--On Laysan Island, the endangered, endemic Laysan Finch (Telespiza cantans) nests almost exclusively in the native bunchgrass Eragrostis variabilis. Experimental nest boxes provided were never used for nesting. Marine debris was not used as nest substrate on Laysan Island. In contrast, the introduced Laysan Finch populations on four islands at Pearl and Hermes Reef used a wide variety of native and alien plants as nest substrates, as well as various kinds of human-made debris. However, nest boxes provided at Pearl and Hermes Reef were not used as nest substrates by finches. Eragrostis variabilis is uncommon on Pearl and Hermes Reef, except on Seal-Kittery Island, but is common on Laysan where it is the preferred nest substrate. Eragrostis is a dense bunchgrass which probably provides the nest with good protection from sun, rain, wind, disturbance, and predators. On Pearl and Hermes Reef, where Eragrostis variabilis is uncommon, other plants that provide dense cover are used as nest substrates, and human-made debris that provides some cover is also utilized. It is unclear why nest boxes were never used as nest substrates at either site. We suggest that the conservation of Laysan Finches on Laysan Island will require the maintenance of a native ecosystem where Eragrostis variabilis is a major vegetation component. Otherwise, changes in behavior, morphology, and energy expenditure associated with environmental differences are likely to occur, and may have already occurred in the introduced populations on Pearl and Hermes Reef. Received 13 Nov. 1989, accepted 23 Mar. 1990.

The endangered Laysan Finch (Telespiza cantans, Wilson 1890) is a little known Hawaiian honeycreeper (Fringillidae: Drepanidinae). It is considered an endangered species due to its small natural distribution and its extreme vulnerability to predators and disease (USFWS 1984, van Riper and van Riper 1985:331, Throp 1970). Laysan Finches are known from the islands of Oahu and Molokai as fossils (Olson and James 1982). Historically, Laysan Finches are known to occur naturally only on Laysan Island (Fig. 1), although a small population now also occurs on four of the islands at Pearl and Hermes Reef(PHR; Fig. 2) to which finches were introduced in 1967 (Amerson et al. 1974). At both of these sites, Laysan Finches are the only passerine birds present, although seabirds are nu- merous and shorebirds are seasonally common. Laysan and PHR are uninhabited except for periodic visits by research biologists. The islands are part of the Hawaiian Islands National Wildlife Refuge which is ad- ministered by the U.S. Fish and Wildlife Service. Dept. of Zoology, Univ. of Hawaii at Manoa, Present address: P.O. Box 3543, Kailua-Kona, Hawaii 96745-3543. 2 Dept. of General Science, Univ. of Hawaii at Manoa, 2450 Campus Rd., Honolulu, Hawaii 96822. 591 592 THE WILSON BULLETIN ß Vol. 102, No. 4, December 1990 180' 20 170'W 160' I I Kure ß Midway ß Pearl and Hermes Reef Lisianski ß Laysan Gardner Pinnacles French Frigate Shoals -Necker ß Nihoa KAUAI N iihau. t ' OAHU KauJa ' ,,MOL OK AI Lanai,. MAUl KahooJawe' HAWAI I-- I I 180 ų 170 ų W 160 ų FIO. 1. Map of the Hawaiian archipelago showing the locations of Laysan Island and Pearl and Hermes Reef. Laysan has a total area of about 397 ha, of which 187 ha are vegetated. This island supports approximately 10,000 Laysan Finches (see Table 1 in U.S. Fish and Wildlife Service 1984). The four main vegetated islands in PHR total 56.2 ha in area, of which 21.3 ha are vegetated (Conant 1988). The current population from this 1967 introduction numbers about 800 birds (Table 1). Conant has researched the Laysan Finch on Laysan and PHR since 1984, and Morin studied the Laysan Island population from 1986 through 1988. Our work has included records of Laysan Finch nest-site substrates; TABLE 1 ISLAND SIZE, SUITABLE HABITAT AREA LAYSAN Fnc POPULATION SIZE* Estimated finch Total area (ha) Vegetated area (ha) population Laysan 397 187 10,000 Pearl and Hermes Reef 56.2 (total) 21.3 (total) 820 (total) Southeast Island 13.8 12.5 520 North Island 6.4 4.4 200 Grass Island 4.4 2.2 50 Seal-Kittery Island 31.6 2.2 50 U.S. Fish and Wildlife Service (1984). Morin and Conant ß LAYSAN FINCH NEST SUBSTRATES 593 I I I I I 55' N Little North Island 27. Sand Bird Island Island zsu ,.