Numbers of Horned Lark (Eremophila alpestris) are increasing at high alpine and arctic breeding sites in Norway

Cover photo: Female Horned Lark Eremophila alpestris. Photo: Terje Lislevand. Strong declines in number of breeding Horned Larks Eremophila alpestris were reported from several Fennoscandian breeding grounds in the 1960s and 1970s. Counts from the species’ high alpine breeding grounds at Hardangervidda, southern Norway in the early 1980s and the first couple of decades in the 2000s, and from its arctic breeding grounds in the Varanger region, northern Norway in the period 1996-2021, show a reversal of the trend. The increase in numbers is suggested to have resulted primarily from recovery of nonbreeding habitat after cessation of extensive building of embankments to prevent flooding in the German Wadden Sea area, which is the main wintering area of Fennoscandian Horned Larks

Prolonged aerial chase of Willow Grouse Lagopus lagopus by Common Raven Corvus corax

Two vigorously fighting male Willow Grouse Lagopus lagopus were simultaneously attacked by a Common Raven Corvus corax and a Rough-legged Buzzard Buteo lagopus. The raven pursued one of the grouse over 900 m; the chase ended when the grouse dived into dense willows. The two birds kept the same distance, meaning that the raven flew at roughly 75 km/h (maximum level flight speed of Willow Grouse)

Pied Flycatchers Ficedula hypoleuca prefer ectoparasite-free nest sites when old nest material is present

Nest-dwelling ectoparasitic arthropods may have detrimental effects on avian breeding success and fitness. Birds should therefore be selected to avoid nest sites where the risk of being infested by ectoparasites is high. However, studies testing this hypothesis have produced mixed results. We performed an experiment in south Norway to test whether Pied Flycatchers Ficedula hypoleuca select nest site according to the presence of ectoparasites. We used artificial nest boxes in this experiment which had all been successfully used by conspecifics in the previous breeding season and still contained the old nest material. Five different groups of ectoparasites were recorded in flycatcher nests in the study area, of which the haematophagous hen flea Ceratophyllus gallinae and mites (Dermanyssus sp.) occurred in all examined nests. We offered each flycatcher pair (n = 13) a choice between 1) a box where ectoparasites had been removed by insecticide fumigation and 2) a box in which the old nest had not been fumigated. Flycatchers were highly selective in their choice of nest site, all but one settling in the fumigated, parasite-free nest box. This finding differs from a similar Swedish study (Olsson & Allander 1995) which did not find any evidence that Pied Flycatchers avoided nest boxes with ectoparasites. A likely explanation for this discrepancy is between-population differences in parasite abundance, as the mean number of hen fleas per infested nest was about five times higher in Norway than in Sweden

Lemming–Food Plant Interactions, Density Effects, and Cyclic Dynamics on the Siberian Tundra

Theory predicts that trophic interactions can produce cyclic dynamics of microtine rodents, but that in addition, social interactions are necessary to create the cyclicity. We tested the induced defence hypothesis as a component driving multi-annual cycles by analyzing data on Siberian lemming (Lemmus sibiricus Kerr) populations and the levels of trypsin inhibitors (TI) and free proteins (SPP) in their food plants. We collected data at 12 sites along the Palaearctic tundra coast in 1994 and correlated these measures with lemming density and cycle phase. A negative correlation between lemming density and TI/SPP in Carex was found at the 12 sites. Cycle phase tended to correlate significantly with TI/SPP, and plants being grazed by lemmings respond with some delay. Mass of pancreas, the organ producing proteolytic enzymes, co-varied negatively with TI/SPP. These findings are in accord with predictions from the induced defence hypothesis. In contrast, reproductive effort did not conform to the predictions but co-varied strongly with density. Data are in accord with theory predicting that, in addition to trophic interactions, some self-regulation is necessary to create cyclic dynamics. Our data show that the plant defence hypothesis alone is not a sufficient explanation for the cyclicity. Several factors interact, including predation, food quality (including induced defence chemicals), and intra-specific competition.En théorie, les interactions trophiques peuvent produire une dynamique cyclique de rongeurs microtinés, mais en plus de cela, il faut des interactions sociales pour donner lieu à la cyclicité. Nous avons mis à l’épreuve l’hypothèse induite de défense en tant que composante intégrale des cycles multi-annuels en analysant les données relatives aux populations de lemming brun (Lemmus sibiricus Kerr) et les taux d’inhibiteurs de la trypsine (TI) et de protéines libres (SPP) se trouvant dans leur nourriture végétale. Nous avons recueilli des données à 12 emplacements le long de la côte paléarctique des toundras en 1994 et avons corrélé ces mesures à la densité des lemmings ainsi qu’à la phase du cycle. Une corrélation négative entre la densité des lemmings et TI/SPP dans Carex a été trouvée à 12 emplacements. La phase du cycle avait tendance à donner une corrélation significative avec TI/SPP, et les végétaux faisant l’objet d’un pâturage par les lemmings réagissaient avec un certain retard. Les masses de pancréas, soit l’organe producteur des enzymes protéolytiques, co-variait négativement avec TI/SPP. Ces constatations cadrent avec les prédictions émanant de l’hypothèse induite de défense. Par contre, les efforts de reproduction ne se conformaient pas aux prédictions mais co-variaient fortement en fonction de la densité. Les données sont en accord avec la théorie prédisant qu’en plus des interactions trophiques, il faut une certaine autorégulation pour créer une dynamique cyclique. Nos données montrent qu’à elle seule, l’hypothèse de défense des végétaux ne constitue pas une explication suffisante à la cyclicité. Plusieurs facteurs entrent en interaction, dont la prédation, la qualité de la nourriture (ce qui comprend les produits chimiques induits de la défense) et la compétition intraspécifique

