Yards as important habitat for urban birds

We often think of the term land management as describing large-scale activities that are carried out by groups such as government bodies and NGOs–the creation of dams, for example, or the restoration of forests and the reintroduction of species. However, studies are increasingly making it clear that individual landowners–even those whose land only comprises a few square meters of lawn stretching out to the sidewalk–can have significant impacts on local wildlife. This is particularly true when those individuals live in proximity to each other, so that their many small patches of land add up to a larger mosaic of potential habitat.

This has been highlighted by a recent study conducted in residential neighborhoods in Chicago, Illinois–one of the biggest cities in the United States. Focusing on homes located near some of the city’s nearly 70,000 acres of forest preserves, a research team from the University of Illinois explored whether the richness of local bird communities might be impacted by characteristics of yards located within one kilometer of the forest edge. They also investigated which yard features were most influential, and whether the impacts of these traits depended on the birds’ natural history characteristics.

Some of Chicago's many suburbs. Image courtesy of
Some of Chicago’s many suburbs. Image courtesy of Charles Tilford.

The research team visited 25 different sites around the city; all study areas were adjacent to preserves found along the Chicago River, the DesPlaines River, and their tributaries. In each study site, an observer conducted two bird surveys during the breeding season–the time of year when richness tends to be highest because both migrants and non-migrants are utilizing the habitat. A total of 36 species were recorded during the study; the mean number per site was 16, though some areas had as few as 11 and others had as many as 21. Twenty of the observed species were migratory, 12 were permanent residents, and 4 were non-natives–including the house sparrow, which was one of the four most common species (the others being American robins, American goldfinches, and northern cardinals).

Across all the neighborhoods, over 900 residents responded to a questionnaire designed to assess whether their yards contained wildlife resources (including features such as plants with berries, bird feeders, and brush piles); the survey also collected data on backyard activities. Of the 11 wildlife resources listed in the questionnaire, the average yard had about six. Over half of respondents (55%) reported having vegetation with fruit or berries, and 34% had a bird feeder; of this latter group, 81% indicated that the feeders were filled for at least a few days each month.

American goldfinches, enjoying seeds at one of the 11 wildlife resources considered in this study–a bird feeder. Image courtesy of Wikimedia.

Six yard characteristics seemed to be particularly important for birds. The one with the biggest impact was trees–both the presence of trees in general and a high ratio of evergreen to deciduous species. These two features probably had such a positive effect on bird richness because a tall canopy and increased structural complexity offer more places in the habitat for roosting, nesting, hiding, and foraging. The other important vegetative features were plants that provide fruits and berries–both of which offer a natural source of high-energy food to foraging birds. Features with negative impacts included, unsurprisingly, the presence of insecticides, dogs, and outdoor cats–the last of which can reduce richness both by acting as a deterrent and through direct predation. The effect of outdoor pets was particularly noticeable on migratory birds, which were found on the transects with the lowest numbers of both cats and dogs; these birds also clearly preferred areas with more trees (especially evergreens), fruits and berries, and an overall higher number of wildlife resources.

To assess larger-scale habitat patterns within each neighborhood and across the landscape as a whole, the team put together a second dataset using remote sensing techniques. Within neighborhoods, they looked at percent canopy cover and vegetation within 50 m of the transect; across the landscape, they measured amount of open space, percent canopy cover, and distance to nearest river. These variables were important for assessing the relative impacts of yards, neighborhoods, and landscapes on avian richness. The researchers accomplished this by building seven different mathematical models–one each describing yard, neighborhood, and landscape values; three with the different pairs of those terms; and then a final model with all three terms combined. They then looked to see which model best explained the number of native birds found in the habitat.

Evergreen trees, and the presence of trees in general, had a positive effect on avian richness. Image courtesy of Overlook Circle.

The best model was the one that incorporated only the data on yards–values that had been calculated by collecting survey responses, extrapolating to fill in the blanks that were left by non-responders, and then creating aggregate scores representing, cumulatively, all the private landowner space within the neighborhood. Overall, yard characteristics explained 42.3% of all variance in bird richness–a remarkably high value for an ecological study, given the vast number of other environmental features (e.g., soil characteristics, local fluctuations in humidity and rainfall, disturbance events, windspeed, temperature, and so on…) that have to go un-measured for logistical reasons.

