Orientation of juvenile barn swallows (<Emphasis Type="Italic">Hirundo rustica</Emphasis>) tested in Emlen funnels during autumn migration

Although hirundines have been used extensively in homing experiments, to date no investigation of their migratory orientation has been carried out, despite the well-known migratory habits of many species of this family. This paper reports on a study of the orientation of the barn swallow (Hirundo rustica), a typical diurnal trans-Saharan migrant. Modified Emlen funnels were used to verify the suitability of this species for cage experiments and investigate the role of visual and magnetic cues during the birds first migratory journey. Juvenile swallows were mist-netted at a roost site in central Italy and then tested in a site 19 km apart. Orientation experiments were performed under four experimental conditions: natural clear sky and simulated overcast, in both local and shifted magnetic fields (magnetic North=geographical West). Under clear sky, the swallows tended to orient phototactically toward the best-lit part of the funnel and failed to respond to the magnetic field shift. Under overcast conditions, they oriented northward and modified their directional choices as expected in response to the shifted magnetic North. On the whole, our data indicate that swallows can use magnetic information for compass orientation. Possible explanations for the northward orientation of birds tested under overcast conditions are discussed.Communicated by W. Wiltschko     

Estimating the complexity of bird song by using capture-recapture approaches from community ecology

Repertoire size, the number of unique song or syllable types in the repertoire, is a widely used measure of song complexity in birds, but it is difficult to calculate this exactly in species with large repertoires. A new method of repertoire size estimation applies species richness estimation procedures from community ecology, but such capture-recapture approaches have not been much tested. Here, we establish standardized sampling schemes and estimation procedures using capture-recapture models for syllable repertoires from 18 bird species, and suggest how these may be used to tackle problems of repertoire estimation. Different models, with different assumptions regarding the heterogeneity of the use of syllable types, performed best for different species with different song organizations. For most species, models assuming heterogeneous probability of occurrence of syllables (so-called detection probability) were selected due to the presence of both rare and frequent syllables. Capture-recapture estimates of syllable repertoire size from our small sample did not differ significantly from previous estimates using larger samples of count data. However, the enumeration of syllables in 15 songs yielded significantly lower estimates than previous reports. Hence, heterogeneity in detection probability of syllables should be addressed when estimating repertoire size. This is neglected using simple enumeration procedures, but is taken into account when repertoire size is estimated by appropriate capture-recapture models adjusted for species-specific song organization characteristics. We suggest that such approaches, in combination with standardized sampling, should be applied in species with potentially large repertoire size. On the other hand, in species with small repertoire size and homogenous syllable usage, enumerations may be satisfactory. Although researchers often use repertoire size as a measure of song complexity, listeners to songs are unlikely to count entire repertoires and they may rely on other cues, such as syllable detection probability.Communicated by A. Cockburn     

The strategy of fly-and-forage migration,illustrated for the osprey (<Emphasis Type="Italic">Pandion haliaetus</Emphasis>)

Migrating birds often alternate between flight steps, when distance is covered and energy consumed, and stopover periods, when energy reserves are restored. An alternative strategy is fly-and-forage migration, useful mainly for birds that hunt or locate their prey in flight, and thus, enables birds to combine foraging with covering migration distance. The favourability of this strategy in comparison with the traditional stopover strategy depends on costs of reduced effective travel speed and benefits of offsetting energy consumption during migration flights. Evaluating these cost-benefit effects, we predict that fly-and-forage migration is favourable under many conditions (increasing total migration speed), both as a pure strategy and in combination with stopover behaviour. We used the osprey (Pandion haliaetus) as test case for investigating the importance of this strategy during spring and autumn migration at a lake in southern Sweden. The majority, 78%, of passing ospreys behaved according to the fly-and-forage migration strategy by deviating from their migratory track to visit or forage at the lake, while 12% migrated past the lake without response, and 10% made stopovers at the lake. Foraging success of passing ospreys was almost as good as for birds on stopover. Timing of foraging demonstrated that the birds adopted a genuine fly-and-forage strategy rather than intensified foraging before and after the daily travelling period. We predict that fly-and-forage migration is widely used and important among many species besides the osprey, and the exploration of its occurrence and consequences will be a challenging task in the field of optimal migration.     

