I originally wrote this for peer review and publication, but never went through with it. It has been recently excavated from a dead website, thought I would make it available. Enjoy!
Oh HEY! If you aren’t familiar with research papers, I suggest skipping to the summary. That way you can see if you’re even interested!
10 March 2012
Project, Wildlife Management, Hawaiian Raven
RH: Ravens and Anthropogenesis ٠ CMH
REVIEW OF ANTHROPOGENIC IMPACT ON RAVENS
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Abstract: Ravens have been shown to be sensitive to human impacts on their environment.
Examples of adaptive foraging strategy in the Continental U.S. include the ability to track forage sites by following gunshots, and by learning to manipulate contrived mechanisms to obtain food. The ravens of the Islands of Hawaii and several states within the continental United States reveal key elements of raven survivability in areas of anthropogenic impact. Samples of raven inability to adapt include the nearly extinct Hawaii crow, locally called ´alalā. Ravens are an integral component of a balanced ecosystem, and when anthropogenic developments displace or alter their habitats, more is at stake than the ravens themselves.
JOURNAL OF WILDLIFE MANAGEMENT 00(0):000-000
Key Words: Adaptive foraging, Anthropogenesis, Continental United States, Corvidae, Corvus Corax, Corvus hawaiiensis, Habitat, Hawaii, interspecial, Raven,
The Raven is a large blue-purple-irridescent black, non-migratory passerine with black beak and feet. The iris of the eye is brown. They are typically 24 to 27 inches long, with a wingspan double that. Ravens are considered somewhat intelligent, and are generally adaptive to changes in their environment. They have often been pinned as a vermin bird because of their tendency to undergo population increases in response to human activity. On the other hand, they have lost habitat and population stability due to human practices in some cases. There are several types of raven found in the United States. For this paper however, two types will be prominent due to the value of research that has been completed. The common raven (Corvus corax) is an indicator species in the continental U.S, and the Hawaiian crow (Corvus hawaiiensis) (noted by Mark Walters to be more similar to raven than crow [Walters 2006]) is now listed as ‘extinct in the wild’ by the International Union for Conservation of Nature (Bird Life International 2012).
Common ravens occur across most of the Northern Hemisphere, except for eastern forests and Great Plains. Their habitat includes beaches, islands, deserts, mountains, grasslands,
deciduous and coniferous forests, ice floes, tundra, and agricultural fields. They adapt well to human habitation, except notably that they could not adapt to fragmentation of the eastern forests, which was a byproduct of lumber harvesting. Omnivorous and opportunistic, they forage dump sites and use irrigation to survive where they would not normally be found (Kristan and Boarman 2007). In cities, the common raven is usually replaced by the American crow (Corvus brachyrhynchos) .
Hawaiian `alalā occurred primarily in the western and southwestern forests of Hawaii, on Mauna Loa and Hualālai (300-2500 m), but they are no longer found in the wild, the existing captive-bred population is in the San Diego Zoo. They preferred the specific habitat of native trees and undergrowth in their mountainside zones.
Common ravens are scavengers, most of their consumption is carrion. However, they are also very opportunistic and will eat small mammals, bird eggs and nestlings, insects, berries, seeds, nuts, and garbage (Knight and Call 1980). Alternatively, the Hawaiian version depended mostly on fledglings and eggs, fruit, and small invertebrates; carrion was a small part of their natural diet (Walters 2006).
Young unpaired ravens associate, similar yet different than the flocking of other birds (Heinrich et. al. 1994), and will engage in mating rituals until about 3 or 4 years of age, when they will have matured and found a mate. Ravens nest in single pairs, apart from others (they do not form rookeries), though they will engage in cooperative sharing (food source location-sharing and defense) among localized pairs that are familiar with one another (Heinrich 1999 pp.131-145). Multiple researchers indicate that they may mate for life, utilizing the same nest or a ready-made alternative every year. Nests are constructed from twigs, bark, leaves, string, and even trash if available and attractive. The nests are usually built in deciduous trees or cliff ledges, and measure a few feet in diameter, with about a 15” bowl1.
They typically begin laying eggs at two to four years of age, after settling down with a mate. Clutch sizes range from 1 to 7 eggs (Boarman and Heinrich 1999). Incubation time is 20 to 25 days, nesting time ranges from 28 to 50 days. Both parents will feed the young and defend the territory. Clutch size and health is directly related to resource availability (Heinrich 1999).
Hatchling survival is increased when paired parents ally with other local pairs to defend resources from roving juvenile ‘flocks.’ This is especially true at opportunistic nesting locations near dumps.
