Why do we see more black bears in the Fall?

American black bear

American black bears are one of three species of bears found in North America.  The largest is the polar bear, followed by the brown bear, and finally the black bear.  The name black bear is a bit of a misnomer since the species can be found in several different colorations.  While black is most common, they also occur in cinnamon, brown, blue/gray, blonde, and occasionally even white.

The black bear is the most abundant and widely distributed of the bear species in North America, occurring throughout most of the United States, Canada, and in the northern half of Mexico.  As such, people interact with this species most often.  Black bears are opportunistic feeders, and their diets consist of leaves, grasses, crops, roots, fruits, insects, and fish.  Being opportunistic, though, they will feed on carrion and other food sources, and occasionally kill other animals for food.  This opportunistic behavior can result in bears becoming conditioned to readily available human food sources such as trash and food around campgrounds and houses, resulting in frequent visitation of bears to these areas.  When bears become conditioned to a readily available human food source, there is a greater opportunity for negative interactions with people.

Black bear approaches screen door of house adjacent to woodland. Photo Credit:  Alyssa DeLiberto

Most human-black bear interactions occur in spring through fall. Encounters can happen in winter if bears are disturbed in their dens in the North and in the southern United States and Mexico where long periods of hibernation are less frequent.  In late summer and fall, prior to hibernation, bears enter a physiologic state called hyperphagia characterized by a dramatic increase in the search for and consumption of food. During this time, bears can eat 15,000-20,000 calories per day.  This high caloric need can result in increased visitation to readily available, high energy, food sources such as fruit trees, berry bushes, bird food, beehives, pet food, and trash commonly found around houses.  Eliminating such food sources will decrease the attractiveness of a property to bears.

Black Bears eating food scraps.

After hyperphagia and prior to hibernation, bears enter a transition period when they become increasingly lethargic, sleeping up to 22 hours per day, and their metabolism gradually slows in preparation for hibernation.  In more northern regions, bears generally enter the den upon arrival of the first snow and when the temperature reaches 32°F.  However, in western arid areas, where food resources are traditionally scarce in the fall, bears may enter hibernation early in the season regardless of food supply.  Alternatively, in eastern North America where food resources such as acorns and nuts can remain throughout the winter, bears begin hibernation in late November or December.  The first group of bears to start hibernating are pregnant females, followed by females with older dependent offspring and subadult bears. Adult males enter dens and start hibernating the latest.

Although aggressive behavior to humans by black bears is not common, habituation to food sources around human dwellings increases the likelihood of defensive or offensive aggressive behavior towards people.  Most encounters with bears near houses result in an animal fleeing or climbing a tree for safety.  In the latter instance, simply bringing family members and pets indoors and allowing the bear time to safely leave the tree and property, resolves the conflict.

Many of us are empathetic to wildlife and want to help them, often by providing food. Unfortunately, doing so acclimates them to our presence and encourages unsafe interactions.  The best way to help bears and other wildlife is to keep them wild.  When bears do come into towns and onto our properties, remove bird feeders, secure trash, and do not provide them with other food sources.  Respect them by giving them space, and not approaching them.

A Unique Gull: Red-Legged Kittiwake

Red-legged kittiwake on St. George Island, Alaska.

Of the more than 50 gull species found worldwide, only the kittiwakes are known to venture far out to sea. All the other species live and feed along coastal and inland areas. There are two species of kittiwake, the red-legged and black-legged kittiwakes. The black-legged kittiwake is far more common than its counterpart, nesting in coastal areas throughout the North Atlantic and Pacific Oceans, and wintering as far south as southern Japan, Baja California, Florida, and northern Africa. On the other hand, the red-legged kittiwake is confined to the Bering sea and North Pacific Ocean. They breed on just a few islands in Alaska and Russia and winter in the open ocean, often near the edge of sea ice. About 80 percent of their population breeds on the Pribilof Islands in Alaska.

From Robinson et al, 2019. Potential northward expansion of the breeding range of Red-legged Kittiwake Rissa brevirostris. Marine Ornithology: 47: 229–234.

Kittiwakes are relatively small as gulls go. They are both about the size of a crow, but the red-legged is a few inches smaller than the black-legged. Red-legged kittiwakes are not only distinguished by the color of their legs, but they also have a shorter bill and bigger eyes than black-legged kittiwakes. The larger eyes are thought to aid red-legged kittiwakes in hunting at night especially when searching for one of their preferred foods, squid. When they hunt, they form large groups called “melees” often with black-legged kittiwakes.

Red-legged kittiwake colony on St. George Island, Alaska.

Red-legged kittiwakes breed in colonies on steep, rocky cliffs up to 900ft high on islands in the Bering Sea, with other colony nesting sea birds including black-legged kittiwakes, puffins, and murres. When born, the chicks instinctively know to stay still so they do not fall from their nests on the steep cliffs. The colony on St. George Island, Alaska contains over 80% of the world’s population of red-legged kittiwakes. Given the restricted distribution of the species, limited breeding habitat, and decreasing population size, the species is listed as vulnerable.

Adult red-legged kittiwake on St. George Island, Alaska.

Why is that flamingo Grey?

