OVERVIEW
BACKGROUND
BREEDING
HISTORY OF MYNAS AT MIDWAY
OBSERVATIONS AT THE LANDFILL
BREEDING ACTIVITY
TRANSECTS
MANAGEMENT
ESTIMATE AND SPECULATION
REFERENCES
TRIP REPORTS CHECKED FOR MYNA RECORDS
Common Mynas have received scant attention since they were first recorded on Midway more than twenty years ago. Concern over this species' deleterious effects on seabirds may lead to consideration of control measures. This paper provides reference material necessary for monitoring the myna population, including general background, breeding biology, historical records, and indexing methods. An estimated 500 individuals comprise the April 1992 population.
Common Mynas are indigenous to south Asia, but have been introduced to South Africa, Australia, New Zealand, and Pacific islands (Pizzey 1980). They were brought to the main islands of Hawaii in 1865 (Eddinger 1967).
Throughout their range mynas are closely associated with human habitation. Because they are adaptable, opportunistic, and do not specialize they often become common enough to be considered a nuisance.
An advantageous aspect of myna presence is their appetite for insect pests, but this benefit is tempered on the Leeward Hawaiian Islands by their damage to crops. On islands supporting seabird colonies, mynas are known to prey upon eggs and chicks.
Myna predation on Wedge-tailed Shearwater eggs has been documented at Kauai (Byrd 1979) and attacks on nestling and incubating adult White Terns has been observed at Midway (Tyler 1988). Mynas also have been observed pecking open the eggs of Sooty Terns and noddies (Fisher 1948).
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Nest site selection generally begins in March; both adults build the nest. Eggs are laid one per day until completion of a 2-5 egg clutch. Egg dates occur March through July. Incubation is shared and lasts 13 days (cp. 16-18 days in India). Fledging occurs at age 29-35. Whether more than one successful brood is raised per year is uncertain. During July and August flocks begin to form, and mynas continue to flock through the non-breeding season. Yellow eye skin characteristic of adults begins to show at about 125 days and birds may breed in their first year.
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I found no record for the introduction of mynas to Midway. Therefore I could not determine whether the pioneers were assisted by humans or if myna presence is the result of natural immigration from the leeward islands.
R. L. Pyle (pers. comm., April 1992) recalled rumors of low myna numbers (i.e. 1 or 2 individuals; perhaps up to 5) at Midway in the 1960s. In July 1974, C. P. Sekora searched for and saw 6 mynas (Sincock et al. 1974), for the first USFWS verified record. In their report, Sincock et al. (1974) stated, "presence of the mynah bird at Midway was first reported two years ago." Berger (1981) considered mynas established by 1974, probably based on Sekora's record.
The first attempts to quantify the myna population after its expansion were by Byrd (1979, 1980). He estimated 150-200 individuals on Sand Island and none on Eastern. He counted mynas visible along certain streets to provide a population index (Table 1).
| Street | Byrd 1979 | Byrd 1980 |
|---|---|---|
| Decatur | 16 | 2 |
| Halsey | 29 | 1 |
| Radford | 3 | 3 |
| Morrell | 28 | 2 |
| Commodore | 13 | 2 |
| Henderson | 0 | 3 |
| Kramer | 0 | 4 |
| Bauer | 0 | - |
Clapp's (1980) reference to Hill Mynahs must be a mistaken reference to Common Mynas. He stated the "population has increased explosively since the summer of 1978." Although he admitted to having "no certain idea" of population size, he considered it "unlikely...the island population is under 250 birds."
Following his May visit, Fefer (1982) commented that myna numbers and distribution "seem to be expanding."
P. Pyle (1982) estimated 200 mynas during his stay in the autumn of 1982, and recorded a high count of 128 individuals at the landfill dump.
In February 1983 Joe Jayasinghe, BSI Wildlife Manager, estimated 600-800 mynas at Midway (Fefer 1983a).
Several years passed before the next estimate was made by Tyler (1988); his broad estimate of 750-1500 individuals was made after spending six months at Midway. He is the only observer to have recorded the use of Eastern Island by mynas.
McDermond (1989a) noted in the spring of 1989 a "definite increase since September", but I found no record for a September McDermond trip. McDermond (1989b) returned seven months later and remarked that the increase in myna numbers had continued.
Neither McDermond (1989b) nor Rowland (1990) saw mynas at Eastern Island, while the latter stated simply that mynas were "common" on Sand Island.
