply of Cecropia fruit (Table 5). Among the obligate island species, 11 fed primarily in the obligate island species,only the Brown Elaenia understory within 3 m of the ground (Fig. 3) fed to any extent on Cecropia fruit (4/4 stomachs whereas the other three fed exclusively in the contained Cecropia fruit). In contrast, seven of upper canopy. The mean foraging heights for the the nonobligate island specieswere considered nonobligate island specieswere generally inter- specialized frugivores; the Black-billed Thrush BIRDS OF AMAZONIAN RIVER ISLANDS 435 mainly sallied out to pluck a piece of fruit, and then returned to a perch to eat it (l/l stomach contained Cecropia fruit), whereas the Grayish Saltator, Saltator caerulescens,usually clung to a cluster of fruit from which it fed (no stomachs examined). In addition to the fruit specialists mentioned above (based upon foraging behav- ior), examination of stomachs from specimens collectedon islands (LSUMNS tag data) revealed that the following speciesfed at least partially on Cecropia fruit: the Short-tailed , Graydi- FIGURE 4. Niche breadth values based on foraging dasculusbrachyurus (818 stomachs);the Canary- techniqueand foraging substrate.The six categoriesof winged Parakeet, versicolorus (4/8 techniquesand seven categoriesof substratesare listed in Table 5. Breadth values are presented as a propor- stomachs); the Tui Parakeet, B. sanctithomae, tion of the total number of categoriesfor each variable. (518 stomachs);the Blue-winged Parrotlet, For- Shaded circles represent obligate island species and pus xanthopterygius (4/4 stomachs); the Large open circles represent nonobligate island species.See Elaenia, Elaenia spectabilis(2/4 stomachs); the Table 5 for speciesabbreviations. Small-billed Elaenia, E. parvirostris (2/2 stom- achs); the Short-crested Flycatcher (l/4 stom- achs); the Great Kiskadee (3/4 stomachs); the technique. The Spotted Tody-Flycatcher, Todi- Streaked Flycatcher (l/l stomach); the White- rostrum maculatum, fed by sallying out to pick throated Kingbird (4/8 stomachs); the Hooded off the undersides of leaves, as do many Tanager, Nemosia pileata (l/4 stomachs); and of its congeners(Fitzpatrick 1976). Of the glean- the Blue-gray Tanager (2/2 stomachs). Cecropia ers, the Dark-breasted Spinetail, Synallaxis al- trees do not appear to be seasonalwith regard to bigularis, and the Plain-crowned Spinetail pri- fruit production, with fruit present during visits marily searchtwigs and small branches, whereas in July, as well as January. the BarredAntshrike, Thamnophilusdoliatus, and Among the obligate island species, most fed the Orange-headed Tanager, Thlypopsissordida, by either gleaning or sallying for insectson leaves searched mostly leaves. The Chestnut-bellied or branches, with gleanersoutnumbering salliers Seedeater,Sporophila castaneiventris, fed mostly nine speciesto three. Of the understory species, on grassseeds, and the Yellow-browed Sparrow only the LesserHomer0 and Ash-breasted Ant- was seen “leaping” up into the air (a seemingly bird were seen to feed on the ground. The hor- uncharacteristic behavior for an emberizid) for nero often foragedin clearingsor in exposedsandy flying insects. The two woodpeckers both spe- areasaway from vegetation, whereasthe antbird cialized by hammering for insects on trunks and (along with the Plain-crowned Spinetail, Synal- branches. laxis gujanensis) often fed by moving about on Overall, there appeared to be no difference in exposedCecropia roots occasionally dropping to the degreeof foraging specialization between ob- the ground to searchfor insects.The Olive-spot- ligate and nonobligate island species, as illus- ted Hummingbird, Leucippuschlorocercus, was trated by niche breadths for technique and sub- frequently seen hover-gleaning for insects at a strate (Fig. 4). All species, however, were variety of substrates.This is consistent with re- specialized in foraging technique and substrate. cent findings that most (if not all) tropical hum- mingbirds feed extensively on insects (Remsen DISCUSSION et al. 1986). No obligate island specieswere ex- The extreme geographicrestriction exhibited by clusively bark-foragers, or sallied to any extent island birds in northeastern Peru represents a for aerial prey, except perhapsthe Brown Elaenia situation unique to the Amazon River and its (25% of the observations). tributaries. In no other tropical or temperate riv- Nonobligate island speciesalso mostly gleaned er basin in the world is such a high percentage or sallied for insects, but, in contrast to obligate of the avifauna dependent upon river-created island species,there were as many sallying species habitats (Remsen and Parker 1983). If such a as gleaners. Six speciessallied for flying insects, degreeof river-created specialization were wide- with the two kingbird speciesspecializing on that spread, then, for example, an island in the Mis- 436 GARY H. ROSENBERG

