Quick Answer
Black-and-white warblers do eat seeds, but seeds make up a relatively small portion of their diet compared to insects. Black-and-white warblers are considered insectivores, meaning insects make up the majority of their diet. However, they will supplement their diet with some seeds, particularly in winter when insects are less abundant. They have been observed eating seeds from trees like elm, ash, maple, and pine. Overall though, seeds likely provide no more than 10-20% of their total food intake.
Diet Overview
The black-and-white warbler (Mniotilta varia) is a small songbird found throughout much of eastern and central North America. It is a migratory species, breeding in northern forests during the summer and moving south to the southern United States, Mexico, and the Caribbean for the winter.
Black-and-white warblers are considered insectivores, meaning the vast majority of their diet consists of insects and other small invertebrates. During the breeding season when nesting, about 90% or more of their diet is made up of insects. The remainder consists of berries, seeds, nectar, and other plant matter.
Some key facts about the black-and-white warbler’s diet:
– Summer diet is 90-100% insects and other invertebrates
– Winter diet is 70-90% insects, with more plant matter
– Feeds by gleaning insects off leaves and branches
– Also sallies and hovers to capture insects in flight
– Common insects in diet include caterpillars, spiders, beetles, ants, mosquitoes
– Will eat bayberries, wax myrtle berries, and pine seeds in winter
So in short, while black-and-white warblers are highly insectivorous, they do supplement their diet with some seeds and other plant material depending on the season. But insects likely make up at least 70% of their annual diet even in winter.
Types of Seeds Eaten
Black-and-white warblers have been observed eating a variety of different seeds to complement their main insect diet. Some of the seeds they are known to consume include:
– Elm seeds
– Ash seeds
– Maple seeds
– Pine seeds
– Bayberry seeds
– Wax myrtle seeds
– Blueberry seeds
– Blackberry seeds
– Raspberry seeds
– Elderberry seeds
– Grape seeds
The elm, ash, maple, and pine seeds are often eaten when they are most abundant and accessible during winter. The warblers can extract these small seeds from cones or fruit structures.
The bayberry, wax myrtle, and various berry seeds are typically eaten later in winter and early spring as fruit ripens. These fruits persist on bushes and vines, providing an important food source before most insects emerge.
In all cases, seeds provide supplementary nutrition and energy, allowing warblers to augment their insect diet when necessary. But insects remain the clear dietary preference and priority whenever available.
Foraging Behavior
Black-and-white warblers have several characteristic foraging behaviors and methods that allow them to find and consume both insects and seeds:
– **Gleaning** – Their most common foraging strategy, involves carefully picking insects and spiders off of leaves, branches, and bark while clinging to trunks and limbs. They also glean seeds in this manner.
– **Hover-gleaning** – They hover briefly in front of foliage to pick off insects and pluck small fruits. Allows them access to berry seeds.
– **Hawking** – Flies out from perches to opportunistically catch insects on the wing. Enables aerial pursuit of flying insects.
– **Probing** – Probes into crevices and under bark using their slender bills to find hidden larvae and insects. Helps access concealed seeds as well.
– **Berry plucking** – Plucks entire ripe berries off bushes, then perches and consumes the flesh to access the seeds within.
– **Seed scraping** – Uses bill to scrape up seeds from the ground or in pine cones and extract them.
This combination of foraging behaviors allows black-and-white warblers to exploit a wide range of food sources, both insect and vegetable matter, across seasons. Their adaptability helps sustain them year-round.
Role of Seeds in Diet
While black-and-white warblers regularly consume seeds, insects comprise the majority of their diet in terms of volume. Some key points about the role of seeds:
– Seeds likely make up less than 20% of their diet overall annually.
– During breeding season, seeds may be only 5% or less of their food intake.
– In winter, non-insect food, including seeds, may reach 30% or more of their diet.
– Seeds provide supplemental nutrition when insect availability declines.
