The European Turtle Dove in the ecotone between woodland and farmland: multi-scale habitat associations and implications for the design of management interventions

The European Turtle Dove (turtle dove) is globally threatened after undergoing a sustained and generalised decline across its breeding range, with habitat loss suggested as the main driver. Here, we reviewed the scientific literature on habitat associations across its European breeding range, in relation to distribution, breeding numbers, nesting substrates, food and foraging habitats, to identify optimal habitat management measures. Large-scale distribution seemed related to the availability, but not dominance, of woodland landscapes; abundance was generally higher in woodland than on farmland. However, abundance in woodland increased with additional structural diversity and proximity to farmland, and abundance on farmland increased with greater availability of non-farmland features. Nesting occurred most frequently on trees (secondarily on bushes) but we found geographical differences in the type of nesting substrate, with thorny bushes being used more frequently in the north, and open canopy trees in the south. Turtle doves fed on a wide spectrum of seeds with a predominance of wild, particularly early-flowering, plants; but we could not identify a single plant species whose abundance determined turtle dove numbers. Across the distribution range, a shift from wild to cultivated seeds occurred as the season progressed. However, interventions should favour the availability and access to wild seeds. Efficient management interventions depend on the dominant habitat; overall, interventions should seek to augment landscape heterogeneity by increasing the mixing of farmland and woodland. Combined forestry and agricultural policies must provide the right conditions for ecotone species like the Turtle dove.

Mercury toxicity risk and corticosterone levels across the breeding range of the Yellow-breasted Chat

Mercury (Hg) is an environmental contaminant that can negatively impact human and wildlife health. For songbirds, Hg risk may be elevated near riparian habitats due to the transfer of methylmercury (MeHg) from aquatic to terrestrial food webs. We measured Hg levels in tail feathers sampled across the breeding range of the Yellow-breasted Chat (Icteria virens), a riparian songbird species of conservation concern. We assessed the risk of Hg toxicity based on published benchmarks. Simultaneously, we measured corticosterone, a hormone implicated in the stress response system, released via the hypothalamus-pituitary-adrenal axis. To better understand range-wide trends in Hg and corticosterone, we examined whether age, sex, subspecies, or range position were important predictors. Lastly, we examined whether Hg and corticosterone were correlated. Hg levels in chats were relatively low: 0.30 ± 0.02 µg/g dry weight. 148 out of 150 (98.6%) had Hg levels considered background, and 2 (1.6%) had levels considered low toxicity risk. Hg levels were similar between sexes and subspecies. Younger chats (<1 year) had higher Hg levels than older chats (>1 year). Hg levels were lowest in the northern and central portion of the eastern subspecies’ range. Corticosterone concentrations in feathers averaged 3.68 ± 0.23 pg/mm. Corticosterone levels were similar between ages and sexes. Western chats had higher levels of corticosterone than eastern chats. Hg and corticosterone were not correlated, suggesting these low Hg burdens did not affect the activity of the hypothalamus-pituitary-adrenal axis. Altogether, the chat has low Hg toxicity risk across its breeding range, despite living in riparian habitats.

Population Growth and Long-Distance Vagrancy Leads to Colonization of Europe by Elegant Terns Thalasseus elegans

Elegant terns Thalasseus elegans breed in a very limited area of the northern Gulf of California and the Pacific coast of southern California, with up to 95% (mean 78%, 1991–2014, Perez et al., 2020) of the population nesting on Isla Rasa in the northern Gulf of California. On Isla Rasa, the primary nesting colony, elegant terns suffered predation by rodents which raised the possibility of population extinction, with a substantial proportion of the world population nesting on this single island. Because of this threat, rodents were successfully removed from Isla Rasa in 1995. The removal of rodents from Isla Rasa led to a near immediate increase in the population of elegant terns. That increase was associated with a changing pattern in dispersal by the terns, including extraordinary movements to the Gulf of Mexico, the Atlantic coast of the United States north to Massachusetts, and, remarkably, to western Europe. A few elegant terns successfully bred at these European localities during 2009 to the present. In this paper we use this exceptional example of long-distance dispersal to illustrate how rapid population growth during ∼ 1995 to present can lead to successful colonization of remote sites through repeated instances of vagrancy. We tested four Hypotheses that together support the idea that the growing population of elegant terns has produced increasing numbers of young, and these young have spread, through the mechanism of vagrancy, to the Pacific Northwest, the east coast of the United States, and western Europe. Our Hypotheses are: (1) The nesting population of elegant terns within their core nesting range has increased since removal of rodents from Isla Rasa; (2) Occurrence of vagrant elegant terns in the Pacific Northwest is driven by population growth within the core breeding range. (3) Occurrence of vagrant elegant terns at the east coast of the United States is driven by population growth within the core breeding range. (4) Occurrence and colonization of western Europe by elegant terns is driven by nesting population size within the core breeding range. Corollaries of these Hypotheses are, (i) that there is a time lag in occurrence of vagrants at each of these areas, based on increasing distance from the core breeding range and (ii) the number of vagrants in any given year is also related to sea surface temperature (SST), as expressed by Oceanic Niño Index, a proxy for food resource levels. Generally we found strong statistical support for each of these Hypotheses; an exception was for the occurrence of elegant terns in the Pacific Northwest, which initially occurred following El Niño events (low food supply) and profound breeding failure, but later corresponding to cold water years with high breeding success. We use elegant terns, exceptional for the highly restricted breeding range and sustained population growth over 25 years, to illustrate how growing populations may colonize very distant habitats through repeated instances of vagrancy.