Taken together, these findings clearly show that the design and management of individual yards can have noticeable impacts on native birds in residential areas–probably not just in Chicago, but likely in other urban environments as well. In addition to suggesting that landscape managers and conservationists should remember to include yard habitat when drawing up wildlife preservation plans, the study also reveals that even minor decisions by individual landowners can have significant implications for local birds.

There are lots of easy ways to make a yard more appealing to wildlife. Many bird-friendly features are low-maintenance and aesthetically pleasing. Image courtesy of Pittsburgher in UK.

This should not be seen as intimidating, but, rather, empowering. Working individually or together–via homeowners’ associations, conservation initiatives, or municipal schemes, for example–individuals can turn their plots into wildlife refuges. Results from the current study suggest that planting evergreens and fruiting species might be particularly useful, though specific avian needs will likely vary from one ecosystem to the next. The authors do, however, have one word of warning to those who decide to make their yards more bird-friendly: There are many documented side effects of increased exposure to wildlife, including better health, an improved quality of life, an increasing awareness of biodiversity, and a continuing enthusiasm for conservation efforts.

Belaire, J. Amy et al. 2014. Having our yards and sharing them too: the collective effects of yards on native bird species in an urban landscapeEcological Applications 24(8):2132-2143.

A little disturbance could be a good thing

When you want to maximize biodiversity in a habitat, you should aim to minimize human disturbance there–right? That’s certainly the concept at the heart of many conservation initiatives, and is a tenet espoused by the majority of wildlife preservationists. There is, however, a growing literature documenting the ways in which anthropogenic influences may currently give, or have previously have given, certain communities a biodiversity boost.

This has prompted a number of researchers to seek out systems where human disturbances have occurred in a repetitive way over thousands of years. In these places, wildlife would have had the chance not only to adapt to anthropogenic influences, but actually thrive under human disturbance regimes. Exactly this scenario is described by M. Kat Anderson in her 2005 book Tending the Wild, which focuses on the ways that Native Americans interacted with the California wilderness prior to the arrival of the Europeans. A similar discussion can be found in a new review paper by the University of Montana’s Stephen Siebert and Jill Belsky, who describe the ecological impacts of swidden in Bhutan.

The kingdom of Bhutan. Image courtesy of Merriam-Webster.

Swidden is a slash-and-burn technique used to open up forested areas for agricultural activity. Although swidden had disappeared from Bhutan by 1997, it was previously widespread throughout the country; as many as 200 million swidden farmers are thought to continue the practice throughout the remainder of the eastern Himalayas. Two types of swidden were common: tseri, in which crops were grown for 1-2 years before the field was left to grow over with trees and shrubs for 2-8 years; and pangshing, in which crops were grown for 2-3 years before the field was left to grow over with grass for 6-20 years. Tseri was typically used to produce maize, millet, rice, and vegetables, and could be found at lower altitudes; pangshing was better for wheat, buckwheat, barley, and greens, and was used at higher altitudes. Another major difference between the two techniques is the amount of disturbance required to prepare and tend fields. During tseri, disturbance was minimal because plowing was infrequent and crop maintenance was performed by hand; during pangshing, the top 6 cm of soil were removed, dried, and burned.

If you think these techniques sound fairly invasive, then you’re not alone. The Bhutanese government, wanting to preserve the amazing biodiversity that can be found in its country, passed the Bhutan Forestry Act in 1969. This spelled the beginning of the end for swidden, which many people viewed as antiquated, dangerous, and ecologically unsound. However, it may have provided a service to a variety of wildlife species that needed more sunlight than thick tree canopy allowed into the forest, but also more cover than was provided by completely open meadows. In other words, swidden may have acted as an intermediate disturbance–something more intense than, say, the toppling of a single disease-ridden tree, but less intense than the felling of a whole hillside’s worth of trees during a mudslide.

A patchwork habitat resulting from swidden. Here you can see forests in multiple stages of succession, fallow fields, and current growth of rice crops in a swidden landscape in Yunnan Province. Image courtesy of Wikimedia Commons.

