DISCUSSION POST
B ird s & E c o s y s te m S e rv ic e s | E n v iro n m e n ta lS c ie n c e .o rg
T h e V a lu e o f B ird s
Birds are present throughout alm ost every habitat across the globe. No m atter where you go, there is
always evidence of birds even if you don't see the anim als them selves. Things like holes pecked in tree
bark by woodpeckers or the rem nants of a nest are indicative of the presence of birds. W hile such m arks
left behind by these anim als m ay seem insignificant, in m any cases the activities of birds can have large
consequences for the ecosystem s they inhabit, m aking them incredibly im portant in the overall
functioning of various ecosystem s.
By contributing in such an im portant way to ecosystem health, birds can provide a num ber of direct
benefits to hum ans. The M illennium Ecosystem Assessm ent, a study initiated by the United Nations,
coined the term “ecosystem services” to describe these kinds of services. According to this panel,
ecosystem services fall into four broadly defined categories and as we survey the diversity of birds
across the globe, we find m any ways in which the activities of birds provide services in each one of
these.
S u p p o rtin g S e rv ic e s
1 Actions within this category are those that are required for all other ecosystem services to be produced,
such as nutrient cycling and the form ation of soil. This category can be thought of as a foundation of
processes without which other ecosystem services could not be produced.
Birds can help in these services by nutrient cycling, which has been docum ented in m any habitats. By
spreading activities through different habitats, birds can m ove nutrients from one place to another, which
is particularly relevant in places where plant growth is lim ited by nutrient availability. A study on the
islands in the G ulf of California showed that when birds roosted on them , the guano deposits they left
behind provided nutrients to plants on the island . As a result, islands with seabirds had plants that grew
taller and faster and were m uch m ore productive than those on islands without birds. Because the
quality of these plants im pacts the num ber of consum ers and the structure of the food web, these birds
exerted a bottom up effect on the food web by regulating prim ary productivity.
This exam ple is also interesting from an ecological standpoint because it exem plifies the intricate ways
in which seem ingly disparate habitats are connected and can im pact one another. The prim ary
productivity in the ocean regulates the num ber of fish it can support, which then im pacts the num ber of
birds that can feed on these fish, which then influences how m any birds will roost on the island and leave
guano deposits, ultim ately dictating the prim ary productivity and food web structure on the island. Barry
Com m oner, one of the founders of the environm ental m ovem ent, laid out four laws of ecology in his
1971 book The Closing Circle. O ne of these is “Everything is connected to everything else,” a prem ise
we see clearly dem onstrated in this exam ple as birds serve as a vector for nutrients between aquatic
and terrestrial habitats.
Birds are also capable of stim ulating prim ary productivity in other ways, which supports the functioning of
ecosystem s, an exam ple exhibited by birds in salt m arshes. In Alaska, lesser snow geese and Canada
snow geese stopover in salt m arshes during spring m igrations. W hile they are foraging in these
m arshes, they tram ple the ground, which tears up leaf litter and incorporates it into the soil. The sm aller
particle size and increased contact with the soil prom otes greater decom position, freeing nitrogen from
the leaf litter and allowing it to cycle through the ecosystem .
In the southeastern United States, cordgrass is the dom inant plant in salt m arshes. The salt m arsh
periwinkle is a m ajor predator of cordgrass and in the absence of predation, these snails can overgraze
the grasses and com pletely convert a productive m arsh into m udflats. Predation of snails controls their
num bers, which regulates prim ary productivity of salt m arshes. Several species of birds such as
oystercatchers, curlews, and plovers are predators of these snails and exert topdown population
controls, which prevents overgrazing. In term s of the dollar value of services provided to hum ans,
wetlands are considered one of the m ost valuable habitats, providing an array of im portant services like
shoreline stabilization and water filtration. The presence of birds in these habitats ensures ecosystem
functioning, allowing hum ans to gain the m axim um benefit from these valuable ecosystem s.
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5 P ro v is io n in g S e rv ic e s
M any of the support services m entioned above can also be classified as provisioning services, our next
category. Provisioning services encom passes products that we harvest from ecosystem s and we can
find m any exam ples of activities in this category by exam ining how birds can positively im pact the raising
of crops and livestock.
A com m on traditional practice in the farm ing of rice straw in California was to burn the fields after
harvest. However, this technique was banned in recent years to prevent air pollution and a widely used
alternative is to flood fields instead. These flooded fields create habitat that is used for foraging by
waterfowl. As these birds dive down to where the layer of straw rests on the ground, they tear, shred,
and churn up the pieces of straw looking for grain and invertebrates. Such activities allow for greater
contact of the soil with straw, increasing m icrobial decom position. An experim ental study in which
waterfowl were perm itted into areas of a flooded field and excluded from others showed that when the
birds were present, there was a sm aller biom ass of straw, as well as lower nutrient concentrations. This
study indicated the waterfowl presence successfully led to increased decom position of straw in the field,
which could prevent the need for autum n tillage, saving growers a substantial am ount of m oney.
In agricultural system s, birds can also be beneficial through the regulation of pests. In G uatem alan
coffee plantations with higher abundances of insectivorous birds, there were fewer insects which
resulted in less herbivorous dam age to the leaves of crops. Experim ents in Jam aica showed that the
presence of birds led to a decrease in insect pests and increased the am ount of saleable crops, leading
to an increase in farm profits of up to $310 per hectare per year. Sim ilarly, the construction of nest
boxes for great tits in apple orchards has been shown to lead to greater num bers of birds in the area,
which forage on caterpillars that can cause dam age to crops, resulting in significantly higher crop
yields. If installed and m aintained properly, the construction of bird nest boxes can elim inate the need
for pesticides, saving farm ers m oney and preventing potentially dangerous chem icals from being
applied. Sim ilarly, the use of artificial perches for raptors around agricultural fields m ay increase the
num ber of raptors that prey on rodents that can cause dam age to crops.
