Collared flycatchers do better when reared by pied flycatchers: Nestlings swapped between nests of two species
By Jenny Vogel
Ecologically similar species that use similar resources need to differ in one way or another, to be able to coexist and thereby avoid competitive extinction. Collared and pied flycatchers are almost identical ecologically, e.g. habitat preference and mate choice cues, though collared flycatchers are dominant in interference competition, e.g. keeping territories, but also more sensitive to environmental variations, while pied flycatcher is more robust to harsh environments since they are thought to have a better inner ability to transport resources towards growth during poorer conditions. This trade-offin traits ameliorates the conditions for coexistence, since there is a seasonal deterioration of the environment to which the two species respond differently. This difference results in a seasonal switch in relative condition, i.e. how well they do compared to others at that time, between the two species’ fledglings. There have been signs of competitive exclusion of the pied flycatcher so for how long coexistence will go on, will probably depend on the degree of environmental deterioration over the season. A question is which underlying factors there might be for this. To be able to see if there are differences between the two species of parents I swapped half of the broods of one species’ nestlings for an equal number of nestlings from the other species, also known as cross fostering. With the information of the nestlings weight gain along with video recordings I could see that this seasonal switch, where nestling collared flycatchers fledge in a relatively higher condition, measured in weight, earlier in the season and pied flycatcher later, is only apparent in nests attended by collared flycatchers but not in nests attended by pied flycatchers. My conclusion is that this is not only due to physiological differences in the nestlings but also due to behavioural differences between the adult pairs attending the nests as well as between the nestlings of the two species. The overall advantage that the nestling collared flycatcher experience early in the season and in nests attended by pied flycatchers seems to be a result of their begging behaviour, i.e. they are the first to beg more often than expected. My overall conclusion is that it is not always enough to look at the behavioural strategies of the adults to understand the species’ differences in condition response to changes in the environment, but it is also important to look at behavioural strategies in the young individuals to get a greater understanding of why one species have certain traits/strategies in life and not others.
Undergraduate thesis in Biology
Examensarbete i biologi, 20 p, HT 2004
Department of Animal Ecology, Uppsala University
Supervisor: Anna Qvarnström