The Natural Resources Management Plan for Naval Air Facility Midway Islands (USFWS 1991) indicated the population to be 500-1000 birds and increasing.
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It is difficult to obtain an accurate estimate of the population size of Common Mynas at Midway, but opportunities exist to establish population indexes. I used two methods: site counts and transect counts.
The landfill dump south of the harbor has a long history of attracting large numbers of foraging and roosting mynas. I estimated myna abundance at the dump on eleven occasions (Table 2). I approached the flocks on foot, pausing frequently to count visible birds. Eventually most of the flock would flush simultaneously, at which time I would estimate abundance by tens before the birds dispersed and landed in trees. In the afternoon of 10 January, I made a ground count followed by a flush estimate and determined that ground counts reveal only about two-thirds of birds present when individuals are scattered across the open area. Also, when mynas are concentrated on dump piles many individuals are hidden.
It is likely that most of Midway's mynas can be found at the dump at certain times. When my dump counts were high I found very few mynas over the remainder of the eastern half of Sand Island. Similarly, when I observed widespread dispersal, the dump counts were predictably low. The largest flocks seemed to occur when dump piles contained exposed waste from the galley, whether or not the piles were burning or smoldering, but available material did not guarantee heavy myna use.
| DATE | TIME | DUMP COUNT |
|---|---|---|
| 22 Dec | NR | ~100 |
| 4 Jan | 1725 | < 12 * |
| 6 Jan | 1725 | > 100 * |
| 10 Jan | 0945 | 280 |
| 10 Jan | 1610 | 190 |
| 22 Jan | 1650 | < 300 |
| 23 Jan | 0825 | < 100 |
| 23 Jan | 0910 | 110 |
| 25 Jan | 1700 | 75 |
| 28 Feb | 1255 | 17 |
| 29 Feb | 1340 | 35 |
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I began to see mynas gathering nest material (cellophane, plastic bags) on 1 March. I monitored one cavity for five weeks beginning 3 March but saw no eggs, despite regularly finding new material on the nest. Air conditioners appear to be favorite nest sites, as do openings on buildings. Old stick nests were found in Area 7.
Transects were developed at the end of March (Figure 1--not yet online). Transect 1 began at the Fuel Farm gate, proceeded south to the end of Nimitz, and continued on the same line across the field to the wood edge. Transect 2 began at the Power Plant, proceeded west on Brannon, and continued north on Morrell to Halsey. Transect 3 began at the corner of Halsey and Commodore, proceeded north on Commodore, and curved south to the school flagpole.
Each transect was walked between 0800 and 0900 on the mostly clear and calm mornings of 27 and 30 March and 1 April (Table 3). I noted the position (on ground, perched, in flight) of each myna when first seen and also noted birds heard but not seen. I walked steadily and used no binoculars. I defined pairs by association and behavior.
Mynas on the ground and in flight were seen easily. Those perched in trees generally were not visible, but some could be detected by voice.
Date |
27 March | 30 March | 1 April | ||||||
|---|---|---|---|---|---|---|---|---|---|
Transect |
1 | 2 | 3 | 1 | 2 | 3 | 1 | 2 | 3 |
No. of mynas | |||||||||
| On ground | 5 | 8 | 9 | 16 | 12 | 17 | 15 | 9 | 15 |
| Perched | 4 | 1 | 5 | 0 | 0 | 1 | 2 | 0 | 0 |
| In flight | 2 | 0 | 5 | 0 | 0 | 0 | 0 | 0 | 0 |
| Heard | 5 | 0 | 3 | 0 | 0 | 2 | 1 | 0 | 0 |
| Total | 16 | 9 | 22 | 16 | 12 | 18 | 19 | 10 | 15 |
| Total 1 + 2 + 3 | 47 | 46 | 44 | ||||||
| Pairs | 2 | 4 | 4 | 7 | 2 | 8 | 8 | 4 | 5 |
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The Common Myna is of questionable worth to the avian community at Midway Atoll. The species' proclivity for disruption and destruction of seabird nesting efforts prompted Harrison et al. (1984) to suggest it be exterminated.
On Oahu, Eddinger (1967:2) remarked, "The myna is a wary bird, and although man may be able to check its increase, extermination is practically impossible." Compared to mynas on Oahu, Midway's population is relatively small, less dispersed, and highly accessible.
