"Species","Countries of impact","Impact mechanism","EICAT Category","Evidence for EICAT category","Confidence rating","Justification for confidence rating","Impacted native species","Reference",
"Dicrurus macrocercus","U.S.A. (sovereign state) Mariana Islands","Predation","MO","Abstract: Black drongo and Rota bridled white-eye (Rota BWE) relationships were addressed using current and historical survey data. Black drongos were found to prey on Rota bridled white-eyes but they probably only played at most a partial role in the decline of the Rota bridled white-eye (Amidon, 2000).

Page 41: On 18 August 1998 we observed a black drongo eating a Rota BWE in an Elaeocarpus joga tree in study plot 2HA. When the black drongo was first observed, it was plucking the feathers of the white-eye while a nearby Rota BWE gave alarm calls. When we attempted to approach the drongo a Micronesian starling chased it out of view. The Rota BWE was not a nestling (eye ring was present) but we were unable to determine if it was an adult or juvenile. No other observations of attempted or successful predation of drongos on Rota BWEs were observed (Amidon, 2000).

Page 54: However, we detected no negative relationship between black drongo numbers and any of the small native passerines, including Rota BWEs, that drongo predation could impact. Therefore, we are still uncertain what role black drongos played in the decline and range restriction of the Rota BWE. We believe that the habitat alteration discussed earlier may have played the major role in the decline by reducing the availability of preferred Rota BWE habitat. However, this habitat alteration may have also helped increase the incidence of black drongo and collared kingfisher predation on Rota BWEs by making the habitat more suitable for black drongo and collared kingfishers and increasing their populations on the Sabana (Amidon, 2000).","Low","Whilst the black drongo certainly preys on the Rita white-eye there is some uncertainty as to how significant this impact is, and whether it is responsible for causing a decline in the population of the Rota white-eye. Other contributing factors include predation by rats and habitat modification.","Zosterops rotensis","Amidon, F. A. (2000). Habitat relationships and life history of the Rota Bridled White-eye (Zosterops rotensis). Thesis submitted to the Faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of Master of Sc, 121. Retrieved from http://scholar.lib.vt.edu/theses/available/etd-12072000-091007/",
"Dicrurus macrocercus","U.S.A. (sovereign state) Mariana Islands","Predation","MN","Page 72: Song birds appeared as prey only once in stomach contents. Both femora and the one tobiotarsus (18 mm) found were compared with similar specimens located at DAWR. The bones seemed too small to have come from resident species other than the black-headed munia (Lonchura malacca) or the brindled white-eye (Maben, 1982).","Low","Uncertainty regarding the correct identification of the impacted species.","Zosterops rotensis, Lonchura malacca","Maben AF. 1982. The feeding ecology of the black drongo (Dicrurus macrocercus) on Guam. A thesis presented to the Department of Biology, California State University, Long Beach. Online. Available from https://www.fwspubs.org/doi/suppl/10.3996/112014-JFWM-085/suppl_file/112014-jfwm-085.s20.pdf. Accessed 01/05/20.

