There are few animals in North America that have been persecuted for as long, or as intensively, as the coyote, Canis latrans. The coyote has been targeted by wildlife agencies at every level and in every state (excluding Hawaii, which it doesn’t inhabit. Yet…) and an estimated 500,000 coyotes are killed annually. There are competitive coyote-killing events in many states, and almost no state has a limit on the number of coyotes that can be killed. The coyote is reviled by ranchers, hunters, and suburban pet-owners alike.

And yet, in the face of all this loathing, and campaigns to eradicate it, the coyote has thrived and has dramatically expanded its range. Prior to 1700 the coyote was restricted to the deserts and prairies of North America, and now it occupies most of the continent. In addition to this range expansion, the coyote has taken up residence in suburban and urban habitats across North America, including megacities like Chicago, Denver, L.A., and New York. One of my favorite coyote stories comes from 2007, when people were beginning to recognize the urban wildlife phenomenon. One hot spring day, a coyote casually strolled into a downtown Chicago Quiznos sub shop that had its door propped open, and proceeded to climb into an open beverage cooler unit and lie down. The patrons and employees relinquished control of the restaurant to the coyote, and it remained in the cooler until animal control officers collected it and released it elsewhere.

According to coyote expert Dan Flores, there is actually a long history of urban cohabitation between coyotes and humans; 1,000 years ago coyotes lived in large urban areas in the Aztec empire of Mexico, and modern coyotes have been a part of the L.A. scene for at least a century. Despite this shared history, we have only recently begun to understand what coyotes are doing in the cities, and how they’ve managed to flourish in these concrete jungles.

​Part of what makes coyotes so successful is their highly flexible nature. Rather than being strict carnivores, coyotes are broad generalists, consuming everything from seeds, fruits, and insects to rodents, rabbits, and deer. When I lived in Santa Barbara, I would often walk at a local suburban park that had a small pack of coyotes living in it. During the olive-fruiting season, the coyote scat would be full of olive pits and skins from fruits they had vacuumed up from the ground. And in spite of their reputation as major predators on cats and dogs, a study of coyotes in the Chicago area found that cat DNA was present in only 1.3% of 1,400 scat examined. The most frequently consumed food items were rodents, which jives with work done in other coyote populations and my own observations. Whenever I have seen coyotes hunting, either singly or in packs, they have been going after rodents. In areas with prairie dogs, these ground squirrels often make up the bulk of the coyotes’ diet. When traveling through Grasslands National Park in Saskatchewan this past June, I repeatedly came across coyote packs loping through the prairie dog colonies, causing the ground squirrels to issue their predator alarm calls. I see the same here in Colorado, although I have only seen one or two individuals hunting in the prairie dog colonies rather than the packs I saw in Grasslands.

The coyote’s ground squirrel strategy seems to be the following: get as low to the ground as possible, keep as much vegetation between you and the prairie dog as you can, creep up on an individual foraging away from its burrow, sprint to catch it before it disappears down the burrow. The further away from a burrow a prairie dog is, the better a coyote’s chances.

Up here in the mountains where there are no prairie dogs, the coyotes appear to target voles and other small mammals. On multiple occasions I have watched coyotes in the area perform the quintessential canid maneuver; standing motionless in a field, head focused intently on the ground, and then raising up on the hind limbs and pouncing down on the ground with the front legs. Just a few days ago, in fact, we had a coyote performing exactly this behavior about 20 meters from the house. We were in the midst of a moderate snowfall, and a lone coyote was repeatedly pouncing in an area with a good covering of dried grasses and flowers under the snow. ​

​After the hawk landed, it watched the coyote for a few minutes, and then swooped low over the coyote’s head. The goshawk was almost certainly hoping to profit from the coyote’s actions by picking off any small mammals attempting to escape from the coyote. It wasn’t successful during that hunting episode, but I suspect that bird has used similar tactics in the past with more luck. This avian hunting strategy is clever (and there are many species of bird that cue in on other predators), but it is the coyote that has earned a reputation for cunning, intelligence, and mischief. The coyote features prominently in dozens of Native American and First Nations mythologies, and in many of them the coyote figure is a savvy trickster. 

