9/23/2010
I.
Food
A.
Food and Cover
Digestive Systems
Birds and mammals have evolved a wide
range of adaptations for utilizing
potential foods that occur in their
surroundings - lichens, fungi, leaves,
stems, tubers, roots, nectar...
Snail Kite with Apple Snail
Diet is diverse and includes - nuts, berries, fruits, acorns, roots, deer,
moose, carrion, and spawning salmon.
The process of converting plant and animal
materials into usable food occurs in the digestive
system.
1. Birds Digestive Tract
Esophagus – tube connecting oral cavity and stomach
• produces peristalsis
• large in diameter (relative to other verts)
• usually provided with mucous glands and somewhat
muscular
• lined with heavy epithelium
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• Storage
Seed-eating finches - side of esophagus has
paired out - pockets for storage (swallowed or
g g
for nestlings)
g )
regurgitated
Geese pack full of food
Large structure for food storage
– Crop
Food can be stored ~ 1 day+
• Shapes
Variable in shape across taxonomic
groups
If amylase in saliva some
digestion occurs in crop
Fusiform – Trochlidae, Emberizidae
Bilobed – Columbiformes
Single Sac – Falconiformes, House Sparrows
• Pigeons and Doves – Crop
Milk
• Grinding Function
Hoatzin – crop serves as
grinding organ
Mourning Dove –
• proliferation of lining begins after 8 days incubation
Muscular, numerous
glands, contains
bacteria
• sloughing 14 – 18 days
• continues to 16 days after hatching
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• Other Functions
Greater Prairie Chicken – anterior end modified
as resonating chamber
Flamingoes and male Emperor Penguins
Oily esophageal secretion
Air forced into sac from trachea via pharynx
59% protein
28% lipid
Stomach
Birds possess two kinds of stomachs:
Anterior glandular stomach
Posterior muscular stomach
Proventriculus
Ventriculus
Strong muscular organ (granivores)
Spindle-shaped glandular stomach – avian innovation
Prepares food for digestion (analog of teeth)
Not found in reptiles
Size related to bulk of food intake
Mucous glands present in
walls – secrete koilin lining
Large – piscivores, frugivores, granivores
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Functions as principle barrier to indigestible material
• In granivores may contain grit
• feathers
• lined with tough, abrasive, keratin layer (koilin) – cutica
gastrica
• hair
• bone
• teeth
avian gastrointestinal tract - distinct
reverse peristaltic movements (Duke
1994).
allows material in the gizzard to reenter
the proventriculus for additional
treatment with acid and pepsin.
Seasonal change in in structure of stomachs corresponding
to seasonal change in diet
Bearded Tits
Winter diet – seeds, stomach 0.88 – 1.2g
Summer diet – insects, stomach 0.5 – 0.6g
Small Intestine
„
• duodenal loop
• ilium
Chief organ of digestion and absorption
„
Once food enters intestine undergoes complete
chemical ateration via enzymes
Small intestine
generally
g
y shorter
than mammals
Contents mixed and absorbed by intestinal mucosa
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Function
Receives – bile ducts,
pancreatic ducts and
secretions from glands in
mucosa
3. Length variable – varies with diet,
Long and tightly coiled– granivores,
omnivores
1. Enzymatic activity – carbohydrases, lipases,
proteases, and nucleases
2. Primary site of absorption – by time product
reaches large intestine it is completely absorbed
4. Retention time related to diet
Long – granivores
Short – carnivores, frugivores
Short and slightly coiled – raptors,
insectivores frugivores
Large Intestine
Primary function is for water & electrolyte
reabsorption
No relation between diet and structure
Relatively short organ
Contains minimum amount of non-digestable waste
quicklyy as possible
p
• wastes voided as q
• wastes sometimes voided in other ways
(e.g. pellets)
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Intestinal Caeca
Posterior end of intestine occur pair of caeca
Size variable
Large – Folivores (Cranes, ducks, geese)
Small – Falcons, woodpeckers, insectivores, passerines,
piscivores
Absent - Parrots
Functions:
1. Absorption of water
2. Absorption
b
off non-protein nitrogen
3. Digestion of carbohydrates and proteins
4. Microbial breakdown of cellulose
5. Microbial synthesis of vitamins(?)
I.