FIGURE 5. Distribution of four river-island bird species.Open circles represent all the collection localities for all river-island speciescombined basedupon an extensivemuseum search.Shaded circles represent collecting localities at which specimensof that specieswere attained.

sissippi River would have 15-20 speciespresent small (e.g., Fuscous Flycatcher, Cnemotriccus that were absent from the adjacent mainland de- fuscatus,Red-backed Spinetail, Cranioleuca vul- ciduous forest (and absent from nonforested re- pina, and Leaden Antwren); and (3) speciesre- gions outside of the Mississippi drainage). What stricted to western Amazonia along the Amazon, are the primary factors causing the habitat and Napo, and Ucayali rivers (e.g., Black-and-white geographicrestriction found in northeasternPeru? Antbird and Olive-spotted Hummingbird). Are bird speciesthat are restrictedto river islands Away from northeastern Peru, several obligate in northeastern Peru restricted to islands island specieshave been found in similarly struc- throughout their range, or are they attracted to tured habitats away from islands. For example, specific habitats that are found only on islands in southeasternPeru, Terborgh and Weske (1969) in this region of Amazonia? found the River Tyrannulet in “matorral” hab- Most obligate island specieshave widespread itat. Also, the Ash-breasted Antbird is known but linear distributions that fall into three cate- from river-edge forest on the mainland of Co- gories (Fig. 5): (1) species found throughout lombia, near Letecia, although the record rep- Amazonia but restricted to the Amazon River resentsonly one sightingaway from a river island and its largest tributaries, such as the Ucayali in more than 10 months of fieldwork in varzea and Napo rivers (e.g., Ash-breasted Antbird, forest (J. V. Remsen, Jr., pers. comm.). Another Yellow-hooded Blackbird, Agelaius icterocepha- pair was also recordedfrom varzea on the “main- lus, White-bellied Spinetail, and others); (2) like land near Letecia in January 1984” (R. S. Ridge- (1) but also found on most tributaries, large or ly, pers. comm.). The Fuscous Flycatcher occurs BIRDS OF AMAZONIAN RIVER ISLANDS 431 in Tessaria- and Cecropia-dominated second- Several of the obligate island speciesbelong to growth, river-edge, and lake margins in south- families (e.g.,Formicariidae and Fumariidae) that eastern Peru (T. A. Parker, III, pers. comm.). In are considered poor dispersers. Although vir- addition, this speciesis found along sand ridges tually nothing is known about the dispersal ca- and in swampy forest in Suriname (Haver- pabilities of island species,the variety and abun- Schmidt 1968). The Bicolored Conebill is found dance of birds recorded on Tuhuayo during my in coastal along the northern coast of censuses,including several speciesnot normally (Haverschmidt 1968, Hilty and found in Tessaria-scrubhabitat (e.g., Great Kis- Brown 1986). kadee, Black-billed Thrush, Bicolored Conebill, Evidence that island speciesmay occasionally and Blue-gray Tanager), implies that many birds occur away from islands, even in western Ama- can disperseand find new islands, and that some zonia, comes from a sandbar along the lower may wander from island to island in search of Napo that, in 1983, was covered with Tessaria their preferred habitat. Several species(e.g., both scrub (later replaced by short Cecropia forest). kingbirds, Chestnut-backed Oropendola, Psar- All the bird speciesof Tessaria scrub were found ocolius angustifrons, and Yellow-rumped Ca- on visits to this sandbar, even though it was con- cique, Cacicus cela) were regularly seen to tly nected to the mainland on one end. However, between the mainland and the islands, and even none was found in adjacent successionalhabitats roost on the islands. Amazingly, even a poor- along the mainland riverbank that lacked Tes- flying terrestrial Undulated Tinamou, Cryptu- saria. The formation of thesesandbar peninsulas rellus undulatus, has been seen to fly from the is apparently a rare phenomenon in northeastern mainland to islands (J. V. Remsen, Jr. and R. S. Peru, but the presence of Tessaria-scrub birds Ridgely, pers. observ.). there illustrates the likelihood that theseobligate Further anecdotal evidence of high dispersal island species select particular habitats, rather capabilities in obligate island speciescomes from than islands per se. a visit to another small island in the Napo River Given such habitat restriction, what features in January 1989, which was less than 1 year old of this habitat were most important to the island and partially covered with grass, and Cecropia birds? In general, little foraging-site specializa- and Tessariasaplings. The island was only about tion was apparent among island birds. This can 200 x 75 m in size, and although I made only be attributed to the simple structure of the vege- a short visit, I was able to determine that the tation (Terborgh 198Oa), as well as to the lack White-bellied Spinetail was already “common” of, or scarcity of many “novel” resourceson the in the sparse vegetation. Other speciespresent islands that contribute greatly to foraging-site included the Ladder-tailed Nightjar, Hydropsalis specialization in mainland forests. These in- climacocerca,the River Tyrannulet, the Chest- clude: army (Willis and Oniki 1978); epi- nut-bellied Seedeater,and the Red-capped Car- phytes (Orians 1969); suspendeddead leaf clus- dinal, Paroaria gularis. Absent (despite playback ters (Terborgh 1980b, Remsen and Parker 1984); of recorded song and calls in an attempt to de- and bamboo thickets (Parker and Parker 1982, termine presenceor absence)were the following Remsen 1985). However, the most important Tessaria-scrub species: the Black-and-white distinction between obligate and nonobligate is- Antbird, the LesserWagtail-Tyrant, and the Riv- land species was the specialization by obligate erside Tyrant, Knipolegusorenocensis. island specieson understory and, in particular, In addition, almost nothing is known about Tessaria-scrubvegetation, which is largely absent the immediate responsesof island speciesto the from the mainland. seasonalinundation of their habitat. In those ex- Specialization on these particular microhabi- treme caseswhen entire islands are completely tats poses special problems because they are submerged, it is obvious that all the birds are ephemeral, and often completely under water forced to vacate the islands. However, during during the high-water season(Remsen and Par- partial flooding, which most likely occurs on an ker 1983). For speciesto take advantage of these annual basis, anecdotal evidence suggeststhat habitats as they become available during the low- some speciesmay leave the islands, while others water season requires a degree of mobility and appear to undergo vertical shifts depending on dispersal greater than what is considered usual the height of the water. During a visit to a par- for tropical understory birds (Diamond 1975). tially flooded young island, the White-bellied 438 GARY H. ROSENBERG

