Category Archives: nature

Behavioral plasticity in pumas may be a boon to smaller predators

In many areas where human activities have resulted in the decline of top predators, smaller carnivores–species such as foxes, raccoons, and rats–benefit from no longer being prey items, as well as from the decreased competition over resources in the habitat. Until recently, this “mesopredator release” was thought to occur only when apex carnivores–things like tigers, wolves, and wild dogs–had been locally extirpated, leaving vacancies in the food web that their smaller brethren could step in to fill. However, a new study on pumas suggests that mesopredator release could happen by another mechanism altogether: changes to the feeding behaviors of top predators.

Scientists from the University of California’s Santa Cruz campus discovered this by collaring and tracking 30 pumas between 2008 and 2013. Every four hours, the collars collected information on the location of the cats, and the resulting data points were plotted on a map. Where points were clustered, the researchers suspected a kill site and went to investigate for signs of predation. For logistical reasons, it wasn’t possible to visit all potential kill sites, so, to overcome this difficulty, the researchers created computer models into which they could plug variables associated with confirmed kills–factors such as how long the pumas stayed there, whether they were there at night or during the day, and how far the cats strayed from the area. These traits were then used to determine the likelihood that the putative kill sites were, in fact, the location of a puma kill.

Close-up of a puma. Image courtesy of Bas Lammers.

What made this information so interesting was that the hunting data could be plotted on maps showing human housing densities. The study area, the Santa Cruz Mountains of California’s Central Coast region, encompassed a range of anthropogenic sites, from rural areas with fewer than 1 house per hectare, to suburban locations with nearly 10. Along this disturbance gradient, the hunting behavior of pumas–specifically, female pumas–varied. As housing density increased, these huntresses spent up to 42% less time consuming prey. Their site fidelity was 36% lower, and the farthest distance traveled from the kill site was up to 31% higher.

To make sense of these numbers, it is necessary to understand a bit about the feeding strategies of apex predators like pumas. They can expend quite a lot of energy while stalking, chasing, and taking down prey. These calories can be replaced by eating whatever has just been caught, but big carnivores don’t have large enough stomachs to accommodate many of their prey items–things like deer, for example–in a single sitting; instead, the hunters have to drag the body somewhere safe and revisit it until they’ve had their fill.

Mountain lion eating. Image courtesy of
Mountain lion eating. Image courtesy of Benjamint444

The current results suggest that this is a much trickier prospect for female pumas living in anthropogenically disturbed areas. These cats weren’t able to spend as much time eating, and seemed to roam much farther from where they had stashed their kills; the low site fidelity values suggest that many of the animals left the area altogether. Given these figures, it is, perhaps, unsurprising that some of the hunters in these areas were estimated to kill as many as 20 more deer per year than pumas living in the most rural areas. These data suggest that predators in high-human-density areas are having to target more prey because they are starting over after being interrupted while feeding on their previous kills.

Males seem to get off easy because they already spend less time at kills; they are adapted to eat quickly and head back out to patrol the borders of the large territories they defend. The size of their home ranges (up to 170 square km) also means that if humans become disruptive in one area, the cats can withdraw to more natural spots for a bit of privacy. Given that male territories only have approximately 16 houses per square km, this isn’t too hard to do. Female pumas, however, don’t have as much flexibility; their territories are smaller (as small as 51 square km), and may comprise only exurban or suburban land; their home ranges sometimes contain as many as 27 houses per square km.

Mountain lion kitten about to be outfitted with a tracking device. Image courtesy of the NPS.

Female pumas must also take care of kittens, a responsibility that requires them to bring down even more prey. To adequately feed their young, mothers may need to make more than a dozen additional kills per year. For females living in high-human-density areas, where disruptions to feeding sessions are already inflating hunting rates, this could be untenable; these mothers could begin to lose weight, suffer poor health, or even be driven to abandon their young. Indeed, the researchers provided anecdotal evidence of the last of these possibilities, suggesting that puma populations in human-disturbed sites may only be viable so long as they are replenished by young pumas migrating in from more rural areas.

While this is bad news for pumas, it is potentially great news for mesopredators. Female pumas are leaving a larger number of kills for longer periods of time, giving scavengers more of an opportunity to swoop in and have a free meal. This increased source of nutrition could allow the ecosystem to sustain larger populations of middle predators and give individual animals the energy boost they need to live longer and/or procreate more successfully. Beneficiaries could include a range of species, from raccoons and foxes all the way up to coyotes. Additional work would need to be conducted to explore whether these species are commoner or more successful in more human-dense areas, and, if so, whether those patterns can be directly attributed to puma behavior rather than other characteristics of anthropogenic environments.