Amidon, F. A. (2000). Habitat relationships and life history of the Rota Bridled White-eye (Zosterops rotensis). Thesis submitted to the Faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of Master of Sc, 121. Online. Available from: http://scholar.lib.vt.edu/theses/available/etd-12072000-091007/. Accessed 07/04/20.",
"Dicrurus macrocercus","U.S.A. (sovereign state) Mariana Islands","Predation","DD","Similarly, the impacts of invasive plants, including Scarlet Gourd and Lantana (Lantana camara), and predators, including Monitor Lizards (Varanus indicus), rats (Rattus spp.) and dogs (Canis lupus familiaris), may be variable among the islands. The only exception is the Black Drongo, which occurs only on Rota and Guam and has been observed harassing and depredating native birds (Maben 1982, Amidon 2000). However, results of this study indicate that Black Drongo numbers on Rota are also declining. It is unclear what potential drivers, other than the Brown Tree Snake, may be influencing bird trends on each island.","","","","Camp, R.J. et al., 2014. Technical Report HCSU-048. Status of forest birds on Rota, Mariana Islands.",
"Dicrurus macrocercus","U.S.A. (sovereign state) Mariana Islands","Predation","DD","Survey data by Engbring et al. (1986) showed that the density of potential Black Drongo prey species, like the Rota BWE and Rufous Fantail, were lower in areas with high Black Drongo densities. Then we used data on bird numbers collected in this study and from previous surveys to look for relationships between Black Drongos and small passerines, like Rota BWEs and Rufous Fantails, that could be potential prey for Black Drongos. Significant relationship between Black Drongo detections and Micronesian Honeyeater detections were observed in 1982 and 1994 (table 14). In addition, a significant relationship between Rufous Fantail and Black Drongo detections was observed in 1994 (Table 14).","","","","Amidon, F. A. (2000). Habitat relationships and life history of the Rota Bridled White-eye (Zosterops rotensis). Thesis submitted to the Faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of Master of Science.",
"Dicrurus macrocercus","U.S.A. (sovereign state) Mariana Islands","Predation","MN","On Guam Black Drongos have been observed eating small birds as Eurasian Tree Sparrows (Passer montanus) (Maben 1982), Roufous Fantails (Rhipidura rufifrons) and Guam Swiftlets (Aerodramus vanikorensis) (Perez 1968).","Low","Whilst there is observational evidence, it is difficult to establish the extent and severity of predation impacts. These impacts could be more severe than assessed.","Rhipidura rufifrons, Aerodramus vanikorensis","Amidon, F. A. (2000). Habitat relationships and life history of the Rota Bridled White-eye (Zosterops rotensis). Thesis submitted to the Faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of Master of Science.",
"Dicrurus macrocercus","U.S.A. (sovereign state) Mariana Islands","Predation","DD","Several agents, particularly disease and introduction predators, have been implicated in causing population collapses of bird on Pacific islands (van Riper III et al. 1986, Savidge 1987). However, no evidence links disease to bird declines on Guam in the Mariana Islands (Savidge 1986). Predation by the introduced Brown Tree Snake (Boigu irregularis), responsible for the extinction of forest birds on Guam (Savidge 1987), also appears unrelated to the Rota Bridled White-eye decline, because the snakes are unknown on Rota. Instead, the predatory Black Drongo (Dicrurus macrocercus), introduced on Rota in 1935 (Baker 1951), is implicated in causing the population declines of several native bird species. Black Drongos did not become abundant until the 1960s (E. Taisacan, pers. obs.), the time when the decline in Rota Bridled White-eye populations was first noted. Maben (1982) demonstrated that introduced Black Drongos on Guam preyed on small passerines, although she believed drongos had little effect on their populations. Despite this belief, the present distribution of Black drongos on Rota shows a negative relationship with that of white-eyes, which are now found mostly in extensive stands of native Sabana forest. Engbring et al. (1986) found drongos abundant in lowlands (4042 bird/10 stations), particularly in open habitat, but uncommon in the forest of the Sabana plateau (15 birds/10 stations). The Rota Bridled White-eye appears particularly susceptable to predation by Black Drongos because it is very small and feeds in exposed microhabitats. Like the Saipan subspecies, it is a flocking, vocal bird that forages in the forest canopy and flies above the forest (see Craig 1989, 1990). Notably, all birds on Rota too large for drongo predation are abundant and widespread (Engbring et al. 1986). Only the small Rufous Fantail (Rhipiduru rufifrons) is also uncommon.","Low","The evidence for population declines is somewhat speculative. Other studies failed to link predation by Black Drongos with declining populations of native bird species on Rota.","Zosterops rotensis","Craig R, Taisacan E (1994). Notes on the ecology and population decline of the Rota Bridled White-eye. Wilson Bulletin 106: 165-169.",