Western civilization has dealt with raven populations in various forms and for various reasons over the years. Ravens have learned to live near people, benefiting from our waste, agriculture, buildings, and irrigation. For this reason, it is understandable that ravens would not be regarded as a precious commodity. They are often associated with trouble. For instance, they have destroyed power-line transformers, attacked new-birth livestock, eaten crops, and have even been blamed for tearing apart a radiation shield at a defense facility. It had been assumed that this was the natural behavior of ravens, they are (folklore tells us) capricious creatures of mischief. Due to limited data about wild Corvidae at the time anti-raven folklore was crafted in in post medieval western culture, this was a reasonable assumption. So, in the course of the years ravens have been hunted as vermin, even to exterpation from at least one state. Unfortunately, this may have been incredibly detrimental to the ecological balance of many regions in the U.S. in which the raven would naturally be found. The raven is a key indicator of ecosystem stability. There are several far reaching examples that can be synergized into a single concept; that the ecological framework of an ecosystem cannot be maintained while any of its parts are ostracized or manipulated through secondary conditioning. The raven has been dealt both hands over time, and there is enough data to begin to understand the delicacy of ecological balance that urbanization disturbs, no matter how well-planned and managed that ecosystem may be.
Case 1. Eastern Forests
The forests of the eastern expanse of North America were home to various Corvidae when the settlers began expanding their holdings into the Midwest. At that time, trees were a source of building material and fuel that could not be replaced with other sources. Unfortunately, the Europeans brought with them the industrial ideals of post-plague Europe. Clear cutting was the order of the day. People needed homes and they needed fuel. The forest was fragmented so badly that the raven, shown in a 1992 study by Henrick Andren to be “a habitat specialist at home in the deep forest” (Andren 1992), was pushed into dense populations that began to prey on each others’ eggs. Eventually the raven departed the eastern forests altogether and have only recently begun reoccurring as the forest has been managed back to health. For example, in Tennessee, the Common raven was first identified as more numerous that the Common crow by Alexander Wilson in 1811 (Robinson 1990), and was found throughout the states’ vast forests. By 1975, the raven was limited to habitats at about 2,700 ft elevation along the North Carolina State line. Tennessee added the raven to the endangered list in 1975 and there it remained until 1994 when the population was stabilized (Nicholson 1997). This is a basic example of human impact to an environment. There was a need to be met (lumber), and it was met at the cost of other needs (ecological balance).
Case2. The Wolf and the Human
“Durward Allen, a pioneer of wolf studies, remarked that the ravens of Isle Royale in Lake Superior accompany wolves on their travels, feed at their kills, and sometimes even eat their scats” (Heinrich 1999 pp.236).
Wolves (Canis lupus) and ravens have been observed, by various researchers over a large expanse of time, to play, eat, travel, and protect carrion together. Ravens have been noted to go so far as to chase eagles from carrion in order to share it with the wolves, and the two animals seem to ignore each other when feeding together. Ravens, according to Heinrich (ibid pp. 226-244), wolves and ravens learned to listen to the scavenge calls of each other, and respond by locating carrion and feasting together. Interestingly, wolves are part of a sensitive ecological equilibrium themselves, and have recently been shown to be central to the preservation of riparian zones, and to be nature’s forest ranger to keep elk and deer populations under control. Wolf presence in a forest ensures the diversity and sustainability of the forest. Wolves are a bane to agriculture, however, and their numbers have been reduced over the centuries to a degree that the raven has selected the new forest ranger to share the land with. Humans are the new wolves for the ravens. As they followed the canines in the wild, they now follow and cohabit with humans. Similarly, as a study in Minnesota showed, they now listen to gunshots rather than wolf calls to locate scavenge sites (White 2005). Even as they harvested wolf scat, they now harvest our refuse. The problem is not as innocent as it may seem on the surface, though. Ravens are capable and flexible, and they excel in the vast amounts of resources that humans provide. This has elevated raven populations, not only in their natural habitats, but also in places that they would not have been able to survive in without humans (Restani et al 2001). We provide food, irrigation, and cover. Ravens have taken to nesting on power lines and billboards. No longer dependent on old growth forest, ravens have become a troublesome invasive species in many regions. There are numerous studies cataloging their impact on wildlife all over the country. Various means have been used to try to limit their impact, yet they are continuing to push more
and more animals to the brink of endangerment. One example is the desert tortoise in the West Mojave Desert, where researchers Kristan and Boarman have determined that ravens are “anthropogenic subsidized predators” and the blame for the effects of raven predation on native fauna is to be laid on humans (Kristan and Boarman 2007).
