Browsing by Subject "BIRD"

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  • Nokelainen, Ossi; Rezende, Francisko de Moraes; Valkonen, Janne K.; Mappes, Johanna (2022)
    A big question in behavioral ecology is what drives diversity of color signals. One possible explanation is that environmental conditions, such as light environment, may alter visual signaling of prey, which could affect predator decision-making. Here, we tested the context-dependent predator selection on prey coloration. In the first experiment, we tested detectability of artificial visual stimuli to blue tits (Cyanistes caeruleus) by manipulating stimulus luminance and chromatic context of the background. We expected the presence of the chromatic context to facilitate faster target detection. As expected, blue tits found targets on chromatic yellow background faster than on achromatic grey background whereas in the latter, targets were found with smaller contrast differences to the background. In the second experiment, we tested the effect of two light environments on the survival of aposematic, color polymorphic wood tiger moth (Arctia plantaginis). As luminance contrast should be more detectable than chromatic contrast in low light intensities, we expected birds, if they find the moths aversive, to avoid the white morph which is more conspicuous than the yellow morph in low light (and vice versa in bright light). Alternatively, birds may attack first moths that are more detectable. We found birds to attack yellow moths first in low light conditions, whereas white moths were attacked first more frequently in bright light conditions. Our results show that light environments affect predator foraging decisions, which may facilitate context-dependent selection on visual signals and diversity of prey phenotypes in the wild. Light environments are constantly changing and may alter visual appearance of prey, but also bias predators' decision making. Our findings using blue tits in visual search tasks and the wood tiger moth prey under two light environments demonstrate that birds show context-dependent predatory behavior. This suggests that light environments can play a major selective role and influence visual signaling in the wild.
  • Lever, D.; Rush, L.V.; Thorogood, R.; Gotanda, K. M. (2022)
    Urbanization is rapidly changing ecological niches. On the inhabited Galapagos Islands, Darwin's finches consume human-introduced foods preferentially; however, it remains unclear why. Here, we presented pastry with flavour profiles typical of human foods (oily, salty and sweet) to small ground finches (Geospiza fuliginosa) and medium ground finches (Geospiza fortis) to test if latent taste preferences might drive the selection of human foods. If human food flavours were consumed more than a neutral or bitter control only at sites with human foods, then we predicted tastes were acquired after urbanization; however, if no site differences were found then this would indicate latent taste preferences. Contrary to both predictions, we found little evidence that human food flavours were preferred compared with control flavours at any site. Instead, finches showed a weak aversion to oily foods, but only at remote (no human foods present) sites. This was further supported by behavioural responses, with beak-wiping occurring more often at remote sites after finches tasted flavours associated with human foods. Our results suggest, therefore, that while Darwin's finches regularly exposed to human foods might have acquired a tolerance to human food flavours, latent taste preferences are unlikely to have played a major role in their dietary response to increased urbanization.
  • Ramula, Satu; Öst, Markus; Lindén, Andreas; Karell, Patrik; Kilpi, Mikael (2018)
    In contrast to theoretical predictions of even adult sex ratios, males are dominating in many bird populations. Such bias among adults may be critical to population growth and viability. Nevertheless, demographic mechanisms for biased adult sex ratios are still poorly understood. Here, we examined potential demographic mechanisms for the recent dramatic shift from a slight female bias among adult eider ducks (Somateria mollissima) to a male bias (about 65% males) in the Baltic Sea, where the species is currently declining. We analysed a nine-year dataset on offspring sex ratio at hatching based on molecularly sexed ducklings of individually known mothers. Moreover, using demographic data from long-term individual-based capture-recapture records, we investigated how sex-specific survival at different ages after fledgling can modify the adult sex ratio. More specifically, we constructed a stochastic two-sex matrix population model and simulated scenarios of different survival probabilities for males and females. We found that sex ratio at hatching was slightly female-biased (52.8%) and therefore unlikely to explain the observed male bias among adult birds. Our stochastic simulations with higher survival for males than for females revealed that despite a slight female bias at hatching, study populations shifted to a male-biased adult sex ratio (> 60% males) in a few decades. This shift was driven by prime reproductive-age individuals(>5-year-old), with sex-specific survival of younger age classes playing a minor role. Hence, different age classes contributed disproportion ally to population dynamics. We argue that an alternative explanation for the observed male dominance among adults sex-biased dispersal can be considered redundant and is unlikely, given the ecology of the species. The present study highlights the importance of considering population structure and age-specific vital rates when assessing population dynamics and management targets.