Spinetail, normally abundant, was conspicuously LITERATURE CITED absent,whereas the LesserHomer0 and the Dark- DL~MOND,J. M. 1975. Assembly of species com- breasted Spinetail were both seen to feed un- munities, p. 3421144. In M. Cody and J. Diamond characteristically high in willow trees well above [eds.], Ecology and evolution of communities. the water level (T. A. Parker, III, pers. comm.). Harvard Univ. Press, Cambridge, MA. FITZPATRICK,J. W. 1976. Systematicsand biogeog- Equally important to the birds may be the con- raphy of the tyrannid Todirostrumand re- sequences of natural succession of the island lated genera (Aves). Bull. Mus. Comp. Zool. 147: vegetation. As Tessaria-scrub vegetation gives 435-463. way to Cecropia-dominated forest, many indi- GENTRY, A. H., AND J. LOPEZ-PARODI.1980. Defor- viduals must be forced to leave a particular is- estation and increasedflooding of the upper Am- azon. Science 210:1354-1356. land and search for a new home. Speciesfound HAVERSCHMIDT,F. 1968. Birds of Suriname. Oliver primarily in Cecropia forest encounter the same and Boyd, Edinburgh. predicament as their preferred habitat gives way HILTY. S. L.. AND W. L. BROWN. 1986. A guideto to older, more complex vegetation. Much more the birds of . Princeton Univ. Press, Princeton, NJ. information on dispersal capabilities is needed I(ARR, J. 1976. Seasonality,resource availability, and before we can fully understand the temporal and community diversity in tropical bird communi- spatial movements of obligate island birds. ties. Am. Nat. 110:973-994. The total area of river islands is certainly tiny LEVINS, R. 1968. Evolution in changing environ- relative to the Amazon basin as a whole, thus ments. Princeton Univ. Press, Princeton, NJ. ORIANS,G. H. 1969. The number of bird speciesin populations of obligate island species must be some tropical forests. Ecology 50:783-801. tiny relative to speciesof more widely distributed PARKER,T. A., III, AND S. A. PARKER. 1982. Behav- habitats (even though many of the island species ioral and distributionalnotes of someunusual birds are incredibly abundant). Furthermore, the ex- of a lower montane cloud forest in Peru. Bull. Br. Omithol. Club 102:63-70. istence of stable populations of several obligate REMSEN,J. V., JR. 1985. Community organization island species depends on the continued for- and ecology of high elevation humid forest of the mation and presence of new islands. Therefore, Bolivian Andes, p. 733-756. In P. A. Buckley, M. several of these speciesmay be threatened by the S. Foster, E. S. Morton, R. S. Ridgely, and F. G. higher flooding and increased erosion that may Buckley [eds.],Neotropical ornithology. Omithol. Monogr. No. 36. American Ornithologists’ Union, result from increased runoff attributed to defor- Washington, DC. estation in the Andes (Gentry and Lopez-Parodi REMSEN,J. V., JR.,AND T. A. PARKER,III. 1983. Con- 1980). Conservation plans for Amazonia should tribution of river-created habitats to bird species take into account this significant aspect of the richnessin Amazonia. Biotropica 15:223-23 1. REMSEN,J. V., JR., ANDT. A. PARKER,III. 1984. Ar- avifauna and should protect river-created habi- boreal dead-leaf-searchingbirds of the Neotropics. tats, especially islands. Condor 86:364 1. REMSEN,J. V., JR., F. G. STILES,AND P. E. Scar-r. ACKNOWLEDGMENTS 1986. Frequency of in stomachs of tronical humminabirds. Auk 103:436-44 1. I would like thank my major advisor, J. V. Remsen, TERBO&, J. 1980a.- Vertical stratification of a Neo- Jr., for his guidancethroughout the many stagesof this tropical forest bird community. Proc. XVII Int. study. I thank Theodore A. Parker, III, Robert S. Omithol. Congr. (1978):1005-1012. Ridgely, Scott Robinson, and Kenneth V. Rosenberg TERBORGH,J. 1980b. Causesof tropical speciesdi- for helpful comments on earlier drafts of this manu- versitv. Proc. XVII Int. Omithol. Conar. (1978): script. T. A. Parker, III and J. V. Remsen, Jr. graciously _% , 955-961. provided their field notes on Amazonian river-island TERBORGH,J., ANDJ. S. WESKE. 1969. Colonization birds. of secondaryhabitats by Peruvian birds. Ecology I thank the following curatorsfor supplyingme with 50:765-782. specimen information: L. Short (American Museum); D. Zusi (National Museum); D. Snow (British Mu- WILLIS, E. O., AND Y. ONIKI. 1978. Birds at army ants. Annu. Rev. Ecol. Syst. 9~243-263. seum);K. C. Parkes(Carnegie Museum); J. Fitzpatrick (Field Museum): R. A. Pavnter (Museum of Compar- ative Zoology);‘ F. Gill (Academy of Natural Sciences); R. W. Schreiber(Los Angeles County Museum); N. K. APPENDIX Johnson (Museum of Vertebrate Zoology); and J. V. Remsen, Jr. (Louisiana State University Museum of List of speciesthat have been found on river islands Natural Science). I especially thank Peter Jenson of along the Amazon and Napo rivers in northeastern Explorama Tours in Iquitos, Peru, for graciouslysup- Peru and southeasternColombia. Data reflect infor- plying a boat and lodging, both of which were essential mation gatheredby the LSUMNS, as well as the field to my study. experience of J. V. Remsen, Jr., Theodore A. Parker, BIRDS OF AMAZONIAN RIVER ISLANDS 439

