This is a bit of a different Dawn Chorus but feel free to post bird photos, identification questions, and anything else that catches your fancy in the comments. Sorry for the lack of pictures.
Ornithology is the biological study of birds. It encompasses such fields as physiology, paleontology, developmental biology, conservation, and so on, as long as the studies in these disciplines have birds as their subjects. Ornithology is distinct from birding although the vast majority of ornithologists are also birders.
The link between birding as a pass time and the professional study of birds is particularly strong among scientists who work on birds in the field, studying their ecology, evolution, and conservation. Birds are appealing subjects for field studies for a number of reasons but chief among them is that birds are mostly active in the day and vision is the primary sense. Just like us. So they are much more obvious to us and, in many ways, their lives are more easily interpretable than the lives of most mammals which are active at night and primarily use scent and sound. The bright plumage of cardinal or a goldfinch seem beautiful to us and we can much more readily appreciate them than the odors produced by a fox or a deer for much the same purposes.
The great interest in birds and the fact that so much of their lives can be readily observed in the field led to ornithologists being among the scientists who made great strides in understanding the basic principles of ecology and evolution. The concept of an ecological niche was first used in a study of the California Thrasher by Thomas Grinnell in 1917. The very important biological species concept, the idea that species are formed through a process of populations becoming reproductively isolated, was developed by Ernst Mayr based on his detailed studies of birds in New Guinea and elsewhere.
Today I want to focus on an ornithologist whom I wager many of you haven’t heard of who was an important link between the descriptive natural history that formed the basis of field ornithology before world war II and studies based on a rigorous understanding of evolutionary theory starting in the 1960s. David Lack (1910-1973) was a British ornithologist who was a crucial figure in the founding of the field known as evolutionary ecology. He was also the second director of the renowned Edward Grey Institute of Ornithology at Oxford University, serving in that position for almost thirty years, ending with his death.
Lack’s career trajectory was a bit unconventional. He had been an avid naturalist and birder from an early age. After getting his undergraduate degree he had gone to work as a schoolmaster in the early 1930s. In the late 1930s he took a year off from his job to pursue bird research and made an extensive visit to the Galapagos followed by visits to the California Academy of Science and the afore-mentioned Ernst Mayr. Following these trips, Lack enlisted during World War II, working in radar research throughout the war, experience he would later put to good use studying bird migration. In 1945, at the conclusion of the war, he was made director of the Institute of Ornithology as I mentioned above. How he got such a prestigious position with such meager professional credentials is a bit baffling from the perspective of the current hyper competitive academic environment. He didn’t get a graduate degree until 1948.
In any event, he turned out to be an excellent choice. Lack was fairly unique at the time in his emphasis on ornithology as the study of living birds in their environment rather than the collection and study of museum specimens. He also appeared at a crucial time when ecology and evolutionary biology were converging. The early evolutionary biologists were ‘ecologists’ (a term that didn’t exist at the time) such as Darwin and Wallace but evolutionary biology hit a temporary dead end in the late 1900s due to a lack of understanding of genetics. As a result the dominant figures in evolution from world war one until the 1940s were the geneticists moving the field forward. Ecologists were often interested in evolution but their views were fairly unsophisticated. A major problem with the ecological ideas about evolution at the time can be summarized by the term ‘for the good of the species’.
Unfortunately this term pops up in TV nature shows to this very day making evolutionary biologists tear out their hair in exasperation. So what’s wrong with ‘for the good of the species’? Certainly we see all kinds of traits in nature that allow species to be successful. And if there were traits that didn’t benefit species then said species would likely go extinct. The problem is that natural selection acting at the level of an entire species is relative weak compared to natural selection acting on individual organisms. It is extremely difficult for characteristics to evolve via natural selection that are ‘good’ for the species but bad for the individuals that bear them. For example Darwin was greatly troubled and perturbed by social insects such as ants in which most individuals don’t reproduce and work to help other individuals reproduce. For this trait to evolve the tendency to not have offspring needs to be passed from parent to offspring which can’t happen for individuals that don’t have offspring. Hence Darwin’s puzzlement at the non-reproductive castes of social insects. This was eventually explained in the 1960s by W.D. Hamilton with his idea of inclusive fitness.
Ornithologists of the era explained a lot of interesting characteristics of birds as being related to two things: species recognition and population regulation. The idea was that characteristics such as clutch size, mating displays, and traits that differed between two closely related species kept species intact (i.e. not merging into other species) by preventing mating with individuals of the wrong species and maintaining populations at sizes the environment would support. In other words individuals would avoid over-populating their habitat by estimating population size through observation of displays of other individuals. Individuals would also limit their clutch size to avoid over-populating their habitat. They would avoid mating with members of other species because that would harm their species.