Compensatory behaviour after displacement in migratory birds

Using a meta-analysis approach we re-analysed orientation cage experiments with displaced migrants found in the literature. A rather large proportion of the orientation experiments showed directional shifts after displacements, indicating ability for birds to detect and react on such displacements. There was a clear difference between overcast and experiments where birds had a view of the starry sky. In experiments under a starry sky, the birds compensated the displacements, whilst under overcast unaltered or reverse orientations were generally displayed. This indicates a role for the stars to be involved in detection of the changes in position. Such a role of celestial cues is further stressed by the results of several studies manipulating a planetarium sky. Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users.     

Differences in acoustic directionality among vocalizations of the male red-winged blackbird (<Emphasis Type="Italic">Agelaius pheoniceus</Emphasis>) are related to function in communication

Studies of animal acoustic communication have found that the frequency and temporal structure of acoustic signals can be shaped by selection for efficient communication. The directionality of acoustic radiation may also be adapted for communication, but we know relatively little about how directionality varies with signal function, sender morphology, and the environment in which the sound is transmitted. We tested the hypothesis that the directionality of a vocalization is adapted to its function in communication. This hypothesis predicts that vocalizations that are directed to multiple conspecifics (e.g., advertisements and alarms) will be relatively omnidirectional because this will maximize the number of neighbors and mates that receive the signal, and that vocalizations directed to particular individuals will be relatively directional because this will maximize detection of the signal by the targeted receiver and minimize eavesdropping. To test these predictions, we measured the directionality and amplitude of red-winged blackbird (Agelaius pheoniceus) vocalizations in the field by recording vocalizations simultaneously on eight calibrated microphones encircling the bird. We found significant variation in directionality among vocalizations. Supporting our predictions, we found that the most omnidirectional vocalizations were those used to alert conspecifics to danger, and the most directional vocalizations are those used during courtship and solicitation of copulation, when the costs of eavesdropping are likely to be high. These results suggest that the directionality of red-winged blackbird vocalizations is shaped by selection for effective communication. This study is the first to provide statistical support for the hypothesis that directionality is related to the function of a signal in communication.     

Metals contamination in the foraging area of Milky Stork: evidence of anthropogenic inputs in the aquatic environment of Kuala Gula,Malaysia

The rapid decline of the wild Milky Stork population in Malaysia has led to the reintroduction of the captive bred species in Kuala Gula, Perak. The area is known as an important migratory stopover and sanctuary for both visitors and resident birds. Although Kuala Gula and its adjacent areas are regarded as pristine and unpolluted, recent study suggested that accumulation of certain pollutants is occurring in the aquatic environment of the area. Surface sediment samples from five foraging areas considered important to the reintroduced Milky Storks have been analyzed for metals contamination. The results show that elevations of Cu, Zn, and Pb ranging from 9.7 to 57 mg kg^?1, 71 to 120 mg kg^?1, and 28 to 47 mg kg^?1 have occurred, except for Cd (0.9–1.7 mg kg^?1). The accumulation of these metals is site-specific which reflects continuous anthropogenic inputs into the aquatic environment of Kuala Gula. In addition, metal levels in some areas have exceeded the effects range low values, and thus urgent action is needed to ensure good practice and sustainable management of Kuala Gula by responsible parties.     