Image courtesy of Tony Hisgett.

As the authors point out, “behavioral responses are often overlooked as ecosystem drivers in modified systems, overshadowed by population declines and extirpations.” Their current study, however, shows that behavioral flexibility can allow species to persist in modified environments–but that this persistence may come at a cost, and have widespread implications for the habitat.

Source material: Smith, Justine A., Yiwei Wang, and Christopher C. Wilmers. 2015. Top carnivores increase their kill rates on prey as a response to human-induced fear. Proceedings B. 282: 20142711.


Pink birds in the red: conservation of flamingos

Flamingos have been described as both the most charismatic of all bird species and one of the most recognizable. While some might argue with the former claim, few would challenge the latter. Thanks to their bright, cheerful plumage, hefty, crooked bill, and spindly legs—one often held aloft in that iconic balanced position—flamingos can easily be identified by people around the world.

Though the birds are often referred to generically as ‘pink flamingos’, there are actually six different species: American (also called Caribbean, Cuban, or rosy; Phoenicopterus ruber); greater (Phoenicopterus roseus); Chilean (previously also known as red-kneed; Phoenicopterus chilensus); lesser (Phoeniconaias minor); Andean (Phoenicoparrus andinus); and puna, or James (Phoenicoparrus jamesi). Evidence of ancient flamingo ancestors has been unearthed in both Australia and Antarctica. Today, however, free-living flamingos are only found in North America (American), South America (Andean, Chilean, and puna), Europe (greater), Africa (lesser and greater), and Asia (lesser and greater).

All extant flamingos require habitats linked by a single common feature: shallow saline pools. These can be fed by underwater springs, ocean waves, rivers, and—perhaps most importantly—rain. Water in flamingo habitats is often saltier than the sea and may contain compounds that are toxic to many species if consumed in large doses. This seemingly inhospitable habitat is perfect for brine shrimp, small molluscs, diatoms, and cyanobacteria—all potential prey items for flamingos. Because so few animals can tolerate extremely salty environments or figure out how to collect the tiny particles of food available there, flamingos have been able to exploit this niche virtually uncontested.

Lesser flamingo
Lesser flamingo

It can be difficult to census flamingos because they tend to live in such remote, impenetrable wetlands. To make matters worse, the birds have a habit of relocating frequently and unexpectedly, which means that researchers may show up to known flamingo haunts only to discover they have just been vacated in favour of grounds that are tens or even hundreds of kilometres away. Available data indicate that global population sizes vary widely from one species to the next; the least abundant species is the Andean, with only 34,000 individuals, while the most common is the lesser, with as many 3.2 million birds.

These numbers, however, belie the complexity of flamingos’ conservation situations. All three South American species are threatened by anthropogenic disturbance and habitat destruction; while Andeans are considered ‘vulnerable’, punas (100,000 individuals) and Chileans (200,000 individuals) are listed as ‘near threatened’. This is also the status of lesser flamingos, 90% of which breed at a single site that is threatened by industrial developers. Only the American (330,000) and greater (680,000) flamingos are listed as being of ‘least conservation concern’.

American flamingo. Image courtesy of Martin Pettitt

It’s not entirely surprising that so many flamingo species should be under threat; the pink birds have a long history of unpleasant interactions with humans. Phoenician traders are reported to have transported flamingos to Cornwall, where the birds were passed off as phoenixes and traded for tin. Flamingos were kept in captivity by the Egyptians and some groups of Native Americans, and flamingo meat was enjoyed people of several cultures—though perhaps most of all by the Romans, who have recorded for posterity recipes for properly preparing flamingo tongues for delectation. Even today, the birds are sport-hunted or poached across their range. The illegal slaughter of dozens of adult birds caused an uproar in India in early 2012 because it occurred when hundreds of preeminent ornithologists and birdwatchers were visiting the Gujarat for the Global Bird Watcher’s Conference.

Flamingos are also known to be negatively impacted by nearly all forms of human traffic, including planes, boats, and all-terrain vehicles. Both the noise and visual disturbance caused by these vehicles disrupts feeding and breeding efforts and may even lead to habitat abandonment. Ironically, much of this traffic is associated with ecotourism activities that are supposed to generate funds for protecting the birds over the long term.

Greater flamingo. Image courtesy of Yathin S Krishnappa

Even more worrying is the fact that flamingo habitat is under nearly constant threat from human activities such as mining, farming, and urban expansion. These activities can reduce the quality of feeding and breeding sites by altering water pH, introducing invasive species that out-compete flamingos for food, removing water (for use in irrigation or to facilitate easier access to minerals), and introducing dangerous structures such as power lines, with which flamingos can become entangled while flying. In the Mediterranean, where native greater flamingos often come into contact with escaped lesser, Chilean, and American flamingos, researchers worry about the potential detrimental genetic and behavioural effects of mixed-species breeding attempts.