- ss s, I I i 0 I'0 2 0 km 175'40' I Flo. 2. Map of Pearl and Hermes Reef. Names of islands with Laysan Finch populations are printed in capital letters. we have also gathered anecdotal information from other researchers (L. Hiruki, B. Choy, C. Rowland and K. McDermond, unpubl. data). Using those data we document in this paper differences in nest-site selection on Laysan versus PHR. The differences appear to be at least partly due to the presence or absence of certain nest substrates. MATERIALS AND METHODS In 1986, 62 nest boxes were erected in the northwest quadrant of Laysan Island in an attempt to facilitate the location and monitoring of finch nests. Fifty of the nest boxes were made of plywood, and the remainder were plastic or aluminum elbow pipes and concrete cinder blocks. The nest boxes were randomly located, half of them within Eragrostis variabilis clumps, and all but the cinder blocks were approximately 0.3 m above the ground anchored to a stake. Nest boxes were at least 4.5 m from each other, and all were placed in the Eragrostis vegetation association (Lamoureux 1963, Newman 1988). The boxes were taken down at the end of the 1986 field season on Laysan. In 1987 20 were reerected on Laysan, and 20 were erected on Pearl and Hermes Reef, where they were placed directly on the ground in the sparse vegetation. All nest boxes were removed from Laysan at the end of the field season in 1988, and most of the boxes at Pearl and Hermes Reef had disintegrated by August of 1989. Natural nest sites were located on PHR from 1984 to 1989 by Conant and on Laysan 594 THE WILSON BULLETIN ß Vol. 102, No. 4, December 1990 FI. 3. A clump of the bunchgrass Eragrostis variabilis on Laysan Island. When it was photographed, this clump contained an active Laysan Finch nest. from 1986 to 1988 by Morin. These were discovered using a variety of cues, including male song, female and nestling begging calls, courtship feeding and by following females with nesting material. Unless otherwise noted, only nests which contained eggs and/or chicks are included in the results section. During a one-day visit to PHR in 1983 Conant (on Southeast and North Islands) and Gagne (on Grass and Seal-Kittery islands) estimated the number of Eragrostis clumps on the four vegetated PHR islands. In July 1989, Conant counted Eragrostis clumps on each of the four PHR islands with finches. On Laysan, she counted Eragrostis clumps in 30 10 m x 10 m quadrats, with quadrats in the two major vegetation associations where the bunchgrass occurs: 10 in the viney association (Ipomoea-Boerhavia-Sicyos-Eragrostis) and 20 in the pure bunchgrass (Eragrostis) association. On both Laysan and PHR, Conant noted that she did not count the small (under about 15 cm in diameter) clumps. All plant names used in this paper follow Wagner et al. (1990). Not a single wooden, pipe, or cement nest box was used as a nest substrate on Laysan in 1986, 1987, or 1988, although in 1987 a finch made a natural nest in the bunchgrass (Eragrostis variabt7is) 31 cm in front of a wooden nest box in the same bunchgrass clump. The 20 wooden nest boxes placed on PHR in 1987 were erected too late in that breeding season to be used that year. Half of the PHR nest boxes were checked by other researchers in 1988 and all were checked by Conant in 1989, but Morin and Conant ß LAYSAN FINCH NEST SUBSTRATES 595 TABLE 2 LAYSAN FINCH NEST SUBSTRATES ON LAYSAN ISLAND AND PEARL AND H4ES Setaria Solanum Tribulus Erag Erag' Other Debris b Laysan 0 0 0 199 69 2 0 Pearl and Hermes Reef Southeast Island 38 1 0 0 0 7 8 North Island 0 5 4 1 0 5 0 Grass Island 0 1 0 0 0 I 0 Seal-Kittery Island 1 0 0 0 1 I 0 PHR totals 39 7 4 1 1 14 8 Eragrostis with one or more other plant species on or mixed in