I experienced a little of this cunning firsthand at Grasslands National Park. As I mentioned above, I saw a number of coyotes while I was in the park, and one time when I was out hiking, I saw a pair of adult coyotes just cresting a hill. They were a few hundred meters away, but I was curious to see what they were up to, so I followed along, but at a good distance. They led me to a small valley, and on an east-facing slope in the valley there were four small coyote pups playing on the hillside near their den. They were still a couple hundred meters away, so I went into stealth mode in an attempt to get closer. I shrugged out of my backpack and kept low to the ground as I crept closer, keeping another hill’s ridge in between me and the pups so they would not see me, and hopefully not smell me either. The adult coyotes had disappeared, and I kept looking for them as I made my way closer to the den. When I had made it to within 100 or 150 meters of the den, I slowly climbed to the ridge, and looked across the valley towards the den. The pups were still there, but just as I was getting ready to take some photos, a short howl, followed by a series of yips came from behind me. I turned around and 150 meters away stood one of the adults, howling, barking, and yipping. And from the top of a hill on the other side of the valley another coyote adult emerged, joining the one behind me in a chorus of howls and yips, and then a third from another hilltop. They had triangulated themselves around me.
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Apparently while I had been stalking the coyotes, they had been stalking me. Not to hunt, but to determine what I was doing, and to sound the alarm if necessary. I guess they determined that the alarm was necessary. And once the first alarm had sounded, the pups had vanished into their den.

​I sat down, thinking perhaps I could wait for the adults to move along, and that the pups might reemerge, but as long as I was in the vicinity of the den, the adults continued to vocalize. I decided I would continue with my hike, and that I would revisit the den on my way back in an hour or two. I hoped that by that point the adults would have gone back to hunting, and that the pups’ curious nature would have lured them back out of the den. When I returned to the coyote den valley, that is exactly what had happened; the adults were gone and two of the pups were out on the hillside. I assumed the other two pups were following the parents’ orders and were still down in the den.

​I spent about 45 minutes watching the pups from across the valley, and for most of that time, the two pups napped, or sat and looked around. One attempted to engage in some play with its sibling, but his efforts were mostly met with indifference. A couple of times the pups would lift their noses to the sky, and I wondered if they were catching my scent, or if they were still on alert from earlier. 

​To my surprise, the other two pups emerged from the grass up-slope and after a quick greeting with their siblings, disappeared into the den. One of the siblings I had been watching followed, and the remaining pup curled up in the grass, and went to sleep. I decided that was a good cue to leave, so I slunk quietly out of sight.

A litter of four pups is on the low to average size, and I suspect the relatively small size had to do with high levels of competition in the park. Coyotes are capable of adjusting their litter size in response to available resources and competition levels. If food is scarce, or home range size is limited by the presence of other coyotes, a breeding pair may have only one or two pups. When food is plentiful and there are few other coyotes around, they can raise upwards of 11 pups. All this flexibility allows coyotes to respond to prevailing conditions relatively rapidly and helps explain why efforts at decreasing coyote populations almost always fail. If a bunch of coyotes are removed from an area, the remaining coyotes simply increase their litter size to take advantage of the now-available resources.
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The combination of behavioral, reproductive, and diet flexibility goes a long way towards explaining how and why coyotes have successfully colonized most of the continent. But we have also played a large role in that expansion by removing their predators and competition. Wolves and mountain lions have been extirpated from much of their historical range, especially in the eastern part of the continent, and these predators helped limit coyote numbers. In Yellowstone National Park, for example, coyote numbers have dropped by 50% since wolves were reestablished in the park in the late 1990's, and this pattern is repeated just about everywhere wolves are returning to. But even with wolf and mountain lion numbers increasing, it is unlikely we will see a large drop-off in coyote numbers across the continent. These adaptable canids now occur in almost every available habitat type. There are an estimated 2,000 coyotes in metropolitan Chicago, and aside from the occasional Quiznos encounter, these wraiths go almost completely unnoticed by the 9 million human inhabitants. So whether you love or hate these animals, you have to respect their ability to survive, and flourish, in our human-dominated world. 

Next post: TBD
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Note: The View Out the Door will be transitioning to an every-other-week schedule for the time being.
 
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To help set the stage for this series of posts examining different winter-coping strategies, Mother Nature gave us the first taste of winter last week. Air temperatures dropped to 11 degrees Fahrenheit, wind chills plummeted to below 0F, and we received about 4 inches of snow. I ventured out a couple of times in the hopes of collecting images that captured the collision between fall and winter and came away with shots of golden aspen coated in snow, steaming ponds, and frosted moose. 