One of the most contentious issues is the proposed construction of roads through irreplaceable flamingo habitat. This has been one of the biggest threats to lesser flamingos at Tanzania’s Lake Natron—the single most important breeding ground in the world for lesser flamingos. As detrimental as the road itself could be, even worse is the accompanying plan to open a soda extraction plant that could alter water levels at the lake, thereby potentially reducing the quality and quantity of food available to the birds. Over the years, several proposed developments have also threatened to degrade habitat near the ‘flamingo city’ in India’s Rann of Kutch. Biologists fear that construction in this area will alter water flow and reduce the accessibility of vital flamingo food resources.

Andean flamingos. Image courtesy of Wikimedia

Another worry is climate change, which could render favourite habitats unsuitable for feeding or breeding by either drying them up or flooding them to the point that they no longer have the pH required to sustain flamingos’ primary prey. Changing water conditions might also encourage blooms of toxic algal species or the spread of harmful bacteria—issues that have already been implicated in the deaths of large numbers of water birds in Africa. Flamingos are incredibly sensitive to subtle variations in their microhabitat and may decide to forego breeding if they decide that environmental conditions are not optimal for nesting. While some flamingo populations have readily adapted to anthropogenic environments, this is not generally true. This suggests that the birds would not be likely to utilize man-made alternatives introduced as replacements for degraded natural areas.

Worldwide, conservationists have already initiated several efforts to get the threatened birds out of harm’s way. Important habitats for the South American species have been given official protected status, and activists are hard at work to achieve a similar goal at Lake Natron and other African lesser flamingo haunts. Anti-poaching laws have been introduced in some regions and guards have been hired to protect flamingo colonies throughout the breeding season. Perhaps most importantly, researchers have been working on surveying more flamingo habitats—particularly in South America. These intensive efforts are vital for finding out how many birds remain, whether populations are stable or fluctuating, and which flamingo habitats most need to be protected.

Puna flamingos. Image courtesy of Christian Mehlfuhrer

However, flamingo conservation efforts do not just involve wild birds and field researchers, but also captive birds and aviculturists. Over the years, observations of flamingos at zoos and parks have provided a wealth of information on the birds’ natural histories—particularly for the three South American species, which are difficult to locate and study in the wild. Another benefit of captive flamingo populations is that they are a huge draw to visitors whose admission fees are often funnelled directly into conservation efforts. Outside of zoos, the majority of visitors are unlikely to have an opportunity to see flamingos in the wild. As a result, captive facilities are a vital tool in the campaign to raise awareness of, and support for, these threatened birds.

Although it has taken many years, aviculturists have finally worked out how to keep flamingos happy and healthy enough to breed in captivity. This has been a boon to conservation efforts for two main reasons. First, sustainable captive populations reduce, or even remove, the need to import wild-caught birds—a process that is always associated with the risk of injury and death to the birds, during both trapping and shipping. Second, maintenance of a large and healthy global population of captive birds acts as an insurance policy against any catastrophes that happen in the wild. Captive flamingos may some day be an important source of genetic diversity required for re-invigorating wild stocks, or, if captive breeding programs reach their full potential, they could even be used to produce birds that can be released into natural flamingo habitats.

Chilean flamingos. Image courtesy of Claudio Dias Timm

Recently, there has been increasing interest in keeping captive flamingos happy as well as healthy. Perhaps unsurprisingly given the fact that where there is one flamingo, there is usually another, an integral part of happiness is a satisfactory social life. Observations of ‘friendships’ and ‘coalitions’ within flocks can help managers decide, among other things, what the optimal flock size is, how much space birds need before they start getting on each other’s nerves, and which sex ratios are optimal for promoting breeding behaviour. By being aware of which birds prefer to flock together, aviculturists can also avoid separating ‘friends’ when moving birds between enclosures or giving animals away to other facilities. Studies of sociality in flamingos could also provide insights into group dynamics of other species—including humans.

Typical flamingo habitat (Lake Nakuru, Kenya)
Typical flamingo habitat (Lake Nakuru, Kenya)

Regardless of whether we’re watching flamingos in order to learn something about ourselves or just to admire their beauty, it is hard not to be impressed. Although they may look delicate and slight, these deceptively hearty birds manage to survive in some of the harshest habitats on earth, and have been doing so for millions of years. We can only hope that efforts to protect flamingos and their habitats will keep these living fossils around to brighten many more days over the generations to come.


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.