Grassland Habitat – A “Sensitive” Subject

Grassland birds are naturally adapted to native grasslands and prairie ecosystems throughout much of North America. While these are of the highest quality and “ideal” nesting habitats, they are now extremely rare and are fading quickly. As our grasslands fade, our resident bird species are forced to overcome and adapt. Nowadays, surrogate grasslands (hayfields, small grain farms, and fallow pastures) provide most of the important nesting habitat for our grassland-nesting birds. Strip habitats (utility right of ways, highway corridors, and field borders) that are maintained in an early successional state also offer valuable nesting and foraging habitats for several species.

Grassland birds rely upon herbaceous cover for natural foraging and nesting behavior. There are many nuances to the individual cover requirements amongst the different species. Some species are area-sensitive and require vast acreages of unbroken grassland habitat for nesting. Others are edge-sensitive, and shy away from fragmented landscapes to which they perceive as threats to them and their nests. As I have touched on in previous posts, the steps that we take as land practitioners that are meant to invite some species can be deterrents to others. What I hope to provide here is a CliffsNotes version of a much broader and highly complicated subject. Who would have thought that grass could be so dense (pun intended)?

Variables to Consider When Developing a Plan

Ask any neighborhood “Randy” who spends hundreds of dollars annually maintaining his chemically laden green turf, and you quickly find out that not all “grass” is created equal. This also applies to native and non-native grasses. The density and height, as well as surrounding land usages all influence the assemblage of birds that occur within a given area. Generally speaking, large, undisturbed plots of grassland habitat is more desirable and provides the most diverse grouping of grassland bird species. The expansive area allows birds to fulfill most of their courtship, nesting, brood-rearing, feeding, and leisure behavior with the added security requirements they prefer during nesting season. In addition, the larger habitat will also provide winter and migratory cover for many species.

Adequate cover of undisturbed grassland is among the greatest factors affecting grassland bird populations, and the continued loss and conversion of grassland breeding and nesting habitat remains the largest threat to the future of many of our grassland birds. Preserving existing and properly designing new grassland communities will help to maintain current species that are in decline. With proper management, local grassland bird populations will increase, and populations of other wildlife species will benefit from these same habitats.

Since hundreds or thousands of fallow acres aren’t lying in wait, it is up to us to think outside of the box and look for ways to improvise and work with what we do have available. Like pocket prairies for pollinators, the same approach can be taken with several of our grassland and early successional bird species.

Small Victories – Winning with “Edge-Sensitive” Species

As we have already established, most grassland species prefer large acreages of unfragmented habitat. Fragmentation in respect to land use is defined as the existence of a number of spatially separate plots of land which are managed singly. Typically, these smaller, isolated plots with heavily wooded edges have limited potential to support grassland birds. Interspersion (diversify in intervals) of various types of grasslands will maximize habitat quality for some species, however, interspersion of grassland habitat with woody vegetation or other land usage that would fragment the area can be detrimental to others.

Edge-sensitive grassland birds are those with the lowest tolerance for fragmented habitats and are typically grassland dependent when it comes to nesting behavior. When grasslands are fragmented, many grassland birds are subjected to nest predation from crows, blue jays, skunks, raccoons, opossums, foxes, and you guessed it, domestic cats.

Grassland birds that are edge-sensitive include the Upland Sandpiper (Bartramia longicauda), Bobolink (Dolichonyx oryzivorus), and Savannah (Passerculus sandwichensis) and Henslow’s (Centronyx henslowii) sparrows. The Eastern Meadowlark (Sturnella magna) and Grasshopper Sparrow (Ammodramus savannarumare) are moderately sensitive to habitat fragmentation. Grassland birds that are tolerant to an abundance of edge include the Northern Bobwhite (Colinus virginianus), Red-winged Blackbird (Agelaius phoeniceus), American Goldfinch (Spinus tristis), Vesper (Pooecetes gramineus), Field (Spizella pusilla), and Song (Melospiza melodia) sparrows, Dickcissel (Spiza americana), and Common Yellowthroat (Geothlypis trichas).

On landscapes where intensive row crop agriculture is the dominant land use, we can design strip habitats which are extremely important not only for grassland birds but for other wildlife as well. Grassland bird assemblages will vary with the physical habitat structure and seasonal disturbance patterns (i.e., crop planting & harvesting).

Size Matters – “Area-Sensitive” Species

Many “area-sensitive” grassland bird species require a certain amount of habitat to be present, usually in contiguous patches or unbroken blocks, before individuals will use a given site. Estimates of the minimum size of suitable nesting and breeding habitat required to support breeding populations of grassland birds vary greatly amongst species. If your goal is to support a wide array of grassland-nesting bird species within a given area, then contiguous grassland blocks of at least 500 acres will provide the greatest potential. However, smaller grassland blocks provide viable habitat patches for many grassland bird species. A general rule may be to maximize the size and interconnectedness of grassland habitat patches available, while conducting management actions that maximize the habitat quality within the smaller patches.