III, and the author. Included is information on what to the island but still a resident in this region of Ama- age classof islands the speciesare found, on the type zonia; R-V = a portion of the population is resident of habitat the speciesfrequents on the mainland, on but visitors from elsewhereoccur as well; M = migrant whether the speciesis a resident or visitor to the is- from North America; Ma = austral migrant from lands, on the relative abundanceof the specieson the southern South America. islands, and on the foraging position when on the is- Relativeabundance. C = common (encountereddai- lands. ly); U = uncommon (encounteredinfrequently); R = Island age (as describedearlier). 0 = old; M = mid- rare (seen only occasionally but expected in proper dle-aged;Y = young. habitat); X = accidental (seen fewer than three times, Mainland habitat. FYI= terrafirme forest; Vz = var- not expected). zea (seasonallyflooded) forest; SH = secondaryhabi- Foraging position. 1 = canopy of old, tall, river- tats including second-growthand man-influenced hab- island forest; 2 = canopy of Cecropiaforest; 3 = mid- itats; Rv = riverine habitats including river, stream, dle-storv of old island forest: 4 = middle storv of tall and lake margin, marsh, sandbar, and open water; + Cecroph forest; 5 = understory of old island forest; 6 = all of the above. Note that a blank space in this = understoryof Cecropiaforest; I = Tessariascrub; 8 column means that the species is not found on the = water-relatedhabitats (riverbank, beach,open water); mainland. 9 = aerial habitats (including birds seen flying over Islandstatus.R = resident on the islands;V = visitor islands).

