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Ravens and Anthropogenesis ٠
OF ANTHROPOGENIC IMPACT ON RAVENS
Ravens have been shown to be sensitive to human impacts on their
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.
OF WILDLIFE MANAGEMENT 00(0):000-000
Words: Adaptive foraging, Anthropogenesis, Continental United States,
Corvidae, Corvus Corax, Corvus hawaiiensis, Habitat, Hawaii,
What happened to the Hawaiian Raven?
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).
ravens occur across most of the Northern Hemisphere, except for
eastern forests and Great Plains. Their habitat includes beaches,
islands, deserts, mountains, grasslands,
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
`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.
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).
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.
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).
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.
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.
1. Eastern Forests
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
The Wolf and the Human
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
(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
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).
3. The ´Alalā of Hawaii
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
not salvage the species simply because the habitat was gone. Today,
there are about 100 captive bred alala protected in the San Diego
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.
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
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.
developments have impacted ravens to such a degree that they are
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?
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.
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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