In 1912, William Eagle Clarke [1853-1938] published his monumental ‘Studies in Bird Migration’, marking the end of centuries when some of the secrets of migration were gradually revealed by observations alone. Until about 1900, the recording of arrival and departure dates of breeding and wintering birds, and observations of birds on the move provided some key insights. Then in the early 1900s, John Watson conducted some revealing experiments on the navigation abilities of terns breeding in the Florida Keys, and bird-banding began to reveal the migratory pathways of waterfowl that were hunted for food and sport. Over the past century technological innovations have continued to provide increasingly accurate and novel insights into the patterns and processes that define bird migration: radar, planetaria, Emlen funnels, wind tunnels, radio-isotopes, geolocators, GPS transmitters, satellite tracking, genoscapes, and eBird. I expect that the best is yet to come as transmitters become ever lighter and provide continuous information (elevation, temperature, travel speed, llocal movements) about individual birds for months or even years.
Eagle Clarke was trained as a surveyor and civil engineer but was increasingly drawn to natural history, becoming Curator of the Leeds (Philosophical Society’s) Museum in 1884, at the age of 31. Then in 1888 he moved to Edinburgh to join the Natural History department at what is now the Royal Scottish Museum. He was elected President of the BOU in 1918.
In 1880, the British Association (for the Advancement of Science), at the recommendation of Alfred Newton, established a ‘Committee on the Migration of Birds’ to collate and interpret information on bird migration throughout Britain. Newton headed that committee until 1903. He felt that there would be much to learn by bringing together the myriad observations of passage migrants and arrival/departure dates from the many naturalists watching birds, particularly along the coasts of the British Isles. Newton knew that migrants were particularly common on some peninsulas and nearshore islands, as well as at lightships and lighthouses along the coast. He was particularly interested in solving three controversial issues: (1) why birds left their summer quarters after the breeding season (Newton argued it was due to the lack of food), (2) whether migrants traveled alone or in flocks, and (3) how the were able to navigate to their wintering grounds and back again. The navigation problem, he said, was one “Which to me seems the most inexplicable part of the whole matter.” (Birkhead & Gallivan 2012). Even today, almost 150 years later, that’s still a bit of a mystery.
In 1883, Eagle Clarke was asked to join that committee to help analyzing the data and preparing reports, particularly about ‘Migration of Birds at Lighthouses and Lightships’ (Brown et al. 1885). In their 1885 report, they concluded that ”A marked migratory movement might be expected in our northeastern counties between Scotland and Ireland, where the Channel is narrowest; but we have no evidence that such is the case. The usual course taken by birds seems to be either N.W. or S.E. The number of birds which only occur singly and do not seem to migrate in flocks is large. In such instances it is difficult to trace the line of migration.” Intriguing…and clear evidence that Newton was correct in suggesting that the committee might gain insights into the second of his key questions.
After almost 20 years of accumulating and analyzing observations of migrants, Eagle Clarke decided it was time to get some in-depth, first-hand experience at a few of these key migration sites. To that end, he first spent an entire month in the fall of 1901 at the lighthouse on the Eddystone Rocks, a series of islets in the English Channel about 20 km south of Plymouth. He had previously made many short trips to coastal migration sites but now he felt he “had practically failed to obtain satisfactory knowledge, by direct personal observation, as to one of the most important phases of the phenomenon—namely, that of emigration… the movement of all others which is performed under conditions of obscurity…undertaken during the hours of darkness, so that it escapes the notice of all save those few peculiarly placed observers, the light-keepers; and…only under certain meteorological conditions that the migrants seek the beacon’s light and reveal themselves to the watcher.” (Eagle Clarke 1903).