Nest distribution and nest habitat of the Tibetan Partridge ( Perdix hodgsoniae ) near Lhasa, Tibet

Background: Little is hitherto known about the breeding ecology of the Tibetan Partridge (Perdix hodgsoniae) which is endemic to the Tibetan plateau. Here we describe nest densities, inter-nest distances and general nest site characteristics in this gallinaceous bird species and explore the possibilities that certain shrub and plant types are preferred as nest surroundings. Method: A total of 56 nests were found over three breeding seasons near Lhasa, Tibet. Nest site characteristics were compared with random control plots and the proportions of specific plant species covering nests were compared with their estimated general occurrence in the study area. Results: Nest density in the two years with highest search effort was estimated at 1.43/km2 and 1.04/km2 but was clearly higher in the part of the study area facing north (1.86–2.35/km2) than that facing south (0.11–0.34/ km2). The average nearest neighbour distance of nests was about 300 m. Nests were situated in relatively lush vegetation and covered by a total of eight shrub species and three herbs. In contrast to previous reports, Caragana shrub did not constitute an important part of the nest habitat. The flowering, non-thorny bush Potentilla fruticosa was significantly over-represented as nest cover, while Rhododendron nivale was similarly under-represented. Nest bush foliage covered a larger area of ground, and the shrub surrounding nests was generally denser, than in control samples. Also, nests were placed closer to paths and in areas with lower densities of Yak (Bos grunniens) dung than in control samples. Except that soil temperatures were lower on nest sites than on control sites, micro-climate variables measured in this study did not differ between nest sites and control plots. Conclusions: Opportunity for nest concealment is probably an important quality of the nest habitat in Tibetan Partridges, yet it is unclear why the species should prefer P. fruticosa as nest cover. It is possible that nest sites are chosen to secure escape exits in the case of approaching predators and to reduce the risk of nest trampling. Tibetan Partridges may also select nest sites according to micro-climate, either directly or indirectly through climate-related differences in shrub vegetation

Period lenght in cyclic animal populations

Although cyclic animal dynamics have long been a focus of scientific interest, the variable cycle lengths are poorly understood. Based on a review of the literature, we suggest that period length in animals showing multiannual cycles is related to the life span of their food plant rather than to any trait of the animal, such as mass or fecundity. We envisage that this pattern is brought about by a prolonged mobilization of induced defenses in longer lived plants, which can better afford periods of low reproductive output than can short-lived plants. On the basis of this hypothesis we expect animals with similar diets to show similar cycle lengths, irrespective of taxonomy and size. A path analysis, on the vertebrate herbivores, shows that 92% of the variation in cycle length is explained by foodplant longevity and that body mass adds little to this

Explaining the Evolution of Warning Coloration: Secreted Secondary Defence Chemicals May Facilitate the Evolution of Visual Aposematic Signals

Several pathways have been postulated to explain the evolution of warning coloration, which is a perplexing phenomenon. Many of these attempt to circumvent the problem of naïve predators by inferring kin selection or neophobia. Through a stochastic model, we show that a secreted secondary defence chemical can provide selective pressure, on the individual level, towards developing warning coloration. Our fundamental assumption is that increased conspicuousness will result in longer assessment periods and divergence from the predators ’ searching image, thus reducing the probability of a predator making mistakes. We conclude that strong olfactory signaling by means of chemical secretions can lead to the evolution of warning coloration

Numbers of Horned Lark Eremophila alpestris are increasing at high alpine and arctic breeding sites in Norway

Strong declines in number of breeding Horned Larks Eremophila alpestris were reported from several Fennoscandian breeding grounds in the 1960s and 1970s. Counts from the species’ high alpine breeding grounds at Hardangervidda, southern Norway in the early 1980s and the first couple of decades in the 2000s, and from its arctic breeding grounds in the Varanger region, northern Norway in the period 1996-2021, show a reversal of the trend. The increase in numbers is suggested to have resulted primarily from recovery of nonbreeding habitat after cessation of extensive building of embankments to prevent flooding in the German Wadden Sea area, which is the main wintering area of Fennoscandian Horned Larks.publishedVersio

Conditions favouring hard seededness as a dispersal and predator escape strategy

1. The water-impermeable seed coat of ‘hard’ seeds is commonly considered a dormancy trait. Seed smell is, however, strongly correlated with seed water content, and hard seeds are therefore olfactionally cryptic to foraging rodents. This is the rationale for the crypsis hypothesis, which proposes that the primary functions of hard seeds are to reduce seed predation and promote rodent seed dispersal. 2. We use a mechanistic model to describe seed survival success of plants with different dimorphic soft and hard seed strategies. The model is based on established empirical–ecological relationships of moisture requirements for germination and benefits of seed dispersal, and on experimentally demonstrated relationships between seed volatile emission, predation and predator escape. 3. We find that water-impermeable seed coats can reduce seed predation under a wide range of natural humidity conditions. Plants with rodent dispersed seeds benefit from producing dimorphic soft and hard seeds at ratios where the anti-predator advantages of hard seeds are balanced by the dispersal benefits gained by producing some soft seeds. 4. The seed pathway predicted from the model is similar to those of experimental seed-tracking studies. This validates the relevance and realism of the ecological mechanisms and relationships incorporated in the model. 5. Synthesis. Rodent seed predators are often also important seed dispersers and have the potential to exert strong selective pressures on seeds to evolve methods of avoiding detection, and hard seeds seem to do just that. This work suggests that water-impermeable hard seeds may evolve in the absence of a dormancy function and that optimal seed survival in many environments with rodent seed predators is obtained by plants having a dimorphic soft and hard seed strategy