Food
A.
Digestive Systems
Vampire Bats – simple straight stomach, expandable for
digesting and storing.
2. Mammals
Herbivores – combination of complex stomachs, long ceca
and long intestines.
Similar to birds in that length of tract corresponds with diet
Hindgut fermenters
Foregut fermenters
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Ruminants
Forestomach divided
• 3 chambers store and process
food
• 1 chamber
h
b with
ith digestion
di
ti
Rumen – fermented
and regurgitated
Microbial fermentation provides 60-70% of the energy
requirements for ruminants
Cud chewed
Reticulum – fermented
Omasum &
Abomasum
B. Energy
Herbivorous mammals experience a period of adjustment
when changing diets.
1. Carbohydrates
Includes cellulose, starch and sugars
Cellulose contain a great deal of energy but only a few species
can take advantage of it.
2 Fats
2.
F
Contain more than 2x per unit wght as do carbohydrates but
digestive system extracts at slower rate.
Grazing animals not adapted for fat utilization.
Deer lack gall bladder and secrete bile into small intestine in
small amounts
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3. Proteins
Energy content equivalent to that found in carbohydrates.
Because protein scarce, the abundance of protein in
vegetation good measure of food quality.
Not abundant in vegetation but concentrated at tips of growing
stems, some seeds.
4. Vitamins
Legumes (alfalfa, clover, beans and peas) fix N and thus good
source of protein.
Function as enzymes. In some locations vitamins naturally
deficient.
Lagomorphs conserve vitamins produced by bacteria in
digestive tract by coprophagy.
II.
Ecology and Evolution of Feeding Behavior and Defense
Similar to hindgut fermentation, little time for absorption in
large intestine once cellulose is broken down by bacteria in the
caecum
Feeding relationship represents ongoing struggle
predator
prey
Produce two types of feces, wet and dry.
Dry – intestinal not ingested
Wet – cecum, ingested
Plants have evolved mechanisms for resisting herbivory and
herbivores evolved means for coping with plant defenses.
Denied – vitamin K deficiency
Smith, C. 1970. Ecol Monographs 40:349-371
Coevolution – the joint evolution of two or more organisms with
close ecological relationships, but lack any exchange of genes.
Douglas Squirrels and pine trees in
Northwestern US.
Conifer seeds main food items
Squirrels can remove all pine cones from single tree
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T
resd
u
cesq
u
irelfectivensan
d
eh
an
cesurvialb
y
Squirrels evolved behaviors to deal with defense mechanisms
• produce cones difficult to open
• cones with fewer seeds
• increase thickness of seed coat
• careful selection of cones to avoid those with few seeds
• stockpiling cones for low production years
• produce less nutritious seeds
• drop seeds early in year before young squirrels begin to feed
• periodically producing almost no cones
A. Food Quality
For herbivores nature and availability of plant materials varies
from place to place, season to season, as well as structure of
plant.
1. Importance of soil fertility
Herbivores select parts of plants (time and space) which they
can extract energy and nutrients.
Diets of carnivores varies little in quality. Food deficiency of
carnivores typically problems of quantity rather than quality.
Missouri – size and bone strength of adult cottontails varies
according to soil fertility.
Nutritional quality of vegetation depends on fertility of soil
Michigan – sandy soils 2x increase in population (spring – fall)
fertile soils 5x increase.
Agricultural production preempted richest soils and
wildlife forced into less than optimal habitat.
Cottontails in Alabama (Hill 1972)
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3. Effects on reproduction
2. Effects of nutrition on body condition
Antler development and body size greatly influenced by nutrition in
White-tails.
