It is generally accepted that eating a balanced diet, especially one that contains plenty of fruits and vegetables, is one of the key requirements for good health. Most folks are therefore mindful of what they eat. But sometimes it is easy to forget about all the seeds we, as humans, consume. Sure, we sometimes snack on sunflower seeds, or enjoy sesame seeds on our burgers. But when we take a closer look at the list of the world’s most common foods, we can then appreciate the fact that breads (made from the seeds of wheat, rye, and other grains), the large variety of beans and peas, corn (and corn products), rice, and many others all come from seeds, and we can then see how important they are to humans on a local and global scale.
The same concept is true for many wild bird species, and the seasonal availability of seeds to many birds is truly a matter of survival, not just preference. What makes seeds so valuable as a food resource? We all know that seeds are propagules for the reproduction of flowering and some non-flowering plants. The dormant plant embryo is obviously contained inside, but the parent plant also packs the seed with the energy reserves the embryo will need to germinate, often in the absence of sunlight. Depending on the species and nature of their germination and dispersal, seeds may be small if they are likely to germinate quickly on top of the soil or other exposed substrate, or if likely to be buried under deeper soil or debris, they may be large and chocked full of carbohydrates, fats, and other essential nutrients to allow the growing embryo to successfully sprout, develop, and even build a few leaves, before those nutrient reserves run out. After that, a seedling can generally make its own food using photosynthesis. All of these stored nutrients are what makes seeds such important food resources to humans and wildlife.
For wild birds, summer in the fields and open woodlands is a time of plenty. During the warmer months, insects and other arthropods and invertebrates abound. Even seed-eating birds like Northern cardinals, Indigo buntings, Chipping sparrows, Eastern towhees, and American goldfinches can easily catch them. Virtually all passerine bird species prey heavily on these nutritious arthropod food sources to kick-start fat reserves and pay the heavy toll required to lay and incubate eggs and raise offspring. However, when the summer ends and the cool winds of autumn begin to blow, insects become scarce and most of the bird species that stay for the winter must rely on other forms of nutrition. Since birds are warm-blooded and can thermoregulate just like we can, they can usually make it ok as long as they have enough food. Seeds are the resources that provide many species the energy needed to survive the frigid winter nights. It is common knowledge among wildlife managers that Northern bobwhite quail, Wild turkey, and Mourning doves seasonally target grain crops like wheat, corn, and millets. However, these traditional commercial agricultural crop plants, as well as the many trees and shrubs that produce seeds and fruits that are utilized by wildlife will not be the focus of this discussion. Instead, in this article we will concentrate on herbaceous seed-producing plants that are most important to native birds, including Northern bobwhite quail.
Which seed is most important to a wild bird? The answer is, of course, a seed worth eating that is available at the time the bird needs it. This may seem to be a strange and over-simplified answer to such a broad question, but consider the plight of a typical bobwhite or sparrow. Wild birds must locate their food each and every day. Sometimes all they find to be available are a few high quality (large and/or highly nutritious) seeds. At other times and locations, they may find abundant stands of low or medium quality seed-producing plant communities. Some backyard birds (like Carolina chickadees and Purple finches) would argue that proso millet and black oil sunflower seeds are the best choice, mainly because they can just belly up to a bird feeder that never seems to run out. Some managers may spread milo or wheat along bare roadsides throughout the fall and winter. In that scenario those seed are probably readily available and are easy to fill up on and therefore they may be the best choice. Sometimes seeds can be abundant, and of high quality, yet inaccessible due to the thatch of sod-forming grasses like Bahia, Dallis, Bermuda, or Fescue. So, the tradeoff of availability (seasonal abundance) at the time the bird needs to eat, and quality (size, and fat and protein content) of the seed creates a kind of matrix that will determine what is the best seed for a bird. This matrix is further complicated by forage habits, physiological adaptations, and range of individual bird species, as well as harshness of conditions, etc. For example, most seed-eating birds have gizzards that help them grind seeds and break their hard coats. Some species however have more efficient seed-digesting systems than others. Also, while almost all seed-eating birds have thick stubby beaks for cracking seeds, some smaller species obviously might have weaker mandibles and less leverage, a force that is required to handle larger seeds. Therefore, different species of birds will prefer and focus on different species of herbaceous plant seeds. Rodents and insects often compete for seed resources too so when a seed falls to the ground the clock often starts ticking for its availability.
