Wednesday, August 19, 2020

Mourning Doves

Mourning dove (internet download)
Recently, our backyard revealed a ‘puddle’ of feathers about a yard across. Best guess is that a hawk had caught and killed a mourning dove, and then proceeded to pluck feathers before flying away with the carcass.

Mourning doves – older names turtle dove and Carolina turtledove – are a common bird across America, with a population estimated at 300 to 400 million birds. Doves are a light grey and brown in color, with only subtle differences in appearance for males and females. Mated pairs are monogamous. Two eggs are laid per nesting cycle. A pair will raise several broods each year. Both parents participate in nest building, egg incubation and feeding the chicks (also referred to as squab). Although doves feed on seeds and grains, very young chicks are not fed seeds, but rather a protein- and fat-rich secretion from the parent birds’ crop, called “crop milk.” [The crop is a pouch just below the throat. Many species of birds can fill this with food to digest later or else regurgitate into their chicks’ mouths.]  As chicks get larger, seeds the parents have swallowed into their crop are combined with crop milk. With such a rich diet, chick fledge – are able to fly – within two weeks from hatching. The parents will continue to feed them for an additional week or two, but will have also laid eggs for the next brood.

In captivity, lifespan can approach 20 years. This, plus all the fecundity would cover the countryside knee-deep in mourning doves, except that predators find them easy to catch. In the wild, average lifespan is less than two years. Ravens and crows take chicks from nests, fledged chicks are easily caught by many predators, and adults end up in the food chain because they are ground feeders. Prior to European colonization, the major predators of adult dove were hawks and falcons, attacking from above. Add to that cats (pet and feral), and the life of a dove can be brutally short.  

Feathered evidence of a hawk kill
The predator that left us the feathered evidence was most likely a Cooper’s hawk. This is a relatively small but very agile hawk that preys primarily on birds. Red-tailed hawks are larger, but a bit too slow to be bird predators, preferring instead rabbits and squirrels. The other possible culprits would have been peregrine falcon, or sharp-shinned hawk, but these are relatively rare in eastern Massachusetts. In addition to doves, Cooper’s hawks will also prey on robins, starlings and sparrows – also ground feeders. Attacked birds are taken either on the ground or while trying to take off. One estimate has each hawk killing on average two birds a day.

In describing mourning doves, John J. Audubon wrote “Whenever it starts from a tree or the ground, on being unexpectedly approached, its wings produce a whistling noise, heard at a considerable distance.” This is an example of “sonation,” defined as sounds produced by birds, using mechanisms other than the vocal organ. Humans make sounds by means other than voice: we snap our fingers, clap our hands, slap our thighs, stomp our feet and click our heels. For some bird species the sound making is voluntary, typically related to males claiming territory or their mating display. The male palm cockatoo of New Guinea uses a claw-held stick to drum on a hollow tree he has selected as a possible nest site. The female, attracted by the noise, checks out the real estate.

For mourning doves, the taking off sound is involuntary but mallable. Birds often form flocks to increase collective vigilance, thus allowing early detection of predators. This benefit of sociality relies on rapid transfer of information. For many species, an alarm call, but for pigeons and doves, one of the flight feathers on each wing is modified so that on take-off, with the wings fully extended for extra lift, the modified feather rapidly flutters against the next feather during the wings’ downstroke, making an easily heard noise. This noise is present whenever mourning doves take off, but if the cause is alarm from detecting a predator, wings beat faster and the pitch is higher. Taped recordings of regular and alarmed take-offs confirm that other doves respond more to the sound of alarmed take-offs.

Is this altruism or self-interest? Assuming this evolved under predation by hawks, one bird taking off from a group on the ground may just be making itself the best target. But if all the birds take off, the visual complexity of the group may cause the attacking hawk to lose sight of an individual bird, and perhaps even miss all of them. Once in the air, mourning doves can reach speeds in excess of 50 miles per hour. Bye Bye Birdie.   