Although elimination of this alien predator of seabird eggs and chicks is conceivable, justification for the action is subject to question. A quantitative measure of damage to seabird nesting efforts at Midway is lacking, although there is little doubt they destroy eggs or chicks of at least two species. And it is possible that mynas play some role in improving nesting conditions for seabirds (e.g., consumption of insect pests, clean up of broken eggs to reduce rat fodder). It is unlikely that the beneficial aspects of myna presence at Midway outweigh their negative impacts, and continued expansion of the population may pose greater risk of irreversible damage.
Natural attrition is difficult to quantify, but some hint may be gleaned from rat control records (Table 4). Also, as Midway's human population continues to decrease there will probably be an appreciable change in myna distribution for nesting and foraging. Whether the loss of the dump piles will exact a toll on the population or cause the birds to become more aggressive predators is open to speculation.
| Year | Number of dead mynas |
|---|---|
| 1987 | N/C |
| 1988 | N/C |
| 1989 | 86 |
| 1990 | 47 |
| 1991 | 25 |
| 1992 | 12* |
* Through 31 March.
When it becomes desirable to remove all or some of the mynas, some
alternatives are available. Poisoning probably is not realistic due to effects
on non-target species; curlews, tattlers, golden-plovers, and turnstones
all share the mynas' preferred foraging areas, including the landfill dump.
A shotgun blast into a dense flock at the dump would kill many birds, and
this method could reduce numbers. Stone (1989:93) suggests that the social
nature of mynas may make them susceptible to decoy trapping.
Mynas are intelligent, so any control method probably would diminish in effectiveness over time.
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I estimate 500 mynas were at Midway this winter, based on general observations made through the period and specific observations of pocket distribution.
Repeat counts at the landfill dump probably will provide the most reliable index of abundance, while repeat transects (and additional transects) may shed light on carrying capacity for specific areas.
Historical estimates and future impressions of myna abundance should be interpreted with awareness of seasonal behavior changes. During the breeding season low numbers may be widely distributed, while flock sizes will increase through the winter.
It is obvious the population has undergone rapid expansion during the two decades or so since its arrival at Midway, and it is likely some control measures will be necessary in the future. At this time, many residents find in the myna a reminder of their distant home, so the determination of the birds' fate should be made with consideration for the community's loss.
After such a recent introduction the mynas at Midway offer a wealth of research opportunities which might shed light on many of the uncertainties outlined above.
References to Trip Reports are in the Appendix.
Berger, A. J. 1981. Common Myna. Pages 202-204 in Hawaiian Birdlife, 2d edition. University Press of Hawaii, Honolulu.
Byrd, G. V. 1979. Common Myna predation on Wedge-tailed Shearwater eggs. `Elepaio 39:69-70.
Eddinger, C. R. 1967. A study of the breeding behavior of the mynah (Acridotheres tristis L.). `Elepaio 28:1-5, 11-18.
Grant, G. S. 1982. Wildlife on Midway Atoll during the winter and spring of 1980-1981. `Elepaio 43:1-4.
Harrison, C. S., M. B. Naughton, and S. I. Fefer. 1984. The status and conservation of seabirds in the Hawaiian Archipelago and Johnston Atoll. Pages 513-526 in R. W. Grigg and K. Y. Tanoue, editors. Proceedings of the second symposium on resource investigations in the Northwestern Hawaiian Islands, vol. 1. University of Hawaii Sea Grant Miscellaneous Report, Honolulu.
Pizzey, G. 1980. A field guide to the birds of Australia. Princeton University Press, Princeton, New Jersey.
Stone, C. P. 1989. Non-native land vertebrates. In C. P. Stone and D. B. Stone, editors. Biological diversity in Hawaii. University of Hawaii Press, Honolulu.
Tyler, W. B. 1988. Trip report. Unpublished report, U.S. Fish and Wildlife Service, Honolulu, Hawaii.
USFWS trip report authors, year and dates of trips. All reports found
in Honolulu or Midway files were checked for references to mynas.
TRIP REPORTS FOR MIDWAY ONLY
TRIP REPORTS FOR MIDWAY VISIT COMBINED WITH OTHER ISLANDS
Midway trip reports not found in FWS Honolulu or Midway files
Comments and questions may be directed to Scott Richardson.
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Latest revision: 25 March 1997.
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