Of Lemmings and Mussels: Trophic Cascade Drives Population Dynamics of Long-Tailed Ducks Breeding in Siberia

Migratory animals experience very different environmental conditions at different times of the year, i.e., at the breeding grounds, during migration, and in winter. The long-tailed duck Clangula hyemalis breeds in the Arctic regions of the northern hemisphere and migrates to temperate climate zones, where it winters in marine environments. The breeding success of the long-tailed duck is affected by the abundances of predators (mainly Arctic fox Alopex lagopus) and their main prey species, lemmings Lemmus sibiricus and Dicrostonyx torquatus, whose population fluctuation is subject to climate change. In the winter quarters, long-tailed ducks mainly eat the blue mussel Mytilus edulis. We examined how North-west Siberian lemming dynamics affect long-tailed duck breeding success via predation pressure and how nutrient availability in the Baltic Sea influences long-tailed duck population size via mussel biomass and quality. The long-tailed duck population dynamics was predator-driven on the breeding grounds and resource-driven on the wintering grounds. Nutrients from fertilizer runoff from farmland stimulate mussel stocks and quality, supporting high long-tailed duck population sizes. The applied hierarchical analysis combining several trophic levels can be used for evaluating large-scale environmental factors that affect the population dynamics and abundance of migrants from one environment to another.

Review of deaths and behavior of large birds of prey on power grid facilities in Tatarstan and Udmurtia (Russia), problems of modernization of 6–10 kV overhead power lines

The report analyzes the deaths of large birds of prey on power grid facilities of Tatarstan previously published in the literature since 2012 and additional ones, identified since 2019, including in the neighboring region – Udmurt Republic. Analysis of the data shows that immature Imperial Eagles (Aquila heliaca) up to 3 years old (n=11) died on the 6–10 kV power lines dangerous for birds. The percentage of fledglings that died near breeding territories after leaving their nests was 81.8% (n=9); one bird died in its second year of life and one bird died in its third year. The death of fledglings was identified in 8 breeding areas (in one of them twice), which is 3.9% of all known breeding areas of the Imperial Eagle in Tatarstan by the end of 2021 (n=205) and about 7.2% of 111 breeding areas in 16 administrative districts of southeastern Tatarstan where oil production is taking place. Two out of six fledglings, for which a time interval of death was established, died in the second half of August, and 2 eagles also died in the first and second halves of September. Distances from precisely known nests to locations where the fledglings died ranged from 0.26 to 11.7 km, 2.56 km on average (n=7). In 57.1% of cases deaths occurred at distances less than 1 km (from 260 to 600 m), and in 28.6% of cases at distances from 2 to 3 km. Observations of the behavior of imperial eagles in breeding grounds show a certain selectivity, namely avoidance of the most dangerous power lines. Adaptation of imperial eagles to the electric grid environment continues – 3 new breeding territories on the electric poles of high-voltage power lines were found. Two cases of death of immature White-Tailed Eagles (Haliaeetus albicilla) were identified on 6–10 kV power lines dangerous for birds deep in the forestland on narrow forest cleared strips in Tatarstan and Udmurtia, as well as the Steppe Eagle (Aquila nipalensis) in Udmurtia. Illegal exploitation and even construction of new 6–10 kV power lines dangerous for birds continues. Despite the measures taken to protect birds from death in the electric grid environment, the rate and quality of these measures are such that in the near future power lines will have a negative impact on eagles in the native area as they do now.