Crypturellusundulatus 0, M Ft R-V 536 Phalacrocoraxolivaceus 0 Rv V 8 Ardea cocoi 0, M Rv R Casmerodiusalbus 0, M Rv R uu : Egretta thula 0, M Rv R U 8 Hydranassa caerulea 0, M Rv R R 8 Butoridesstriatus 0, M, Y Rv R C I,8 Agamia agami 0 Rv R R Pilherodiuspileatus 0, M Rv R : Tigrisoma lineatum 0 Rv R Zxobychus exilis Y Rv R s8 Mesembrinibiscayennensis 0 Rv R 8 Anhima cornuta O,WY Rv R 5-8 Cairina moschata 0 Rv V Sarcoramphuspapa QM,Y + V 9” Coragypsstratus 0, M, Y V Cathartesaura 0, M, Y + V ; C. burrovianus Y Rv V C. melambrotus 0, M, Y V ; Elanoidesforficatus @WY + V 9 Chondoheiraxuncinatus Rv R 9 Zctiniaplumbea 00 + R Rostrhamussociabilis 0 Rv R ;9 Helicolesteshamatus 0 Rv R 8: 9 Buteo albonotatus 0, M V 9 B. magnirostris WY :H R 2,4,9 Busarellusnigricollis Rv R 8,9 Buteogallusurubitinga : Ft R 1,3,8,9 Spizastur melanoleucus ? V 9 Spizaetustyrannus : vz V 9 Geranospizacaerulescens Rv R 1,3,9 Pandion haliaetus :MY Rv V 8, 9 Herpetotherescachinans 0: M’ Rv R-V 1,2,9 Daptius ater 0 Rv V 89 Milvago chimachima M,Y Rv, SH R-V 8,9 Falco rujigularis 0 Rv V 179 Ortalis guttata Rv R 1,338 Opisthocomushoazin : Rv R 3,8 Aramides cayanae 0 Vz, Rv R 58 440 GARY H. ROSENBERG

APPENDIX. Continued.

Relative Species Island age Mainland habitat Island status abundance Foraging position Laterallusfascia&s 0 Vz, SH R 5 Porphyrula martinica Y Rv R E 8 P. jlavirostris 0 Rv R? R 8 Heliornisfulica Rv R 8 Jacana jacana : Rv R : Hoploxypteruscayanus Y Rv R-V : Charadrius collaris Y Rv R-V :: Tringa solitaria 0, M, Y Rv M : T. jlavipes 0, M, Y Rv M : T. melanoleuca O,M,Y Rv M U : Actitis macularia 0, M, Y Rv M U Calidris fuscicollis 0, M, Y Rv M X : C. melanotis 0, M, Y Rv M Phaetusasimplex O,M,Y Rv R-V : : Sterna superciliaris QWY Rv R-V C Rynchopsniger Rv R-V U : Columba cayennensis :MY Rv, SH R-V C la&7 C. subvinacea 0: M’ vz V 1,2 Columbina talpacoti M,Y Rv, SH R c” 6,7 Leptotila verreauxi M SH R 6 L. rufaxilla 0, M SH R : 596 Ara ararauna 0, M, Y + V R A. macao 0, M + V R ; A. chloroptera V 9 A. serva :M :V R : 1,2,9 A. manilata 0’ Rv R 1, 9 Aratinga leucophthalmus 0, M VZ R : 1+9 A. weddellii 0 VZ R U 1,3,9 Forpus xanthopterygius M xx R 5,9 Brotogerisversicolorus 0, M Rv R : 14 B. cyanopterus Rh, Vz, SH R 14,7,9 B. sanctithomae :c Fh, Rv, SH R : l-4,9 Graydidasculusbrachyurus 0: M Vz, Rv R C 1,239 Pionus menstruus 0 Vz, Rv, SH R C 1,9 Amazona,festiva ? R U 1,9 A. ochrocephala : + V 199 A. amazonica 0, M Vz, Rv R : 1,2,9 Coccyzusamericana ? M X 1 C. melacoryphus : M,Y SH R U l-7 Piaya minuta ti SH R U 4,6 Crotophagamajor Vz, Rv R U 3,8 C. ani :,M,Y Rv, SH R C 3-7 Tapera naevia Rv, SH R U 637 Otus choliba r Vz, SH R Glaucidium brasilianum M Vz, SH R 8 2: Rhinoptynx clamator M, Y ? R R 6: 7 Nyctibiusgriseus 0 Vz, Rv V 1 Chordeilesrupestris Rv V : 7,8,9 C. minor r;MY Rv M 9 Nyctidromusalbicollis 0: M: Y SH R : 5,627 Hydropsalisclimacocerca Y Rv R C Podagernacunda 0 ? V X ; Caprimulguspar&us Y ? V X 7 Chaetura cinerieventris O,M,Y + V U 9 C. brachyura 0, M, Y + V C Panyptila cayennensis 0, M, Y + V ; Reinarda squamata 0, M, Y + V : 9 Glaucishirsuta 0, M vz R C 5,6 Phaethornishispidus 0, M vz R C 5,6 Campylopteruslargipennis 0 Vz, SH R U 1, 3 BIRDS OF AMAZONIAN RIVER ISLANDS 441

