Friday, February 29, 2008

phylogenetic inertia and cooperative breeding

I spent yesterday evening reading the literature on the extent to which there is phylogenetic inertia (the tendency for related species to have similar traits because they both inherited those traits from the common ancestral population) in cooperative breeding (the habit of having more than two individuals caring for the young).

My general conclusions are:
1. A species whose relatives ae cooperative breeders are often cooperative breeders themselves.
2. It is not entirely clear if cooperative breeding itself is phylogenetically conserved in many groups, or if the traits that make it a useful strategy are conserved, leading to the impression of inertia in the evolution of cooperative breding.
3. Phylogenists spend a lot of time and ink poodling on about the flaws in each other's methods, but always end by saying that the conclusion about the trait is probably robust to minor variations in the shape of the tree.
4. Cooperative breeding is a blanket term for several different phenomena, and papers that deal with this explicitly are more convincing than those that only pay it lipservice.
5. The data I am already putting together on who provides how much care in 120 primate species could probably also be used for a very useful paper on phylogenetic inertia in cooperative breeding.

Monday, February 25, 2008

Biofuels won't fix it.

Pretty much every issue of Trends in Ecology and Evolution has a paper or two worth the reading. I thought this one was worth drawing your attention to:

Christopher B. Field, J. Elliott Campbell and David B. Lobell. 2008. Biomass energy: the scale of the potential resource. Trends in Ecology & Evolution. Volume 23, Issue 2, Pages 65-72

Increased production of biomass for energy has the potential to offset substantial use of fossil fuels, but it also has the potential to threaten conservation areas, pollute water resources and decrease food security. The net effect of biomass energy agriculture on climate could be either cooling or warming, depending on the crop, the technology for converting biomass into useable energy, and the difference in carbon stocks and reflectance of solar radiation between the biomass crop and the pre-existing vegetation. The area with the greatest potential for yielding biomass energy that reduces net warming and avoids competition with food production is land that was previously used for agriculture or pasture but that has been abandoned and not converted to forest or urban areas. At the global scale, potential above-ground plant growth on these abandoned lands has an energy content representing ~5% of world primary energy consumption in 2006. The global potential for biomass energy production is large in absolute terms, but it is not enough to replace more than a few percent of current fossil fuel usage. Increasing biomass energy production beyond this level would probably reduce food security and exacerbate forcing of climate change.

Sunday, February 24, 2008

Global Amphibian Declines call for frog costumes.

There are few, if any, taxa losing species diversity as quickly and thoroughly as the amphibians.


"Amphibians, a unique group of vertebrates containing over 6,200 known species, are threatened worldwide. A recent assessment of the entire group ( found that nearly one-third (32%) of the world’s amphibian species are threatened, representing 1,856 species. Amphibians have existed on earth for over 300 million years, yet in just the last two decades there have been an alarming number of extinctions, nearly 168 species are believed to have gone extinct and at least 2,469 (43%) more have populations that are declining. This indicates that the number of extinct and threatened species will probably continue to rise (Stuart et al. 2004)."

And this is almost surely an overly optimistic view. The thousands of species for which we have no data are not considered threatened, and an unknown number of others, likely in the hundreds, has gone extinct without ever being discovered.

Amphibian lineages that have existed for tens of millions of years are ending shockingly quickly. The factors that are killing off these ancient groups are all the works of humanity: pesticides, industrial pollutants, introduced species and diseases, habitat destruction and alteration and rapid climate change. There is no reasonable doubt but that we have driven the rate of amphibian extinction to several thousand times its natural rate. We could barely kill them off more quickly if we tried. Genocide is not too strong a term.

Amphibians are widely seen as indicator species. Healthy ecosystems have healthy amphibians. Indications are poor.

So to help raise (the currently abysmally low) awareness of the scope of amphibian declines, Iris and I have decided to walk Bay to Breakers wearing homemade from costumes. And we hope to organize a group of friends and colleagues to walk with us, similarly garbed. A costume recognizable as an amphibian, or even a shirt with amphibian pictures on it. Perhaps we will hand out informational pamphlets to people who ask what we are about. If you are interested in joining us, please email me.