For mourning doves, much like robins, migration is optional. Given enough food, males of both species will remain behind, forming loose flocks of 10-30 birds. Their reason for not leaving is to have dibs on the best territory when the females return in the spring. Robins will find and plunder berries such as winterberry and Asian bittersweet. Mourning doves will seek out remnant grains in farm fields and cluster under birdfeeders to benefit from what perching birds have spilled to the ground.

Lastly, from James Lipton’s “An Exaltation of Larks”: a group of doves is called a "dule," (pronounced ‘dool’) taken from the French word deuil (mourning), because “The soft, sad ululation of the dove has always evoked the sense of mourning.”

Wednesday, August 12, 2020

Science Is Real

Science is real. Science is also slow, and sometimes science takes detours. A May 2018 column was about the rise and fall of vitamin E. Briefly, back in the 1990s, claimed benefits led with reducing risk of cardiovascular disease and some types of cancer, but piled on with claims for results for macular degeneration, pregnancy, dementia and other diseases. With no apparent concerns about safety, there was a race up to mega-dose amounts being widely sold as non-prescription dietary supplements. Then the bad news – results from large, placebo-controlled human trials – started to trickle in. As Thomas Huxley put it, “The great tragedy of science – the slaying of a beautiful hypothesis by an ugly fact.”

Yes, vitamin E was confirmed as an antioxidant, and the oxidation theory of diseases of aging is one of cumulative damage. Healthcare professionals who chose to consume a vitamin E dietary supplement had a 1/3 reduction for risk of cardiovascular disease. Sadly, subsequent years-long clinical trials concluded that there was at best a modest reduced risk of heart attack at low doses, increased risk at high doses, no benefit for risk of stroke, and no improvement in all-cause mortality. With hindsight, in the initial research, health professionals who had decided to consume vitamin E supplements may have made other lifestyle decisions that promoted good health. It is an example of correlation not necessarily reflecting causality. Research for other diseases also had mixed results: nothing for pregnancy, nor hair, nor for topical applications for burns or wound healing; mixed results for cancer. There was a trickle of evidence that amounts over 200 mg/day had negative consequences. Sales of dietary supplement vitamin E declined dramatically.

Niacin is both a vitamin and a prescription medication. As a vitamin, intake recommendations made by several countries are that for adults, intakes of 14–18 mg/day are sufficient to meet the needs of healthy people. When niacin is used as a medicine to treat elevated triglycerides and serum low-density lipoprotein cholesterol (LDL-C), daily doses range from 500 to 3,000 mg/day. The LDL-C lowering effect was discovered by accident; niacin was being investigated as a treatment for hypertension, and then in 1952 a group of Russian scientists reported cholesterol-lowering as a side effect. Prescription niacin became widely used as a hyperlipidemia treatment drug some 30 years before the approval of the first statin drug in 1987.

All that is well and good and still true, although the advent of statins, which were more effective that niacin and with fewer side effects, reduced niacin prescriptions by 90 percent. Where niacin veered into a science detour was a second purported health benefit. In addition to lowering LDL-C, niacin also raises high-density lipoprotein cholesterol (HDL-C), often referred to as “good” cholesterol. Population studies showed that people with higher HDL-C were at lower risk for cardiovascular disease. Lifestyle interventions that raised HDL-C, such as exercise or moderate consumption of alcohol, also correlated with lower risk. Collectively, this suggested that HDL-C was a valid biomarker. However (the beautiful hypothesis slain by the ugly fact), niacin in combination with a statin drug proved no better for clinical outcomes than the statin alone, despite having raised HDL-C. Prescription products that had combined niacin with a statin (Simcor, Advicor) were discontinued in 2016.

And now, almost every known drug is being tested for COVID-19 benefits, including known antivirals and repurposed other drugs (and not just drugs – vitamins D and C are being evaluated, too). Hydroxychloroquine – an anti-malarial with other approved treatment indications – has its champions in the COVID-19 arena (“It works on my patients.”), but to date, placebo-controlled clinical trials have shown no evidence that it prevents people from contracting the disease if exposed, no evidence for a faster recovery among those afflicted, and no significant reduction in the percentage of COVID-caused deaths. There are serious adverse reactions (heart, liver, kidney), known to be associated with this drug. There are more trials ongoing, some of which may indicate a benefit, but until there is a clear consensus, doctors are advised to not prescribe this drug for this indication, but because it is approved for other indications, doctors have the option of going “off-label” and prescribing it for COVID, regardless. Again, science is real, science is also slow, and sometimes science takes detours.