Trans-Sahara migrants select flight altitudes to minimize energy costs rather than water loss

Meteorological conditions influence strongly the energy and water budget of birds. By adjusting their flights spatially and temporally with respect to these conditions, birds can reduce their energy expenditure and water loss considerably. By radar, we quantified songbird migration across the western Sahara in spring and autumn. There autumn migrants face the trade-off between (a) favorable winds combined with hot and dry air at low altitudes and (b) unfavorable winds combined with humid and cold air higher up. Thus, it can be tested whether birds may chose altitudes to minimize water loss instead of energy expenditure. We predicted optimal flight altitudes with respect to water loss and energy expenditure based on a physiological flight model when crossing the western Sahara and compared these model predictions spatially and temporally with measured songbird densities. The model aiming for minimal water consumption predicted a mean flight altitude of 3,400 m under autumn conditions. However, 64% of the nocturnal songbird migration flew at altitudes below 1,000 m above ground level profiting from tailwind. This preference for tailwind in autumn, despite the hot and dry air, emphasizes the importance of energy savings and diminishes the significance of possible water stress for the selection of flight altitude. Nevertheless, during daytime, high energy expenditure due to air turbulences and water loss due to warmer air and direct solar radiation prevent songbirds from prolonging their nocturnal flights regularly into the day. Birds crossing the Sahara save water by nocturnal flights and diurnal rests.     

Community richness and stability in agricultural landscapes: The importance of surrounding habitats

In this paper, the role played by habitat diversity in the landscape on species richness and on the stability of farmland bird communities was investigated. Species richness was estimated on 374 samples monitored in farmland by the French breeding bird survey during the 2001–2005 period. A capture–recapture approach was used to estimate species richness accounting for the variation in detection probability among species of the 100 most common species detected in farmland. Landscape structure and composition were measured both in farmland and in adjacent habitats. The independent effect of each variable on community richness and stability was further assessed using hierarchical variance partitioning and taking spatial autocorrelation into account. A strong matrix effect was detected: non-cropped land deeply influenced richness and stability of bird assemblages.     

Ecological Conservation Through Aesthetic Landscape Planning: A Case Study of the Lower Wisconsin State Riverway

A consequence of expanding residential development into rural areas is the potential alteration of ecological communities. Certain novel land-use policies seek practical solutions by accommodating social needs for housing while conserving biodiversity. This study investigates whether regulations designed to protect the aesthetic characteristics of a river corridor simultaneously mitigate negative effects of development on avian biodiversity, despite the absence of explicit conservation objectives. Using housing data from the US Census (1990 and 2000) and the Audubon Christmas Bird Count (1987–2000), we examined changes in housing density, avian communities, and the relationship between these two variables in a location that has adopted aesthetic landscape planning, the Lower Wisconsin State Riverway. We found that overall species diversity increased in the Riverway, but remained constant in reference areas, although the relative increase in housing density in the two areas did not differ. We also found that omnivore populations decreased in the Riverway and increased in reference sites. On the whole, our study provides preliminary evidence that aesthetic landscape planning, such as employed in the Lower Wisconsin State Riverway, might constitute a politically viable approach to conserve ecological resources.     

A dynamic hydrological Monte Carlo simulation model to inform decision-making at Lake Toolibin,Western Australia

Lake Toolibin, an ephemeral lake in the agricultural zone of Western Australia, is under threat from secondary salinity due to land clearance throughout the catchment. The lake is extensively covered with native vegetation and is a Ramsar listed wetland, being one of the few remaining significant migratory bird habitats in the region. Currently, inflow with salinity greater than 1000 mg/L TDS is diverted from the lake in an effort to protect sensitive lakebed vegetation. However, this conservative threshold compromises the frequency and extent of lake inundation, which is essential for bird breeding. It is speculated that relaxing the threshold to 5000 mg/L may pose negligible additional risk to the condition of lakebed vegetation. To characterise the magnitude of improvement in the provision of bird breeding habitat that might be generated by relaxing the threshold, a dynamic water and salt balance model of the lake was developed and implemented using Monte Carlo simulation. Results from best estimate model inputs indicate that relaxation of the threshold increases the likelihood of satisfying habitat requirements by a factor of 9.7. A second-order Monte Carlo analysis incorporating incertitude generated plausible bounds of [2.6, 37.5] around the best estimate for the relative likelihood of satisfying habitat requirements. Parameter-specific sensitivity analyses suggest the availability of habitat is most sensitive to pan evaporation, lower than expected inflow volume, and higher than expected inflow salt concentration. The characterisation of uncertainty associated with environmental variation and incertitude allows managers to make informed risk-weighted decisions.