The Scientific Bases for the Preservation of the Hawaiian Crow (1992) / Chapter Skim
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2 HISTORY OF THE WILD POPULATION AND CAUSES OF ITS DECLINE
2 HISTORY OF THE WILD POPULATION AND CAUSES OF ITS DECLINE
Pages 12-44
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From page 12... ...
In He case of the 'Alala, useful and pertinent information is sparse, and it is probably too late to obtain certain types of information. Despite He fragmentary nature of He ~formadon, a species-specific judgment must be made now concerning bow the environmental factors that have contributed to He 'Alala's decline and He recovery actions that are most likely to promote He re-establishment of a self-sustaining wild population.
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From page 13... ...
i' H i''V I .1 ( (, /, Natonal Park //19 25'McCandless Ra't [~.~ I.] Flanges of subpopulations, 197~1980 HILO \ ~ Kilauea ~ ~ Punaluu~i~ South Kona `~' Kipuka Akala ManukaNaturalReserve Area ~NAALEHU Figure 2.1 Map of the island of Hawai'i 13 ISLAND OF HAWAI'I 1 1 0 20 40 Kl LOMETERS Contours in Meters
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From page 14... ...
It is almost certain that former 'Alala populations continually adjusted their distribution in response to shifts in ecological conditions imposed by He penodicity of vuicanism and forest succession. Extensive studies of the modes of natural colonization of new lava flows by plants have been made on a transect on the southeastern slope of Mauna Loa (Atkinson, 1970; MueHerDombois et al., 1981; MueBer-Dombois, 19871.
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From page 15... ...
u/m UnrnaDDed areas / Figure 2.2 Age distribution map of Mauna Loa lava flows, showing in particular the natural parallel arrangement of the flows in present and former 'Alala habitat on the Kona coast. Most flows are more recent than 4,000 years ago.
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From page 16... ...
Even though it is common practice to leave some tree overstory, the resulting pastures effectively discriminate against the maintenance of native herbs and shrubs. Cattle not only browse down the native plants and grasses, which lack spines or chemicals that naturally protect them from herbivores, but also continue to spread both forage and weed grasses and larger weeds effectively.
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From page 17... ...
The only exception to the decline appears to be on the privately owned McCandIess Ranch, also in central Kona, where the only known wild population of 'Alala occurs. The owners of the ranch have reported that 10-25 birds have been present for the last decade.
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From page 18... ...
gives three locations in the Kona District where at least one pair nested in the 1970s: Hualalai snore Kona) , Honaunau (central Kona)
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From page 19... ...
Since the Alala Recovery Plan was issued, the population has continued to decline. With He possible exception of a single female in north Kona, the small remaining wild population is now believed to be restricted to a single location in central Kona -- ~e McCandless Ranch.
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From page 20... ...
INDIRECT FACTORS 1. Ecological succession on lava flows of various ages Agriculture, and ranching ~Logging DIRECT FACTORS Habitat and Food 1.
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From page 21... ...
. Logging was often accompanied by the introduction of pigs, goats, sheep, and cattle, and grazing further modified the forest by preventing regeneration of koa trees and eliminating many native understory plants (Ralph and van Riper, 1985)
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From page 22... ...
Ranching practices and the behavior of foraging cattle commonly result in reduction and even elimination of understory and subcanopy vegetation, and ground vegetation is replaced with introduced forage grasses and weeds. Even on ranches where mature Bees are left in abundance, the resulting parklike environment often supports a greatly reduced diversity of plant species, in which natural regeneration of canopy trees is dramaticaDy reduced (Baldwin and Fageriund, 19431.
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From page 23... ...
The McCandless Ranch lies directly at the center of the region where 'Alala historically was most common (middle elevations of central Kona)
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From page 24... ...
. Avian pox is caused by an arbovirus and is transmitted by direct contact with an infected bird, by secondary contact with a contaminated object, or mechanical by vectors, such as mosquitoes and biting flies (van Riper and van Riper, 1980; Cavill, 1982~.
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From page 25... ...
. Avian pox apparently was widespread in the native Hawaiian avifauna, including 'Alala, by the turn of the century (Perkins, 1903)
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From page 26... ...
That cannot be done, in part because no set population size is sufficient to ensure survival within the changing, fragmented landscape of the Hawaiian forests. We can only estimate probabilities of extinction as a function of population size.
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From page 27... ...
Comparative data for other tropical corvids, however, do not exist. Existing information on age structure and age distribution of the 'Alala is in Box Table 1.
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From page 28... ...
R4WAlldN CROW C)
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From page 29... ...
HISTORY OF THE ICED POPULATION AliID CAUSES OFITS DECLINE as i: e_ en D U O ~ I 0\ .
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From page 30... ...
HAWAIIAN CROW cat 0 TO c _ ~ Liz 0 _ ~ cot ~ c cot := ~ c, _' ~ Zig _.
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From page 31... ...
. lhe results are differed from that of most previous authors regarding the proxirrulte causes of 'Alala d~eclinefrom 1974 through 1982: reproduction arid recruitment were nearly normal among breeding pairs, but adult survival and nesting attempts were exceedingly low, except on the McCar~less Ranch.
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From page 32... ...
However, an extremely important observation is that fledgling production drops to 0.66 away from the McCandless Ranch when all pairs Hat failed to nest (or whose failed nests went unobserved) are added to Be sample (Box Tables 3 and 4~.
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From page 38... ...
HAWAllAN CROW = ~ .
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From page 39... ...
It is not clear why adult survivorship on the McCandless Ranch has remained high or why it was lower elsewhere. It Should be noted that these estimates of adult survival are strongly influenced by the one or two longest-lived individuals at each location (Box Table 2~.
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From page 40... ...
It is possible that only two territories exist and that records suggesting Me middle territory (including McCandless personnel records at sandalwood enclosure downslope from Komokawai Lodge) represent birds from Me over two territories.
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From page 41... ...
Experience with small animal and plant populations shows that small populations, even if they are not declining, are extremely vulnerable to extinction caused by such chance events. The resulting fluctuations in population size impose a considerable risk of extinction, especially for populations that have high year-to-year variations in numbers.
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From page 42... ...
The effective population size of the 'Alala on the McCandless Ranch is likely to be three or fewer breeding pairs. There is the estimate of "3 young produced in He wild in 1991" provided by Peter Simmons, manager of the McCandless Ranch.
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From page 43... ...
Indeed, one reason why some of the British island populations last so long might be that the populations received immigrants from the mainland. The immigrants might also rescue a population genetically -- providing an influx of genes that helps to overcome the dangers of inbreeding.
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From page 44... ...
Of course, serious environmental disturbance or disease could extirpate a population even much larger than this one. Population projections based on these admittedly limited demographic parameters suggest that, although the McCandless Ranch population appears stable and may even export a few dispersers, the population win remain at levels at which demographic accidents alone will continue to be a highly probable cause of extinction for Me next several decades.
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