Swidden farmers left in their wake a variety of patches of different ages–and, therefore, at different stages of succession. The entire landscape would have been a mosaic of areas with closed canopies, open canopies, and everything in between. These conditions would have provided habitat for shade-lovers, sun-lovers, shy species that prefer to stay hidden in the undergrowth, and bolder ones not afraid to venture out into the open. From a single habitat–forest–the swidden farmers were creating multiple types of new habitat, each with its own niches. This, in turn, would have facilitated biological heterogeneity–probably not just in terms of the number and type of species present, but also the roles of those species in the local food web, and the functions that the entire ecosystem could collectively perform.

It’s difficult to know for sure, because swidden vanished in Bhutan over 30 years ago, and wasn’t well quantified before that time. As a result, the authors can’t make a clear before-and-after comparison that would allow them to see whether biodiversity levels have dropped since the discontinuation of swidden. (With proper permission, however, it would be possible to investigate this experimentally.) In other countries where swidden is still used, researchers have noted that fallow plots provide habitat for different types of species than those found in the adjacent forest; as a result, the swidden-and-forest patchwork is more biodiverse than tracts of uninterrupted forest alone. We also know that fallow-type habitats are used by sambar deer, wild pigs, and gaur–potential prey items for tigers. This suggests that swidden could facilitate the coexistence of predators and humans even in disturbed, densely populated areas.

Ironically, the curtailing of swidden has not led to a uniform decrease in disturbance across Bhutan’s forests, some of which are shown above. Some areas are protected from human activities, but other areas have been subjected to intense logging efforts, which may, over the long run, be more ecologically harmful than traditional slash-and-burn practices. Image courtesy of Rashid Faridi.

The best way to know this for sure is to explore the possibility using rigorous scientific methods. That’s one of the reasons the authors have used Bhutan as a case study. They suggest that the country missed a trick by outlawing swidden without collecting more data and thinking about the situation more critically. Their hope is that conservationists and policy makers will do better elsewhere–not just in places with swidden practitioners, but in any area where humans continue to use traditional land management techniques that have been employed for thousands, if not tens of thousands, of years.

Although we tend to think of humans as separate from nature, we do, in fact, have a long history of interacting with species, communities, ecosystems, and entire landscapes; removing us from the equation may have unintended consequences. The authors advise us to keep that in mind, and to consider the possibility that a little bit of disturbance might actually be a good thing–both for humans and for wildlife.

Stephen F. Siebert and Jill M. Belsky. 2014. Historic livelihoods and land uses as ecological disturbances and their role in enhancing biodiversity: an example from BhutanBiological Conservation 177:82-89.


Neolithic farming at the northern frontier

The high northern latitudes have been inhabited by humans since the end of the last Ice Age, approximately 12,000 years ago. Conditions that far north, where the Earth’s circumference is about half that at the Equator, are extreme. On the 60th parallel north, for example, the sun is visible for just under 19 hours on the summer solstice, but only for about 6 hours during the winter solstice. Although temperatures may soar above 30°C in exceptional years, the average daily mean is closer to a chilly 6°C (depending on your exact location along the parallel), with record lows in the -30’s–and, of course, you can expect at least a meter of snow in the winter. In other words, this is not an easy place to live even now, with our modern conveniences; it’s hard to imagine what it must have been like for the region’s earliest settlers, who eked out a living by hunting, fishing, and gathering.

A sampling of Neolithic tools. Image courtesy of Wikipedia Commons.

At some point, these intrepid northern colonizers began farming, making use of techniques originally developed in the Fertile Crescent 11,000 years ago. Above the 60th parallel, however, farmers were more vulnerable to climatic stochasticity; archaeologists have uncovered settlements that appear to have been abandoned after the environment became too hostile. In northwestern Europe, exposure to the Gulf Stream allowed Early Neolithic people to initiate farming economies that last to this day. Elsewhere on the continent, however–in Finland, for example–the low average temperature, persistent snow cover, and not-infrequent appearance of summertime snow and ice combined to diminish vegetation periods and make farming a more challenging endeavor.