It was breathtakingly beautiful and brutally cold, but it was short-lived. Within two days temperatures rebounded into the 60s and most of the snow had vanished except for patches lurking in the shade of north-facing slopes. I think the foliage season is pretty much done, however, as the extreme cold temperatures really accelerated the leaf senescence process. Many aspen groves now stand naked, and others are dressed in crisp, brown leaves. Despite the loss of their leaves, aspen can continue to photosynthesize using the relatively high levels of chlorophyll in their bark. This is just one of many tricks that organisms at high elevations and latitudes use to deal with the relatively short growing season.

Cachers:
Caching food is a strategy that some animals use to take advantage of temporarily abundant food resources like seeds and nuts. Cachers generally store food in hidden locations across the landscape for consumption at times when other food isn’t available. A few weeks back I wrote about the impressive memory capabilities of some of these food-hiders, but how do these animals accomplish feats such as remembering where they cached 80,000 seeds, or avoid having their stashes raided by hungry thieves? Regarding the first task, animals that store food across the landscape typically have a highly developed hippocampus—this is the region of the brain responsible for spatial memory. In addition, the hippocampus can undergo seasonal changes, increasing in size during periods when the animal relies heavily on recalling where it placed its snacks, and decreasing for the months when it feeds on fresh food. This is handy because the brain eats lots of calories, and downsizing a portion of the brain that isn’t needed for months of the year can save a lot of energy.
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In addition to seasonal plasticity, the hippocampus can exhibit neurogenesis of new hippocampal cells in response to certain types of stimulation. Research in birds has found that some forms of memory stimulation result in high levels of neurogenesis, and wild birds typically have much higher levels of neurogenesis than captive birds. Perhaps there’s hope for those of us who have a hard time recalling where they placed their keys, phone, or car. For some memory exercises I suggest hiding 100 M&Ms around your house, and then trying to find them again in a week. You’ll either have a better spatial memory, or your house will be overrun by rodents and/or children.

​One thing to keep in mind when you’re hiding your candies is that many cachers use tricks to help reduce the memory load. One widely used tactic is stashing multiple food items in the same area. Clarke’s nutcrackers, for example, often stash four or five seeds together at the base of a given tree. Squirrels do this too. One of my squirrel-friends at the nearby Caribou Ranch Open Space has stashed dozens if not hundreds of pine cones in one 3-meter square area. This little fellow has taken caching to another level; I’ve sat and watched as he stuffed four large pinecones, one after another, into a single hole. Once a hole is full of pinecones, he carefully covers it up, tamps it down, and moves on to the next hole.

​An important aspect of caching is that the food item being stashed needs to have a good shelf-life; perishable items that spoil rapidly are not good candidates for caching. Nuts and seeds, which are well-suited to long-term storage, make up the bulk of cached food items. In very cold or very dry areas, however, normally inappropriate food items like meat can be stored long-term without spoilage. In our neck of the woods, the primary cachers are the chickadees, nuthatches, jays, crows, ravens, magpies, red squirrels, and the champion cachers, the Clarke’s nutcracker. Many of these species visit backyard bird feeders, and you may have seen a nuthatch stashing sunflower seeds in bark crevices around your yard. This is caching in action.

​Other than trying to remember where you placed your food, cachers have to contend with sneaky cache-thieves who would gladly dig up and eat the buried treasure. In fact, some individuals make a living as thieves, and invest a good portion of their time spying on others. What’s an honest, hard-working squirrel supposed to do when thieving spies are everywhere? Researchers have discovered that caching squirrels will engage in some deception of their own; if they think they are being watched, they will pretend to bury something in the ground. The would-be thief then wastes his time searching for a non-existent food item, while the honest cacher can go hide his food somewhere else. Birds also have to contend with thieves, and some species exhibit exceptional levels of awareness. Western scrub-jays, for example, keep track of which of their colleagues are watching them when they cache food. If an individual that is a known cache-thief was watching, the original bird will return to the cache, dig it up, and move it when they aren’t being watched by the thief. And for good measure, in addition to being able to identify likely thieves, and remember where they stashed hundreds or thousands of food items, scrub-jays keep track of the duration of time a food item has been stored, and if it has passed the “use by” date, they won’t return to dig it up. Not bad for a bird brain.

