Generally speaking, when I set out to explore nature I’m seeking the most pristine places I can find. These places are ancient – old growth forests with towering trees or virgin prairie on a bed of soil that has never been plowed. I like to see things the way they may have looked prior to European settlement, and transport myself to a distant, wilder time.
But if I chose to ignore those more disturbed habitats, I would be robbing myself of a wealth of beauty and diversity. In fact, there are many species that have evolved to take advantage of early successional communities created in the wake of some disturbance. Historically, these habitats may have formed by a variety of means. For example, when a massive tree falls in an old growth forest. Imagine ten tons of timber crashing to the earth. A tree like this could take out a swath of forest totaling a third of an acre or more, especially if it brings adjacent trees down with it. This new gap in the canopy would undergo the process of succession, responding much the way a fallow field does when it slowly reverts back to woodland.
The patch of disturbed land could increase significantly in the face of some natural disaster. A tornado could take out a swath of forest hundreds of feet wide and miles long. A severe hurricane could level acres of forest near the coast, and a wildfire could remove forest cover on the scale of thousands of acres.
Events like this are particularly important in the eastern United States, where much of the landscape was historically forested. There existed, however, a multitude of non-forested communities interspersed among the old growth timber. These included prairie inclusions, barrens, and similar habitats that were kept open by a variety of factors including soil conditions, grazing by American bison, and regular wildfire. If one of these communities went too long without the introduction of some natural disturbance, it would begin to revert back to forest through the process of succession.
Today, however, the U.S. is far removed from the natural eden it was just a few hundred years ago. That is not to say, however, that suitable habitat for these disturbance dependent species no longer exists. Take the Prairie Warbler (Setophaga discolor), for example. The “Prairie” in its name is misleading, as this is not a species of prairie or grassland habitats, but rather one of those early successional habitats described above. They breed throughout much of the eastern U.S., from Maine to east Texas. Here I most frequently observe them in regenerating pine stands 5 to 10 years after harvest.
A male Prairie Warbler sings in defense of his territory.
These sites undergo succession much in the way a forest would following some natural clearing event. First a variety of grasses and forbs will invade. Soon after the pines will sprout. Before long, however, the trees will grow to tall, the canopy will close, and the habitat will no longer be suitable for the Prairie Warbler.
The ephemeral nature of these ever changing habitats means that species like the Prairie Warbler do not have a reliable territory to return to each year, and must seek out new breeding sites once their old territories are no longer suitable. I speculate that, given a certain element of unpredictability with their preferred habitat, Prairie Warblers, and other disturbance-dependent bird species likely experience local cycles of “boom and bust”, potentially increasing in numbers following large disturbance events, and decreasing as the disturbed areas reach later successional stages.
Another species found in these disturbed habitats is the Yellow-breasted Chat (Icteria virens). The chat was once considered our largest warbler species, but recent research indicates that is more closely related to blackbirds, and it has been placed in its own family (Icteriidae). Chats are well known for their loud, varied songs which consist of a variety of raucous warbles, whistles, rattles, and more. The males perform elaborate courtship displays on the wing, slowly descending in choreographed fashion.
Yellow-breasted Chats can be found throughout much of the contiguous U.S and portions of Mexico and southern Canada. They are less specific in their habitat preference than prairie warblers, and can be found in a variety of disturbed habitats. They are easy to hear, but difficult to see, often skulking low in dense vegetation.
Unlike the chat, the Painted Buntings (Passerina ciris) maintain a visible presence in their territory, frequently singing from the highest perches available. These sparrow-sized songbirds are considered by many to be among the most beautiful birds in the country, and they certainly leave a lasting impression on those fortunate enough to encounter them. I’ll always remember the first one I saw birding with my mom.
The Painted Bunting breeds in the south-central states, along the Atlantic coast in the southeast, and portions of northern Mexico. They can be found in a variety of disturbed habitats, as long as there is some shrub or small tree component.
Though it lacks the varied color scheme of its cousin the Painted Bunting, the Indigo Bunting (Passerina cyanea) is no less striking. With its metallic cyan plumage, this is one of my favorite birds to observe in the spring and summer here in the Pineywoods.
Indigo Buntings breed throughout much of the eastern U.S. with a few isolated populations in the southeast. Though I most often associate this species with disturbed areas, I also frequently observe them in high quality habitats such as mature longleaf pine savannas. This is not entirely surprising, however, as these once vast longleaf pine forests depend on regular disturbance to maintain an open understory and rich herbaceous layer.
Another disturbance loving blue beauty is the Blue Grosbeak (Passerina caerulea). They are quite similar to the Indigos, but can be differentiated by their heavier bill and chestnut wing bars. To me, the blue of the grosbeak is more cobalt, and the bunting more cyan.
One might encounter Blue Grosbeaks across the southern and central United States and northern Mexico. They can be found in a variety of shrubby habitats. In the eastern U.S. this usually means areas that have undergone some recent or continuing disturbance, however further west this can include mature desert scrub and woodlands.
The image below is of a regenerating pine plantation where I observed Prairie Warblers, Yellow-breasted Chats, Painted Buntings, Indigo Buntings, and Blue Grosbeaks. Also present in the area were White-eyed Vireos, Northern Cardinals, and Northern Mockingbirds. In East Texas, Northern Bobwhites may also utilize habitats like this, though they have all but disappeared from the Pineywoods.
When a disturbed habitat occurs in close proximity to water, additional bird species may be encountered. The Eastern Kingbird (Tyrannus tyrannus), for example, inhabits disturbed areas such as marshes, shrublands, forest edge, and riparian areas, and are generally closely associated with water. Kingbirds are so-named for the voracity with which they defend their territories against intruders of all shapes and sizes.
Perhaps our most familiar denizen of wet, disturbed habitats is the Common Yellowthroat – the little masked crusader that announces its presence to the world with its trademark wichity-wichity-wichity song. Though they can be found away from water, yellowthroats are most commonly associated with weedy or scrubby habitats on the margins of marshes, ponds, and streams.
The Common Yellowthroat is a member of the Warbler family (Parulidae). They are widespread in the U.S., Canada, and portions of Mexico. We are lucky enough to have a few birds present year round in the southern half of the Pineywoods and on the Upper Texas Coast.
In modern times, areas of significant disturbance have increased dramatically as old growth forest has been cleared to make way for pasture, agriculture, development, and managed timber. It is clear that having some early and mid successional areas on the landscape is beneficial to biodiversity on a macro scale, however it becomes a concern when this occurs over a large scale, which is too often the case. They key, like in so many things in life, is moderation. Fortunately, modern forestry practices have improved dramatically, and programs like the Sustainable Forestry Initiative promote managing the landscape as a patchwork of successional stages.
Despite an increased abundance of disturbed areas across the U.S., many of these bird species remain uncommon and some are declining. The problem is, disturbance in and of itself is not enough. The nature, and method of the disturbance is important. Areas that undergo intensive herbicide or pesticide use, for example, are not suitable breeding sites for birds. Additionally, areas that are too heavily managed, where woody vegetation is not allowed to reach appropriate heights are similarly unproductive for all but the most generalist of species.
As lovers of biodiversity, it is important that we support and promote best management practices in land disturbing activities, so that we can simultaneously provide a sustainable resource and enhance local biodiversity.