With all the snow and ice melting this week, I decided to get some photos of frozen waterfalls before they disappeared. The largest waterfall in the Twin Cities, Minnehaha Falls, was pretty spectacular in the morning sun.
We have entered the ice-melt stage of winter (or is it spring, now?), and with temperatures soaring into the low 40s (F), Minnesotans begin to shed clothing.
The weatherman commented today: “Isn’t it strange that 40 F in October feels so cold, yet 40 F in March feels so warm — why is that?”
This is a result of seasonal acclimatization, and almost every animal experiences it in response to long-term exposure to a particular climate.
In October, at the end of the summer’s dog days, we humans are still in heat dissipation mode, flushing heat to the skin to unload it and trimming metabolic furnaces back to reduce heat production. With acclimatization to heat, we lack protection against the chilling effects of 40 F temperatures.
However, after a prolonged spell of exposure to freezing temperatures, we have revved up the metabolic furnace considerably to keep us warm (the thyroid gland plays an important role here), and the blood flows to all extremities via a central core of vessels (deep to the skin surface) to conserve heat. Other warm-blooded animals would have added a thick layer of insulating body fat, fur, or feathers to protect them from losing heat.
So, it’s really no surprise that a day above freezing would be considered a heat wave. It must be time for a picnic!
Walking along the Mississippi River among the trees of the flood plain forest this morning, I heard a deep, resonant drumming that could only come from one bird, so I followed the noise and found…
After a succession of drumming solos, he disappeared around the back side of the tree, so I followed and got closer.
The male and female Pileated pair stay together on their territory in mature forest all year, but almost always construct a new nest each year. These abandoned nest holes are highly sought after by other bird or mammal species to raise their own broods.
The male starts the nest construction process and the female completes it, but the whole process takes 3-6 weeks. Apparently in this part of the construction phase, there was quite a lot of debris that required clearing out, before he could enlarge the hole or excavate any further. Eventually the nest hole will be 10-24 inches deep.
Pileated Woodpeckers are a kind of keystone species in these mature forests, that is, a species on which many other species depend. Their excavations open up resources for a variety of other animals, both for food and for nesting sites. Flying squirrels, red and gray squirrels, owls, tree-nesting ducks, and a variety of small songbirds make use of the (con) and (de)structive work of Pileated Woodpeckers.
At various times throughout the winter, I have seen either the male or the female Red-bellied Woodpecker at the bird feeder or on the trees near the feeder, but never together at the same time in the same place.
I have to admit that this shot is fake — I inserted the female into the photo of the male, just to test out another, different feature of Photoshop, and I haven’t quite got the knack of cutting and pasting an object into another photo yet.
But my purpose in showing them like this is to emphasize how similar in size they are, often not the case in many species where either the male or the female is substantially larger. Similar size and anatomy means that males would potentially compete with females for food resources in their breeding territory, unless they harvested it in different ways somehow.
If you watch closely, it does seem that the two sexes prefer to forage on different parts of the tree — the males more on the trunk and thicker branches, the females more on the higher, thinner branches. And, even though they are similar in body weight, males have a stouter bill and a longer tongue with a broader tip and barbed end, for harvesting insects deeper in the wood.
Still in the grip of winter here…the world is mostly gray, white, and brown. But there are some bright red spots that add beautiful color to the monochromatic landscape.
I found a wealth of helpful videos on the web for people like me who don’t seem to take the time to read a book to find out how to do something. Rick Peterson’s YouTube website is particularly good at illustrating various techniques, for almost all versions of Photoshop Elements.
It’s often difficult to separate the subject being photographed from its background, especially when that background involves numerous tree branches and leaves that distract glaringly from the subject.
A male House Finch posed for several minutes on the tree outside my porch window, but even though I thought he was in the clear, the photos looked cluttered with excess numbers of twigs, stems, and branches.
So I decided to improve on getting rid of unwanted features in photos, and put some of the power of Photoshop Elements to work that I hadn’t used much.
I’m not a fan of highly manipulated photos, but sometimes it’s fun to see what it could look like, with better shooting conditions. Which type of photo do you like best?
The House Finches are definitely feeling spring-ey and are singing up a storm, even if the cardinals are just half-hearted about it. The male finches seem particularly bright red these days, as their hormones rev up. I assume the outer duller portions of their fall molted feathers have finally worn off to show their rosy glow.
A second generality that has been described for assemblages of communities of island fauna derives from competition between species there. Based on the fact that “complete competitors cannot coexist“, a species that tries to colonize an island must be, or do, something different than the ones already there.