the clump. b The "debris" category includes such items as plastic crates, "Sono-Buoy" tubes, fishing gear, bamboo poles, a plastic bucket, pipes, hard hats, a TV set, old fuel containers, a generator, swim fins, and a wetsuit. none had been used. On both Laysan and Pearl and Hermes, Laysan Finches and a variety of seabirds were observed loafing or roosting on or in the shade of the boxes. Over 270 nests with eggs or chicks were located in natural substrates on Laysan from 1986 to 1988. Of those nests, 73.7% were in Eragrostis alone, and 25.5% were in Eragrostis with one or more other plant species in or on the bunchgrass clump; only two (< 1.0%) of the nests were situated on other substrates. Over 99% were situated in Eragrostis (Fig. 3) or were in Eragrostis mixed with one or more other plant species (Table 2). When other species were part of the substrate, Eragrostis was nearly always the dominant plant, usually with a vine of some sort (most commonly the morning glory Ipomoea pes-caprae and/or the native cucumber Sicyos maximowiczii) growing over the bunchgrass clump. Only two Laysan nests did not have Eragrostis as some or all of the substrate; one was a nest found on the ground under the sedge Cyperus laevigatus and the other was a nest built on very low branches of a dead Pluchea indica bush heavily overgrown with the succulent ground cover Sesuvium portula- castrum. On PHR the grass Setaria verticillata was the most common (38 out of 46) natural nest substrate recorded on Southeast Island. The perennial shrub Solanum nelsonii (five out of 12) and the annual herb Tribulus cistoides were the most common nest sites on North Island (see Table 2). Other plant species, including Lepturus repens, Lepidium bidentatum, Boerhavia repens, and various combinations were used as well. There were several nests built under both active and abandoned Great Frigate- bird (Fregata minor) nests (particularly in 1989), and a single nest found 596 THE WILSON BULLETIN ß Vol. 102, No. 4, December 1990 TABLE 3 LIST OF PLANT SPECIES ON LAYSAN ISLAh AhD THE FOUR VEGETATED ISLANDS OF PEARL AhD I-IEgM REEF* Seal- Plant species (status) (alphabetical order) Laysan Southeast North Grass Kittery Boerhavia repens (I b) + + + + + Brassica campestris (A) + Casuarina equisetifolia (A) + Cenchrus echinatus (A) + Chenopodium oahuense (H) + Cocos nucifera (A) + Conyza bonariensis (A) + Coronopus didymus (A) + Cynodon dactylon (A) + + Cyperus laevigatus (I) + Eragrostis paupera (I) + + E. variabilis (H c) + + + + + Fimbristylis cymosa subsp. spathacea (I) + F. cymosa subsp. umbello-capitata (I) + Heliotropium currasavicum (I) + Ipomoea indica (I) + I. pes-caprae subsp. brasiliensis (I) + Lepidium bidentatum var. o-waihiense (H) + + + + Lepturas repens (I) + + + + + Malvastrum coromandelianum (A) + Mariscus pennatiformis subsp. bryanii (L ) + Nama sandwicensis (H) + Nicotiana tabacum (A) + Pluchea indica (A) + Portulaca lutea (I) + + P. oleracea (A d) + +f +f Scaevola sericea + Sesuvium portulacastrum (I) + + + + Setaria verticillata (A) + + +f Sicyos maximowiczii (H) + + + +f + S. pachycarpus (H) + S. semitonsus (H) + Solanum americanurn (A) + + S. nelsonii (H) + + + + Sonchrus oleraceus (A) + Tournefortia argentea (A) + + Tribulus cistoides (I) + + + + + a This list includes all species of plants observed or collected from 1983 through 1989, except that Portulaca oleracea and Eragrostis paupera were seen but not collected on North Island. Hisrically, other species were known from the islands. b I Indigenous to the Haw 'arian Islands. = H = Endemic the Hawaiian Islands. d A = Alien, introduced m the Haw 'arian Islands. e L = Endemic to Laysan Island. f New island record (Herbst and Wagner, 1990, this study). Morin and Conant ß LAYSAN FINCH NEST SUBSTRATES 597 Fio. 4. A two- or thru-gallon plastic container for liquids contsining an old Laysan Finch nest at Southeast Island, Pearl and Hermes Reef. The side of the container was cracked off and removed so the nest could b photographed. Apparently finches