Verme (1965) studied fawn production of white-tails on
different experimental diets.
High
Low
27
0
22
2
47
21
Fawns/doe
1.74
0.95
Male fawns
16
13
Female
fawns
29
6
35.6
68.4
Yearling bucks on good diet --- 6-8 points
Poor diet --- small unbranched, spikes
# Does
Does not
g
breeding
Fawns
produced
% Males
Differences of reproductive
success of female white-tailed
deer on good and poor ranges
in New York State (Cheatum
and Severinghaus 1950).
Spruce Grouse select most nutritious needles.
Selected needles sig higher protein, and mineral content than
non-selected needles. Sensory mechanism unknown.
4. Selective feeding
May partially compensate for scarcity of some nutrients.
Bison and grazing lawns
Ruffed Grouse often select flower buds from aspen that appear
less vigorous.
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5. Effects on milk production
Young animals require more protein than adults.
Fawns born to does that have struggled through difficult winter
more likely to die – carryover effect.
Carnivores often supplement milk with regurgitated food.
Herbivores rely solely on milk
Whi
White-tailed
il d deer
d - quality
li off milk
ilk doesn’t
d
’ change
h
but
b quantity
i does.
d
6. Protein requirement in birds
Almost all young birds require diet rich in protein.
Oilbirds only nocturnal fruit eating birds. Young fed
protein rich nuts.
Young fed primarily animal material even if adults consume
different foods.
Exceptions – young geese eat newly sprouted grass
Mallard ducklings feed almost exclusively on insects and
other arthropods --but by 2 months old vegetarian.
7. Sex-specific differences in diet
Other studies consistently show that bucks dominate does
when competing for winter food.
Results bucks enter spring in better condition.
Female White-tailed deer wintering on good range in Michigan
consumed more grass and less browse than males.
Feces contained larger quantities of nitrogen than did bucks.
Female Pintails switch from diet of seeds and other plant
material to one of insects during nesting season.
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B. Quantity of food
Aldo Leopold documented 100+ cases where herds of Mule
and/or White-tailed Deer populations increased to such #s
that food supply threatened
How can animal consume more food than is available in
given habitat?
½ of cases disaster averted when hunting pressure increased to
reduce herd size or made habitat improvements.
Other cases overbrowsing resulted in mass starvation
Healthy
understory
Problem – woody plants grow seasonally – new twigs in spring
and summer.
If too much consumed plants can’t regenerate additional twigs.
Understory and
ground cover
impacted by deer
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Some species more severely affected than others –
White Cedar regeneration is impaired when as little as 20% of
new growth is removed.
Elk overpopulation drastically altering regeneration of Aspen
stands.
Consume Aspen seedlings and suckers.
The ultimate result is starvation and low birth rates.
White-tailed deer affecting eastern deciduous forest
communities.
Agriculture exacerbating problem.
Poorwills may hibernate for as long as 88 days.
1. Response to food shortages
a. Birds
Some spp. can live without food for extended periods.
Hummingbirds, swifts etc. survive by entering torpor for few
hours to several days.
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Other birds can still withstand temporary food shortages.
Both Wild Turkey and Pheasants can survive 1-2 weeks of
severe winter weather without food.
Wild Mallards kept alive 3wks without food but lost 43% of
body wght.
When returned to normal diet regained mass in 28 days.
b. Mammals
Hibernation – specialized adaptive, seasonal reduction in
metabolism concurrent with environmental pressures of lack of
food and low temperatures.
c. Case studies
Length of hibernation period varies among mammals.
i.
Beaver-Basin Deer Herd
Ground squirrel – few degrees above freezing
Mammals that are not true hibernators can also lower body
temps and metabolic rates for energy savings.
Blackk Bears
Bl
B
– Tb falls
f ll only
l ~ 7° below
b l normall (saves
(
600Kcal / day).
