ID | Nesting | Food Habits | Migration | Facts
Wood storks (Mycteria americana) use highly specialized tactile strategies to catch their food. The article examines the methods, habitats, conditions, and maneuvers used by the wood stork to catch small fish.
- What does the wood stork eat?
- Where does the wood stork feed?
- How do wood storks capture life prey?
- What is the diet of the wood stork?
- Do they have a preference for certain types of food?
- Morphological and behavioral adaptations
- Behavioral adaptations
- Types of prey in the diet of the wood stork
- What does it mean when wood storks congregate in one place?
- The wood stork feeds mainly on fish.
- They also include insects and small birds, and mammals.
- They use a tactile strategy to catch their prey.
- It can forage day and night.
- They feed in bodies of water 15 to 50 cm deep.
- The average size of their prey is between 4 and 8 cm long.
- It does not seem to prefer one type of prey but instead fishes for what is most available.
- They have special adaptations of form and behavior for their foraging mode.
What does the wood stork eat?
The wood stork feeds mainly on fish but also includes frogs, shrimp, large larvae, insects, and other invertebrates in its diet.
Opportunistically, it also feeds on nestlings of small birds, lizards, small lizards, and even mice if they can catch them.
Usually, it hunts (captures) live prey, but it will also eat dead fish.
Studies of the wood stork diet found algae and other plant parts in their stomachs. But these may have been accidentally ingested wrapped in live prey.
At fishing piers and similar locations, wood storks gather where fish are cleaned, waiting for scraps and discarded fish.
Wood storks have been observed eating cow dung in the field.
Where does the wood stork feed?
The wood stork feeds in bodies of water of almost any type, including lakeshores, wetlands, swamps, mangroves, wetlands, and irrigation canals.
The most important factor in foraging sites is adequate depth, relatively low density of submerged and emergent plants, and relatively high density of prey.
Field observations in the state of Florida in the USA indicate that storks find much of their food in the water at a depth of 0.5 to 1.6 feet.
Foraging studies of Wood Storks found that the ideal foraging habitat has a density of 12% submerged vegetation, 22% emergent vegetation, and 16% canopy cover.
How do wood storks capture life prey?
The Wood Stork is a tactile hunter. It uses its extremely sensitive beak and quick reactions to catch its prey.
The hunting strategy consists of submerging its open beak (the two mandibles) about 2.8 to 3.1 inches apart.
The submerged open beak is a trap. The wood stork lightly swings or keeps its beak stationary, waiting for the slightest movement of prey passing between its open beak to snap it shut to catch the prey quickly.
Feeling the vibration of the water caused by the movement of the prey and closing and catching the prey extremely quickly without any visual aids is an amazing adaptation.
Prey capture process
Keeping the bill submerged and depending on the density of the prey, the stork can remain static or walk while moving its head from side to side in a semicircle.
They can also zero in on spots where prey may be hiding.
They usually feed in mixed flocks that include herons and ibises or with other storks.
Other foraging strategies
Another alternative strategy is to use their vision to catch prey out of the water.
The use of vision is used by the wood stork opportunistically.
When the opportunity arises while foraging in or on the edge of the water, the stork catches frogs, lizards, small rodents, or baby birds purely by sight.
The wood stork feeds throughout the day and night. It does not depend on vision to catch prey. They forage for food based on when and where it is most productive to do so.
In areas where tidal creeks and freshwater wetlands were present, wood storks concentrated their foraging activities on tidal creeks during low tide. During high tide, they moved to freshwater wetlands.
The wood stork monitors the activities of other wading birds. As other birds gather around pools with fish, wood storks join in the feeding frenzy at any time of day.
Whether the water is clear or turbid does not deter wood storks from foraging in wetlands since they rely entirely on their sense of touch in the beak to catch their prey.
What is the diet of the wood stork?
The wood stork’s diet is varied and is basically influenced by the type of prey available in the places where it forages.
The stork uses only touch to capture its prey in the water and cannot choose the type of prey.
Based on the size of prey they typically catch, their beaks can select the size based on the stimulus it feels in the water to snap it shut.
According to a study of the diet of the wood stork in Venezuela, the diet changes with the seasons.
During the dry season (November-May) their diet consists almost exclusively of fish.
In the wet season (June-October), fish made up 50% of their diet, followed by 35% crustaceans and 15% insects and amphibians.
The prevailing environmental conditions and the extent to which they influence the proliferation of certain prey species are reflected in the diet of the wood stork.
Do they have a preference for certain types of food?
It can be said that the wood stork does not have a real preference for a type of prey but consumes the most abundant and easy-to-obtain prey in the bodies of water in which it hunts.