I've written here before about what a poor job journalists generally do in describing science to the public. I was just reading this Op-Ed piece in the NYTimes and wincing over phrases such as "sharks are very primitive living fish" and "ensure the survival of a species," which reveal a very out of date and human-centric misunderstanding of evolution. The piece includes at least half a dozen points contradictory to modern evolutionary theory. I was just considering writing yet another response letter explaining to the author that natural selection does not favor traits because they help ensure the survival of the species, and so forth, when I looked at who the author is.

The attribution:
"Neil Shubin, an associate dean at the University of Chicago and the provost of the Field Museum, is the author of 'Your Inner Fish: A Journey Into the 3.5-Billion-Year History of the Human Body.'"

Neil Shubin knows that evolution doesn't work that way. So why is he writing like a journalist? I can only guess it is because he wants to sell more books, and someone (the NYTimes, his publicist or him) felt that one has to adopt the public's misunderstanding in order to interest them. It is sad when scientists start writing like science journalists.

Saturday, February 23, 2008

Field Notes

FEB. 23 2008
D. Levitis
Hillside Natural Area (North Unit) El Cerrito, Contra Costa County, CA

Sijie Mao, Nichole Winters and I went out from 1300 to 1530. It was quite windy with very strong gusts, temp in the lower 50s and varying between slight drizzle and significant rain. Our fist stop was the detritus field around the storm drain at the lowest point in the park, just behind my house, under the Eucalyptus. A lot of good cover items, but nothing under there. From there we went just up the hill to the small pile of shipping pallets on the grass. Under the first one I lifted was an Aneides lugubris (Arboreal Salamander)! The first I'd seen here. We took this as a sign of good salamandering to come.

We followed a route approximated by that marked on this map, but with many side excursions to check under log, rocks and other cover objects:

Much of this part of the Nature Area has many of the cover objects removed for yearly mowing, so much of the available cover is in piles of cut log pieces or small rocks piled at the base of trees and in gullies.

Sijie and Nichole are extremely contentious about putting every cover item back exactly as it was, and are energetic and enthusiastic herpers. We found almost nothing under rocks, but the logs were very productive today. We checked under approximately 400 wood bits and 100 rocks/cement bits and found 71 Batrachoseps attenuatus (California Slender Salamanders) 3 Aneides and one Elgaria multicarinata (Southern Alligator Lizard).

The Aneides were all near oaks, as Dave Wake told me to expect, while the Batrachoseps were under logs and a few rocks in every habitat we checked. The Elgaria was under a pine log in grassy habitat.

In addition to the herps, invertebrates were extremely numerous under cover objects, including Jerusalem crickets, cave crickets, ants, termites, ground beetles, several kinds of spiders including a couple of Black Widows, copious pill-bugs, snails, slugs, worms and sundry.

Many fresh gopher diggings were evident in the soft wet earth, and many of the logs and rocks we lifted had smaller rodent tunnels, quite possibly vole. Deer prints and fox scat were in abundance.

One bird species to add to my list for the nature area, Wild Turkey. One was seen at the northwest corner of our route, just north of Snowdon Ave. and another was heard responding to its calls. Nichole took pictures of the turkey, which was tame enough to allow her to approach to within 6 meters.

Our explorations revealed no standing water in which frogs could breed, which may explain their absence from our observations.

Birding today wasn't great, due to wind and rain, but saw/heard following birds today:

Western Scrub-Jay (2)
American Crow (10)
Northern Raven (2)
Black Phoebe (1)
Yellow-rumped Warbler (25)
Chestnut-backed Chickadee (4)
House Sparrow (15)
Ruby-Crowned Kinglet (2)
American Robin (40)
California Towhee (3)
Dark-eyed Junco (4)
Wild Turkey (2)
Red-shouldered Hawk (1)
Anna's Hummingbird (3)
Mourning Dove (6)