Wednesday, August 5, 2020

Ruby-throated Hummingbirds

"Why is this bird different from all other birds?" Hummingbirds represent an evolutionary expansion into a niche frequented by flower-pollenating moths and butterflies. Downsizing and an elongated beak and tongue combination allows these birds to feed on flower nectar. The adaptation initially took place in tropical climates where the ability to retain body heat – typically a function of larger body size – was not critical.

More than 300 hummingbird species inhabit the Central American tropics. Only 16 frequent the U.S., and of these only one species - the ruby-throated hummingbird - migrates east of the Mississippi River. The rest go west. The risks of a longer eastward migration are offset by having a monopoly on the hummingbird niche once they arrive.

Painting of a male Ruby-throated Hummingbird
Ruby-throated hummingbirds winter in Mexico, then migrate as far north as Canada in the spring. Their journey begins with gorging on insects until body weight is almost doubled, then launching into a night-long flight from the Yucatan peninsula of Mexico to the U.S. Gulf Coast. The fuel for this comes from gorging on small insects and flower nectar. Once over land again, they revert to daylight eating every 10-15 minutes, consuming more than half their body weight over the course of each day.

In eastern Massachusetts these birds are in residence from May through September. The slightly larger, less brightly colored females arrive a week or two after the males. Males do not help with nest construction, egg incubation or feeding. Hummingbirds do not flock. A yard with multiple feeders can be host to several birds at the same time – a “charm” of hummingbirds – but in reality, what is seen is a temporary truce around a shared resource. Each bird, sated, goes back to its own territory.

Females lay two eggs. Nests are the size of a ping-pong ball, eggs the size of a coffee bean. Gestation is two weeks. Chicks are ready to leave the nest three weeks after hatching. Fledgling survival to adulthood is high compared to other species, and lifespan about five years if the fledglings survive the first migration. By comparison, a nesting pair of golden-crowned kinglets (a small, Maine-dwelling bird twice the weight of a hummingbird) will hatch two broods over the course of a summer, each numbering 8-10 fledglings, yet only one or two survive to the following year’s breeding season.

Hummingbirds are omnivores - they get carbohydrate calories from flowers - but all of their protein, fat, vitamins and minerals from eating gnat-sized insects. Sugar-water feeders supplement the energy needs also met by flower nectar. A well-managed feeder should attract visitors from May to September. For a natural alternative, plant monarda, honeysuckle, trumpet vine, and other hummingbird-friendly perennials. Do not use pesticides, as these will kill the small bugs hummingbirds also need to consume. Feeders do not deter hummingbirds from the urge to migrate south in the fall. 

Ruby-throated hummingbirds have some interesting dependencies on other species. Males arrive in the northeast before most of the flowers have opened. Instead of relying on nectar, the birds also feed on tree sap from holes drilled in trees by yellow-bellied sapsuckers. Females construct nests incorporating spiderweb silk.

Part of mural on the building at the corner of  Parker 
& Waltham Streets = male, broad-billed hummingbird.
In addition to small size and hover capacity hummingbirds employ an unusual energy conservation strategy - extreme body temperature modulation. During cool summer nights these birds allow their body temperature to drop from 105 to about 70 degrees Fahrenheit. Resting heart rate drops from 500 to 50 beats per minute (rate while flying can exceed 1,000). Without this trick of lowering energy expenditure via torpor they risk overnight starvation. Muscles are rewarmed in the morning by shivering.

Maynard is blessed with a hummingbird mural on the south side of the building at the corner of Waltham and Parker Streets. The bird in question is a male, broad-billed hummingbird, a species that winters in central Mexico but migrates as far north as southern Arizona during breeding season.   

A version of this column was published in 2012