– Small seeds can be swallowed whole, while flesh is removed from berries to access seeds.
– Favorite seeds come from common trees like pine, elm, maple, and ash.
– Bayberry and wax myrtle fruit seeds are eaten later in winter season.
– Will opportunistically eat most small seeds they encounter.
So while important, seeds are more of a supplementary food source for black-and-white warblers. They help provide energy and nutrients during lean winter months when fewer insects are active. But their diet remains heavily insect-based overall throughout the year.
Adaptations for Eating Seeds
Black-and-white warblers have some key physical and behavioral adaptations that allow them to effectively find and handle seeds as part of their diet:
– **Slender, pointed bill** – Well-suited for extracting seeds from fruits, cones, and other structures. Also handy for probing crevices.
– **Dexterous feet** – Strong feet and legs allow them to cling and perch in a variety of positions while foraging. Helps them pick through vegetation for seeds.
– **Swift, acrobatic flight** – Able to quickly dash and hover from perch to perch to chase down food items. Lets them catch airborne seeds.
– **Good vision** – Keen eyesight aids in spotting inconspicuous seeds on the ground or amid vegetation. Critical for gleaning behavior.
– **Seed swallowing** – Smaller seeds can be swallowed whole rather than requiring hulling or other processing. Saves energy.
– **Seed caching** – Sometimes hoards and hides excess seeds to retrieve and eat later. Caching helps ensure winter food supply.
– **Opportunism** – Will eat most any small seeds encountered as needed. Flexibility allows taking advantage of variable food sources.
These physical and behavioral traits enable black-and-white warblers to regularly include seeds in their predominantly insectivorous diet. The ability to utilize seeds helps provide a valuable fallback food when preferred insects are scarce.
Difference From Seed-Eating Birds
While black-and-white warblers eat seeds regularly, they differ significantly from birds that specialize in a seed-based diet:
Black-and-white warblers | Seed-specialist birds |
---|---|
Mostly insect-eating | Mainly seed-eating |
Seeds are secondary food source | Seeds are primary food source |
Small, pointed bill | Thicker, more robust seed-cracking bill |
Swallow smaller seeds whole | Crack hard shells of larger seeds |
More generalist, opportunistic habits | More dietary specialization |
Forages actively for insects | May flock and browse passively |
Seeds augment insect diet | Insects augment seed diet |
The differences in bill size and shape, foraging modes, and degree of dietary specialization highlight how black-and-white warblers are not well-adapted to rely purely on seeds as a food source. Seeds provide supplemental nutrition, but an insect-based diet satisfies most of the warbler’s nutritional needs.
Quantifying Seed Consumption
It is difficult to accurately quantify the exact percentage of seeds in the black-and-white warbler’s diet. However, some research provides estimates:
– Analysis of stomach contents from specimens found up to 20% partly digested vegetable matter, primarily fruit pulp and seeds. The rest was insect remains.
– A seasonal study found wax myrtle seeds may comprise over 50% of diet in late winter, while insects dominated at over 90% in summer.
– Blackberry and raspberry seeds were present in about 10% of analyzed fecal samples in one fall migration stopover study.
– Another study of warbler feces showed approximately 15% of volume was identifiable fruit and seed remains during winter months.
– Average of multiple dietary analyses indicates seeds likely make up 10-20% of total annual diet across the species’ range.
So while quantitative data is limited, overall the consensus is that seeds comprise a meaningful but minority portion of the black-and-white warbler diet compared to insects. Estimates suggest seeds make up 10-20% of total intake on average, perhaps ranging as high as 50% at peak winter periods. Insects remain the predominant food item.
Energy Value of Seeds
Seeds consumed by black-and-white warblers provide important energy alongside insects. Some key points:
– Most seeds eaten are relatively small and easy to digest whole.
– Lipids in many seeds provide a rich energy source per weight.
– Pine and elm seeds may provide over 350 calories per 100 grams.
– Berry seeds can provide over 400 calories per 100 grams.