Hoarders:
We all know some hoarders in our lives, but in this case, I’m referring to animals that stuff their larder with food so as to sustain them over the course of the winter. A number of rodents are fervid hoarders; if you’ve ever had a pet hamster or rat, you’re likely familiar with this behavior. I happened to have a trio of pet rats when I was younger, and in one of my more misguided moves, I decided that they could live a free-range life in my room. Things seemed to be working out for the first couple of weeks, and then I noticed one of the rats scurrying along the floor with some dog kibble in his mouth. I followed the rat (named Brownie), and he led me under the dresser to a massive pile of dog food. Turns out that in their spare time, my rats had found the food bin, gnawed a hole in it, and had been stockpiling kibble under my dresser for the impending rat Armageddon. But these rats hadn’t put all their eggs, or kibble, in one basket; they also had stashes in my desk drawers and under the desk. Thus ended the short-lived experiment with free-range rodents in my room.

​It also happens that the second largest rodent in the world, the North American beaver, is a hoarder, with a twist. Beavers are well-known ecological engineers, modifying the landscape with the construction of their dams. It has been proposed that one reason beavers build dams is to create deep pockets of water in which they can store a winter’s supply of sticks and branches. Beavers subsist on a delightfully varied diet of twigs, branches, bark, and sticks. I’m kidding, of course; that’s just their winter diet. In the spring and summer they really spice things up by adding leaves and aquatic plants to the mix. Once the ponds freeze over, these industrious hoarders are able reach their larders under the ice via underwater entrances in their lodges. So in essence, beavers drastically alter the landscape in the process of making aquatic tree-branch refrigerators that only they can access during the winter. That’s a pretty neat trick for a rodent.

Hyperphagists:
The term “hyperphagia” really just means elevated levels of food consumption and can be applied to animals that have increased appetites prior to migrating or hibernating. The supermigrants I covered last week experience pronounced periods of hyperphagia because they need to rapidly put on fat reserves before their marathon flights. But birds have to balance energy reserves with flight efficiency, and in case you’ve ever wondered, those fat turkeys that get served up for Thanksgiving meals are not flight capable. Being more earth-bound can free one up to pack on the pounds. Bears eat almost non-stop during the late summer and fall months in preparation for hibernating. Previously I covered some of the incredible statistics regarding caloric intake during the hyperphagia period, and caloric output during hibernation. But I didn’t cover this: Fat Bear Week. Alaska’s Katmai National Park and Preserve puts on a bracket-style competition in which the public votes for the fattest brown bear each October. These bears have been feasting on salmon for the previous month, and the results are impressive. Check out all the images in the link—the champion (Holly) was crowned last week, and it’s a crown well-deserved.

​Yellow-bellied marmots also experience significant weight-gain prior to hibernation. These rotund ground-squirrels are close relatives of the woodchuck or groundhog (or better yet, the “whistle-pig”), and spend 7-8 months each year hibernating. Like the hibernating bears, marmots depend on their fat reserves to get them through this 200 day-long snooze. During this period, the marmot’s heart rate dips from 180+ beats/minute to 30 beats/min, their body temperature drops to 41 degrees Fahrenheit, and they take only one or two breaths/min. These physiological changes are crucial to helping them survive until the following spring. At that point they will slowly transition from zombie-marmot to living marmot, and resume their lives of socializing and eating. 

​Next week: TBD
 
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​Animal migrations capture our attention like few other events in nature. When you picture nature’s greatest spectacles, it is likely that at least one flavor of animal migration is in there; the massive herds of ungulates crossing Africa’s Serengeti in search of high quality forage; the leaping, boiling, churning masses of salmon returning from the ocean to spawn in their natal rivers; the monarch butterflies coating every available inch of leaf and trunk on the oyamel trees in their wintering regions of Mexico; the “arribadas” of sea turtles congregating on tropical beaches to lay their eggs; and the undisputed winner of long distance migration, the Arctic tern, which undertakes a zigzag route between the Arctic and Antarctic each year, a total annual journey of 44,000 miles. And these represent just a few of the flashiest migrations that have made it into the public’s collective awareness over the years. There are dragonfly migrations that exceed 10,000 miles round trip, a flying fox migration in Africa that approaches 10,000,000 animals, and daily vertical migrations for trillions of planktonic organisms that travel up towards the water surface each night to feed, and down into the dark depths each morning to escape predators. As our ability to track animals’ movements has improved, so has our understanding of the physiological and behavioral mechanisms involved in these feats. I’ll touch on a few of North America’s migrations this week to highlight the variety of tactics that animals employ when embarking on these voyages. 

