Åke Lindström

Rapid reversible changes in organ size as a component of adaptive behaviour

Organ structures and correlated metabolic features (e.g. metabolic rate) have often taken as fixed attributes of fully grown individual vertebrates. When measurements of these attributes became available they were often used as representative values for the species, disregarding the specific conditions during which the mesurement were made. Evidence is accumulating that the functional size of organs and aspects of the metabolic physiology of an individual may show great flexibility over timescales of weeks and even days depending on physiological status, environmental conditions and behavioural goals. This flexibility is a way for animals to cope successfully with a much wider range of conditions occurring during various life-cycle events than fixed metabolic machinery would allow. Such phenotypic flexibility is likely to be a common adaptive syndrome, typical of vertebrates living in variable environments.

Differences in the climatic debts of birds and butterflies at a continental scale

Climate changes have profound effects on the distribution of numerous plant and animal species(1-3). However, whether and how different taxonomic groups are able to track climate changes at large spatial scales is still unclear. Here, we measure and compare the climatic debt accumulated by bird and butterfly communities at a European scale over two decades (1990-2008). We quantified the yearly change in community composition in response to climate change for 9,490 bird and 2,130 butterfly communities distributed across Europe(4). We show that changes in community composition are rapid but different between birds and butterflies and equivalent to a 37 and 114 km northward shift in bird and butterfly communities, respectively. We further found that, during the same period, the northward shift in temperature in Europe was even faster, so that the climatic debts of birds and butterflies correspond to a 212 and 135 km lag behind climate. Our results indicate both that birds and butterflies do not keep up with temperature increase and the accumulation of different climatic debts for these groups at national and continental scales.

Optimal fat loads in migrating birds: a test of the time-minimization hypothesis

We tested the hypothesis that birds are selected to minimize the time spent on migration, that is, to migrate as fast as possible. Optimal fat loads in time-selected migration were predicted for different rates of fat accumulation at stopover sites. We analyzed departure fat loads of migrating bluethroats Luscinia svecica svecica, experimentally provided with extra food at a stopover site, and of migrating rufous hummingbirds Selasphorus rufus, which showed considerable individual variation in fat-deposition rate, in relation to these predictions. We found qualitative agreement with the time-minimization hypothesis. However, quantitative agreement requires that specific assumptions be fulfilled for both species: (1) consistent differences in expected speed of migration should exist between different individuals of the same species and/or (2) the expected speed of migration should increase along the route Both of these assumptions are probably valid, and ringing data suggest an increase in bluethroat autumn migration speed along the route Physiological and flight mechanical constraints will prevent birds from depositing excessively large amounts of fuel. These assumptions and constraints should be taken into account in future critical tests of the hypothesis that natural selection operates to maximize the speed of migration.

Carrying large fuel loads during sustained bird flight is cheaper than expected

Birds on migration alternate between consuming fuel stores during flights and accumulating fuel stores during stopovers. The optimal timing and length of flights and stopovers for successful migration depend heavily on the extra metabolic power input (fuel use) required to carry the fuel stores during flight. The effect of large fuel loads on metabolic power input has never been empirically determined. We measured the total metabolic power input of a long-distance migrant, the red knot (Calidris canutus), flying for 6 to 10 h in a wind tunnel, using the doubly labelled water technique. Here we show that total metabolic power input increased with fuel load, but proportionally less than the predicted mechanical power output from the flight muscles. The most likely explanation is that the efficiency with which metabolic power input is converted into mechanical output by the flight muscles increases with fuel load. This will influence current models of bird flight and bird migration. It may also help to explain why some shorebirds, despite the high metabolic power input required to fly, routinely make nonstop flights of 4,000 km longer.

Fuel deposition rates in migrating birds: Causes, constraints and consequences.

Most, if not all, migrants deposit fuel before they fly. Some migrants can more than double their mass from fuelling (Piersma and Gill 1998), whereas others, like the white stork, Ciconia cconia, put on small amounts and stop for feeding every day (Berthold et al. 2001).