Does the expansion of the species' breeding range also involve the establishment of new migratory routes and new wintering ranges? The case of the citrine wagtail Motacilla citreola (Pallas, 1776)

From the second half of the 20th century, some Asian or Eastern European species expanded their breeding range westward. These include red-flanked bluetail Tarsiger cyanurus, black-headed bunting Emberiza melanocephala, common rosefinch Carpodacus erythrinus, and citrine wagtail Motacilla citreola. All of these species are long-range migratory species that historically have their own wintering ranges concentrated in Southern Asia. Although migratory behavior is mainly controlled by genetic factors, there is evidence of a high degree of flexibility and adaptability. Therefore, in the event of specific environmental changes, the genetic basis for a rapid and diverse micro-evolutionary development that affects the future migration patterns of birds is already in place. Possible adaptations also include changes to migratory directions and the choice of new and closer winter quarters. It is therefore prudent to ask whether the long-range migratory species that have expanded their breeding range westward in Europe have also established new migration routes and wintering ranges. This research shows that over the last few decades, the wintering area of Motacilla citreola has expanded westwards, including significantly the Middle East and, to a lesser extent, Africa and Europe. Especially in the activation of the most western routes, a fundamental role was played by the phenomenon of post-fledging dispersal, manifested by young who, as also observed in other Asian passerines (e.g., Pallas's warbler Phylloscopus proregulus, yellow-browed warbler Phylloscopus inornatus, pine bunting Emberiza leucocephalos), in autumn moved in different directions than the typical migratory route of their species. The Middle East and the neighboring Horn of Africa are progressively increasing in relevance as an additional area for the wintering of the species as a whole. Similarly, if in Europe the expansion of the breeding range towards the west continues in the future, West Africa, reached through Gibraltar, could become important as additional wintering ranges. In analogy with what is being observed for the western yellow wagtail Motacilla flava, Europe itself is also becoming part of the wintering range of the species. In fact, there is an increase in cases of wintering not only in the south of the continent, but there is also a progression towards the north.

Using Song Dialects to Assess the Migration Strategy of the Golden-crowned Sparrow

Most techniques used to study migration of wild birds require capture for banding or for attachment and/or recovery of tags or transmitters. We took advantage of the fact that the Golden-crowned Sparrow (Zonotrichia atricapilla) sings in winter, combined with published data on the distribution of its distinct song dialects in the breeding range, to assess its migration strategy and migratory connectivity by means of these dialects. Using recordings of the Golden-crowned Sparrow’s song across much of its winter range, we categorized these birds by song type to identify their likely origin in some subset of the breeding range. This method allows examination of migration without the need to capture birds. Our results fit best with a pattern of chain migration, with the northernmost breeders wintering in the northernmost part of the winter range, and the southerly breeders wintering farther south. The results suggest strong migratory connectivity between segments of the breeding and winter ranges, though our small sample size makes it difficult to draw firm conclusions on connectivity.

