Effect of testosterone on the behaviour of yellow-legged gulls (Larus cachinnans) in a high-density colony during the courtship period

Alonso-Alvarez, C. & Velando, A., 2001. Effect of testosterone on the behaviour of yellow-legged gulls (Larus cachinnans) in a high-density colony during the courtship period. Ethology Ecology & Evolution, 13(4), pp.341-349.


Yellow-legged gulls breed in high density areas, and the condition dependent hypothesis suggests that birds with high physical condition can obtain breeding benefits in high-density areas because they are able to pay off the energetic costs of aggressive behaviour and territory defence. This study and others showed a relationship between aggressiveness or copulation behaviour and nest-density during the pre-laying period in gulls. The link between density and behaviour can be explained by the strong competition for space and mates. Testosterone regulates male behaviour and can play an important role in the condition-dependent hypothesis. We tested the effects of testosterone implants on male breeding behaviour. In a high-density colony, testosterone-implanted male yellow-legged gulls showed higher aggression and copulation frequencies than controls during the courtship period. In addition, these testosterone-treated birds acquired larger territories than the controls. Thus, a high testosterone level can increase individual fitness in densely populated areas given the benefits derived, on the one hand, from a large territory and, on the other, from an increased copulation rate that would guarantee the male’s paternity of the chicks born in his own nest. Since testosterone increases energetic requirements, only high-quality males would be able to pay off the costs of high levels of testosterone and so obtain the benefits of breeding in high-density areas. Testosterone could therefore provide a proximate mechanism regulating nest density in gull colonies.

Effects of testosterone implants on pair behaviour during incubation in the Yellow‐legged Gull Larus cachinnans

Alonso‐Alvarez, C., 2001. Effects of testosterone implants on pair behaviour during incubation in the Yellow‐legged Gull Larus cachinnans. Journal of Avian Biology, 32(4), pp.326-332.


The Yellow-legged Gull Larus cachinnans is monogamous with bi-parental incubation. In this study, the effects of high levels of plasma testosterone in male Yellow-legged Gulls during the incubation period were analysed. Free-living male gulls were implanted with testosterone (T-males), and their sexual behaviour within the pair was observed and compared with that of control pairs. Egg temperatures, length of incubation and hatching success were also analysed. T-males and their mates displayed more sexual behaviour than the controls. T-males engaged in mounting behaviour with their mates, whereas control males did not. Proportionally less time was spent incubating (in relation to time present in the colony) by T-males than control males. However, the mates of T-males did not spend more time incubating than control females to compensate for male neglect, although they did spend more time on the territory. Egg temperature in T-male nests was significantly lower than in control nests, but no significant difference in the length of incubation or hatching success between the two groups was found. In birds, the effects of high testosterone levels on male behaviour during incubation have only been analysed in a polyandrous species whose females usually do not contribute to incubation. The present results thus suggest that those males of a monogamous species with biparental incubation that sustain high testosterone levels after laying, thus reducing their contributions to incubation, will be confronted with a lack of compensation from their mates during incubation. Finally, this lack of female compensation seems to be mediated by behavioural interactions with the male rather than by her absence
from the colony.