entered the container through its neck or "spouL" in a partially collapsed seabird burrow on North Island. Table 3 is a hst (alphabetic) of all plants that were observed or collected on Laysan and the four vegetated islands of PHR from 1983 through 1989 (Newman 1988, Herbst and Wagner, in press, Morin and Conant, unpubl. data). Nearly all plant records are substantiated by voucher specimens collected by Conant and deposited in the Department of Botany at the B. P. Bishop Museum. The list includes some new island records and suggests that at least one species, Achyranthe$ $plendens may no longer occur at PHR. It should be noted that Eragrostis paupera is a diminutive bunchgrass un- suitable as a nest substrate. Another major nest substrate used on PHR was marine debris (Fig. 4). Marine debris is a highly heterogeneous assortment of man-made flotsam which washes ashore on these very remote islands; these objects are buoy- ant and are frequently made of plastic or styrofoam. Common marine debris on both Laysan and PHR includes plastic line or rope; plastic or styrofoam floats; various types of fishing nets; plastic toys, bottles, and cigarette lighters; glass bottles and floats; plastic crates, and laundry bas- kets (1Vlorin 1987). Marine debris was never used as a nest substrate on Laysan. 598 THE WILSON BULLETIN ß Vol. 102, No. 4, December 1990 TABLE 4 ALrtgDANCE OF BLrNcORASS (ERAGROSTI$ VARIABILI$) ON LAYSAN ISLAND AND PEARL AND H EILM REEF Number of Eragrostis clumps lr island Total vegetation (ha) 1983 1989 Laysan Island 187 Pearl and Hermes Reef 21.3 Southeast Island 12.5 North Island 4.4 Grass Island 2.2 Seal-Kittery Island 2.2 no estimate 349,300 -+ 53,660 a 337 to 437 538+ (total) b (total) 20 2 200 to 300 34 17 42 100 460+ Based on an estimate from counts of 30 10 x 10 m quadrata. Based on estimates made by Sheila Conant and Wayne Oagne in 1983. The 30 quadrats in which Eragrostis clumps were counted on Laysan Island averaged 34.9 _ 14.37 clumps per 10 m x 10 m quadrat (Table 4). The average number of clumps in the two vegetation associations sampled was not significantly different at the 0.05 level, so the data were lumped. Conservatively estimating that a minimum of 100 ha of Laysan's 187 vegetated ha are either the pure Eragrostis or the Ipomoea-Boerhavia- Sicyos-Eragrostis association yields a minimum estimate of 349,300 _ 53,660 clumps of bunchgrass on Laysan. On PHR, Conant's 1989 total Eragrostis counts yielded 538+ for the entire atoll. In 1983, estimates made by Conant and Wayne Gagne (Table 4) were only slightly lower than the 1989 counts, but Conant, who has spent two to five weeks at PHR in 1984, 1985, 1986, 1987, and 1989 feels Gaghe's 1983 estimates (made during half hour insect collecting visits) of clump numbers were low on Grass and Seal-Kittery islands. Thirteen man-made nest substrates have been used at PHR (Table 2), although not all of these objects are marine debris: the generator, swim flippers, and wetsuit were brought to PHR by researchers. At least eight of the nests found in debris had eggs or chicks, but the remainder may have had neither. All of the nests in man-made objects were on Southeast Island at PHR. DISCUSSION We believe there are four factors that influence nest-site selection in Laysan Finches. The first is weather, which varies from intense heat and dryness to windy, cold rain. The extremes of temperature and humidity undoubtedly pose thermoregulatory challenges to finches, especially to Morin and Conant ß LAYSAN FINCH NEST SUBSTRATES 599 young chicks incapable of temperature regulation. The second is distur- bance; seabirds such as Laysan Albatross (Diomedea immutabilis) chicks may stand on plants containing finch nests, and Wedge-tailed Shearwaters (Puffinus pacificus) burrow under plants containing nests. Third, nest sub- strate availability is important; if a preferred plant substrate is uncommon or not present at all, a different substrate will be used, possibly at some cost to the bird, such as increased clutch