​I’ll start with something called “partial migration,” and while this category may not be well known, one bird that uses it is: the American robin. The robin holds the title of “America’s favorite worm-eater” although I’m not sure that A) it has much competition, or B) this title actually exists. Nonetheless, the robin is one of the most widespread and abundant birds in North America. Despite their abundance and conspicuous nature, robin migratory movements have been the source of confusion for millions of people over the years. People tend to get excited when they see a robin in their yard in mid-February or early March, and are ready to proclaim winter over, and to heck with Punxsutawney Phil’s dire predictions of 6 more weeks of winter.

​The reality is that robins exhibit partial migration; some populations, and some individuals within a given population, migrate for part of, or all, the winter months. Populations in the far north of Alaska, northern Canada, and northern New England all tend to head south for the winter, although where they migrate to is highly variable. Some head down to relatively warmer, but still chilly areas like southern Maine, New York, and Illinois, while others eschew the cold entirely and go off to nice sub-tropical locations like Florida, Cuba, and Mexico. Populations throughout the lower 48 and coastal British Columbia are more variable still; some individuals may remain in their breeding area throughout the year, while others may head a few hundred miles to the south, east or west for the winter. The real driver of these movements is thought to be food availability. When the ground is frozen and delicious invertebrates (i.e. worms!) are hard to come by, robins switch to a berry-based diet. If the area where a bird bred has great berry resources (think honeysuckles, junipers, hawthorns, Pinkberries…) it may remain there as long as there are fruits left to eat. Robins tend to move around a lot during the winter months as they search for reliable food sources, meaning that a noisy flock may be present in your yard one day, gleefully gobbling down freeze-dried berries, and gone the next.

The Cornell Lab of Ornithology has put together this wonderful graphic depicting robin presence across North America over a one-year period using data generated by birdwatchers who import their bird sightings into eBird. You can see the big shifts at the northern and southern edges of the range, and the other, more subtle shifts across the middle portions. I think these graphics are amazing, and a brilliant use of Citizen Science data. So, this winter if you have robins in your yard, try listening to them to distinguish whether they are year-round residents, or visitors from up north in Canada. It’s always easy to tell if they’re friends from the north by their accents, eh?

​A related form of migration that is relatively common in mountainous regions of the world, and one that is well-represented here in Colorado, is elevational, or altitudinal, migration. Organisms that undertake elevational migration often don’t need to travel great distances because climatic conditions change rapidly as one ascends or descends. A drop in elevation of 1,000—3,000 feet can be the equivalent of hundreds of miles of latitudinal change. Because of the relatively short-distances involved, elevational migrants often have more flexibility in their migratory movements; rather than initiating their travel based on some indirect cue associated with the changing conditions such as decreasing day-length, these animals often have the luxury of using more direct cues such food availability, to guide their departure. Here in the Colorado High Rockies, there are a number of species that exhibit this sort of migration: mountain chickadees, mountain bluebirds, mountain goats…I guess any animal named after mountains. 

​That’s really only partly true as there are many other species without the mountain moniker that slide up and down the slopes with the changing seasons. In addition to the above-mentioned species, some populations of elk, red-breasted and white-breasted nuthatches, dark-eyed juncos, and a suite of other species descend to milder elevations in the winter. For many of these species, the occurrence and degree of elevational change can be linked to an individual’s condition, age, and sex, as well as the severity of the winter conditions. Individuals in good condition, and/or those that can claim ownership over a good food resource may not migrate downslope at all, whereas those in poorer condition and/or subordinate in the social hierarchy may drop down early in fall. Conversely, extreme winter conditions may force all individuals down to more moderate elevations. My wife and I could very well turn into elevational migrants if winter conditions force us from our home at 9,000 feet.

​In stark contrast to these partial and situational migrants are the long-distance super-migrants. As I mentioned above, the Arctic tern is the undisputed champion of this category, but there are many variants on the theme of super-migrants. Let’s take a look at the ruby-throated hummingbird for starters. These iridescent, nectar-sipping, hovering dynamos breed throughout eastern North America, and are a common backyard inhabitant. 