Eastern Fox Squirrel (Sciurus niger) (2)
Mule Dear (Odocoileus hemionus) (tracks)
Voles (Microtus californicus? runways and burrows)
Pocket Gophers (burrows)
Fox (Grey fox? scat)

Southern Alligator Lizard (Elgaria multicarinata) (1)
California Slender Salamander (Batrachoseps attenuatus) (71)
Arboreal Salamander (Aneides lugubris) (3)

Thursday, February 21, 2008

"Science" "Journalism"

Even taking into account how poor the state of science journalism is in this country, and what a sorry rag the San Fransisco Chronicle is, this piece on the danger posed to San Francisco by invasive pythons is well below the curve.
To summarize, there is an introduced population of Burmese pythons in the Everglades, 3100 miles away. A USGS lab used an off the shelf climate model to predict where in the US Burmese Pythons could deal with the climate, and San Francisco (along with pretty much the southern half of the US) showed up as one potential habitat.

The idiot who wrote the article then follows this train of thought to show that pythons will be eating pedestrians on Market Street by 2020:
•One python showed up at Lake Okeechobee, 100 miles north of the Everglades, and in the same direction it would travel if its single-minded goal was to reach Fisherman's Wharf.
•Pythons can travel up to 20 miles a month, and the road to SF is 3000 miles, so it will be here in 150 months, or about 12 years.
•Pythons eat mammals.
"Human beings - like rodents, beavers and deer - are mammals, government scientists confirmed."
•Giant snakes falling from office buildings and eating you.

The sad thing is, reading the article, I am not sure if he is joking, but I am sure there are some people who will think this is a real threat.

Wednesday, February 20, 2008

Chemicals of Science

A very kind scientist at McGill sent me samples of four different strains of rotifers, along with the formula for the medium he keeps them in. The rotifers look so lively and healthful that I decided to buy the chemicals and mix up some of his medium. The problem is that while I need a few milligrams of this and a couple of grams of that, nobody sells the stuff in quantities smaller than 500 grams of this and 1kg of that. So at the end of the project, I have almost the entire container left over, and because it came in a form that is so concentrated as to be toxic if swallowed, it all has to be treated as toxic waste. Iron-chloride is not very toxic, but if you swallow 500g you would be very unhappy. So what I will probably end up doing is mixing lots of extra solution, basically making artificial pond water, because that does not need to be disposed of as toxic waste.
I was complaining about all this to some colleagues, who replied that this is a perennial problem, and that almost any time one does lab work, one has to budget for disposal of the left over chemicals, because one can't buy them in small enough quantities. The College of Chemistry on campus has a chemical reuse library for this purpose (drop off unused chemicals with out paying for disposal, pick up extra chemicals without buying a whole container) but they don't allow people from other departments to participate, even if we ask real nice.
I looked through the various suppliers and ordered the smallest quantities possible, even when it cost more.
How thoroughly wasteful and silly this whole system is.

Sunday, February 17, 2008

Deep thoughts

It is striking to think that over the billions of years there has been life on earth, there have been countless billions of individual organisms that have died before reproducing successfully, and billions of organisms who would end up being the ancestors of the living things alive on earth today, but there has been absolutely no overlap between these two groups.

Why no "grandfather effect"?

Much of my time at present is consumed by setting up an experimental test of what is known as the grandmother hypothesis. The grandmother hypothesis, in short, is the best guess we have as to why the females of humans and a few other species can live well past the age of reproductive cessation. In most species, and indeed in human males, there is no significant post-reproductive lifespan. Individuals are physiologically capable of reproducing for as long as they live. But the females of humans, a few other primates, a couple of cetations and maybe elephants go through menopause and then can live a significant portion of their lifespan after that. Our closest relatives, the chimps and bonobos, apparently go through menopause at the same age as our females, but live at most a few years after that.

Evolutionarily, this makes sense. If one is no longer increasing one's lifetime reproductive success, staying alive offers no obvious selective advantage. No point in investing in physiologies and structures that will last 100 years if one is only going to reproduce for 50 years. Better to put those resources into having more kids now.