APPENDIX. Continued.

R<k Species Island age Mainland habitat Island status abundance Foraging position

Florisuga mellivora M Fh, Vz, SH R C 224 Anthracothoraxnigricollis vz R U 294, 7 Lophornischalybea 3; ? R R Chlorestesnotatus 0: M ? R U :2 Chlorostilbonmellisugus M ? R 476 Leucippuschlorocercus M,Y R : 4,6,7 Amazilia jimbriata M SH R C 476 A. lactea SH R R ? Heliomaster longirostris :M SH R U 1,2 Ceryle torquata 0: M Rv R Chloroceryleamazona Rv R : : C. americana x Rv R C 8 C. aenea 0: M Rv R U 5-8 Galbalcyrhynchusleucotis 0 Vz, Rv, SH R C 193 Monasa nigrifrons 0 Vz, SH R C 123 Capito aurivirens 0, M vz R U l-4 Pteroglossuscastanotis vz R C Picumnuscastelnau x R R :“4 Chrysoptiluspunctigula 0: M SH R U 314 Celeuselegans Fh, vz R R 3 C. flaws : vz R U 1,3 Dryocopuslineatus 0, M Vz, SH R R l-4 Melanerpescruentatus 0 SH R U 3 Veniliornispasserinus 0, M SH R 374 Campephilusmelanoleucus 0 vz R R” 193 Nasica longirostris vz R R 1,3 Dendrexetastesrujigula OOM vz R U 14 Xiphorhynchuspicus 0: M Vz, SH R U 374 Furnarius torridus 0, M R U 576 F. minor M, Y R C 627 Synallaxis albescens 0 SH M X S. albigularis M,Y SH R 27 S. gujanensis 0, M SH R : 5: 6 S. propinqua M, Y R C 697 Cranioleuca vulpina M,Y R C 627 Certhiaxiscinnamomea R R C. mustelina : R R : Metropothrix aurantiacus M SH R R 6 Taraba major 0 SH R U 5 Thamnophilusdoliatus M,Y SH R U 6,7 T. cryptoleucus 0, M R 4,6 Myrmotherula assimilis 0, M R fJ 3-6 Cercomacranigrescens 0, M SH R U 596 Myrmoborus lugubris R 5,6 Myrmochaneshemileucus 2: R : 6,7 Cotinga maynana 0’ Vz, Rv R 1 Gymnoderusfoetidus Vz, Rv R : 1 Cephalopterusornatus : Vz, Rv R-V Schiffornismajor 0 Vz, Rv R : : Camptostomaobsoletum SH R U 274 Tyrannuluselatus 2: Vz, Rv R U Sublegatusarenarum M ? R R :, Elaenia soectabilis Ma U %4 E. pelzelni !z Ma U 2,4 E. parvirostris M, Y Ma R 4,6,7 Serpophagahypoleuca Y R U I Stigmatura napensis Y R U Todirostrumlatirostre M SH R U : T. maculatum O,M,Y SH R C 3,4,7 Tolmomyiasflaviventris M SH R u 4 442 GARY H. ROSENBERG

APPENDIX. Continued.