mortality. Finally, although predation on the finches has rarely been observed, field observations suggest that Great Frigatebirds (Fregata minorpalmerstont), Bristle-thighed Curlews (Numenius tahitiensis) and Laysan Finches themselves are ca- pable of preying on finch chicks or eggs (Dill and Bryan 1912, Walker 1961, Morin and Conant, unpubl. data). The closely related, endangered Nihoa Finch (Telespyza ultima) has nested in captivity in cement blocks and pipes (Berger 1981), and on Nihoa Island they nest in rock crevices and holes (Sincock and Kridler 1977, Conant, unpubl. data). In the early part of this century, when the vegetation on Laysan was nearly eliminated by introduced rabbits, Laysan Finches nested in the crannies of human-made piles of guano blocks, in a manner reminiscent of their Nihoa relatives, and even in one of the guano mining buildings, which no longer exists (Ely and Clapp 1973). We propose that substrate availability is an important factor that causes Laysan Finches to use different nest substrates on the two atolls. There were early reports of Laysan Finches nesting in the native bush Cheno- podium oahuense (Fisher 1903a, Fisher 1903b, Rothschild 1893-1900), but by 1923 the plant had been extirpated by the introduced rabbits, which were themselves extirpated by 1924. However, observations made both before and after the devegetation of Laysan mentioned Eragrostis variabilis as the primary nest substrate on Laysan Island (Fisher 1903b, Ely and Clapp 1973, Sincock and Kridler 1977, Amadon 1950, Morin, unpubl. data). Laysan and the four islands at PHR have at least some Eragrostis variabilis, but Solanum nelsonii and the grass Setaria verticilla- ta only occur at PHR (Table 4). Setaria was most commonly used on Southeast Island in PHR (Table 2), but on North Island, where Setaria does not occur, Solanum nelsonii and Tribulus cistoides were the most common nest substrates. To summarize, Eragrostis occurs on all the islands, and is the preferred nest substrate on Laysan (Table 2), but it is seldom used on PHR, probably because it is relatively uncommon (Table 3). There are about 10,000 finches on Laysan,'and about 800 finches at PHR. The ratio ofbunchgrass clumps to finches on the two islands is dramatically different: about 35 clumps per finch on Laysan and < 1 clump per finch at PHR. The PHR island with the most Laysan Finches, Southeast Island, has almost no 600 THE WILSON BULLETIN ß Vol. 102, No. 4, December 1990 Eragrostis. This probably accounts for the fact that so many other nest substrates, such as Setaria and marine debris, were used there. Setaria is an introduced sod-forming (rather than bunch-forming) grass. Although the growth forms of Setaria and Eragrostis differ, the type of cover they provide for nests is similar. However, Setaria is shorter and less dense. North and Seal-Kittery Islands were the only PHR islands where Era- grostis was used as a nest substrate, either alone or in combination with other plants. In the absence of data on the introduced finch population at PHR, one might conclude that Laysan Finches were obligate Eragrostis nesters. However, other plants that provide suitable, dense cover are selected as nest substrates when Eragrostis is uncommon. Although Laysan Finches are endemic to the hot, treeless atoll environment, their physiological heat tolerance is no better than that of most passedfies (Weathers and van Riper III 1982). However, the basal metabolic rate of Laysan Finches is 20 per cent lower than would be predicted for a passedfne of this size, indicating some adaptation to the warm environment (Weathers and van Riper III 1982). Because heat tolerance would be important to incubating birds forced to remain in the nest, nest substrate selection may represent a behavioral adaptation to the extremes of heat and insolation. The presumed nesting requirements of the Laysan Finch (i.e., shelter from sun, rain, wind, and avoidance of predators or other disturbances) appear to be met by the plants or other substrates (e.g., Great Frigatebird nests) that provide the densest cover. It is unclear why finches on Southeast Island will nest in a wide variety ofmadfne debris, but will not use wooden nest boxes. Inadequate size, poor ventilation and the presence of intro- duced, moisture-loving ants may explain the puzzle. The fact that marine debris was not used as a nest substrate on Laysan Island suggests that appropriate nest sites are not limited. The frequent use of debris and other man-made objects as nesting sites on Southeast Island can be explained in several ways. First, suitable natural nest sites may be limited at Southeast Island at PHR. Second, relatively more man- made nest substrates are available because researchers (and their attendant gear) spend most of their time on Southeast Island when working at PHR. Third, more marine debris washes ashore on Southeast Island (Amerson et al. 1974), possibly due to its location in the reef(Fig. 2). Finally, the island was used for military exercises during World War II, was the site of unauthorized military operations in the 1950s, and was the site of a pearl oyster fishery in the late 1920s (Amerson et al. 1974). All of these human activities left various kinds of debris on the island. Regardless of whether finches on Southeast Island prefer marine debris as a nest site or simply use it because suitable natural sites are limiting, Morin and Conant ß LAYSAN FINCH NEST SUBSTRATES 601 it is clear that our nest box designs appear to be unsuitable nest substrates. Should it be desirable to increase nest substrate availability (at least on Southeast Island), it may be most expeditious to simply increase certain types of marine debris. The results of this study raise the question, "How do human actions affect adaptation of an introduced species to its new habitat?" Conant (1988a) has documented significant morphological differences in the Lay- san and the introduced PHR Laysan Finch populations. Although these two atolls share many plant species, plant community structure is more complex on Laysan than on PHR, particularly at the level of nest substrate for a passefine bird. It seems quite possible that the differences in vege- tation may exert selective pressure on finches in a number of ways. One might speculate, for example, that a nest in open and/or sparse vegetation or in a plastic crate may require different parental behaviors and energy expenditures than a nest in dense vegetation. How Laysan Finches affect the plant species in which they nest is also of concern. In addition to invertebrates, eggs, and carrion, Laysan Finches eat a wide variety of plant species and plant parts, including Eragrostis seeds; the birds also destroy grass leaves when they mandibulate the stems. Descriptions of Southeast Island from the early 1920s and 1930s (Amer- son et al. 1974) reported Eragrostis to be a dominant plant in the com- munity. Wave overwash of this low (<4.5 m) island during a severe storm in 1930 is believed to have caused a major plant die-off. By 1974, Era- grostis was considered an insignificant component of the vegetation on Southeast Island (Herbst 1980, Amerson et al. 1974). Estimates in 1983 and counts in 1989 of the number of Eragrostis clumps (Table 4) show that at least one of the four islands at PHR experienced a decline of Eragrostis between 1983 and 1989. Laysan Finch breeding was monitored after their introduction to South- east Island at PHR in 1967. Summarizing data collected up to 1969, Amerson et al. (1974) stated that (on Southeast Island) "Most nests are in Eragrostis clumps and a few are in the moderately dense Solanum." Later, Sincock and Kridler (1977) reported that 90% of the Southeast Island nests found from 1967 through 1974 were located in Eragrostis. Finches feed on seeds of Setaria, Tribulus, Eragrostis, Boerhavia, and Sonchrus. We have observed them eating the seeds of nearly every species of plant at PHR, and Herbst (pers. comm.) found that Eragrostis intto- rescences he examined on trips in 1981 and 