But under a certain set of circumstances, reproduction does not end with, or shortly after, childbirth. If your young aren't really able to take care of themselves for a decade or two, you aren't done reproducing until they don't need you any more. In most hunter gatherer societies, the survival rate of five year olds whose mothers die is quite low. So for human women, having a kid in the last several years of life was likely a waste of time.

Worse, the kid who didn't make it took time and resources that could have been put into other kids, and childbirth, particularly late in life, is dangerous. Plus, elder human females are important for helping their daughters raise their own young, and learn how to do so. It has been shown that young mothers in several societies have a higher success rate raising kids if their mothers are around. The women who stopped having kids and focussed on the kids and grandkids they already had, and avoided the risk of late life childbirth, are thought to have ended up getting more of their genes into future generations than women who kept giving birth as long as they lived. If so, and if this variation in life history was heritable, which seems likely, this differential reproductive success would inevitably lead to a population with more and more women stopping early and fewer and fewer giving birth late in life. This is, we think, why we ended up with this "grandmother effect" of women living well past reproductive age.

The benefit of having a grandmother around seems to be restricted to maternal grandmothers. And this observation, that paternal grandmothers don't seem to make as much of a difference (at least in the societies studied) to the survival of their grandkids, points to at least two possible reasons why we don't see a "grandfather effect" to go along with this "grandmother effect."

First, in most societies, at least those studied in this context, males are providing less in the way of vital care. So if a women has a son who has kids, perhaps she is less involved in care, or in teaching how to care, because her son is not as involved as his mate in that care, and the daughter-in-law is not nearly as likely to look for advice and help from her husband's mother than her own mother. And perhaps this same logic applies to grandfathers on both sides. If they are not who the primary caregiver can go to for help and advice, the advantage of having them around to help is smaller.

Second, paternal grandmothers are less certain of which is really their genetic grandchild. If a woman gives birth to a daughter, and watches that daughter give birth to babies, she can be very confident that those are her descendants. If a woman gives birth to a son, and then watches that husband's mate give birth, there is a significant chance (and we have the genetic data to substantiate this) that the baby was fathered by some other man, and those babies aren't her genetic kin. So investing in them heavily may not be doing her any good. This argument is doubly true for grandfathers. The daughter who is giving birth may not even be his. A couple of generations removed, and who can be sure?

A final reason males may not have evolved to have a post reproductive period comes back to that risk in late life childbirth. Men don't give birth, so the risk to late life survival posed by late life reproduction may be greatly reduced, or completely absent. Without that trade-off, why not keep on breeding as long as possible?

Saturday, February 16, 2008

Deer Populations and Ecological Illiteracy

The New York Times this week has an article about deer overpopulation in New Jersey (although the problem is just as bad throughout the forested northeast) and efforts to control it through culls.

The problem, and reactions to it, demonstrate the deep ecological illiteracy informing both sides of the debate. Groups that value the deer see them as a natural and beautiful part of the landscape. They are beautiful, and individually they are natural, but their populations are much higher than they would ever have been naturally. This is partially because of removal of predators (deer evolved to breed faster than the wolves and mountain lions could eat them) and partially because we have created so much high quality feeding habitat for them. Deer find the easiest and best food at forest edges, and because of human land use there is so much more forest edge than there has ever been before. Somebody or other, maybe Audubon, said that a squirrel could travel from Maine to Louisiana without ever having to come down from the trees. These were big trees with their leaves way up where deer can't reach, and very few breaks. The forests of the east are now young and fragmented; basically an all you can eat for the deer. And we can no longer rely on long snowy winters to cull deer populations every year. As a result, the effects that deer are having on the forest is very far from natural.

Experiments with deer exclosures (basically large fenced areas, chosen randomly in the forest to see what happens without deer) are fairly unambiguous. I've seen these experiments first hand in the old growth forest of upper Michigan. Working for ecologist Dr. Kerry Woods the summer after I graduated from college, one of my tasks was to revisit exclosures he'd built three years earlier. Outside the exclosures, where the deer can get, extremely few seedlings make it. The forest has an open, park like feeling, no understory. The deer population is so dense everything gets mowed. Inside the exclosures, dense hedges of rapidly growing saplings compete for light, but any branch that reaches outside the enclosure is quickly nipped off. This forest that had never been cut by humans was being kept from replacing itself by the deer overpopulation. The same pattern is being found all over the north-east.

