how birds forage Flashcards
importance of nutrients
require both micro (vitamins, ions, amino acids) and macro (protein, carbohydrates, fats and water) nutrients
low in calcium: low clutch size, eggs fail to hatch, small brood size or abandoning nests
plant exudate eater
exudativores (e.g. sapsuckers)
all food eater
omnivores (e.g. crows, gulls)
animal flesh eater
carnivores (e.g. falcons, vultures)
fruit eaters
frugivores (e.g. hornbills, toucans)
grass eater
graminivores (e.g. geese, swans)
seed eater
granivores (e.g. finches, sparrows)
insect eater
insectivores (e.g. swallows, wrens)
fish eater
piscivores (e.g. cormorants, the Osprey [Pandion haliaetus])
niches
foraging niches are formed due to digestive machinery and specialised feeding behaviours.
reducing competition with others of the same species (or conspecifics) and with birds of other species (or heterospecifics).
specialised foraging charecteristics
bills, feet, digestive machine and behaviours specialised based on diet
specialised bill examples: flamingo
flamingo: suck water into mouth cavity and force it out side of the bill to collect macroinvertebrates on sieve elements and tounge onto bolus (all of food)
specialised bill examples: wader bills
example of niche separation
wetland birds consume different prey across the inter tidal zone. e.g. turn stones have a robust bill to turn stones. whimbrel have very long bills to insert into sand and very touch sensitive. oyster catchers reduce competition by nocturnally foraging. divided into two groups: hammer and pryers
birds and speciation Darwin’s finches
niche separation
adaptive radiation on the Galapagos islands.
wide range of food types by using bills to extract: termites, insect, blood, egg, fruit, pollen, leaves etc
specialised feet
feet are generally specialised for locomotion
however feet in Osprey are use for feeding and hunting fish bellow the water surface.
specialised leg
gymnogene (African Harrier-hawk)
can disarticulate the lower leg to fir into rocky cervices to hunt down reptiles.
specialised gut
there are varying degrees of specialisation of gut component
- crop: pouch for collecting food
- stomach: separate proventriculus (mechanical digestion) and gizzard (chemical digestion
- Caecum: specialised to extract as much energy as possible
- cloaca and vent
crop variation
chamber at top of digestive tract
large diversity across species.
meat eaters store less food because food is nutrient rich.
larger crop for less nutrient rich food or rapid consumption of food e.g. vultures.
pigeon crop is large possibly due to production of crop milk for young
the avian ‘stomach’
two separate structures.
glandular proventriculus secretes pepsin, HCl and mucus when food arrives from oesophagus.
muscular gizzard is avian equivalent of teeth. mechanical part of digestion to grind food.
gizzard is better developed in birds that eat hard items
caecum
voluminous to absent depending on species
developed in herbivores and omnivores
in closely related species (e.g. ducks) caeca developed in true herbivores and tiny in piscivores
over two-thirds of avian species have small or non-existent caeca
cloaca and vent
eggs made and faecal matter from same structure .
lips close over during egg laying so male sperm doesn’t mix with female waste product.
specialised behaviours
enables to occupy a specific niche e.g. skimming
- detects pray through touch
- upper mandible shuts when fish is detected
- instantaneous response
specialised behaviour: ambush
used by many birds of prey
e.g. Verreaux Eagle attacks Rock Hyrax when sunning on a rock
specialised behaviour: pursuit
e.g. sawbill duck pursue fish under water: swallow fish head first to avoid spines
serrated bill allows slippery fish to be caught