  • Fink, Christoph; Toivonen, Tuuli; Correia, Ricardo A.; Di Minin, Enrico (2021)
    Wildlife trade, when unsustainable, can be an important threat to biodiversity conservation. In this contribution, we explored the use of digital data to investigate the online market for songbirds in Indonesia, where keeping pet songbirds is a deeply rooted cultural practice. We examined the spatial characteristics of three dimensions of the songbird trade using data from online sources: birdwatchers’ sightings as a proxy for the supply of the songbird market, small advertisements from an online marketplace platform, representing the trade itself and its transactions, and videos by pet songbird owners to represent the demand side of the songbird market. We found that, geographically, these three stages of the songbird supply chain did not overlap, which potentially hints at the roles extended transport networks and commercial captive breeding play for the songbird trade. The trade was not confined to major cities but spread out through the country, indicating both a possible democratisation of the trade (i.e. a larger group of sellers, and consumers selling to consumers) and an opportunity to observe previously covert parts of the trade. We further found that the asking prices on online marketplaces were significantly higher than the prices stated in an independently carried out consumer survey, and discuss possible reasons. Data from digital sources can give rich insights into the spatial, temporal and taxonomic structure of wildlife trade, can help understand the motivations of buyers and sellers, and can help direct wildlife trade towards a more sustainable fashion. Our methodology toolbox that allows automatic and continuous monitoring of online marketplaces and includes data preparation and cleaning, and follows the highest standards of data privacy principles, is openly available.
  • Velmala, William; Helle, Samuli; Ahola, Markus P.; Klaassen, Marcel; Lehikoinen, Esa; Rainio, Kalle; Sirkiä, Päivi; Laaksonen, Toni (2015)
    For migratory birds, the earlier arrival of males to breeding grounds is often expected to have fitness benefits. However, the selection differential on male arrival time has rarely been decomposed into the direct effect of male arrival and potential indirect effects through female traits. We measured the directional selection differential on male arrival time in the pied flycatcher (Ficedula hypoleuca) using data from 6years and annual number of fledglings as the fitness proxy. Using structural equation modeling, we were able to take into account the temporal structure of the breeding cycle and the hierarchy between the examined traits. We found directional selection differentials for earlier male arrival date and earlier female laying date, as well as strong selection differential for larger clutch size. These selection differentials were due to direct selection only as indirect selection for these traits was nonsignificant. When decomposing the direct selection for earlier male arrival into direct and indirect effects, we discovered that it was almost exclusively due to the direct effect of male arrival date on fitness and not due to its indirect effects via female traits. In other words, we showed for the first time that there is a direct effect of male arrival date on fitness while accounting for those effects that are mediated by effects of the social partner. Our study thus indicates that natural selection directly favored earlier male arrival in this flycatcher population.
  • Lehikoinen, Aleksi; Linden, Andreas; Karlsson, Mans; Andersson, Arne; Crewe, Tara L.; Dunn, Erica H.; Gregory, George; Karlsson, Lennart; Kristiansen, Vidar; Mackenzie, Stuart; Newman, Steve; Roer, Jan Erik; Sharpe, Chris; Sokolov, Leonid V.; Steinholtz, Asa; Stervander, Martin; Tirri, Ina-Sabrina; Tjornlov, Rune Skjold (2019)
    Climate change has been shown to shift the seasonal timing (i.e. phenology) and distribution of species. The phenological effects of climate change on living organisms have often been tested using first occurrence dates, which may be uninformative and biased. More rarely investigated is how different phases of a phenological sequence (e.g. beginning, central tendency and end) or its duration have changed over time. This type of analysis requires continuous observation throughout the phenological event over multiple years, and such data sets are rare. In this study we examined the impact of temperature on long-term change of passage timing and duration of the spring migration period in birds, and which species' traits explain species-specific variation. Data used covered 195 species from 21 European and Canadian bird observatories from which systematic daily sampling protocols were available. Migration dates were negatively associated with early spring temperature and timings had in general advanced in 57 years. Short-distance migrants advanced the beginning of their migration more than long-distance migrants when corrected for phylogenic relatedness, but such a difference was not found in other phases of migration. The advancement of migration has generally been greater for the beginning and median phases of migration relative to the end, leading to extended spring migration seasons. Duration of the migration season increased with increasing temperature. Phenological changes have also been less noticeable in Canada even when corrected for rate of change in temperature. To visualize long-term changes in phenology, we constructed the first multi-species spring migration phenology indicator to describe general changes in median migration dates in the northern hemisphere. The indicator showed an average advancement of one week during five decades across the continents (period 1959-2015). The indicator is easy to update with new data and we therefore encourage future research to investigate whether the trend towards longer periods of occurrence or emergence in spring is also evident in other migratory populations. Such phenological changes may influence detectability in monitoring schemes, and may have broader implications on population and community dynamics.