M utualistic relationships between birds and livestock can also be beneficial to hum ans. M any birds perch
on livestock like cattle and forage on insects that live on them . Cattle egrets are particularly well known
for m aking a living this way, and although they are native to Africa, their range has expanded
dram atically concurrent with increases in the clearing of land for farm ing. W hile the birds benefit from a
readily available food source, the anim als on which they forage benefit from the rem oval of harm ful
parasites. In m any parts of the world, people rely on cows for food and for m ilk. W hen infested with ticks,
cows can becom e anem ic and m ilk production flags. In Pakistan, birds are capable of effectively preying
on these parasites, leading to healthier and m ore productive cows. This predation by birds is even
m ore effective than pesticides in som e cases. Through these interactions, hum ans gain a benefit by not
spending m oney on expensive pesticides and by having m ore productive and healthier livestock.
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12 R e g u la tin g S e rv ic e s
In this category, w e group the benefits that are gained from the regulation of ecosystem processes. This
includes services such as carbon sequestration, waste decom position, and air purification. As with the
other categories, there is no shortage of bird contributions to services in this arena.
Birds are im portant scavengers in m any ecosystem s, rem oving the carcasses of dead anim als. W hile
vultures are probably the best known for this, m any types of birds opportunistically scavenge on this
food source when it is available. In the Serengeti of Africa, vultures are capable of consum ing hundreds
of pounds of dead m eat per kilom eter annually and in Yem en, vultures can rem ove up to 25% of the
organic waste produced in towns by hum ans. Scavenging by birds is an im portant m echanism of
waste disposal in m any areas and prevents the outbreak of diseases than can occur through the
accum ulation of anim al carcasses. In India, declines in vultures led to increases in feral dogs as there
was less com petition for carrion as a food source. The explosion of the dog population led to increases
in rabies outbreaks and hum an injuries from dog attacks. The total estim ated health cost of vulture
declines between 1993 and 2006 is a whopping $34 billion. It is obvious in this case that the value of
birds to hum ans can be quite high and underscores the direct im portance of healthy birds populations to
hum ans.
Another way that birds can provide regulating services is through prom oting forest growth. This is
im portant to hum ans because forests can sequester carbon and prevent it from going into the
atm osphere where it would contribute to clim ate change. Birds are able to perform this role through
dispersing plant seeds during foraging. W hen they pick a seed or fruit from a plant and fly off with it, they
end up transporting the seed to another place where it can germ inate. This behavior is a m ajor
m echanism for seed dispersal in m any plants and can increase the genetic diversity of plants in a
particular area by spreading seeds. In som e cases, anim als can carry seeds m ore than 40 m eters away
from the source tree.
By germ inating the seeds of trees, birds can contribute to the reforesting of deforested lands,
dim inishing the costs of restoration. In oak forests in Sweden, the cost of replacing the seed dispersal
services of Eurasian jays in oak regeneration is an estim ated $9,400 per hectare. Birds provide a
valuable service in the expansion of forests, which sequester carbon and perform a num ber of other
services that stand to benefit hum ans.
C u ltu ra l S e rv ic e s
The last category is cultural services and is a bit different from the others because it m ore abstract and
includes less m aterial benefits. As opposed to m ore tangible things like crop yields or water purification,
services within the cultural category include things such as spiritual enrichm ent and the appreciation of
nature.
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18 An exam ple of a service in this category is bird watching, which can be used as to foster ecotourism as a
source of incom e. M any nature centers and nonprofit environm ental organizations create revenue
through taking visitors on bird watching tours. These kinds of activities can also be used to introduce
students and children to the outdoors in order to foster an appreciation for nature. Sim ilarly, zoos often
acquire rare birds and then use them as a heavily m arketed feature attraction to increase traffic and
visitor revenue.
Birds also serve a num ber of cultural roles and factor heavily into religions across the globe. For
exam ple, eagles are considered sacred m essengers that carry prayers to the spiritual world in m any
Native Am erican religions. Eagle feathers are believed to have holy powers and capturing eagles to
rem ove the feathers is part of a sacred ritual. In m any religions, vultures are considered deities that
play a large part in their m ythology and traditions. W hile it is difficult to place a dollar value on services
within the cultural category, they are just as im portant because the spiritual enrichm ent and appreciation
of nature that birds provide is an essential part of the hum an experience.
Sum m ary
In this review, we have taken an ecological approach by focusing on ways that birds provide services to
hum ans through their interactions with the environm ent. However, it should also be noted that the direct
take of birds and their products also provides econom ic benefit in m any cases. Cultures across the world
hunt birds and eggs for subsistence and to m ake a living. In M alaysia, the nests of swiftlets are
harvested for their use in cooking. They are considered a delicacy and are an extrem ely valuable
com m odity, with a single nest of good quality having a value of m ore than $700 in som e cases. M any
cultures also harvest birds for uses in traditional m edicine. In the cultural category, m any people gain
recreational benefit by hunting birds. In cases where this hunting is regulated, the sale of perm its raises
m oney that is used to fund governm ental agencies and services.
Because birds are so com m on in m ost habitats, we often overlook their ecological significance.
However, their ecological roles are incredibly im portant and hum ans can benefit m onetarily through the
m any actions of birds. The exam ples described above are just a few of the m any ways that birds provide
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21 ecosystem services. Q uantifying the m onetary benefit from birds around the world is nearly im possible,
but likely num bers in the billions of dollars annually. The value we gain from birds warrants a serious
investigation into causes of declines and provides additional rationale for the continued study and
conservation of these anim als.
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