​The blackpoll warbler is a bit larger than the hummingbird, clocking in around 10 grams, and this denizen of the northern forests has one of the most physically taxing fall migrations of any bird. The blackpoll breeds from northern New England over to western Alaska, and birds winter primarily in South America. To get to their wintering grounds, birds head east to the eastern seaboard of the US, and then from various staging points on the coast they plummet off the map into the ocean. 

Well, not exactly. But birds do continue to head east where they hope to catch northwesterly winds that will help propel them to South America. In the process, these birds cross an average of almost 2,000 miles of open ocean. Like the ruby-throated hummingbird, these birds make this crossing in one go, which typically takes 80-90 hours of non-stop flying. To put this in perspective, researchers Tim and Janet Williams came up with some comparable statistics:

“The trip… requires a degree of exertion not matched by any other vertebrate. For a man, the metabolic equivalent would be to run 4-minute miles for 80 hours…If a blackpoll warbler burned gasoline for fuel instead of its reserves of body fat, it could boast of getting 720,000 miles to the gallon!”

​Researchers have looked into other aspects of the physiological changes birds undergo prior to and during these migratory events. Most obvious are the changes in fat deposition; birds can more than double their weight prior to migration by putting on large fat reserves. Fat is the perfect fuel for these journeys—it provides more energy per unit than carbohydrates or proteins, it can be stored dry without accompanying water or protein, it can be oxidized efficiently and completely by most body tissues, and fat catabolism results in the production of water, which can be used by the bird. Birds also undergo rapid changes in tissue size, in which organs that are not going to be used during the flight (like the stomach and intestines, some immune organs, and leg muscles) are more or less absorbed by the body, whereas others that will be heavily relied upon (such as flight muscles) increase in mass. Upon arriving at their destination, these broadscale changes to muscles, gut, and immune organs occur in reverse and in short-order—typically within just a few days. The ability to undergo these rapid and reversible changes is known as “phenotypic flexibility” and migratory birds exhibit some of the most flexible phenotypes we know. I wonder if they do much yoga…

​We have acquired a wealth of information about animal migration in the past few decades, but there are still huge gaps in our understanding of migratory patterns, habitat usage, behavior, and physiology for many if not most migratory species. However, when you consider that historically people thought birds that vanished in the fall and reappeared in the spring spent the winter hibernating under the mud like frogs and turtles, we’ve come a long way.
 
Next week: Cachers, Hoarders, and Hyperphagists (Super-eaters)
 
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Autumn is a season defined by change; everything is in flux as the sun slides towards the south and the temperatures slip downwards. In northerly latitudes animals adopt one of three general strategies for coping with the approach of winter; they migrate to warmer areas, enter a state of partial or complete hibernation, or remain active. Plants aren’t really great at migration, so they are left with two principle options; go dormant or continue to photosynthesize. But before we deck the halls and wax the skis, there are a wealth of autumnal events that are worth discussing. This week’s post will be a short introduction to some of these phenomena which I’ll cover in more detail in the coming weeks.

Southward Migration: Birds and Butterflies
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I talked about avian spring migration back in March, and the feelings of excitement and anticipation wrapped up with the return of so many colorful birds. Bird migration in the fall is a little different; many of the birds have traded their bright breeding plumage for drabber tones and their boisterous songs for quiet chip notes or silence. 

​But the absolute number of birds is generally much higher because the young that were produced during the breeding period join the adults on the southward journey. On average, 4.7 billion birds travel from the US into Mexico and beyond in the fall, whereas only 3.5 billion make the return journey in the spring. Much of that difference is a result of mortality that occurs during migration. Many species migrate across the Gulf of Mexico, embarking on a non-stop journey of up to 20 hours. This undertaking requires large energy reserves and favorable weather conditions. Not all individuals survive the crossing, however, and recent research has shown that at least one marine predator takes advantage of this unfortunate windfall. Gut content analyses of young tiger sharks in the gulf showed that 39% of sharks sampled had neotropical migrants in their bellies. Researchers speculate that these birds may provide a critical food resource for baby tiger sharks that are not yet skilled at catching live prey. Most birds crossing the gulf avoid becoming shark food, but that’s not the only peril that these birds face; migrating raptors are looking to catch a snack on the wing.

