On his honeymoon, Julian Huxley [1887-1975] spent his mornings watching the breeding habits of the Great Crested Grebe. Soon after their marriage in the spring of 1919, Julian and his new wife, Juliette, repaired to a cottage about 50 km southwest of London, England, not far from Frensham Pond where Julian set up a hide to watch his birds. Juliette was not impressed: “Julian erected a very small bird-watcher’s canvas hide, just big enough for one. He settled in every morning, equipped with telescope and notebook, to watch the Great Crested Grebes at their ritual courtship and display. I joined him later, marking time in the bitter April wind. The birds did not display, defeated by the cold wind, and I was bored and frozen.” (Huxley 1986). She lamented that Julian seemed more interested in the nuptials of grebes than in his own nascent love life.
Huxley had begun his grebe research in the spring of 1912 on a pond at Tring, on the estate of Walter Rothschild. For two weeks there, aided by his brother Trevenen, Huxley watched a pair of grebes courting, copulating, and incubating. The result was a landmark paper describing in intimate detail the behaviour of this mated pair, and interpreting what he saw in light of Darwin’s theories. Here is Juliette again:
“The grebe, of course, as I only discovered later, was Julian’s seraphic symbol: the bird whose secret he unravelled, writing his first paper in 1914 (reprinted in 1964), a paper which was an historic milestone in the study of animal behaviour and which later led Konrad Lorenz to refer to Huxley as one of the Founding Fathers of Ethology.”
Edmund Selous (1901-02) had previously studied the breeding habits of Great-crested Grebes, anticipating some of Huxley’s interpretations of their behaviour, as Huxley fully acknowledged. But Huxley was a better writer and salesman, using his grebe studies to comment on the parallels to human behaviour and society. Indeed, as Bartley (1995) has argued: “…Huxley’s work on birds was largely constructed around the social and political goals he held for humans; bird courtship behavior provided him with a case study to promote his agenda on human progress.”
Huxley was understandably perplexed by the fact that the male and female both had the same colourful, ornamented plumage, and engaged in mutual courtship displays well after they had paired and begun incubating. This suggested to him that Darwin was wrong about female choice being a mechanism underlying sexual selection (Huxley 1938). His studies of the courtship behaviours of birds were so influential that interest in sexual selection in general, and female choice in particular, remained in the shadows of evolutionary biology for another half century.
Huxley correctly surmised that there are hormonal and neurobiological underpinnings to that sort of male-female attachment (Bales et al. 2021, Young and Wang 2004), and that those mechanisms are likely widespread in animals, including humans. Thus, he had no trouble using terms like ‘emotion’ and ‘love’ when referring to the birds’ behaviours: “These latter are often very emotional, and the courtship habits of the Grebe afford a very specialized example of this emotional bond between members of a pair.” And because the birds performed their mutual displays after the pair was formed and the ‘bond’ established: “…the word Courtship is perhaps misleading as applied to the incidents here recorded…”Love-habits” would be a better term in some ways…” (Huxley 1914).
Niko Tinbergen (1936) also referred to “the formation of sexual bonds” in his paper on the function of territoriality, suggesting that there was some kind of special ‘bond’ between the members of a mated pair. Three years later, David Lack coined the enduring term ‘pair bond’ in his paper on the life history of the robin: ”In some species of birds, the sexes meet solely for copulation, in some they form a very temporary pair-bond, in most they pair for the brood or the breeding season, in some they pair for life.” (Lack 1939). ‘Pair bond’ had all the characteristics of a viral meme, soon spreading throughout the scientific literature and popular press. Ever since Lack coined the term, it has appeared in no less than 235 papers in the IBIS alone.
Figure 1. The number of papers published in the Ibis that refer to the ‘pair bond’ © Bob Montgomerie.
Despite its obvious usefulness as a concept, the term ‘pair bond’ has proven to be hard to define. Or rather, definitions abound, and several different types of pair bond have been characterized (Bales et al. 2021). And although the duration of a pair bond is surely shaped by natural selection, the benefits of pairing with the same mate from year to year can be difficult to document and sometimes appear to be slight (Botero-Delgadillo 2024).
In birds like bowerbirds, manakins, and peacocks, the pair association is fleeting, involving only a few social interactions between a particular male and female and ending with a copulation. In others, like albatrosses, swans and eagle, the mated pair stays together year-round and the association ends when one of them dies. I would not be surprised to learn that, in each case, the underlying hormonal and neurobiological mechanisms are the same, with the duration of the interactions between the pair members shaped by natural and sexual selection.
As research over the past three decades has shown, the pair bond in some bird species is short lived and can involve more than two individuals during the same breeding period. Indeed, though David Lack reported in 1968 that most bird species are monogamous, it turns out that extrapair paternity is widespread, especially in passerine birds. Julian Huxley would undoubtedly be disappointed to discover the folly of his agenda to use the mating habits of birds to inform the transformation and betterment of human society.
Further Reading
Bales, K.L., Ardekani, C.S., Baxter, A., Karaskiewicz, C.L., Kuske, J.X., Lau, A.R., Savidge, L.E., Sayler, K.R., Witczak, L.R. 2021. What is a pair bond? Hormones and Behavior 136: 105062.
Bartley, M.M. 1995. Courtship and continued progress: Julian Huxley’s studies on bird behavior. Journal of the History of Biology 28: 91–108.
Botero-Delgadillo, E., Vásquez, R.A., Kempenaers, B. 2024. Assessing the reproductive consequences of mate retention and pair bond duration in Thorn-tailed Rayadito (Aphrastura spinicauda), a short-lived, socially monogamous neotropical bird. Ibis 166: 396-410. https://doi.org/10.1111/ibi.13183
Huxley, J.S. 1914. The courtship-habits of the great crested grebe (Podiceps cristatus); with an addition to the theory of sexual selection. Proceedings of the Zoological Society of London 35: 491–562.
Huxley, J.S. 1938. Darwin’s theory of sexual selection and the data subsumed by it, in the light of recent research. American Naturalist 72: 416–433.
Huxley, J. 1986. Leaves of the Tulip Tree : Autobiography. London: J. Murray.
Lack, D.L. 1939. The behaviour of the robin. Proceedings of the Zoological Society of London, Series A 109: 169-219.
Lack, D.L.1968. Ecological adaptations for breeding in birds. London: Chapman and Hall.
Selous, E. 1901-1902. An observational diary of the habits—mostly domestic—of the Great Crested Grebe (Podicipes cristatus), and of the Peewit (Vanellus vulgaris), with some general remarks. The Zoologist, 4th series 5: 161–183, 339–350, 454–462 and 6: 133–144.
Tinbergen, N. 1936. The function of sexual fighting in birds and the problem of the origin of territory. Bird-banding 7: 1-8.
Young, L., Wang, Z. 2004. The neurobiology of pair bonding. Nature Neuroscience 7: 1048–1054. https://doi.org/10.1038/nn1327
Image credits
Top right: The ‘penguin dance’ of the Great Crested Grebe. Modified from plate II:13 Huxley (1914) in the public domain.
Blog posts express the views of the individual author(s) and not those of the BOU.
If you want to write about your research in #theBOUblog, then please see here