When it comes to aquatic animals that it catches using the tactile strategy, the wood stork does not discriminate between the prey that it catches with its beak because it does not see them but only reacts to the stimulus.
It is only by spending more time foraging in places that contain their favorite prey that a wood stork can show a preference for that particular prey type.
Studies on the diet of wood storks generally reveal that they eat mostly fish.
This does not necessarily reveal a preference for these, but rather that they are generally the most abundant prey in the places where it forages.
In times of food scarcity, storks can eat almost any kind of small prey they can catch, including small mammals and reptiles, large insects, snails, and more.
At fishing piers and similar places, wood storks gather where fish are cleaned, waiting for scraps and discarded fish.
What size of prey does the wood stork feed on?
In three localities where the diet of the wood stork was studied, it revealed a variation in the size of the prey.
The measurement of the consumed prey was of an average length of 1.6 inches in one study, 2.1 inches in the other, and 3.3 inches in the third.
It was not determined if the size of the prey responds to a preference or is simply the size of the most abundant prey and therefore easier to catch.
Morphological and behavioral adaptations
Bare head and neck
The wood stork has a neck and head without feathers to prevent them from getting dirty when feeding.
This is because it usually submerges its head in murky and even muddy waters, and the feathers on its head and neck would be constantly muddy.
Long conical and curved beak
Male wood storks have thicker and longer bills than females, perhaps to enable them to catch a wider range of prey sizes.
The wide base and somewhat curved narrow tip act as a pair of extremely sensitive pincers that close quickly at the slightest stimulus, trapping their prey.
Tarsal (leg) length
Males have longer tarsus (legs) than females, perhaps to enable breeding pairs to forage in places with a greater variety of water depths.
|Peak Length||tarsal length|
Use of legs to startle its prey
In situations where there are algae and aquatic plants, the stork plants the open beak and uses one leg to shake the aquatic plants around its beak to startle and dislodge the hidden prey. As prey escapes, it is likely to pass through the open beak and be caught by the stork.
Use of wings to startle prey
The wood stork spreads a wing rapidly over the water to create a shadow and startle and dislodge its prey into moving past the open beak. Sometimes uses both one leg and one wing together.
Types of prey in the diet of the wood stork
The studies by Ogden et al. 1976 and Ogden et al. 1978) revealed that Wood stork prey varies geographically in type and size.
As indicated above, in three localities where the diet of the wood stork was studied, the size of the prey varied in size.
In freshwater wetlands, storks consume a greater diversity of prey than in brackish water bodies.
These studies also determined that certain types of prey were consumed by storks more often than others.
Sunfish of the Centrarchidae family are among the most commonly consumed fish across studies in various locations.
While the sunfish can be considered a fundamental prey in the diet of the wood stork, it is not known exactly if a bird chooses it by preference or simply because it is a common species in the water bodies where they forage.
To give an example of the stork’s diet, a study in the state of Florida reported that the diet is composed of:
- Sunfish (Centrarchidae) 14% of individuals, 44% of biomass)
- Yellow catfish (Ictalurus natalis; 2%, 12%),
- Marsh killis (Fundulus confluentus; 18%, 11%),
- Flagfish (Jordanella floridae); 32%, 7%) and,
- Sailfin Molly (Poecilia latipinna); 20%, 11%
What does it mean when wood storks congregate in one place?
Wood Storks are gregarious birds that congregate for many reasons
If they are congregated out of the water, it means they are resting.
If they congregate in the water and actively forage, it means they have found a place where prey are concentrated, and it is a good place to feed.
These unusually good foraging spots are often ephemeral and occur when water levels have dropped, and fish and other aquatic animals are forced into confined spaces where they are easier for wood storks to catch.
- Bryan, Jr., A. L., M. C. Coulter, and C. J. Pennycuick. (1995). Foraging strategies and energetic costs of foraging flights by breeding Wood Storks. Condor 97:133-140.
- Depkin, F. C., M. C. Coulter, and Jr. Bryan, A. L. (1992). Food of nestling Wood Storks in east-central Georgia. Colonial Waterbirds 15:219-225.
- Gonzalez, J. A. (1997). Seasonal variation in the foraging ecology of the Wood Stork in the southern Llanos of Venezuela. Condor 99:671-680.
- Ogden, J.C., Kushlan, J.A. and Tilmant, J.T. (1976). Prey selectivity by the Wood Stork. Condor. 78: 324-330.
- Ogden, J.C., Kushlan, J.A. and Tilmant, J.T. (1978). The food habits and nesting success of Wood Storks in Everglades National Park, 1974. US Natl. Park Serv. Nat. Resour. Publ. 16.