One of the great natural wonders is the fall migration of raptors in North and Central America. Places such as Hawk Mountain Sanctuary in Pennsylvania, or Cape May in New Jersey provide opportunities to see hundreds or even thousands of these birds passing by on crisp September days with a brisk northerly wind. The real mecca for viewing this migration, however, is in sections of Mexico and Central America where the birds are funneled over narrow swathes of land. At these locales, single day tallies can exceed 1 million birds in what is known as the River of Raptors. I visited a hawk-watching platform in Veracruz, Mexico in 2006 and watched as raptors passed overhead in fantastic numbers. The flow of birds southward happened in many layers; from the small hawks and falcons zipping past at tree-top level to the larger hawks and eagles streaming past at 10,000 feet, too small to see with the naked eye. In the few hours I was there, some 7,000-10,000+ birds crossed through the airspace over us en-route to their wintering destinations.

​No less impressive is the migration of monarch butterflies from the eastern US to the mountains of southern Mexico; a journey of 2,500 miles for some populations. During the spring migration, monarchs exhibit a generational pattern of migration. That is, one generation travels from Mexico to the southern US, at which point they eat, mate, lay eggs, and die. These eggs hatch into caterpillars, the caterpillars pupate into butterflies, and the butterflies head north a few hundred miles before they eat, mate, lay eggs, and die. Individuals that migrating southward from the northern US and southern Canada in September and October may be three or four generations removed from the individuals that left that area the preceding fall. These great-great-grandchildren-flies tap into a genetical flight program that guides them to the same region, and possibly even the same stand of trees, their relatives wintered in the previous year.

​The Rut: Battle for Dominance
I briefly mentioned the moose rut a few weeks prior, but elk, white-tailed deer, mule deer, bison, mountain goats and bighorn sheep are other species here in Colorado that participate in the breeding spectacle referred to as “the rut.” Essentially, males compete with one another to establish dominance, and high-ranking males acquire harems of females. Much of the male social hierarchy can be determined through visual and chemical cues, but when two evenly matched foes face one another, peaceful negotiations give way to violent confrontations. Sheep, bison, and goats bash their horns together, while moose, deer and elk clash antlers and engage in the equivalent of sumo-wrestling matches; whichever male succeeds in pushing the other around usually emerges the victor. Victorious males get the ultimate prize: the opportunity to pass their genes on to the next generation.

​Food Stores: Caches and Winter Weight
Winter is a time of reduced food availability for many animals, but fall provides a rich bounty of dietary options: fruits, nuts and seeds are produced in abundance, and insects and other invertebrates are still active. Small mammals like pikas and squirrels spend the fall collecting and storing foods that they will use during the winter. American pikas are stocky relatives of rabbits and hares and are often found at high elevations, living on talus slopes and other rocky habitats. They spend the fall in a frenzy of food collecting activity as they prepare for winter. Pikas gather grasses, flowers, and forbs, dry them in the sun to prevent rot, and then stash them in their den for leisurely dining once the snows arrive.  

​Squirrels, in contrast, bury nuts, seeds and pinecones in the ground as a way to store them for later consumption. This behavior is called “caching” and it requires some sophisticated memory, and a good sense of smell, on the part of the squirrels.

​More impressive than the squirrel’s memory is that of the Clarke’s nutcracker. These raucous birds cache tens of thousands of seeds in the fall and return to eat them over the course of the winter. The memories of squirrels and nutcrackers are not infallible, however, and many seeds are forgotten. These seeds may then germinate and become part of the next generation of trees. Cachers like the squirrels and nutcrackers are thus thought to play important roles in natural forest regeneration.

​A much easier strategy that requires no memory is that of storing food reserves on your body. These reserves exist as something called adipose tissue or “fat” and many people are familiar with the physiological tendency for our bodies to generate some of these fat stores in preparation for winter. But humans are supreme underachievers in this category compared to some other animals like bears. During the autumn fattening period, bears can consume 20,000 calories a day and put on 30+ pounds of fat per week. Bears need to bulk up because they can burn 4000 calories a day during their hibernation, which may last 100 days or more. Bears eat just about anything they can find during the fall; those in areas with rich fish or other marine resources feast on salmon and seafood, while those in interior locations search for fruits, berries, nuts, insects and tubers. Sounds like a good way to spend the fall if you ask me.

​Side Note: I have six photos on display in the Nederland Community Center Art Exhibition, which opens this Thursday! I’m thrilled to be showing these images in my community, and hope this is the first of many such shows. If you’re in the Boulder or Nederland area, come on out to the Nederland Community Center this Thursday, October 3rd, from 5-7pm.

Next week: Fall Migration
 
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