Just as different birds have different physiological adaptations, wild birds also use different strategies for accessing seeds. “Niche partitioning” allows multiple seed-eating species to occupy and forage in the same habitats. In an eastern Texas study by Allaire and Fisher (1975), three species of sparrows (Bachman’s sparrow, Field sparrow, and Chipping sparrow) were observed to have significantly different foraging traits. Bachman’s sparrows were observed to forage almost exclusively for cast seed on the ground, while the other two species often located and consumed seeds from low broadleaf vegetation and grasses that had not yet been cast. Field sparrows frequently perched on grasses and small stems containing uncast seeds or seed heads, riding them down to the ground where they accessed and consumed them. This study also noted that Chipping sparrows were much more gregarious than the other two species and tended to forage for seed in winter flocks of as many as 50 individuals. American goldfinches are also known to forage in small flocks and they also commonly perch, and pluck seeds the ripened seeds of thistles and sunflowers (Helianthus spp.) from the standing plant.
We have established that different birds prefer and utilize different species of seeds, but there are certainly some herbaceous plants that are “better” than others for quail and other birds. Generally speaking, legumes are any member of the pea family and they are known for their high protein content (in the leaf and foliage as well as in their seed). Deer and other wildlife managers know that it is not uncommon for peas and other legumes to contain upwards of 30% crude protein. Some plants are great habitat components because they tend to serve as good warm-season insect habitat and therefore they make a lot of arthropod biomass for birds and other wildlife to eat. Others are important for the seeds and fruits they offer. Herbaceous legumes can often provide the best of both worlds. Depending on the specific location and the local soil characteristics, legumes are often the most important group of plants when it comes to high quality seed production for bobwhite quail and some other ground-foraging birds. Most legumes produce relatively large seeds. They are also significant because they have a hard durable seed coat which allows them to persist through the fall and winter months, even into spring when many other seeds have degraded. One of the most popular legumes among quail managers is partridge pea (Chamaecrista fasciculata and C. nictitans). These two similar species are easy to identify by their small bi-pinnately compound leaves and abundant showy yellow flowers that form in late summer. Although they do not contain nectar, partridge pea flowers produce abundant pollen resources, and they are sought after and pollenated by bumblebees, honeybees, and other long-tongued bees. From August through October the plants form and set abundant hard black seeds that are highly prized by bobwhites and other seed-eating songbirds. Partridge pea stands create model foraging conditions in summer for brood-rearing bobwhites, as well as in the fall when they have dropped their seeds. The stems are far enough apart that bare, open ground can be accessed while still having plenty of cover overhead. Access to bare ground and the seeds that lie there is critical to bobwhites and other weak scratching birds. Although partridge pea can be readily established by planting (typically during Feb-March), it can usually be encouraged by soil disturbance and established from the existing seedbank by fall disking or frequent prescribed burning. Besides bobwhites, partridge pea seeds are also commonly consumed by Mourning doves.
Partridge pea is certainly popular, but other native legumes such as bush-clovers (Lespedeza spp.) and tick-trefoils (Desmodium spp.) are also important producers of highly nutritious seeds. Native lespedezas (including creeping; L. repens, trailing; L. procumbens, roundhead; L. capitata, slender; L. virginica, and hairy; L. hirta) grow in open woodlands, along roadsides, forest edges, and in old-fields. Hairy and roundhead lespedezas (typically having cream-colored flowers), as well as slender lespedeza (clusters of lavender pink flowers), grow upright to a height of about four to five feet, while the other two species (both producing lavender pink or purple flowers) have running habits and grow low to the ground. All five species produce hard dark seeds that are preferred by seed-eating birds. Asian varieties of lespedeza (like bicolor; L. bicolor, and sericea; L. cuneata) have been used traditionally in southern quail management but these species can become invasive in open, burned habitats, and are therefore now commonly controlled with herbicide by landowners and wildlife managers. Bobwhites and many songbirds readily consume the hard black seeds of bicolor, and the seed is of good quality, but this species can form dense monoculture stands that do not carry fire well. If extensive enough, a bicolor stand can suppress native plants that provide brood-rearing and nesting habitats. Unfortunately, the same habitat management activities (especially burning to increase sunlight reaching the forest floor) that promote abundant native herbaceous ground cover can also spread bicolor. This plant is becoming especially invasive in forests with dry clay soils.