But if the people who see the deer as wonderful parts of nature are ignoring ecology, they are not alone. Those who see deer overpopulation as a problem generally ignore the same ecological facts. Governments organize huge one time culls in limited areas, and are then surprised when deer from next door are attracted by the unexploited greenery. Deer populations with plenty of food and few predators can double every two years or so. Shoot 1500 out of 2000 deer in your county and four years later you are back where you started, even if you don't have deer moving in from adjoining counties.

Basic arithmetic tells us that until White Tailed Deer mortality rates exceed birth rates throughout the northeast, the regional population will not decline. Birthrates are unlikely to decline, unless the structure of the current forest changes so much that the deer are nutritionally limited. Not likely. And plans to control the wild regional population through some sort of sterilization program strike me as ludicrously expensive and incredibly unlikely to work.

So what causes mortality? Disease, winter, cars, predators, hunters. Disease we don't want to encourage, especially considering that many diseases that affect deer can also fell horses, sheep, cows and such. Winters are tending weaker. Sever storms are increasing, but to really knock back the deer population, one needs a winter that is very cold and snowy for months over a large area. Not likely. Few would advocate increased car-deer collisions. Hunters are limited in where they can hunt by the danger of bullets carrying to nearby houses, roads and such. And hunting seasons are limited, in part to make forests safe for other uses the rest of the year. There is also mounting evidence that deer hunters regularly dose themselves and their families with lead when they bring the carcass home. Natural predators are few and far between in the northeast, although coyotes are becoming both more common and larger, making it easier for them to bring deer down. The traditional predators, wolves and mountain lions, are unlikely to be restored to populations in the northeast sufficient to keep the deer in check.

So if reducing deer populations is important and none of our current strategies seem promising, what do I suggest? Integrated pest management. Look at the problem on a broad geographic scale, understand the demography in as much detail as we can, and figure out what the vulnerable point in the demographic cycle is. As an example, hunting seasons were traditionally in the fall and winter, exactly because hunting then reduces the deer herd the least. Fewer winter deaths, no pregnant does, few dependant young. If we really want to keep deer populations down, hunting should be done in the spring. Hunters have traditionally hoped for a buck. But killing a buck does basically nothing to reduce the population in the long term. Some other buck will be happy to inseminate all the does. One buck and a hundred does will produce just as many fawns as one hundred bucks and one hundred does. If our goal is to bring the population down, we need to target does, and let hunters take as many as they please, perhaps requiring the donation of excess meat to charitable food pantries. And we should do it with non-lead ammunition, so we don't poisoning ourselves in the process. And we should be honest enough to admit that we are going to have to do this every year in perpetuity, until the ecology of the northeast changes enough that deer populations are regulated naturally.

Brown Creeper

There are certain birds that, based on experience, I can place a very high prior probability on finding in any patch of trees around here. Anna's Hummingbird. American Robin, California Towhee, Ruby-Crowned Kinglet and so on. They're there, I can find them quickly. Most of these species made my bird list for El Cerrito Hillside Natural Area within the first day or two. But there is one bird I have high confidence is in all these patches, but not high confidence in finding. And that is the Brown Creeper, Certhia americana. The Brown Creeper, as its name suggests, is not a flashy bird. Small, brown, spotted for camo, the only American representative of the family Certhidae moves like its old world relatives; it creeps, foot over foot, up surfaces (in this case the trunks of trees) probing cracks and crevasses with its wrenish bill, looking for arthropods. It doesn't make a lot of noise, it doesn't make sudden movements, it is an extremely common bird that most people will never see unless they look for it. I have seen people walk past Brown Creepers that are at head height, five feet from their eyes and in full view, and never know the bird is there.