Until recently, it has been difficult to pinpoint exactly when early Finnish settlers achieved domestication, since there is very little evidence from prehistoric times; the region’s acidic soils took care of the majority of useful artifacts long ago. However, those same conditions are favorable for the preservation of biomolecules harvested from the few remaining pieces of ancient ceramic cooking vessels. Analysis of these fragments–via techniques such as high-temperature gas chromatography, mass spectrometry, and ion monitoring–allows researchers to determine the composition and structure of the molecules, and to look for pre-identified biomarkers. Cumulatively, these characteristics can be used to determine whether the vessels are saturated with aquatic fats (indicating storage of fish and other seafood), terrestrial fats (from species hunted on land), and dairy fats (from domesticated livestock).

Examples of pottery from the Corded Ware period; these pieces date to ca. 2500 BC. Image courtesy of Wikipedia.

Out of a collection of 70 prehistoric fragments unearthed at sites across southern Finland, an interdisciplinary team of researchers was recently able to isolate 19 that were suitable for just such an analysis. The pottery was representative of a range of prehistoric eras, from the Comb Ware period (ca. 6000-4300 years ago) through the Corded Ware (ca. 4800-4100 years ago) and Kiukainen Ware (ca. 4400-3500 years ago) periods, all the way to the Early Iron Age (ca. 2500-1600 years ago).

The earliest molecular samples (dated to approximately 3900-3300 BC) were predominantly marine in origin, indicating a heavy reliance on fishing; the ceramic fragments themselves may have come from vessels used for cooking, storage, or even transport. On the other hand, residues from pottery shards dating to approximately 2500 BC were from terrestrial ruminants. Though they could have come from either wild or domesticated stock, there was evidence of milk fat–indicating that the settlers had begun farming and were now heavily dependent on land animals despite their relative proximity to the coastline. Interestingly, the final Neolithic samples, dating to the Kiukainen Ware period, contained a mixture of terrestrial and aquatic compounds, suggesting that local climate changes may have required a diversification in subsistence techniques. By the Early Iron Age (approximately 1200-500 BC), however, agricultural intensification seems to have allowed population growth and a renewed focus on farming; pottery fragments from this time yielded only dairy fats.

Iron Age pottery (in this case, from Orkney). Image courtesy of Rita Roberts.

Although these patterns may initially seem relevant only to the small portion of researchers specializing in ancient Finnish history, they actually offer some interesting insights to the rest of us, too. For one thing, these archaeological results map nicely onto spatial patterns showing the prevalence of the lactase persistence (LP) genotype–which confers the ability to continue digesting dairy products well into adulthood. While this may be a fairly common characteristic throughout much of the developed West, it is either rare or lacking in parts of the world without a strong tradition of dairy farming. This correlation helps validate the molecular results, and also can be used to draw conclusions about gene flow in Europe. There is a SW-NE gradient of LP allele frequency in Finland, suggesting several separate waves of immigration over the past 6000 years. Further, low LP frequencies in some parts of the eastern Baltic indicate that this region may have acted as a “genetic refuge” for populations who continued to lead a hunter-fisher-forager lifestyle rather than pursuing farming. Pretty amazing that all of this ancient history can be inferred from gene patterns analyzed thousands of years after the fact.

Another interesting implication of the findings is related to what they reveal about how early humans dealt with their difficult and variable habitat. The analyses suggest that animal domestication occurred in southern Finland much earlier than previously thought (ca. 2500 BC), but that use of aquatic resources lasted much longer, post-domestication, than it did in other places settled by Neolithic peoples. In fact, Late Corded Ware Finns appear to have responded to their changing environment by vacillating between hunting/gathering, farming, and some mixture of the two as required. This sort of flexibility is probably one of the major reasons why early settlers were able to maintain populations in such marginal habitat.

Miina Äkkijyrkkä is an artist and dairy farming expert who combined her two passions during a project making cow sculptures from recycled car parts. Images courtesy of the artist, via Inhabit.

The authors of the study write that, even today, “conventional” farming in this part of the world is not for the faint-hearted. A changing climate may prompt humans to push their boundaries ever northwards, but conditions above the 60th parallel will likely always be challenging. If we hope to utilize this “frontier zone” in order to increase food production and make use of the available land, we will probably have to follow our predecessors’ example and demonstrate a willingness to adapt.

Cramp, Lucy J.E. et al. 2014. Neolithic dairy farming at the extreme of agriculture in northern Europe. Proceedings of the Royal Society B 281:20140819.