Tick-trefoils (also sometimes called beggarweeds) are also excellent seed producers in the late summer and into the fall and winter months. This group of plants look very similar to the lespedezas (both typically have leaves with 3 leaflets) but the tick-trefoils produce segmented fruits called loments. Each small pea-like seed is encapsulated in a seed pod that has tiny hooklets covering the outside. Each sticky segment of the loment can break apart, and as any quail hunter knows very well, easily hitchhike in an animal’s fur or on a person’s field jacket or pants. Wild Desmodium seeds are typically one of the most important foods for bobwhites in the Southeast. Some common species include stiff (D. obtusum), smooth (D. laevigatum), and prostrate (D. rotundifolium) tick-trefoils. These varieties are fairly common in open woodlands and along rights of way where there is at least some available sunlight. All three have pink or purple flowers in late summer and drop seeds in fall and early winter.
Other “miscellaneous legumes” such as pencil flower (Stylosanthes biflora) and dollarleaf (Rhynchosia reniformis) typically occur scattered along roadsides, edges, and in open woods, and both have yellow flowers. Pencil flower is found across the Southeast from Texas into to the New England states, while dollarleaf is typically found only in the sandy soils of the coastal plain. Wild bean (Strophostyles umbellata) occurs across the eastern US and it is a vine-like species that produces a few long black bean pods per plant. Mourning doves and bobwhites prefer the fuzzy bean seeds that are released when the beans ripen and dry. Spurred butterfly peas (Centrosema virginianum) also produce trailing vines that build and cast good quality seeds. All of these miscellaneous legumes are readily consumed by quail and other songbirds, but rarely do they occur in dense stands and therefore their availability limits their importance in many southeastern forests. Vetch (Viscia spp.) on the other hand can form dense stands, especially in fallowed croplands and it can be semi-important for bobwhite and other songbirds in some cases. Indigo bunting for example, is known to focus on vetch seed when it is available. However, wild vetch produces seeds much earlier in the season (typically in summer) than many of the aforementioned legumes, and it often grows amongst grasses and other lush summer vegetation that render the cast seeds inaccessible. Bobwhites supposedly browse the foliage of vetch in summer.
Moving on from legumes, many broadleaf forbs are also good seed-producers. Ragweed, for example, is an herbaceous (sometimes semi-woody) annual that cannot be left out of this discussion. There are over a dozen species of ragweed in North America. In the Southeast however, common ragweed (Ambrosia artemesiifolia) and giant ragweed (A. trifida); which can grow to twelve feet tall) are the most common and most important varieties. Ragweed stands can make good cover and both species produce abundant seed that is high in fat and protein. Like many legumes, these seeds can persist on the plant or on top of the soil well into the winter, making them a very valuable source of nutrition. Several sparrow species, dark-eyed juncos, and bobwhites are known to utilize ragweed during late fall and into the winter. Just like partridge pea, a dense stand of ragweed, often produces ideal conditions underneath its canopy for both bugging in summer and foraging for seed in fall and winter. Birds can forage in relative safety while being concealed from hawks and other avian predators. Many bobwhite managers hold ragweed as the absolute most important plant on their property. It is hard to disagree with that considering the various benefits to quail and upland seed-eating birds. Established ragweed stands can be maintained periodically (ragweed is a pioneering annual and therefore it needs frequent disturbance) with growing season prescribed fire, herbicide release applications, and rotational heavy disking. But what if ragweed is completely absent on a property? Establishment can also be as simple as fall or summer disking in some situations where the seedbank holds the species (especially in fields or on lands with a history of disturbance or farming over the past few decades). In other cases, ragweed seed may be absent, and planting commercially available seed may be the best option of building ragweed stands over time.
Wooly croton (Croton capitatus) is another notable seed-producer for Mourning doves and Common ground doves. It usually occurs as scattered individual plants, but it can also sometimes form stands. Some managers plant it for doves or other gamebirds, and I have seen strong preference by bobwhites for feeding in dense stands of planted croton. On one particular property a covey or two of bobwhites would repeatedly take refuge in a large croton stand and would be there almost every time I went into the stand. After kneeling down to investigate the conditions beneath the croton canopy I could clearly see why. The numerous brown croton seeds were everywhere on the bare ground, and there was essentially a completely closed vegetative canopy about 2 ft tall over the buffet of seeds. There was simply no need for the birds to leave it. Foraging on the open ground while visually searching for seeds can be dangerous for a small bird. Sharp-shinned and Cooper’s hawks are always on the lookout for them. In a Texas study by Worthington et. al. (2004) Northern cardinals preferred the seeds of croton as well. As far as other forbs go, seeds of goldenrods (Solidago spp.), native sunflowers (Helianthus spp.) asters (Aster spp., Symphiotrichum spp.), and many other broad-leaf herbs are consumed to varying degrees by native wild birds. Smartweed (Polygonum spp.) is another very important forb. White-throated sparrows rely on it heavily in fall and winter.