Area-sensitive species prefer treeless areas because trees provide shelter for predators. A familiar nemesis of the suburbs, the Brown-headed Cowbird (Molothrus ater) is also common in the countryside, parasitizing nests along wooded edges. Grassland birds that nest in larger blocks of grasslands that are at greater distances from trees see a higher percentage of fledglings take wing. Some area-sensitive species are obligate and depend upon certain plants to successfully function within a given grassland ecosystem.

To confuse the matter even further, the total area requirements vary from species to species and can also vary amongst geographical regions and the landscapes characteristics. For example, the size of habitat patches needed to attract individuals of a given species may be smaller in landscapes that contain a larger amount of grassland and open habitats nearby. 

Management Considerations

When possible, it’s beneficial to take a community or overall landscape approach to your designing, implementation, and management plans. If you own a small grassland, it helps to determine what the surrounding landscapes look like. If other grasslands or agricultural areas are present, then it may be feasible for you to manage for grassland birds despite having smaller acreage to work with. However, if your grassland is surrounded by forest, you may want to reconsider other goals.

 The following guidelines will not necessarily guarantee the presence or absence of certain species. Restoring and enhancing existing grasslands, and reducing fragmentation are hands down the best management options for grassland birds. Whenever you increase the size of a grassland, you increase the likelihood that grassland birds will benefit.

 Some things to consider when managing for grassland birds within your landscape:

 -          To manage for edge-sensitive species, you will need a minimum of 20 acres. Moderately sensitive species need between 10 and 20 acres, and tolerant species need less than 10 acres. These estimates are the minimum amounts these species need to survive. Again, the larger the grassland, the better.

 -          Avoid fragmenting existing grassland areas. If hiking trails are to be developed, restrict activities to the edges of the area. Avoid maintaining hedgerows that may serve as predator perches.

 -          If large tracts of grassland restorations are not possible, establish several patches. Try to incorporate adjacent grassy habitats such as pastures, hayfields, and grassy waterways as connections between the grassland patches or as non-wooded, open edges.

-          Maintain succession in its earliest stages by managing for grasses and sparse shrubs. Manipulations such as burning, and mowing are required to maintain grass productivity typically within three-to-five-year intervals.

 -          Manipulate your grasslands in 1/3 to 1/4 annual rotations. If several fields are maintained, it is better to manipulate one entire field, rather than a portion of each field per rotation. This will reduce fragmentation of your grasslands. However, if you have only one field, do not manipulate the entire field at once as it will displace the grassland birds. If possible, allow some sections to lie idle each year.

 -          Use prescribed burns to increase the productivity of warm season grasses. Conduct burns in early spring (March or April) or late fall (October or November).

 -          Mow grasslands and hayfields between July 15 and August 31. This will reduce the chance of destroying bird nests and discourages the invasion of problem grass species that move in after late season mowing. Cutting height should be about 6 inches.

 -          If you use the grassland for grazing, permit only light activity by livestock, and leave some areas un-grazed by utilizing rotational grazing practices. Do not graze below 6 inches. Moderate grazing may actually benefit additional wildlife species.

 -          Plant or maintain several types of grasslands in your area. A mosaic of tall and short grass fields will provide habitat diversity. If planting only one area, a mixture of warm season grasses and forbs is best. Cool season grasses mixed with legumes is another option.

 -          Create 100 ft. shrub buffers next to forest edges and human habitations to reduce the harsh edge. An alternative to planting shrubs along the edge of a forest is to allow the fire to burn slowly into the woods so as to create a "feathered" edge. Local fire authorities should always be contacted prior to a burn to discuss permits and/or restrictions.

 -          Chemical treatments of grasslands can also be used to control woody plants. Herbicides can be used to control any type of undesirable plants in your grassland, from woody plants to grasses and weeds. Correct application is important. Damage to non-target vegetation or wildlife is possible if you do not follow the labels instructions. Reducing or eliminating the use of insecticides will provide more valuable insect food for birds.

Hate the Game, Not the Sparrow

My intrigue for the House Sparrow (Passer domesticus) was born, err… hatched from sheer opportunity. Several years back, I repurposed a cheap guitar that was missing a few strings and hung it up under our covered deck to serve as a decorative accent. Ella broke out her paints and created a nice, folky design that flowed well with the rest of the décor on our deck. As it would turn out, the missing B and G strings allotted for just enough clearance for a mated pair of adult sparrows to limbo their way through its small, 1” opening. All things considered, I can’t say that I blame them for picking this spot!

Also out of happenstance, the guitar was hung just outside our kitchen window. The hours spent washing dishes and prepping meals, afforded us the luxury of having a front row seat as the pair began constructing their nest within the guitar’s sound hole in early February. Tirelessly the male would fly off, scouring the neighborhood, in search of nesting materials to bring back and hand off to his maiden whom would remain perched on the guitar’s neck, patiently awaiting his return.

Well, it wasn’t soon thereafter that we were greeted with the constant chirping of their first brood whom fledged the nest, ahem… guitar, roughly 2 weeks later. Well, that was cute now, wasn’t it? Kudos to the ‘rents! Great job guys!!