So I have had my eyes and ears open for the little sneakers ever since we moved to El Cerrito, and been continuously thwarted. Occasionally I will see a flash as something shoots past, flapping like a creeper flaps, but been unable to get a good enough look to confirm the identity. I have heard what I thought was creepers but couldn't be sure. But this morning, Iris and I went for a short walk under the oaks just outside our back yard, and a flash of bitty wings caught my eyes. My brain said "Creeper!" I swung around, unwilling to take my eyes off it as it flitted this way and that through the branches, and then dropped, coming to rest on a tree trunk ten meters from us, fully visible only because my brain knew it was there. Iris and I both raised our binoculars. Sure enough, a Brown Creeper, trickling up the trunk. That swaying foot over foot climbing makes the bird move more like a wavering shadow than a living thing, and the speckles on the bird's back looked like little bits of every kind of bark in the forest. Being reminded of this, I felt a little bit of pride at having spotted this very common backyard bird. I'm sure there are hundreds of them back there.

Friday, February 15, 2008

Journal of the American Forehead Slapping Assosciation

In another big no-shock-shocker that needed to be demonstrated anyway, It has been found that when poor women are given vouchers to local farmers' markets, their families eat more fruits and vegetables. While anyone with two axons to rub together could have predicted this, I am still glad they took the time to prove it.

METHODS: Women who enrolled for postpartum services (n=602) at 3 WIC sites in Los Angeles were assigned to an intervention (farmers' market or supermarket, both with redeemable food vouchers) or control condition (a minimal nonfood incentive). Interventions were carried out for 6 months, and participants' diets were followed for an additional 6 months. RESULTS: Intervention participants increased their consumption of fruits and vegetables and sustained the increase 6 months after the intervention was terminated (model adjusted R(2)=.13, P<.001). Farmers' market participants showed an increase of 1.4 servings per 4186 kJ (1000 kcal) of consumed food (P<.001) from baseline to the end of intervention compared with controls, and supermarket participants showed an increase of 0.8 servings per 4186 kJ (P=.02). CONCLUSIONS: Participants valued fresh fruits and vegetables, and adding them to the WIC food packages will result in increased fruit and vegetable consumption.

Friday, February 08, 2008

Citizen science, and the limits thereof

One of my neighbors sent me a copy of a list that she was given by the people who sold her her house. They told her they saw all these species in El Cerrito Hillside Natural Area. At first was excited to see this list, and the first several species on there are quite reasonable, but a more careful look significantly lowered my level of confidence in these observations. This is a perfect example of why "citizen science" projects that rely on non-experts to gather natural history data require great care. Below I have pasted in the list, with some comments.

chestnut-backed chickadee
common bushtit
turkey vulture
cooper's hawk
american kestrel
red-tailed hawk
common crow
common raven
great-horned owl
ruby-crowned kinglet
woodthrush (Does not occur in CA, probably Hermit Thrush)
red-shafted flicker
winter wren
hairy woodpecker
downy woodpecker
brown towee (Californa Towhee)
rufous-sided towee (Spotted Towhee)
oregon junco (Dark-Eyed Junco)
purple finch
house finch
pine siskin
wilson's warbler
tennessee warbler (does not occur in CA, Orange-Crowned Warbler)
american goldfinch
lesser goldfinch
lawrence's goldfinch
plain titmouse (Oak Titmouse)
scrub jay
steller's jay
mexican jay (Does not occur in CA, probably juv. scrub-jay)
cedar waxwing
western wood pewee
mourning dove
bead-tailed pigeon (Band-tailed Pigeon)
fox sparrow
savannah sparrow
harris's sparrow (Does not occur in CA, probably House Sparrow)
golden-crowned sparrow
anna's hummingbird
allen's hummingbird
black phoebe
marsh hawk (Same as Northern Harrier, listed below)
swainsons's thrush (possible)
mississippi kite (Does not occur in CA, probably Northern Harrier)
rufous hummingbird (nearly impossible to tell from Allen's except in hand)
canada goose
brown pelican (in park or flying in distance over bay?)
slate-colored junco (same as junco listed above)
warbling vireo
lazuli bunting (possible)
western tanager
bluegray gnatcatcher
empidonax flycatcher
bewick's wren
yellow-rumped warbler
townsend's warbler
hermit thrush
myrtle warbler (same as Yellow-rumped arbler)
beardless flycatcher (not found in CA)
red-breasted nuthatch
white warbler (not a real species, no idea)

El Cerrito Hillside Natural Area, February list

Here is the February list. 53 species are listed at present.

