Flight‐initiation response reflects short‐ and long‐term human visits to remote islets. Thibault, M., Weston, M.A., Ravache, A. & Vidal, E. 2020. IBIS. DOI: 10.1111/ibi.12810 VIEW
Many seabird colonies reside on remote islands, largely isolating them from anthropogenic influences. However, the increasing use of island resources and the more frequent visits by tourists is threatening the continued existence of these colonies (Hall 2016). Several studies have measured the indirect effects of human disturbance on seabirds, such as changes in survival rates and reproductive success (Cianchetti-Benedetti et al. 2018). But what about behavioural changes? To see how human visits to remote islands affect bird behaviour, Martin Thibault and his colleagues travelled to the Chesterfield Islands – a French archipelago of New Caledonia – where the Brown Noddy (Anous stolidus) breeds.
On the different islands, the researchers would walk towards a breeding Brown Noddy and note down the distance at which the bird flew off. They repeated this procedure for several weeks to see whether the distance at which the birds left the nest – the so-called flight-initiation distance – changed after several visits. This study reminds me of a course on Island Biology I took as a student. As part of this course, we travelled to Croatia where we executed small research projects. One group of students studied the flight-initiation distance of lizards on different islands. The procedure did not go as planned on one small island where the lizards would approach the students and even crawl into their backpacks. But enough reminiscing about my days as a student, what about the Brown Noddies?
Figure 1 (a) Flight‐initiation distances of Brown Noddies during the first visit at three sites. (b) Decrease flight‐initiation distances over repeated approaches during a 2‐week sampling session on Loop islet.
tThe flight-initiation distances of the Brown Noddies were very short compared to other studies. For example, the highest mean distance for Brown Noddies was measured on Mouillage islet where birds flew off at 4.4 meters distance. That is markedly lower than other species, such as Common Tern (Sterna hirundo) at 29.6 meters and Great Cormorant (Phalocrocorax carbo) at 32.3 meters (Blumstein 2003). The low flight-initiation distance of the Brown Noddies could reflect ‘island tameness’, a reduction in escape response due to a lack of predators on the island (Blumstein & Daniel 2005). Moreover, the Brown Noddies might have adopted a ‘sit-and-defend’ strategy to deal with the occasional predator. The birds would stay on the nest as long as possible, hoping to scare off the predator. Interestingly, at one site on Loop islet, the flight-initiation distance even decreased after several visits (although they did not crawl into backpacks as the Croatian lizards did). This pattern suggests the birds learned that the researchers were harmless and adjusted their behaviour accordingly (Samia et al. 2015). These findings nicely illustrate how the interplay between evolved strategies – island tameness and sit-and-defend – and learning can shape the behavioural response of seabirds to human visitors.
Blumstein, D.T. (2003). Flight‐initiation distance in birds is dependent on intruder starting distance. Journal of Wildlife Management 67: 852– 857. VIEW
Blumstein, D.T. & Daniel, J.C. (2005). The loss of anti‐predator behaviour following isolation on islands. Proceedings of the Royal Society B 272: 1663– 1668. VIEW
Cianchetti‐Benedetti, M., Becciu, P., Massa, B. & Dell’Omo, G. (2018). Conflicts between touristic recreational activities and breeding Shearwaters: short‐term effect of artificial light and sound on chick weight. European Journal of Wildlife Research 64: 19. VIEW
Hall, C.M. (2010). An island biogeographical approach to island tourism and biodiversity: an exploratory study of the Caribbean and Pacific Islands. Asia Pacific Journal of Tourism Research 15: 383– 399. VIEW
Samia, D.S., Nakagawa, S., Nomura, F., Rangel, T.F. & Blumstein, D.T. (2015). Increased tolerance to humans among disturbed wildlife. Nature Communications 6: 8877. VIEW
Top right: Brown Nobby Anous stolidus | Patrick Kavanagh | CC BY-SA 2.0 Wikimedia Commons