Lack was one of the earliest scientists from an ecological background to really understand the logical inconsistencies of there arguments. If individuals have versions of genes that cause them to avoid or reduce reproduction when it would be bad for the population those versions can only persist if they actually give the individuals with those genes higher average reproduction than individuals that ignore population size and reproduce as much as they can. In other words it is necessary to understand something like clutch size, if it is an adaptation, as an adaptation for individual benefit. Otherwise different versions of the gene, that cause individuals to ‘cheat’ and reproduce at a higher rate will spread through the population.
Lack’s major contributions to the field were his studies of Darwin’s finches and then his detailed studies and theoretical work on clutch size in birds. The term Darwin’s finches refers to a group of about 14 songbirds found on the Galapagos islands with one species on Cocos Island (an island in the Pacific belonging to Costa Rica). Although called finches they are now thought to be more closely related to tanagers. Darwin collected specimens of these finches during the voyage of the Beagle but didn’t really understand their significance. John Gould, at the British Museum, recognized them as a single group of species that varied greatly in size and bill characteristics. Darwin used them as an example of evolution of new species on islands (what we would call an adaptive radiation) in the ‘Origin of Species’ and they have served that role in text books ever since.
The term Darwin’s finches was coined for the group in the 1930s and Lack published his own book, entitled ‘Darwin’s finches’ in 1947 based on his brief field work and study of museum specimens. He greatly expanded the ecological side of the story, emphasizing the role of beak characteristics in obtaining food and emphasizing the role of adaptation to different feeding environments in driving speciation. This work really laid the baseline for more detailed studies of these birds in the future (see below).
Lack’s most influential work was his work on clutch size and the formalization of the study of life history traits in birds and other organism. A life history trait is a characteristic that should be closely tied to the evolutionary fitness of the individual. Examples include number of offspring, size of offspring, age at sexual maturity, lifespan, etc. Having more offspring should always make you more evolutionary successful, so why don’t all individuals have as many offspring as they possibly can.
As I stated above, some ornithologists had interpreted clutch size as an adaptation to maintain a population at a viable level. In other words eagles have smaller clutches than ducks because fewer eagle chicks are needed to maintain the population than ducklings because ducklings die off faster. Lack’s idea was that clutch size in birds was determined by the number of chicks a pair of birds could successfully fledge based on food supply. Natural selection would act against birds that produced too many eggs as their offspring would starve. Or the parents would be so harmed by their effort one year to rear a large brood that they (the parents) would be unlikely to survive to the next year to have more offspring. Lack pointed out that under ‘ideal’ circumstances (such as low population size and abundant food) even species with small clutch sizes had rapid population increases. Therefore maintenance of population size was not linked to clutch size. He also argued forcefully that the clutch size in a population is going to be the size that, on average, results in the greatest number of fledged offspring. In other words the clutch size that is most beneficial to the parents.
Lack’s arguments were a bit naive by modern standards; he ignored other evolutionary forces such as genetic drift and he didn’t really consider other ecological factors beyond food supply in determining clutch size. But his thinking, his focus on the link between the characteristic and individual success in reproduction, represented a dramatic step forward from the rather vague ‘good of the species’ thinking.
Birds care for their offspring, usually in nests that are detectable without digging big holes or anything like that. Furthermore, usually both parents care for the offspring and individuals can be potentially marked for life (by banding) before they leave the nest. These characteristics make it possible to follow individuals in populations over multiple generations, recording characteristics and reproductive success. Lack’s work paved the way for many many long-term demographic studies of bird (and other animal) populations in which the characteristics, reproduction, and fates of individuals are recorded over many many years. These studies represent huge amounts of work, work that lasts beyond the career of a single academic in many cases. The longest running study of a single bird population was one started by Lack himself in the late-1940s shortly after becoming the director of the Institute of Ornithology. This is a study of Great and Blue tits in Wytham Woods in Oxford. Examples of long-term studies in North American birds include Glen Woolfenden’s work on Florida Scrub Jays at Archbold Biological Station, Jerram Brown’s work on Mexican Jays in the Chiricahua Mountains in Arizona, Walt Koenig’s work on Acorn Woodpeckers at the Hasting Natural History Reservation in California, Fred Cooke’s study of Snow Geese in the Canadian arctic.
Among the people influenced by Lack were Rosemary and Peter Grant who began detailed studies of a single species of Darwin’s finch on the tiny Isla Daphne Major in 1973. They have spent six months of every year on Daphne Major since that time with field assistants there at other times. Their work is perhaps the greatest example of studying the ecological context of evolution in the field and it has gone from the fundamentals of carefully monitoring every bird to modern studies of molecular evolution. But that’s a tale for another diary.
Note: I’m going to be doing some field work this morning so I probably won’t be around until after 10 AM eastern (at the earliest).
Second Note: I’ll be out of town next week and just returned to town the following week so other Dawn Chorus hosts would be appreciated for those days. Or Kestrel has several diaries waiting in the queue.