To avoid parental care of their young, brood parasite species lay their eggs in the nests of other bird species so that the owner of the nest nurtures their chicks. To effectively parasitize their hosts, brood parasites such as the common cuckoo, Cuculus canorus, coordinate with the annual cycle of their host. Temperature increases can change the biological processes of the host species, disrupting the synchronicity between the parasite and the host, limiting host options for the parasite. To combat these disruptions, C. canorus choose different host species. Møller et al. (2011) predicted that C. canorus would prefer long-distance migratory hosts rather than resident or short term migratory hosts during periods of elevated spring temperatures. To test this prediction, the researchers analyzed the relative frequency of parasitism in long-distance migratory hosts and short-distance migratory or resident hosts in 23 European countries in the time periods: 1958 to 1989 and 1990 to 2009. They found that parasitism in resident and short term migratory species decreased as spring temperatures increased. This result shows that as global temperature continues to increase, brood parasites will have different and fewer options for hosts, which could affect their overall population. — Isabelle Heilman
Møller, A.P, Saino, N., Adamík, P., Ambrosini, R., Antonov, A., Campobello, D., Stokke, B.G., Fossøy, F., Lehikoinen, E., Martin-Vivaldi, A., Moksnes, A., Moskat, C., Røskaft, E., Rubolini, D., Shulze-Hagen, K., Soler, M., Shykoff, M., 2011. Rapid change in host use of the common cuckoo Cuculus canorus linked to climate change. Proceedings of the Royal Society 278, 733-738.
Brood parasites such as the common cuckoo, Cuculus canorus, try to harmonize their reproductive cycle with that of their host. By matching up their reproductive cycles, the parasitic species can lay their eggs in the nest of another species and leave that species to take care of the parasite’s young. Environmental effects such as temperature increases can change reproductive processes of the host species, disrupting the synchronicity between the parasite and the host, which can lead to reproductive limitations for the parasite and in extreme cases, extinction. European temperatures have been rising, which has affected migratory patterns of birds and in turn, the species and amount of hosts available for brood parasites. Møller et al.studied the brood parasite C. canorus to see if the relative frequency of resident or short-distance migratory species selected as hosts changed after 1990. Relative frequency was defined as the number of C. canoruseggs present in the nest of a host species relative to the number of total C. canorus eggs. They also studied the relationship between host selection and changes in spring temperature.
To test their predictions about host selection based on temperature, the researchers used a database containing 32,843 records of cuckoo parasitism in Europe. They grouped the host species into two groups: long-distance migrants who spent winter in Sub-Saharan Africa or the Indian Sub-continent, and short-distance migrants or residents. Mean daily temperature data from individual countries was taken from ECMWF ERA-Interim data for 1989 to 2009 and ERA-40 data was used for the time period before 1989. Countries that were directly bordering and had similar rates of temperature change were grouped. Population trends of the two migratory pattern classifications were also considered. The authors used general linear analyses to find the relationships between relative frequency of parasitism in the years 1990 to 2009 and temperature changes in the country groupings. The year 1990 was used as a cut-off because the rate of climate change has been the greatest after this year. Years 1958 to 1989 were used as covariates in the analyses.
The results showed that there was a significant decrease in the use of resident and short-distance migratory species as hosts. Also, there were a smaller proportion of C. canoruseggs in short-distance migratory or resident hosts’ nests in areas where spring temperatures had increased. These findings support the researcher’s initial predictions that short-distance migratory and resident species where less-regularly selected as hosts for C. canorus during the time period 1990 to 2009 compared to host selection from earlier time periods. After 1990, spring temperatures increased at a greater rate, implying that climate change plays a part in host selection for C. canorus. This finding shows that as temperature increases, C. canorus will have fewer host species to choose from, which could have serious consequences on their population size in the future.