Case 3. The ´Alalā of Hawaii
Hawaiian Crow, or Alala, thrived in the dense natural undergrowth of the old forest canopy. The shrub cover allowed them to hunt and forage for insects and small mammals without the immediate risk of their main predator, the hawk. The story of the decline of the alala is a story of man’s work. It began with the introduction of the European boar to the Hawaiian forest. Hawaii did not have an abundance of game when Caucasian settlers arrived, so they brought their own subsidies to support their families and the growing society. At some point, the pigs escaped domestication and turned into a feral population. Unfortunately, the boar scavenged the forest floor, uprooting shrubs and creating holes in which the rain would stagnate. Added to the reduction of undergrowth (which negatively impacted alala foraging, and which increased hawk predation) was the increased population of malarial mosquitos. In short, the reason many today believe the fall of the alala to be a mystery, is that it is not a single cause. Woodsmen wanted to blame ranchers for allowing cattle to graze the highlands in order to prevent wild fire. Cattlemen wanted to point to the boar. It was all of the impacts at once, but it is also clear that the greatest problem was invasive species, creating a new unbalanced intraspecies competition that the native fauna and flora could not adapt to quickly enough. In 1996 there were only 12 alala left in Hawaii, the last two wild-born had died, 22 out of 27 birds released into the wild were predated upon or died of disease within the first year of management, and years of effort
could not salvage the species simply because the habitat was gone. Today, there are about 100 captive bred alala protected in the San Diego Zoo.
Summary: Anthropogenic Impact
It is clear that by focusing on one solution to a set of complex ecological problems, the end result is a heavy financial cost and burden of conscience on future wildlife managers, and loss of resources to the populace in general. By focusing on the wildfire problem, ranchers in Hawaii inevitably helped starve the Alala population, and coupled with the influx of European Boars who’s foraging provided breeding pools for bird-malaria ridden mosquitos (and both cattle and boar ravaged the landscape), the alala had no chance, even with the best efforts of the state to preserve the species. In Hawaii, it is more clear than anywhere else because of all of the different aspects that caused changes, that a single species is so tied to its ecological balance that such changes can prevent reproductive success, and ultimately cause extinction.
Ravens adapted to the extermination of wolves by becoming surrogates to man’s urbanization and agriculture. In so doing, they have begun threatening the stability of ecological systems all over the country. They once followed the natural forest manager (wolves), and now follow the same invasive species that cut down their forests (humans).
The impact of an invasive species is far-flung and never can be prepared for adequately. Yet everywhere the arm of industry stretches, the first question is; how can industry benefit? After the area is developed, concerned people start asking how the native flora and fauna have adapted. Interestingly, we are quick to identify invasive species, and order their removal. Yet, it remains to be seen whether or not we will recognize that we are the primal invader. Everywhere we take our industrial concepts, species fade from prominence and often enough, from existence.
Anthropogenic developments have impacted ravens to such a degree that they are hardly the
same animal that Alexander Wilson chronicled in 1811 in pristine Tennessee forests. Science and philosophy contend that Western culture has altered its views, that our key concepts are nothing close to the mindless ramblings of medieval Europe, yet we continue to operate on the same totemic principle of ‘man first.’ In the Great Chain of Being from Rhetorica Christiana circa 1579 (see inset), man is depicted as having dominance, or prominence, over the other creatures of earth; in fact over the earth itself. This type of thinking leads to deforested continents (i.e Europe’s Black Forest), extinction of animal species, and ultimately, as the raven is showing on a small scale, we consume our own futures. The story of the raven in America is essentially a microscopic mirror of the story of humans on the planet. If we mindlessly continue the travesty of industry, only stopping to ‘manage’ the ecosystem later, we will end up with few resources to choose from. What is our equivalent of cattle keeping wildfires down, and what is our subsidy equivalent to the boar that turns up Mauna Loa’s undergrowth?
The most popular form of research has been on human impact to timber, and it may be necessary to begin focusing on other arenas of human impact, including recreation, travel, consumerism, and so forth. Human impact should be measured and accounted for before actions are set into motion. It is easy to assume that we can manage nature back into shape after we harvest or alter it as we need. Yet, at what cost? The U.S. Spent $9.9 billion dollars on land management in 2008, and in 2012 the Bureau of Land Management alone requested $1.1 billion . If we compare that to the amount that the Klamath Indians spent to preserve the vast Oregon Coastal Range over their 1500+ year habitation, we can arrive at a simple conclusion that the basic problem is that of cultural concept, not of management. More species will follow the raven in our path of resource acquisition and in all probability, we may be asking our grandchildren for forgiveness for giving them a resource-limited planet. Concepts are at issue; the only way to limit anthropogenic impact on ecological systems is to plan ahead, and not for the best interest of industry, but for the best interest of what already exists where we want to go.
Further studies could include the impact of renewable energy to the subsidized resource acquisition of ravens in urban habitats. Studies of this nature could determine if alternate energy sources, and therefore less waste, have a re-balancing effect on populations that have previously been impacted by invasive species. Rather that discussing the economic impact of renewable resources, the discussion would shift toward a sustainable ecosystem, and whether the ‘green’ changes that are already in progress will have the necessary positive impact on the environment.
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