1959 hunting resort on
5km2 coniferous lowlands
on shore of Lake Superior
Managers at resort
nourished deer with
commercial food each
winter.
White-tailed deer in northern areas – lower metabolic rates,
movement reduced.
Numbers increased but hunting and other sources of
mortality inadequate at keeping herd in check.
Early 1970’s more than 80 tons of feed each winter
• Park Service policy prohibited feeding programs
• Manager treated as resource management issue
• Reduced feeding to 20 tons for each of next 2
winters.
1974 – land donated to National Park Service
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Data indicated that no reduction in Deer herd was
occurring.
• Local sportsmen critical of herd reduction policy.
• Rumors began -> reduced credibility of Agency
Herd size = 600
Carrying Capacity = 150
1976 – NPS proposed special hunt
The plan
• thirty-five hunters access to the area for a threeday period (1 deer/hunter)
Public outcry – Press made hunt sound like turkey
shoot
State legislature passed resolution directing DNR
to devise alternative proposal.
• At the end of the three days another thirty-five
hunters would be granted special permission to
hunt.
• Hunt to run from mid-January to the first day of
March, or until three hundred deer were taken.
Local hunting club challenged proposal, claimed
hunt would decimate herd. Injunction postponed
hunt and club started feeding herd illegally
($27,000).
NPS started issuing citations for illegal
feeding.
Winter of ’76 – chaos
1983 herd reduced to 0
1977-1978 – herd neither fed nor culled,
starvation reduced herd to ~100 animals.
Snowmobilers, sight-seers
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1996 – biologists returned to see if deer had
recolonized, hadn’t and White Cedar and maples
still showed the effects of severe overgrazing
from 20yrs. before.
ii. Kaibab Plateau Herd
Mule Deer herd from Kaibab forest north of Grand Canyon.
Wildlife management didn’t fail
Failure occurred because local residents and a
judge didn’t have adequate knowledge of
consequences to their actions.
Herd benefited from predator control and protection from
hunting during 1900 – 1920’s.
1905 – 4000
1924 – 100,000
Habitat obviously couldn’t support herd
60% of population died in 2 winters
1940 – 10,000
10 000
iii. Giant Panda
Bamboo – synchronous reproduction
Depletion of food resources (bamboo) in China
Flowering cycle 40-120 years
Daily consume ~ 18Kg of leaves and stems
Historically Pandas switched to different species when die-off
occurred.
Not efficient – 17% of food consumed digested
2/3 day
d spent eating.
i
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Agricultural practices reduced diversity of remaining habitats.
Critical food shortages faced with dieoffs.
2. Physical condition and Nutrition
Assume large reserves of body fat are useful indicators of good
condition and survival.
Hepp et al. 1986 JWM 50:177-183
Related hunting mortality with mallard body mass
1970’ss – 138 died starvation
1970
Currently – wild population
(mass/wing length) = Condition Index
~ 1000 - 3000
Current management – replanting, establishing new refuges.
MeasureofNutrionalConditon
Banded 5600 mallards along Mississippi river.
– “state of body components controlled by nutrition and which, in
turn, influence an animal’s fitness”
234 – recovered by hunters, had sig. lower Condition Index than
those not recovered.
• whole body fat – primarily used in small mammals,
birds
• skeletal
k l l measurements andd weights
i h
ConcludedBirds in poor condition may be driven to habitats more
susceptible to hunting pressure.
• kidney fat index – ratio of
fat mass/kidney mass x 100
(ungulates and lagomorphs)
• urine characteristics (snow urine) – assess metabolites present
(wolves and Cervids).
• blood serum analyses
• marrow fat – fat level in bone
marrow, bone marrow fat believed to
be last fat source depleted in starving
animals.
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4 components of blood serum:
1. Urea Nitrogen - used as an indication of protein intake and
energy deficiency, can be affected by the ability of a ruminant
to recycle urea.
2. Creatinine - a non-protein nitrogen compound that is produced
with the catabolism of muscle tissue. Increases can be
associated with muscle necrosis, atrophy and starvation.