1988 had been nearly stripped of seeds by foraging finches. High water in a severe 1969 storm destroyed the largest Eragrostis stand on Southeast, which had not recovered by 1974. How the storm affected the grass on other islands is unknown, although the vegetated portion of Seal-Kittery Island, where Eragrostis 602 THE WILSON BULLETIN ß Vol. 102, No. 4, December 1990 is still quite abundant, is two to three meters higher in elevation than any of the other islands at PHR. We believe it is possible that the finches' feeding habits may have prohibited the recovery of Eragrostis, and pos- sibly even hastened the decline ofAchyranthes splendens at PHR. Thus, the vegetation composition at PHR may be effecting a change in the nest- site selection of the finches, while the finches may simultaneously be changing the composition of the vegetation. Extrinsic factors such as thermal characteristics, substrate availability, protection from predators (especially predation of eggs by other finches) and disturbance, may all affect nest placement. According to Brown and Goertz (1978), Munro and Rounds (1985), and Osborne and Osborne (1980), the characteristics of potential nest substrates, such as height, sturdiness, and density of cover, may be more important than the species of plant used for a nest substrate. However, Eragrostis apparently provides the ideal substrate for Laysan Finch nests: insulation for nests from the sun and rain and protection from predators and other forms of distur- bance. In addition, finches roost in Eragrostis clumps, eat its seeds and glean invertebrates from its foliage. Some shrubs (e.g., Pluchea indica, Scaevola sericea, Tournefortia argentea), and a small number of trees (one Casuarina equisetifolia and about thirty Cocos nucifera) occur on Laysan, but Finches have not used these as nest sites. We have found that the nest substrates used by an introduced popu- lation may be unexpectedly different from those of the parent population if habitat composition and structure differ. Whether or not these differ- ences have influenced divergence of the Laysan and PHR Laysan Finch populations is unknown. How the introduced finches have affected the plants and invertebrates at Pearl and Hermes Reef is also unknown. We believe that the conservation of the endangered Laysan Finch will require the maintenance of an unaltered ecosystem on Laysan where Eragrostis is maintained as a major vegetation component that provides food, roost- ing, and especially nesting sites for Laysan Finches. ACKNOWLEDGMENTS This research was supported in part by grants and logistic support from the Hawaii Audubon Society, the National Marine Fisheries Service, the U.S. Fish and Wildlife Service, the Hawaiian Telephone Company, and A. Yoshinaga. The authors thank the officers and crew of the NOAA Ship Townsend Cromwell, and fellow field biologists, especially B. Becker, B. Choy, L. Hiruki, K. McDermond, and L. Mowwor, for assistance and data collection. D. Herbst carefully reviewed our plant list, and R. Kawamoto prepared the maps. Two anonymous referees and C. R. Blem offered helpful comments on the manuscript. Morin and Conant ß LAYSAN FINCH NEST SUBSTRATES 603 LITERATURE CITED AMADON, D. 1950. The Hawaiian honeycreepers (Aves, Drepaniidae). Bull. Am. Mus. Nat. Hist. 95:155-262. AMEP, SON, A. B., JR., R. B. CLAPP, AND W. O. WmTZ II. 1974. The natural history of Pearl and Hermes Reef, Northwestern Hawaiian Islands. Atoll Research Bulletin, No. 174. Smithsonian Institution, Washington, D.C. BERGER, A.J. 1981. Hawaiian birdlife. 2nd edition. The Univ. of Hawaii Press, Honolulu, Hawaii. BROWN, B. T. ND J. W. GOERTZ. 1978. Reproduction and nest site selection by Red- winged Blackbirds in north Louisiana. Wilson Bull. 90:261-270. CoN,rr, S. 1988a. Geographic variation in the Laysan Finch (Telespyza cantans). Evol. Ecology 2:270-282. DFLL, H. R. ND W. A. BRYAN. 1912. Report of an expedition to Laysan Island in 1911. U.S. Dept. Agr. Biol. 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