But immediately he was back at it. Gathering nesting materials, bringing them back to the female who now, instead of being perched on the guitar’s neck, spent her days dragging debris and grasses from the sound hole and flying off with it. I also noticed that this time the male, who was now arriving at times when the female was away from the nest, would take the nesting materials inside and fly out a short time later empty handed. It would seem that he too was now playing a role in nest construction. A few weeks later, chirping. A few weeks later, fuzzy headed young perched all over the rails of our deck being taught the curriculum of what it takes to be a proper bird. Again… so cute. What an experience. Nature, I see you!

Then, more nesting material was being gathered. You see where this is going? Wash, rinse, repeat. What began in early spring, greeted May, and was now steamrolling its way through early summer. We were well on our way to amassing a small army of LBJ’s (Little Brown Jobs as sparrows are often referred to) on the deck of our suburban/rural-ish home.

This behavior, this fecundity, is what has accounted for the House sparrow’s, an “invasive” species, exemplary success in setting up permanent residency here and just about every other continent on the globe! It should be stated that this original family of sparrows has went on to remain with this guitar every year for the past 5 years. The typical lifespan of House sparrows in the wild is 4 - 5 years, so I am optimistic that being monogamous and mating for life, the same OG’s are still roaming the wilds of my back yard today! One would think that the unorthodox location of the guitar, the constant foot traffic it receives from large dogs and humans, all would be a deterrent, but as history has told us with this species, it is the primary reason for its success.

On August 21st, 1886 a short time after the House sparrow was introduced into the United States, Dr. W.H. Bergtold, of Buffalo, N.Y. observed:

As regards the number of broods and young reared by a pair of Sparrows in a year, I wish to make a statement and put forth a theory that I have never seen advanced before. I have repeatedly examined nests of this bird containing nearly full-fledged young, two or three young in more or less advanced stages of development, and several eggs of various degrees of incubation, some being nearly fresh, while others were about to break through. I gather from these facts that the Sparrow, at least in some cases, lays and continues to lay a succession of eggs so long as the weather is not too cold; and as the young attain a sufficient amount of strength they are expelled from the nest. Assuming such to be the case we can easily see how much of the incubation work is taken from the parents and thrown on the young, who by their bodily heat and proximity, readily take up such duties (quite unintentionally, I imagine), and also how much work can be given to the proper maintenance of a generous food supply for both the old and young.

This constant stream of outpouring Sparrows accounts for the rapid manner in which this species multiplies.

Albeit an astute observation by Dr. Bergtold, the House sparrow was new to science at the time and not a lot was known about it. Although such cases as witnessed by Dr. Bergtold may occur, it certainly is not the rule, as it is certain that in most cases all the eggs are laid before any are hatched, and all the young leave the nest at about the same time as I have witnessed myself on multiple occasions.

Moreover, it is not necessary to resort to such a theory to account for the rapidity with which the sparrow increases. It is a hardy, prolific, and aggressive little bird, possessed of much intelligence and more then ordinary cunning. It is domestic and gregarious in habit and takes advantage of the protection afforded by its proximity to man, thus escaping nearly all enemies which typically prey upon our native birds.

Its fecundity is amazing, and is reflected in the table I have created below. Of course, the actual increase of the House sparrow is a small fraction of the total shown in the table. But, if we were to reduce the number of young produced per pair to just six annually, assuming that half are male and half are female, factor a lifespan of five years for all, then we would expect to see an increase of 33,614 birds from the first mated pair during this five-year period. There has; however, been a twist in recent years. Duh, duh, duhhhh…

Despite thriving during the hundred plus years since introduction into the rest of the world, House sparrows have begun declining rapidly in parts of North America, Australia, and their native Europe where they are now red listed as a species of high conservation concern. Across the whole of the United Kingdom and much of Northwestern Europe, sparrow populations have declined by more than 60 percent from the early 1970s to the late 1990s. Some of the reasons cited are loss of nesting habitat, diminished food items i.e., weed seed and insects, pollution caused by industrial growth, and natural predation. The latter, I would argue is a key influence as I have had evidence of predation strewn through my backyard on countless occasions. Although neighborhood cats permitted to run at will has always been a concern when it comes to our native bird species, local hawk populations have skyrocketed in recent years and can now be seen in almost any city/town, at any time of the day, perched prominently on a power line or radio tower, scouting its next meal.

Yes, I will agree that the males will sometimes “flex” too hard and too often when trying to defend their territory. They also sing incessantly during springtime when trying to garner the attention of a mate. I have even felt the hit in the wallet as the little army of sparrows I quickly amass in my yard consumes way more than their fair share of bird seed. Despite all of this, I have grown rather fond of these bold little birds and their willingness to share their social dynamic with me.

Most of us live hectic lives that don’t allocate as much time as we would like to spend outdoors in nature. Given the chance, the House sparrow will provide a front row seat to the natural world that is always present right outside your window. All we have to do is sit back and take it in!