Diet & Foraging Ciconiiformes Herons, bitterns & egrets, [L. ciconia = stork] Herons, bitterns & egrets, ibises, spoonbills & storks 3 families, 116 species Snowy Egret

Herons, egrets and bitterns Ardeidae Herons, egrets and bitterns 65 species Cattle Egret

Great Blue Heron

Great Egret

Black-crowned Night Heron

Boat-billed Heron

Threskiornithidae Ibises and spoonbills 32 species African Spoonbill

White Ibis

Glossy Ibis

Ciconiidae Storks 19 species Saddlebill Stork

White Stork

Diet & Foraging Shape Life History Diet types Avoiding competition Foraging efficiency

Generalists v Specialists Stenophagous – highly restricted to a very limited number of food items Euryphagous – eats a wide variety of foods

Lesser Flamingo eats only filamentous blue-green algae, Spirulina. Thus monophagus with distribution limited by that of the algae

Ruffed Grouse, eats 300 different plant species and 100 different animal species in a single year

Animal-based diets are superior to plant-based diets in Nutrient balance Energy density Digestibility

Food type. Availability of. % of families primarily. energy (%) Food type Availability of % of families primarily energy (%) or regularly consuming food type Nectar 97-99 5 Meat & fish 66-88 32 Seeds 80 22 Insects 50-80 67 Other invertebrates 50-80 18 Fruit 5-80 33 Green plants, buds 32 9

Vertebrate prey Highly digestible, basically protein & fat <2% carbohydrate Nutritionally complete 50-80% water, many carnivores don’t need to drink Proventriculus dominate

Insects Adult insects are high in protein (50-70% dry matter) and lipid (5-35% dry matter), with low levels of nonchitin carbohydrate. The amino acid balance of insects is almost as good as vertebrate prey and much better than plants. Calcium is low, so egg-laying females often consume snail shells, bone fragments or egg shells. Chitin, which is relatively indigestible, ranges from 18-60%. Long, narrow beak. Larger proventriculus and smaller gizzard than granivorous or herbivorous species.

Seeds Highest nutrient density of any plant part High starch, sometimes high fat, moderate to low in protein Low in calcium Amino acid balance poor, many seed-eaters eat insects and feed young insects Small seeds = high foraging time Handling time high in species which hull seeds

Frugivores Rank second to insects but only 11% of families are primarily fruit eaters most of which live in the tropics Nutrient-dense v nutrient-dilute fruit

Nutrient-dense fruit Bayberry, mistletoe, dates, avocado Large amounts of lipid (10-70%) Moderate protein (5-20%) Less water and sugar Slow passage aids digestion

Nutrient-dilute fruit High in indigestible skin and seeds Pulp high in water & sugar, low in protein Complete digestion gives too much energy too little protein

Skimming strategy Simple guts Fast passage = poor digestive efficiency Maximize AA intake, limit sugar uptake Cedar Waxwings process meal in 25 min

Nectarivores Large crops Short intestines & weak gizzard Nectar mostly dilute sugar-water (20-25%) low in amino acids All nectarivores eat insects to get AAs

Crimson-breasted flowerpecker, purple honeycreeper

facultative frugivory or facultative insectivory Very few species consume a single food category throughout their adult life; e.g., obligate herbivore or obligate planktonivore facultative frugivory or facultative insectivory

Seasonality

Avoiding competition

Close Relatives Avoid Competition by Character displacement Ecological segregation

Character displacement

Ecological Segregation Blue Tit – small branches Marsh Tit – large branches Great Tit – ground

Niche Partitioning in North American Wood Warblers Robert MacArthur

Cape May Warbler

Yellow-rumped Warbler

Black-throated Green Warbler

Blackburnian Warbler

Bay-breasted Warbler

Are birds sensitive to the net energy profit of their foraging effort? Foraging Efficiency Are birds sensitive to the net energy profit of their foraging effort? Profit = energy gain – energy cost = J/sec foraging time

White Wagtail Foraging – John Krebs Page 210 Gill