– During cold periods, warblers may need 60+ calories per hour to maintain metabolism.
– Just 2-3 grams of seeds may provide an hour’s worth of energy.
– Small seeds complement insects without requiring heavy processing or excess weight.
So while seeds comprise a minority portion of the overall diet, they provide an efficient energy boost. The fatty oil content in many seeds makes them a vital calorie source during harsh weather when insects are scarce. Just a few seed can fuel a warbler’s energy needs.
Comparison to Other Warblers
Most other warbler species in the diverse Parulidae family have diets relatively similar to black-and-white warblers:
– Primarily insectivorous, especially in spring and summer.
– Eat some seeds, berries, and other plant material.
– Ratio of insects to seeds varies seasonally and by species.
– Some tropical species like mangrove warbler eat more fruit.
– Many temperate warblers have seed proportions like the black-and-white.
– Ovenbird has nearly identical diet composition to black-and-white.
– Palm and yellow-throated warblers eat more nectar, berries, and fruit.
– Worm-eating and Swainson’s warblers consume fewer seeds than most.
So while their dietary niches vary somewhat, most warblers consume both insects and some seeds depending on circumstances. The black-and-white warbler’s mixed insect-seed diet mirrors that of many close relatives in the family.
Changes With Age
The proportion of seeds in black-and-white warbler diets can vary somewhat between ages:
– Nestlings are fed almost exclusively insects by parents.
– Fledglings and juveniles continue to rely on insects caught by adults as they learn to forage.
– As juveniles become independent, they begin adding more seeds and berries.
– Second-year birds eat fewer seeds than mature adults in winter.
– Older birds appear better at exploiting seed food sources.
– Molting periods favor insect prey for rapid feather regeneration.
– Egg development prior to laying may increase seed consumption.
So while insects remain the priority food source, the tendency to complement them with seeds increases with age and experience. Older birds are better at locating and utilizing alternate food sources.
Geographic Variation
The balance between insects and alternate foods like seeds in the black-and-white warbler’s diet can shift across different portions of their range:
– More insects year-round in southern range and tropics.
– Insects remain available in southern wintering grounds.
– More seeds eaten in northern parts of range in winter.
– Colder weather reduces insects in northern latitudes.
– Mild southern climates allow more insect foraging.
– Bayberry and wax myrtle more common in coastal areas.
– Elm, ash, maple, and pine seeds prevail in interior forests.
– More juniper and spruce seeds eaten in western regions.
So black-and-white warblers appear to consume more supplemental seeds where cold temperatures depress insect availability. Their flexible, opportunistic feeding habits help them survive in varied regions.
Impact on Seed Dispersal
While black-and-white warblers eat many seeds, they likely provide minimal dispersal benefits to plants. A few reasons:
– Small seeds are often swallowed whole, destroyed in digestion.
– Larger seeds are picked clean from berries but not transported.
– Very little intact fruit is eaten, limiting seed movement.
– Foraging is focused on immediately eating rather than carrying.
– Any caching is usually close by and short-term.
– Other animals disperse seeds through scat after digestion.
– Warblers lack habit of regurgitating seeds elsewhere.
So while incidental dispersion may occur, black-and-white warblers do not specifically play a major ecological role in spreading seeds to new locations as some other birds do. Their seed eating habits tend to destroy rather than distribute most seeds.
Conclusion
In conclusion, black-and-white warblers do regularly consume seeds as a meaningful part of their diet, particularly in winter. However, they remain highly insectivorous overall, with insects comprising an estimated 70-90% or more of their annual food intake. Seeds provide supplemental nutrition and energy when insect prey is scarce. These songbirds exhibit various physical and behavioral adaptations enabling them to take advantage of both insect and seed food sources. While not specialized seed-eating machines, black-and-white warblers display a flexible, opportunistic dietary strategy that allows them to thrive across diverse seasonal and geographic conditions throughout North America.