His perseverance was amply rewarded with significant numbers of migrants seen on 16 days between mid-September and mid-October. A couple of nights when the weather was poor, the lights attracted spectacular clouds of southward migrants, beautifully illustrated in a painting by his wife Marian and mirrored in his own poetic description of the migrants on that night of 12 October:
“Throughout the movement, and especially when it was at its height in the earliest hours of the morning, the scene presented was singular in the extreme and beyond adequate description. Resplendent, as it were, in burnished gold, hosts of birds were fluttering in, or crossing at all angles, the brilliant revolving beams of light; those which simply traversed the rays were illumined for a moment only, and became mere spectres on passing into the gloom. The migrants which winged their way up the beams—and they were many—resembled bails or streaks of approaching light, and they either struck the lantern or, being less entranced, passed out of the rays ere the fatal goal was reached. Of those striking some fell like stones from their violent contact with the glass, while others beat violently against the windows in their wild efforts to reach the focal point of the all-fascinating light. Many of those that freed themselves from the dazzling streams came in sharp contact with the copper dome of the lantern, making it resound again, and then fell like flashes into the surf below, followed slowly by a shower of feathers resembling a miniature storm of golden flakes. Finally, above and below the madding crowd in the illumined zone, great numbers of the emigrants flitted around in dim confusion, and in almost weird contrast with the brilliant multitudes gyrating in the adjacent vistas of light.”
As a teenager in the early 1960s, I spent many a weekend during spring and fall migration banding birds at the nascent Long Point Bird Observatory in Ontario. Long Point is a 40-km-long sand spit that juts eastward from the north shore of Lake Erie. The banding station sits at the end of that spit, literally in the shadow of a 30-m tall lighthouse built in 1916. On the occasional foggy, rainy nights hundreds or even thousands of birds were attracted to the light, perfectly captured in Marian Eagle Clarke’s painting of the Eddystone Lantern and in her husband’s prose (above). From the platform outside the light itself, we would watch as disoriented gaggles of birds followed the rotating light beam for hours before landing exhausted on the red railing to be caught and banded by us the next morning.
Each foggy night, though, many birds fell to the marshes below—exhausted or killed by crashing into the windows around the light—where the local foxes and racoons would feast on them while we tried to gather them up to make into study skins. From 1960 through 1989, the average kill of songbirds there on foggy nights was 200 in the spring and 393 in the fall, with the record being 2000. As early as September 1929, there were at least four major kills at that light, when 654, 169, and 1237 (2-night total) birds were picked up by the keeper, and identified by a local naturalist (Saunders 1930). On those four nights, 55 species were picked up, mostly red-eyed vireos (176), wood warblers (1267), and thrushes (332). Then in 1989, the lighthouse was automated with a flashing light, rather than a rotating beam, and the songbird kills plummeted to a foggy-nightly average of just 18 in spring and 10 in the fall.
Although lighthouses may no longer be much of a threat to migratory birds, artificial lighting is an ongoing source of avian mortality and the disruption of their normal behaviours (e.g., Iasiello & Colombelli-Négrel 2025). Newton and Eagle Clarke argued about the possibility that such mortality would be a source of natural selection on birds, Newton felt that it would eventually extinguish the attraction to lights from the birds’ gene pools. That it hasn’t suggests that there simply is not enough heritable variation in the attraction to lights to move the evolutionary needle. But why is that behaviour so hard-wired in so many species?
Further Reading
Birkhead, T.R. & Gallivan, P.T. (2012) Alfred Newton’s contribution to ornithology: a conservative quest for facts rather than grand theories. Ibis 154: 887–905. VIEW
Brown, J.A.H., Cordeaux, J., Barrington, R.M., More, G.A. & Eagle Clarke, W. (1885) Report on the Migration of Birds on the West Coast of England and Wales in 1884. Report on the Migration of Birds, 1884 pp. 101- 124. VIEW
Eagle Clarke, W. (1902) A Month on the Eddystone: a Study in Bird-migration. Ibis 44: 246–269. VIEW
Eagle Clarke, W. (1912) Studies in Bird-migration. LONDON: Gurney and Jackson. VIEW
Iasiello, L. & Colombelli-Négrel, D. (2025) Bright and early: artificial light affects arrival time, but not group size or vigilance in Little Penguins (Eudyptula minor). Ibis 167: 248–262. VIEW
Saunders, W.E. (1930) The destruction of birds at Long Point Light-House, Ontario, on four nights in 1929. The Auk 47: 507–511. VIEW
Image credits
Map from Brown et al. 1884, in the public domain
Eddystone Light from Eagle Clarke (2012) in the public domain.
Long Point lighthouse from Wikimedia Commons, CC-BY-2.0 licence. Photo by Ryan Blyth