Flamingos are one of the most unique of all bird species. Their large hooked bills, long necks, stilt-like legs, webbed feet, and pink to reddish coloration give flamingos a cartoonish appearance. There are six species of flamingos, two of which occur in Africa, Asia, and Europe, and four in North and South America and the Caribbean. While there are size and color variations among them, the American flamingo (Phoenicopterus ruber) is the second largest and brightest colored. Currently, there are no naturally occurring breeding populations in the U.S, but breeding populations in zoos are common as well as a small captive population at Hialeah Park, Florida. Over the last 10 years, an increasing number of wild flamingos have been seen in Florida and the Gulf Coast, raising hopes that breeding populations may re-establish in the U.S.

American flamingo, Denver Zoo, Colorado.

But why are some flamingos grey or white? Are they albinos? Chances are no. Although such mutations do occur in nature they are rare. So if they are not albinos, then why are some flamingos not brightly colored pink or red? There are three reasons for this. First flamingos are born with white down feathers, which turn grey when they leave the nest in 1-2 weeks. They’re also born with bright red, straight bills, and bright red legs. It takes flamingo chicks about 11 weeks for their bills to begin obtaining the characteristic hook shape and they gradually obtain their pink feathers over their first 2-3 years of life.

American flamingo adult and juvenile (grey), San Diego Zoo, California.

The second reason flamingos may not be brightly colored is because of their diet. Flamingos are filter feeders, preferring brackish and salt water habitats. When eating, they place the top of their head in the water with their bill pointing back to their feet. Then they move their head side-to-side along the bottom of shallow waters, using their tongues to draw water containing phytoplankton, invertebrate animals (such as brine shrimp and zooplankton), and algae into their mouths. As their tongues push the water out through laminar (comb-like) plates on the edges of their bills, the food particles get trapped in their mouths. These food items are high in carotenoid compounds. Carotenoids are responsible for giving plants, algae, and some animals their red, orange or yellow colors. In flamingos, their pink color is a result of metabolizing the carotenoids from the their food when molting in new feathers. If a flamingo’s diet does not consist of enough items with carotenoids during molt the feathers will not have enough carotinoid compounds to produce their characteristic bright color.

American flamingo, San Diego Zoo, California. Note the laminar plates between the upper and lower bill.

But even if flamingos get enough carotenoids when their feathers are growing to turn them pink to red, these pigments fade over time with exposure to sunlight. Yet, many flamingos are able to delay such fading by applying their own make-up! This cosmetic coloration occurs when adults use their bills to take secretions high in carotenoid compounds from the preen (uropygial) gland at the base of the tail, and spread it on their feathers. It’s believed that flamingos apply cosmetic coloration as part of their mating and nesting rituals. Both females and males engage in cosmetic coloration. Once chicks leave the nest in spring and early summer, adults reduce their application of make-up and the feathers fade until the next molt.

American flamingo, Aruba. Note the post-nesting season faded coloration.

So next time you see a grey or white flamingo, you may be seeing a chick or a juvenile that has not yet obtained its pink feathers, an adult that is eating a diet low in carotenoids, or one just after breeding season when its has ceased applying its make-up.

Spring Migration

Spring Migration is coming! Every spring over 3 billion birds move north into the United States and Canada after spending the winter in Central and South America, Mexico, and the Caribbean. These extraordinary flights of birds across the continent generally occur between February and June, through what scientists call flyways.

Although these broad pathways of migratory birds have been generalized into the Atlantic, Mississippi, Central, and Pacific Flyways, how closely birds adhere to these corridors depends on the particular species. Some species, such as the mallard, occur across the continent and can be found in all four flyways, while other species, such as the hermit warbler, may be limited to just a single flyway. And then there are species such as the long-tailed duck, in which individual migration patterns can be unpredictable.

Periodically, birds that are usually restricted to a particular region of the country, are sighted in an area they’ve only rarely been observed, if at all. This typically happens during migration, when it’s thought individuals can get shifted out of their traditional flyway by severe weather or other factors. On a trip to Bosque del Apache National Wildlife Refuge, New Mexico, in the Spring of 2021, I was fortunate to observe such an incident of wayward migration. There, I spotted a scarlet tanager, a species that winters in Central and South America and typically summers in the eastern deciduous forests of North America. Only 76 observations of scarlet tanagers in New Mexico have been reported in eBird and of those, only seven were in and around the refuge. This is because scarlet tanagers typically return from their wintering grounds over the Gulf of Mexico through the Atlantic, Mississippi, and Central Flyways.

Scarlet Tanager, Bosque del Apache National Wildlife Refuge, New Mexico, 5 May 2021.

Scarlet tanagers migrate at night, and I saw this bird in the afternoon, voraciously eating insects, presumably preparing for the next leg of its journey. It was not seen again at the refuge after this day.

So this spring, when you’re out hiking, birding, or just enjoying your backyard or local park, look and listen for one of the great animal migrations unfolding around you. The birds will be in their full regalia of breeding plumages and welcoming the return of spring with their enthusiastic songs and behaviors of the mating season. And who knows? You may even see a bird that has wandered out of its traditional flyway!