Spatial Responses to Climate Change in a Long-Distance Migratory Songbird: the Scarlet Tanager (Piranga olivacea)

In the 21st century, climate change is threatening the populations of many species with extinction (Parmesan &amp; Yohe, 2003). Migratory species, some of whose breeding ranges are located in areas of fast-paced change, are at risk (Møller et al., 2008; Sander et al., 2020). We propose an assessment of the spatial response to climate change of such a species, the Scarlet Tanager (Piranga olivacea). P. olivacea migrate to the northern regions of North America (Mowbray, 2020), where rapid climate change may threaten the species’ suitability to their historical breeding areas. To test whether P. olivacea are responding spatially to climate change, we will use a two pronged approach looking at occurrence and morphological change from across their breeding range over time. First, we will assess spatial responses to climate change by comparing historical breeding occurrence and climate data (March-August, ca. 70-50 years ago; 1950-1970), to current occurrence data (years 2000-2020), to build a forecast of potential future breeding distribution for this species using Maxent software (Phillips et al., 2018). Breeding season occurrence data for historical and current time periods will be sourced from museum records from www.gbif.org, and will be matched with environmental data (i.e., temperature, precipitation,land cover). Recent research has supported that migratory birds are growing longer wings in response to climate change, presumably under selection pressure to support improved flight efficiency for migrating longer distances to access appropriate environmental conditions for breeding (Weeks et al., 2020). We will assess morphological changes over time in breeding P. olivacea in response to predictions under climate change hypotheses by measuring museum specimens from the American Museum of Natural History and the Louisiana State University Museum of Natural Science. We intend to infer whether P. olivacea possesses adequate adaptive potential to keep pace with relevant climate change metrics, and more broadly whether climate change is driving selection on morphology to reach a more northern breeding distribution for this species. If the historical distribution is explained by climate variables but P. olivacea has not shifted its breeding range or exhibited morphological shifts, this may be evidence of low adaptive capacity. Climate, morphological and occurrence data will be analyzed to determine the suitability of P. olivacea in its current breeding range, as well as alternative responses including shifts in the species’ reproductive windows. Our data will include bill length, mass, and hand-wing index variables for morphological analyses, while precipitation, temperature, and land cover will be included in the environmental datasets. Statistical analysis will be run by the American Museum of Natural History’s Maxent software, v. 3.4.4. Results will provide support for conservation efforts for forest-dwelling long distance migrant birds threatened by climate change, and can aid in the understanding of climate change’s effects on migratory species as a whole.

The endangered Brown Shrike subspecies Lanius cristatus superciliosus has a male-biased sex ratio and only early arriving males are paired

Summary Along with many long-distance migrant passerine species in the East Asian-Australasian Flyway, the migratory Brown Shrike Lanius cristatus superciliosus has been sharply declining throughout its breeding range. Its breeding range in Japan shrank by 90.9% between the 1910s and 2010s. In contrast, the closely related but resident Bull-headed Shrike L. bucephalus bucephalus has been gradually declining but is still a common resident in Japan. To better understand the drastic decline of Brown Shrike, we compared the pairing success during three consecutive breeding seasons of these two species. About 60–70% of Brown Shrike males were unpaired, which was much higher than the percentage of unpaired male Bull-headed Shrike (c.0–20%). Brown Shrike males arriving later did not pair because the population’s sex proportion is heavily biased toward males. One of the factors of male-biased population of Brown Shrike may be female-biased mortality in wintering sites, or on the migratory journey, and tracking studies will be required to test this.

Successful Long-Distance Breeding Range Expansion of a Top Marine Predator

Little is known about the effects of large-scale breeding range expansions on the ecology of top marine predators. We examined the effects of a recent range expansion on the breeding and foraging ecology of Laysan albatrosses (Phoebastria immutabilis). Laysan albatrosses expanded from historical breeding colonies in the Central Pacific Ocean to the Eastern Pacific Ocean around central Baja California, Mexico, leading to a 4,000-km shift from colonies located adjacent to the productive transition zone in the Central Pacific to colonies embedded within the eastern boundary current upwelling system of the Eastern Pacific California Current. We use electronic tagging and remote sensing data to examine the consequences of this range expansion on at-sea distribution, habitat use, foraging habitat characteristics, and foraging behavior at sea by comparing birds from historic and nascent colonies. We found the expansion resulted in distinct at-sea segregation and differential access to novel oceanographic habitats. Birds from the new Eastern Pacific colony on Guadalupe Island, Mexico have reduced ranges, foraging trip lengths and durations, and spend more time on the water compared to birds breeding in the Central Pacific on Tern Island, United States. Impacts of the range expansion to the post-breeding season were less pronounced where birds maintained some at-sea segregation but utilized similar habitat and environmental variables. These differences have likely benefited the Eastern Pacific colony which has significantly greater reproductive output and population growth rates. Laysan albatrosses have the plasticity to adapt to distinctly different oceanographic habitats and also provide insight on the potential consequences of range shifts to marine organisms.