Take doves, for example:
Doves are strong fliers, able to cross vast spaces of open water or land in search of food and water. They snack almost exclusively on seeds and fruit (and maybe a few insects in the litter), but usually aren’t too fussy about the types of those food items they exploit. On almost every Caribbean island, there is at least one species of dove present, and often more. But there are rules determining which dove species will colonize islands, because, being generalist seed consumers, there is potential competition for the limited food resources of an island.
Island rule #2 suggests that on small islands of limited geographic diversity, species occupying similar ecological niches will differ from each other in body weight by approximately a factor of 2. Some argue that the size differences translate to more efficient use of the resources with less inter-species competition; others argue that size differences prevent potential species hybridization; yet another suggestion is that size variation within the “guild” of seed-eaters prevents further colonization by other, potential competitors. Whatever the reason, the size ratio rule seems to work well for some groups of species on some islands (see Case et al. 1982 for more details)
So, let’s test the validity of this rule with the dove species I saw on Culebra.
White-winged Doves are also found on Culebra, and on Puerto Rico as well as many other Caribbean islands, but they don’t breed there. One reason might be their fondness for the seeds of Saguaro cactus found only in the Sonoran desert of southwestern U.S.and Mexico, but another might be the fact that they are roughly the same size as the Zenaida Dove, which has already established its presence during the nesting season on Culebra and Puerto Rico.
Island visitors are often struck by how large some animals get compared to their mainland ancestors: flightless (extinct) dodos (a pigeon!) on Mauritius, giant hissing cockroaches on Madagascar, Komodo dragons on Indonesian islands, giant tortoises on the Galapagos, to name a few. And Puerto Rico has its “giant” land iguanas, which lay around on sand or shore, unintimidated by human presence.
But not every species that manages to find an island home grows into a giant, and thus Island Rule #1: small-bodied species tend to get larger on islands while large-bodied species tend to get smaller (depending on the existing competition for food there and who got to the island first).
In particular, large-bodied herbivores (e.g., elephants, hippos, deer) develop into dwarfs of their mainland ancestors, and relatively quickly — within just 5,000 years in some cases. This makes sense because there simply wouldn’t be enough food on an island to support a population of large-bodied, warm-blooded, leaf eaters.
Case in point — the Key Deer in the Florida keys are about 1/2 the size of their White-tailed ancestors. Food is limited on the key islands, and deer don’t seem to be great swimmers.
Gigantism occurs most often on islands where there are no mammalian predators, and is more frequent among smaller-bodied mammals (rodents, in particular), reptiles, and some bird species. However, when an increased body size impacts foraging habits, like flight in birds, or hanging from ceilings in geckos, then food acquisition puts constraints on the increased body size.
Warning to those visiting tropical islands: watch out for the giant rats!
When I was a graduate student (in the 1970s), American Kestrels were one of the most common avian predators I saw in upstate New York on almost a daily basis, as they perched along roadsides hoping to spot an errant grasshopper or mouse in the grass.
Kestrels can be found throughout the Americas, from the most northern Alaskan tundra to the tip of South America (except the Amazon basin), including Caribbean islands, in a wide variety of habitats. Although still considered one of the most common raptors, their populations have declined 48% since the 1960s, as the magnitude of the red areas showing population declines in the Breeding Bird census data show.
While I rarely see kestrels in MN these days, I was pleased to see them frequently while we were in Puerto Rico, and even on its small island neighbor, Culebra, where they seem to be fairly common.
Kestrels prospered in the late 18th and 19th centuries in the Americas, when forests were being cleared for agriculture. The open grassy spaces made perfect hunting grounds for their insect, small bird and mammal diet, and forest borders provided the requisite number of tree holes for nesting. So why the decline in more recent times, and especially in the last couple of decades?
Are they vulnerable as prey of other raptors? Cooper’s Hawk populations are increasing as Kestrel populations are shrinking — coincidence or causation? A recent paper found no evidence for Cooper’s Hawk numbers or incidence of West Nile virus as a cause of Kestrel population decline, but suggested that nesting sites were a limiting factor.
Another explanation might be changes in farming practices in the U.S.: clearing the fields of hedge rows and forest edges where the birds might find nest holes, pesticides that eradicate potential insect prey, conversion of more pasture land to cropland, etc.
Progress for humans often take its toll on the wildlife, unfortunately.
nights below 0 F (-18 C)!
I had a two week break from this, and now I am doubly tired of this miserable cold weather. Is this the winter of no end? (whine, whine…)
Meanwhile the east coast is enduring yet another snow/ice fall with all the discomforts that go along with that kind of weather.
But we shall endure….right?