Western Scrub-Jay
Stellar's Jay
American Crow
Northern Raven
Hutton's Vireo
Black Phoebe
Yellow-rumped Warblers
Townsend's Warbler
Brown Creeper
Bewick's Wren
Chestnut-backed Chickadee
Oak Titmouse
House Sparrow
Ruby-Crowned Kinglet
Golden-Crowned Kinglet
American Robin
Bush Tit
Hermit Thrush
Northern Mockingbird
White-crowned Sparrow
Golden-crowned Sparrow
Song Sparrow
Spotted Towhee
California Towhee
Dark-eyed Junco
Cedar Waxwing
American Goldfinch
Lesser Goldfinch
Pine Siskin
House Finch
Wild Turkey
Cooper's Hawk
Red-tailed Hawk
Red-shouldered Hawk
American Kestrel
Great Horned Owl
Red-breasted Nuthatch
Downy Woodpecker
Red-shafted Flicker
Red-breasted Sapsucker
Nuttall's Woodpecker
Anna's Hummingbird
Selasphorus Hummingbird (Either Allen's or Rufous, two nearly indistinguishable)
Turkey Vulture
American Coot
Double-crested Cormorant
Ring-Billed Gull
Rock Pigeon
Mourning Dove

Eastern Fox Squirrel (Sciurus niger)
Mule Dear (Odocoileus hemionus)
Voles (Microtus californicus? runways and burrows)
Pocket Gophers (burrows)
Fox (Grey fox? scat)
Skunk (smelled, species?)

Southern Alligator Lizard (Elgaria multicarinata)
California Slender Salamander (Batrachoseps attenuatus)
Arboreal Salamander (Aneides lugubris)

Sunday, February 03, 2008

Mixed-Species Flock

I've been seeing a lot of cedar waxwings and robins recently, and I'm used to seeing them together, but Saturday in our backyard was the biggest mixed flock of these two species Ive ever seen. Forty birds shooting this way and fifty coming back that way, a clamor of robin whinnies and waxwing whistles from ever tree and bush. The robins numbered in the hundreds and waxwings outnumbered them, but in the whirling bickering flock, I couldn't really tell how many hundreds there were. There were American and Lesser Goldfinches, Chestnut-backed Chickadees, Oak Titmice and at least one Bewick's Wren feeding with the flock. Anything with berries on it was covered in birds, coming, filling their bellies and quickly being replaced by the next wave. I took the opportunity to take a couple of hundred photos, although most of them ended up with streaks as other birds flew into, out of, or through the frame. Some of the best shots are in this album.

I also took the opportunity to teach Iris how to identify these species. She asked the excellent question of why all there birds were moving around together, when it seemed like they were all squabbling over the same food. This is actually a questions several scientists have looked into, and the answer seems to be that like most things, one has to consider the costs and benefits. When the costs of participating in the flock (competition for food, time lost arguing) are outweighed by the benefits (protection in numbers from predators, more guides looking for food) then the birds flock. In the case of waxwings and robins, they are looking for a very patchy resource. While a bush is making berries, it is hard for even a huge flock to use up all the food, but the good berry bushes may be rare. So the cost of competition is low, because there is so much food on each bush, but the benefit is high, because by following the flock one doesn't have to waste time finding the food. Go where the flock is loudest and there is sure to be a bush covered in berries. And with so many eyes around, no predator could possibly sneak up. I saw one scrub-jay (which will occasionally kill and eat smaller birds) being chased by about 40 waxwings and a couple of chickadees. Once the jay was well away, they all went back to feeding.