When it comes to edible seeds, bunchgrasses are typically less important than some of the previously mentioned plant families. While bunchgrasses do provide important nesting and foraging cover and serve as fine fuels for periodic fire (which, in turn, is important for maintaining early seral conditions), they typically offer little in the way of nutritious seeds. Henslow’s sparrows are known to sometimes eat wiregrass (Aristida sp.) seed but they are known to avoid other bunchgrass seeds like little bluestem (DiMiceli, 2006). Other grasses, however, can be very important seed producers. In the 1975 Texas study mentioned earlier, grass seeds were the most popular fall and winter food resource among all three target sparrow species. Crabgrasses (Digitaria spp.), panic grasses (Panicum spp. and Dichanthelium spp.) and foxtails (Setaria spp.) ranked among the most consumed seeds, with Bachman’s sparrow focusing on crabgrasses, while Chipping and Field sparrows shared a similar fall and winter diet of mainly panic grasses and foxtail millets. Grass seeds are typically very important to sparrows in fall and winter. Judd (1901) recorded the winter diet of Song sparrows across Canada and 26 states as containing mainly the seeds of grasses (24% grass seeds; most of which was Digitaria spp.). Martin et al. (1951) noted that seeds of foxtail grasses (along with smartweed; Polygonum spp., and ragweed) were the main winter foods in Song sparrows across the Northeast and in the Pacific regions. Crown grass (Paspalum spp.) is a different variety of grass that is consumed by bobwhite quail, but it is not a primary food in most situations.
Sedges (Cyperaceae family) are sometimes overlooked by wildlife managers, but they can serve as valuable cover and as sources of seeds, especially in wet open habitats. Nutrushes (Scleria spp.), which are in the sedge family, were found to be very important for Henslow’s sparrows in southern Louisiana (DiMiceli, 2006). Beaksedges (Rhynchospora spp.) and Muhly grass (Muhlenbergia sp.) were also commonly utilized in open pine savannahs and wet pine flatwood communities by those Henslow’s sparrows. Nutrushes, as well as Carex spp., provide seeds and cover for other wetland sparrow species including Savannah sparrows and Swamp sparrows.
In summary, native herbaceous plant seeds are a critical food resource for Northern bobwhites and many other North American wild birds, especially in the non-breeding seasons. Different birds have different niches and can therefore utilize seeds of many different plant species on the same landscape, and across a diverse range of habitats. Legumes and forbs are known to be especially important for bobwhites, whereas several species of forbs and grasses are favored by some sparrows. However, availability and seasonality will dictate which seeds are preferred, and which are actually consumed, by an individual bird on a given day.
References
Allaire, P. N., and C. D. Fisher. “Feeding Ecology of Three Resident Sympatric Sparrows in Eastern Texas.” The Auk, vol. 92, no. 2, American Ornithological Society, 1975, pp. 260–69, https://doi.org/10.2307/4084555
DiMiceli, J. K. 2006. Winter diet, seed preferences and foraging behavior of Henslow’s Sparrows (Ammodramus henslowii) in southeastern Louisiana. Master’s Thesis: https://digitalcommons.lsu.edu/gradschool_theses
Judd, S. D. 1901. The relation of sparrows to agriculture. U.S. Dep. Agric. Bull. no. 15.
Martin, A. C., H. S. Zim, and A. L. Nelson (1951). American Wildlife and Plants: A Guide to Wildlife Food Habits: The Use of Trees, Shrubs, Weeds, and Herbs by Birds and Mammals of the United States. Dover Publications Inc, New York, NY, USA.
O’Leske, D. L., Robel, R. J., and K. E Kemp. (1996). Consumption of Hairy Vetch, Sweet Clover, and Foxtail Seeds by Three Granivorous Bird Species. Transactions of the Kansas Academy of Science (1903-), 99(3/4), 146–151. https://doi.org/10.2307/3627987
Somveille, M., Rodrigues, A. and A. Manica. 2018. Energy efficiency drives the global seasonal distribution of birds. Nature Ecology & Evolution, Volume 2, pages 962–969.
Worthington, D. W., R. M. Whiting, Jr. and J. G., Dickson. 2004. Feeding Habits of Songbirds in East Texas Clearcuts During Winter. Texas J. Sci. 56(4):427-440.
Yarrow, G. 2009. Bobwhite Quail Biology and Management. Clemson University Extension Fact Sheet. https://www.landcan.org/pdfs/bobwhiteQuailBiology.pdf