Breeding habitat selection and its consequences in boreal passerines : using the spatial dispersion of predators and heterospecifics as a source of information
|Author:||Thomson, Robert L.1|
1University of Oulu, Faculty of Science, Department of Biology
|Online Access:||PDF Full Text (PDF, 0.6 MB)|
|Persistent link:|| http://urn.fi/urn:isbn:9514280504
|Publish Date:|| 2006-04-25
|Thesis type:||Doctoral Dissertation
|Defence Note:||Academic Dissertation to be presented with the assent of the Faculty of Science, University of Oulu, for public discussion in Kuusamonsali (Auditorium YB210), Linnanmaa, on April 21st, 2006, at 12 noon
Doctor Jon E. Brommer
Doctor Hannu Ylönen
Habitat selection decisions are crucial in determining fitness. Research indicates that individuals of many taxa are flexible in habitat selection and gather information prior to decision-making in order to control for environmental unpredictability. For time limited migrant birds, cues provide a quick and reliable information source with which to make habitat selection decisions. In this thesis I investigate habitat selection decisions, and their fitness consequences, of boreal passerines using heterospecifics or predators as cues.
In support of the heterospecific attraction hypothesis, plots with augmented resident titmice densities attracted increased migrant densities. The predicted negative effects stemming from competition did not occur even at unnaturally high resident densities. This suggests that in the north it may always be beneficial for migrants to use residents as cues in habitat selection decisions.
By manipulating habitat selection, I found that great tits (Parus major) had poorer reproductive success when forced to breed in close proximity to pied flycatcher (Ficedula hypoleuca) compared to when breeding alone. Flycatchers, in contrast, did slightly better when breeding close to tits. These results indirectly suggest that heterospecific attraction may not be a mutually positive species interaction. Indeed, flycatchers seem to parasitize the high quality microhabitat indicated by breeding great tits.
I also tested if residents provide a reliable cue relative to predation risk. However, willow tit (P. montanus) nest location appeared random relative to avian predator nests. They do not appear to reliably indicate safe breeding habitats to later arriving migrants. In addition, closer proximity to breeding avian predators had a negative impact on willow tit reproductive output.
Later arriving migrants may be in a better position to avoid avian predator nests during habitat selection. Pied flycatchers avoid settling in the immediate vicinity of sparrowhawk (Accipiter nisus) nests. However, nest box occupation, laying dates and initial reproductive investment (clutch size) showed a unimodal relationship with distance to sparrowhawk. A unimodal trend in these measures indicates there may be a trade-off between the costs (increased adult predation risk) and potential benefits (decreased nest predation risk) of settling in proximity to avian predator nests. Spatially predictable predation risk gradients that emanate from predator nests are termed a "predation risk landscape". Furthermore, flycatchers nesting closer to sparrowhawks produced fewer and smaller nestlings than those farther away. In addition, measures of maternal physiological stress (body condition and stress protein levels) had a negative linear relationship with distance to sparrowhawk nest. It appears that increased perceived predation risk near avian predator nests results in stressful and poor conditions for adult passerines, which results in lower reproductive output.
This thesis highlights the importance of information gathering prior to making habitat selection decisions in order to optimise territory location relative to heterospecifics or predators. These decisions clearly impact individual fitness.
Acta Universitatis Ouluensis. A, Scientiae rerum naturalium
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