Bird population trends are linearly affected by climate change along species thermal ranges

Beyond the effects of temperature increase on local population trends and on species distribution shifts, how populations of a given species are affected by climate change along a species range is still unclear. We tested whether and how species responses to climate change are related to the populations locations within the species thermal range. We compared the average 20 year growth rates of 62 terrestrial breeding birds in three European countries along the latitudinal gradient of the species ranges. After controlling for factors already reported to affect bird population trends (habitat specialization, migration distance and body mass), we found that populations breeding close to the species thermal maximum have lower growth rates than those in other parts of the thermal range, while those breeding close to the species thermal minimum have higher growth rates. These results were maintained even after having controlled for the effect of latitude per se. Therefore, the results cannot solely be explained by latitudinal clines linked to the geographical structure in local spring warming. Indeed, we found that populations are not just responding to changes in temperature at the hottest and coolest parts of the species range, but that they show a linear graded response across their European thermal range. We thus provide insights into how populations respond to climate changes. We suggest that projections of future species distributions, and also management options and conservation assessments, cannot be based on the assumption of a uniform response to climate change across a species range or at range edges only.

More and more generalists: two decades of changes in the European avifauna.

Biotic homogenization (BH) is a process whereby some species (losers) are systematically replaced by others (winners). While this process has been related to the effects of anthropogenic activities, whether and how BH is occurring across regions and the role of native species as a driver of BH has hardly been investigated. Here, we examine the trend in the community specialization index (CSI) for 234 native species of breeding birds at 10 111 sites in six European countries from 1990 to 2008. Unlike many BH studies, CSI uses abundance information to estimate the balance between generalist and specialist species in local assemblages. We show that bird communities are more and more composed of native generalist species across regions, revealing a strong, ongoing BH process. Our result suggests a rapid and non-random change in community composition at a continental scale is occurring, most likely driven by anthropogenic activities.

Optimal departure decisions of songbirds from an experimental stopover site and the significance of weather

Recent models have worked with the assumption that birds try to minimize either time, energy or predation risk during migration, or some combination of these. The few empirical studies available have suggested that time minimization may be the most common strategy. One way of distinguishing between strategies is to study the departure decisions of migrating birds. We supplied migrating European robins, Erithacus rubecula, with food ad libitum in the field and monitored their changes in body mass prior to departure. The overall mass gain rate (k(tot), the ratio of daily mass increase to lean mass) of 10 birds using the feeding station was on average 0.05 (range 0.03-0.09). Departure fuel loads (f(dep), the ratio of fuel mass to lean mass) were on average 0.53 (range 0.35-0.66). There was no significant correlation between f(dep) and k(tot), which indicates a strategy of minimizing the energy cost of transport, rather than minimizing time but other aspects of the fuel deposition pattern suggest that time minimization may also be important. Whereas the behaviour of the robins was difficult to interpret in the light of optimal migration strategies, the importance of weather was striking. The robins selected the best weather conditions (tail wind, high air pressure and no precipitation) within the likely period of departure

Drought in Africa Caused Delayed Arrival of European Songbirds

A severe drought in the Horn of Africa delayed the spring arrival in Europe of two migratory species. Despite an overall advancement in breeding area arrival, one of the latest spring arrivals in northwest Europe since 1950 of several trans-Saharan songbird species occurred in 2011. Year-round tracking of red-backed shrikes and thrush nightingales revealed that the cause of the delay was a prolongation of stopover time during spring migration at the Horn of Africa, which was affected by extreme drought. Our results help to establish a direct link at the individual level between changes in local climate during migration and arrival and breeding condition in Europe thousands of kilometers further north.

Consequences of organic farming and landscape heterogeneity for species richness and abundance of farmland birds.

It has been suggested that organic farming may benefit farmland biodiversity more in landscapes that have lost a significant part of its former landscape heterogeneity. We tested this hypothesis by comparing bird species richness and abundance during the breeding season in organic and conventional farms, matched to eliminate all differences not directly linked to the farming practice, situated in either homogeneous plains with only a little semi-natural habitat or in heterogeneous farmland landscapes with abundant field borders and semi-natural grasslands. The effect of farm management on species richness interacted with landscape structure, such that there was a positive relationship between organic farming and diversity only in homogeneous landscapes. This pattern was mainly dependent on the species richness of passerine birds, in particular those that were invertebrate feeders. Species richness of non-passerines was positively related to organic farming independent of the landscape context. Bird abundance was positively related to landscape heterogeneity but not to farm management. This was mainly because the abundance of passerines, particularly invertebrate feeders, was positively related to landscape heterogeneity. We suggest that invertebrate feeders particularly benefit from organic farming because of improved foraging conditions through increased invertebrate abundances in otherwise depauperate homogeneous landscapes. Although many seed-eaters also benefit from increased insect abundance, they may also utilize crop seed resources in homogeneous landscapes and conventional farms. The occurrence of an interactive effect of organic farming and landscape heterogeneity on bird diversity will have consequences for the optimal allocation of resources to restore the diversity of farmland birds.