Endogenous biomarkers reveal diet partitioning among three sympatric species of swallows

Since the early 1990s, aerial insectivorous birds have shown serious population declines in North America, but it is not clear if factors common to all species within this guild account for these declines. Among sympatric swallows, population trends differ, and this may be due to differences in ecology operating throughout the annual cycle. Although these species all feed on aerial insects, prey taxa can differ tremendously in their “aeroecology” and use by swallows. We examined the potential for dietary differences among three species of swallows, Barn Swallow (Hirundo rustica), Cliff Swallow (Petrochelidon pyrrhonota), and Tree Swallow (Tachycineta bicolor), breeding sympatrically in southern Ontario, Canada. Potential interspecific differences in nestling diet were examined using two endogenous biomarkers, DNA barcoding of nestling feces and stable isotope analysis (δ 2H, δ 13C, δ 15N) of nestling feathers. We found evidence for differences in dietary sources of provisioned young where Barn Swallows provisioned more terrestrial-based prey, Cliff Swallows provisioned an intermediate diet, and Tree Swallows the most aquatic-emergent insect diet. We suggest this information may help to identify potential factors contributing to differential declines of aerial insectivores operating on the breeding grounds, including diet quality.

Social migratory connectivity: do birds that socialize in winter breed together?

Researching the complete life cycles of migratory animals is essential for understanding conservation and population dynamics. Many studies focus on the breeding season, but surviving winter is equally important. Living in groups during winter can play a vital role as social connections within groups can provide many benefits such as protection from predators and increased access to resources. However, it is often unknown how social connections change across seasons in migratory animals. We focus on social connections in a migratory bird and ask whether social connections in winter continue during breeding. Golden-crowned sparrows have distinct, stable winter communities which include both site and group fidelity across years: birds almost always rejoin the same social community each year. If these birds have social connectivity across migration, we would expect individuals that associate in winter would also associate together on their breeding grounds. Our small-scale GPS tagging study combined with intensive social behavior data revealed that sparrows in the same tightly-knit winter community migrated to highly disparate locations during summer, showing that social connections in winter do not continue in summer. This suggests that golden-crowned sparrows have entirely separate social structures across seasons and that long-term social memories allow them to reform stable groups each winter.

Migration distance affects how closely Eurasian wigeons follow spring phenology during migration

Background The timing of migration for herbivorous migratory birds is thought to coincide with spring phenology as emerging vegetation supplies them with the resources to fuel migration, and, in species with a capital breeding strategy also provides individuals with energy for use on the breeding grounds. Individuals with very long migration distances might however have to trade off between utilising optimal conditions en route and reaching the breeding grounds early, potentially leading to them overtaking spring on the way. Here, we investigate whether migration distance affects how closely individually tracked Eurasian wigeons follow spring phenology during spring migration. Methods We captured wigeons in the Netherlands and Lithuania and tracked them throughout spring migration to identify staging sites and timing of arrival. Using temperature-derived indicators of spring phenology, we investigated how maximum longitude reached and migration distance affected how closely wigeons followed spring. We further estimated the impact of tagging on wigeon migration by comparing spring migratory timing between tracked individuals and ring recovery data sets. Results Wigeons migrated to locations between 300 and 4000 km from the capture site, and migrated up to 1000 km in a single day. We found that wigeons migrating to more north-easterly locations followed spring phenology more closely, and increasingly so the greater distance they had covered during migration. Yet we also found that despite tags equalling only around 2% of individual’s body mass, individuals were on average 11–12 days slower than ring-marked individuals from the same general population. Discussion Overall, our results suggest that migratory strategy can vary dependent on migration distance within species, and even within the same migratory corridor. Individual decisions thus depend not only on environmental cues, but potentially also trade-offs made during later life-history stages.

Birds with multiple homes. The annual cycle of the pallid swift (Apus pallidus brehmorum)

We tracked pallid swifts (Apus pallidus brehmorum) from a single breeding colony in Gibraltar over two years. Our results show movement of birds between specific regions within the non-breeding geographical area at specific times of the year. The tracking of a single individual showed remarkable fidelity to the areas visited between years. Furthermore, two pallid swifts tracked over the entire eight-month non-breeding period, while in Africa, gave no indication of coming to land, supporting previous findings of an airborne existence in swifts outside the breeding season. In addition, the crossing of the Sahara Desert to and from breeding grounds is remarkably fast, with one individual crossing it in just over a day. We discuss our findings in the context of bird migration evolutionary strategies.