3. Total Protein - provides reference for protein intake, liver
function, and immunological status.
4. Free fatty acids - produced in response to breakdown of fat
tissue and is usually inversely related to the amount of energy in
the diet
III. Food Management
A. Food Habit Determination
2 step process
3 broad categories
Determine what organism eats
•
observational
•
feeding site surveys
•
post ingestion surveys
post-ingestion
Manage for that food resource
1. Observational –
2. Feeding Site/Browse Survey
Direct observation widely used for large herbivores.
Earliest approaches developed for use on domestic livestock
Quantified as
-
bite counts (number of bites for particular plant)
Attempt to measure amount of vegetation removed by foraging
animals from area during given time period.
-
feeding minutes (time spent foraging on particular
species)
P id only
Provides
l generall dietary
di t
information.
i f
ti
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3. Post-ingestion Survey
Typically determined by examining digestive tracts or products
Simplest analysis is list of foods eaten
don’t distinguish between
•stomachs, crops
•pellets
•scats
• foods eaten rarely with those that make up majority of diet
• items of high nutritional content
• items of high availability
Amount of detail should be tied to management objectives
B. Food Propagation
ManagementGuid
elns
Some situations may need to aggressively manage a habitat in
order to provide the required food.
1. Limit plantings to those species that are adapted to local
climates, soils and moisture (natives are always preferred).
e.g. oak plantings, food plots
2. Coordinate with other land-use activities (forest cuttings,
controlled burns etc)
3. Share cropping can be cost effective.
4. Size is Important – plots less than 2 ha of unharvested grain not
effective for increasing populations. How effective are food
plots?
C. Difficulties in Food Management
2. Erroneous Conclusions
1. Seasonal changes in diet
Typically food readily available in fall during hunting season
Many dietary studies conducted on hunter-killed specimens –
introduces significant bias.
Can lead to erroneous conclusion that food not limiting for
population.
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Ruffed Grouse
Spring, summer and fall reveal varied diet (clover, strawberry,
grasses, hawthorn fruits, chokecherry, apple, insects)
Found only 15min of feeding can extract enough energy to last
24 hours.
Thus availability of male aspen buds is primary factor in their
survival.
Winter – only male, aspen buds
Then there is “BIOFILM”
Are animals
eating a random
sample of what is
available
Variability in rates of digestion
3. Lessons from Beaver Basin
May seem most humane solution to starvation is food supplements.
Artificial feeding presents serious drawbacks.
Or
S i
Serious
economic
i andd ecological
l i l problems
bl
develop.
d l
Are they selecting
specific items?
• Availability of White Cedar 151 kg per ha – 6 kg per ha
Damage has lasted for decades (seldom considered)
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• Supplemental feeding disrupts digestive physiologies of
starving animals. Sudden shift in diet can result in death.
• Philosophical questions – how much should wild
populations depend on humans.
Not easy to manage for food requirements of organism
Need to know
• nutritional requirements
• Feeding can result in undesirable characteristics.
• rate of production
• dietary
di t
requirements
i
t
• population size
Population data hard to determine
Managers most often measure condition of vegetation as
barometer of wildlife populations.
Forage availability and consumption measured for Utah – Big
Game Forage Condition Report
If population is too large for habitat following course of actions
can be taken
1. Do nothing
g - starvation,, long-term
g
damage
g to vegetation,
g
,
Disadvantage
public image damaged
http://www.wildlife.utah.gov/hunting/
2. Reduce the population by increased hunting, introduction of
predators.
3. Live-trapping, Removal and Relocation
Restores habitat to more natural system
Disadvantage – high cost, where to relocate, survival rates, shortterm only.
Gains public approval.
Disadvantages Liberalized hunting regulations – outcries from public
also when females are added to take.