"Dicrurus macrocercus","U.S.A. (sovereign state) Mariana Islands","Predation","MN","Craig and Taisacan (1994) suggested that Black Drongos were responsible for the decline and range restriction of the Rota BWE based on correlations between the increasing abundance of drongos on the Sabana and the decline of Rota BWEs. They reported that survey data by Engbring et al. (1986) showed that the density of potential Black Drongo prey species, like the Rota BWE and Rufous Fantail, were lower in areas with high Black Drongo densities. They also reported, based on personal observations, that Black Drongos became more abundant in the 1960s, when the decline of Rota BWEs was first noted. However, no data are available to confirm this and the reason for the apparent increase in Black Drongo numbers is unknown. Black Drongo and Rota BWE relationships were addressed using current and historical survey data. Black Drongos were found to prey on Rota BWEs, but they probably only played at most a partial role in the decline of the Rota BWE. On 18 August 1998 we observed a Black Drongo eating a Rota BWE in an Elaeocarpus Joga Tree in study plot 2HA. No other observations of attempted or successful predation of drongos on Rota BWEs were observed. Our results indicate that Black Drongos do prey on Rota BWEs, Black Drongo numbers are lower on the Sabana than other regions of the island, as reported by Craig and Taisacan (1994), and that Black Drongo numbers have increased on the sabana from 1982 to 1994, while Rota BWEs numbers have decreased. However, we dwtected no negative relationship between Black Drongo numbers and any of the small native passerines, including Rota BWEs, that drongo predation could impact. Therefore, we are still uncertain what role Black Drongos played in the decline and range restriction of the Rota BWE. We believe that the habitat alteration discussed earlier may have played the major role in the decline by reducing the availability of preferred Rota BWE habitat.","Low","Whilst there is observational evidence, it is difficult to establish the extent and severity of predation impacts. These impacts could be more severe than assessed.","Zosterops rotensis","Amidon, F. A. (2000). Habitat relationships and life history of the Rota Bridled White-eye (Zosterops rotensis). Thesis submitted to the Faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of Master of Science.",
"Dicrurus macrocercus","U.S.A. (sovereign state) Mariana Islands","Predation","MN","Occasional predation on small birds by Black Drongos is well documented (Vernon 1959, Bea-ty 1966, Ali and Futehally 1970, Drahos 1977, Maben 1982; G. Perez, unpubl. data) and drongos are known for their ''belligerence in territorial defense'' (Maben 1982:3) and their frequent chases of Rufous Fantails (Rhipidura rufifrons), white-eyes, Eurasian Tree Sparrows (Passer montanus) and larger birds. However, it is very unlikely that the Black Drongo, which is primarily insectivorous (Thyagaraju 1934, Ali and Futehally 1970, Drahos 1977, Maben 1982), could have caused an island-wide range contraction and major population decline of the Bridled White-eye. On Guam, Drahos (1977) found trace samples of bird bones in 82 drongo stomachs and Maben (1982) found bird bones in only one of 113 drongo stomachs. Maben (1982:73) wrote that ''despite this well-documented ability to eat small birds, I did not observe drongos regularly attempting to capture and eat small birds even when seemeingly available'' and she concluded that predatory interactions between drongos and other birds were not a significant factor in the decline of Guam's forest bird populations. The drongo hypothesys does not explain why white-eyes are absent from several blocks of seemingly pristine limestone forest at higher elevations, where drongos do not occur, nor why populations of Micronesian Honeyeaters (Myzomela ruhrutru) and Rufous Fantails have not experienced similar population declines.","Low","Whilst there is observational evidence, it is difficult to establish the extent and severity of predation impacts. These impacts could be more severe than assessed.","Zosterops rotensis, Rhipidura rufifrons, Myzomela ruhrutru","Fancy, S. G., and Snetsinger, T. J. (2001). What caused the population decline of the Bridled White-eye on Rota, Mariana Island? Studies in Avian Biology 22: 274-280.",
"Dicrurus macrocercus","U.S.A. (sovereign state) Mariana Islands","Predation","MN","The feeding ecology of the Black Drongo (Dicrurus macrocercus) on Guam. Drongos predominantly were insectivorous, eight orders of prey items recorded in stomach contents and in visual observations of foraging. Hymenopteras were the most frequently taken prey, although lizards and small birds also were eaten.","Low","Whilst there is observational evidence, it is difficult to establish the extent and severity of predation impacts. These impacts could be more severe than assessed.","Arachnida, Orthoptera, Dermaptera, Odonata, Isoptera, Mallophaga, Hemiptera, Coleoptera, Lepidoptera, Hymenoptera, Diptera, Lacertilia, Passeriformes","Maben AF. 1982. The feeding ecology of the Black Drongo (Dicrurus macrocercus) on Guam. Long Beach, California, USA: California State University.",