Picking sources

My work task for this weekend is making me aware of a gap in my education as a scientist. How does one decide which sources to cite when there are many available with the same information?

I and my assistants at Berkeley classified a significant number of primate species based on how much care fathers give to their offspring. For each species we would search the primary literature for sources documenting if fathers in that species provided care to their offspring, and if so how much. We gathered papers, sometimes dozen for a single species, read the relevant pieces and decided that fathers of that species provided no care, little or incidental care, significant care or were, for at least some part of their offspring's lives, the primary caregivers. This compilation allows me to compare the evolution of paternal care with that of other traits, such as the degree to which males fight for access to females in each species (the prediction being that males will tend to either invest heavily in their offspring or fight intensively for mates, but not both).

But what I have to do now is decide, for each species individually, which paper or papers to say I based my decision on when I publish this compilation. I've not actually studied any live primates myself. The many people who have dedicated years of their lives to documenting the behavior of each species, may disagree with my conclusion on their species (some inevitably will, I hope not too many). Those that do will be prone to dismiss the paper as a whole unless I at least give appropriate references to show I wasn't just making my data up. I feel like somehow I've made it this far without really knowing what rules to follow in documenting my sources. One can't just list every paper one consulted, or pick one at random. Should I reference the first paper to suggest that this species had that trait? Or the one with the strongest evidence, or the review article that states that the evidence for that conclusion is overwhelming? Should I include a reference to the dissenting papers, to show that I am aware of them, even if I disagree? Should I try to include references from the journal I plan to submit to?

What I'm actually doing, which may be the wrong approach, is referencing the papers I find most convincing and relevant, regardless of precedence, author or journal. As long as the reviewers don't object, I'll consider this strategy a success.

New York's Geese are exploding in another way

The Christmas Bird Count is one of the great success stories of Citizen Science. Every year in late December, tens of thousands of volunteers across North America brave snow and sleet and Christmas Shopping traffic to go out and see how many birds they can see. Everyone writes down how many individual birds they see of each species, and where they were looking, and all these data are collected into a central database. The Audubon Society's scientists know how many people were looking, and where, and they have large numbers of observers, so they can calculate pretty reliable winter range maps, and calculate rates of population change in each area.

Looking at their data for Canada Geese, a pretty remarkable number emerges. The number of Canada Geese in New York State in December has, for quite a while, been increasing by 22% per year! At that rate of increase, population would double about every three and a half years (1.22^3.5=2), and the population doubled at this rate starting about 1955 and leveled off about 1990, so it had time to double about 10 times. 2^10=1024. So for every goose in New York in late December before the 1950s, there is now a kilogoose in the same area at the same season. To put it another way, most CBC observers in NY in the first half of the 20th century saw not one geese. The average NY state observer these days sees 50 or 60 geese.

Here is a graph from the CBC historical query page.


There is a lot of noise in the data, but the trend is very clear.

So why are there so many more geese in NY in the winter? Partly, there are just more geese everywhere. Humans have been good to Canada Geese. Lawns, golf courses and grain stubble are all feasts for geese. We've killed off a lot of the natural predators, and we don't hunt them ourselves as much as we used to. And New York winters aren't nearly as cold and snow-buried as they used to be, especially around the city, which means fewer of the geese bother migrating any further south than New York.

In considering the causes of the bird-plane collision that caused yesterday's much publicized crash, we should keep in mind that a few decades ago, there would have been no geese to hit in January above the Bronx.

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
robin
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
mockingbird
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
starling
anna's hummingbird
allen's hummingbird
black phoebe
wrentit
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)
osprey
beardless flycatcher (not found in CA)
red-breasted nuthatch
white warbler (not a real species, no idea)