Introduction of predators – outcry from public (ranchers)
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4. Artificial Feeding
Broad public appeal
Disadvantage – encourages further population expansion, justified
where food shortage is temporary
5. Habitat modification
This option increases production of natural foods,
setting back succession or by planting self-perpetuating
vegetation.
Disadvantage - Slow response time and lack of public
enthusiasm,
Advantage – cost effective, permanent
IV. Cover
A.
Plant ecology - % of ground concealed by overlying vegetation
Defined
Can be important - 2 reasons
1. It can be important to protect organism from extremes in
climate and thus wasteage of energy for thermoregulation
Our definition - any physical or biological features that provide
shelter from weather or concealment from predators
2. Protection from predators
“Good Pheasant cover”
B. Cover as Shelter
Homeotherms use cover to prevent heat loss or
build-up
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1. Vegetative Cover
• White-tailed Deer seek conifers for cover –
migrating 50km from summer range.
• Given choice between food and cover – choose
cover
2. Huddling
Birds and mammals find shelter with others
• Deer metabolism changes during winter
Best winter cover =
Closed conifer canopy
Intercepts snow, reduces windchill
• Walk 50 – 100km to
permanent ice shelf to
established rookery
• Female lays single egg,
incubated by male
• Female returns to sea to
fo age
forage
• Male incubates for 60
days (high winds & temps
– 30 –40 F)
• Male wght drops from 36.5 kg -> 20 kg
• Walking 1.5kg
How might a reduction in population size affect
Emperor Penguins?
• exposure to cold could cost 25kg (fatal)
• since they huddle save ½ energy
And thus lose only 15 kg
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C. Cover as concealment
1. Examples
Value of cover as hiding place more often studied
than as shelter from weather
a. Snowshoe Hares
Wolfe et al. 1982. Snowshoe hare cover relationships in northern Utah.
Journal of Wildlife Management 46:662-670.
Found a strong relationship between horizontal
density of cover (up to 2.5 m) and abundance of
snowshoe hare droppings.
Favorite prey of medium – large carnivores
• Hares chose cover with at least 40% density in
1st 1.5m above the snow level.
b. Ruffed Grouse
Cover requirements well – known
• This found in subalpine fir, spruce, Aspen/conifer
edges.
Dense undergrowth in regenerating Aspen stands
– ideal protection!
• Not found in Douglas Fir, stands of pure Aspen
• Low undergrowth is sparse – see approaching
predators
• Thickets of aspen stems usually restrict
movement of mammalian predators
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Other plants such as alder can provide similar
protection but…
As aspen stands mature they become less dense
and progressively poorer cover
Good Grouse Cover should include 3 age classes
within a few hundred meters
• Youngest age class – too immature to provide
cover
• Middle age class – (8-20 years) good cover
• Older age class – (20-40 years) produces
winter food
Tall conifers should be discouraged because
they provide perch sites for hawks and owls
Overall – aspen does not hide grouse from
predators but rather helps them see predators
and impede their access
c. Ring-necked Pheasants
Cultivated plants important component for pheasant
cover (cereal grains, hayfields etc)
WI – no pheasants in Co. < 20% cultivation
Increased 55-70%
Declined > 70%
South Dakota –
IL
Radio tracking data for hens and broods
1940’s crops rotated, ~ 80% brood survival
Available cover = corn, small grain, residual
cover, pasture, summer fallow, alfalfa (<5%),
shelterbelts,, and ditches
1970’s 50% brood survival
Utilized cover =
Alfalfa (13%), ditches, small grain fields
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Yg require diet high in
Row crops problematic
Protein
-Weed free
Satisfy this requirement if they can feed on
insects 3mm or larger
-Few insects
Found – oats, sweet clover, small grains
Afte WW II production
After
p od ction of row
o crops
c ops expanded
e panded
CRP has helped!
Conservation Reserve Program
Pays landowners to allow acres to lay fallow
and replanted with grasses etc.
Potential problem
p oblem on the horizon???
ho i on???
26