Relative Species Island age Mainland habitat Island status abundance Foraging position

Myiophobusfasciatus M, Y SH R 67 Cnemotriccusfuscatus WY R : 476, 7 Pyracephalusrubinus M, Y SH R R 677 dchthornis littoralis 0, M, Y Rv R C 8 Muscisaxicolafluviatilis V U 8 Knipolegusorenocensis T R 7,8 Fluvicola leucocephala Rv R : 7,8 Attila cinnamomeus : Vz, Rv R R 173 A. bolivianus 0 VZ R 193 Myiarchusferox SH R : 4 M. swainsoni E Fh, vz Ma X 3 Pitangussulphuratus O,M,Y Rv, SH R-V C l-7 P. lictor 0 Rv R U 8 Megarynchuspitangua M Vz, SH R C 274 Myiozetetessimilis M,Y R z4, 6, 7 M. granadensis M ;: R 8 2,4 Myiodynastesmaculatus 0, M SH R C 2,3,4 Empidonomus varius Fh, vz Ma X 1 Tyrannus albogularis ZY Rv Ma 2,738 T. melancholicus O,M,‘ Y R-M? cu l-9 T. savana 0, M SH’ Ma U 2,8 T. tyrannus + M R 1 Pachyramphusrufus Tl R R 294 P. castaneus M Vz, SH R 274 P. polychopterus M Vz, SH R : 2,4 Titvra cavana 0, M Fh, vz R 1,2 T. mquisitor 0 vz V :: 1 Tachvcinetaalbiventer O,M,Y Rv V C 879 Prognechalybea 0 Rv V X 9 P. tapera M, Y Rv R-V R 899 Atticorafasciata 0 Rv V Stelgidopteryxrujicollis Rv R-V f? ; Riparia riparia : M,Y Rv M C 8, 9 Hirundo rustica 0 ’ Rv M 9 Petrochelidonpyrrhonota 0 Rv M :: 9 Cyanocoraxviolaceus 0, M Vz, SH R R 1,2 Campylorhynchusturdinus 0 Vz, SH R U 3 Thryothorusleucotis 0, M Vz, SH R C %6 Donacobiusatricapillus O,M,Y Rv R 8 Turdus ignobilis 0, M, Y SH R : l-7 Vireo olivaceus 0, M Vz, SH R 1,2 Molothrus bonariensis M,Y Rv R : 2,798 Scaphiduraoryzivora Y Rv, SH V R 7, 8 Ocyalis latirostris VZ V X 1 Psarocoliusdecumanus : vz R 1 P. angusttfrons 0, M Vz, SH R : 172 Cacicuscela 0, M Fh, Vz, SH R C 1,2 C. solitarius 0, M SH R R 5, 6 Lampropsar tanagrina 0 vz R 193, 5 Agelaiusicterocephalus Rv R : 8 Icterus icterus :MY SH R l-7 Gymnomystaxmexicanus ti, Y ’ Rv R c” 2,4,7,8 Dendroica striata M, Y SH M R 2,497 Conirostrumbicolor M,Y R R 2, 7 C. margaritae M R R 2 Euphonia laniirostris R 192 Thraupis episcopus x Y :: R c” 1,2,7 T. palmarum 0: M ’ SH R 1,2 Ramphoceluscarbo 0, M SH R : 3,496 R. nigrogularis 0 Vz, Rv, SH R U 3,s BIRDS OF AMAZONIAN RIVER ISLANDS 443

APPENDIX. Continued.

R&4iVe Species Island age Mainlandhabitat Island status abundance Foragingposition

Nemosia pileata 0, M Rv, SH R U 192 Thlypopsissordida O,M,Y Rv, SH R C l-7 Eucometispenicillata 0 VZ R Cissopisleveriana SH R : : Saltator caerulescens :M SH R C 14,7 Paroaria gularis O:M,Y Rv, SH R C l-7 Sporophilaamericana O,M,Y Rv, SH R C 6,798 S. lineola 0, Y Rv V cu 6,738798 S. castaneoventris O,M,Y Rv, SH R Oryzoborusangolensis M SH R R Ammodramus aurijiions O,M,Y Rv, SH R C :,7,8