Impact of mustelid predation and ambient temperature on breeding success and population dynamics of Pied Flycatchers Ficedula hypoleuca in Swedish Lapland, 1965–2019

A nest-box breeding population of Pied Flycatcher Ficedula hypoleuca in subalpine birch forest at Ammarnäs in northern Sweden was studied in 1965–2010. The population showed on average a significantly decreasing trend during the initial 25 years, after which it remained on a static level. The yearly variation of the population size was significantly correlated with breeding result in preceding years, which in turn was affected by e.g. nest predation, adverse climatic factors, clutch size, and incidence of defective egg shell formation. It is also suggested that the population decline during the initial 10–15 study years followed from over-establishment of the breeding habitat. The average breeding result was 2.3 fledglings per pair, which is far below the number needed for the population to be self-reproducing. The occurrence of unusually high rates of nest predation and defective egg shells seems to be passing phenomena, predicted to approach zero after about 30 and 60 years, respectively, after the start of the study. But even with these factors eliminated and with other conditions remaining unchanged, the Ammarnäs population will continue to be a sink population.

Return rates of 4,178 female and 1,565 male breeding Pied Flycatchers ringed in 1965–2017 were studied near the species’ upper elevation and climatic limit in northern Sweden. Female return rate was 7.5% in the season subsequent to the first breeding season. Having returned once, 37% continued to return the next three seasons. Corresponding return rates of males were 27% and 39%. Female return rate decreased with more than 30% during the study period whereas that of males did not decrease. This difference was probably due to increased mortality during the non-breeding season that selectively struck females after the 1970s. Local factors affected return rates in both sexes. Return rate was positively correlated with breeding success in females but negatively in males, whereas it was correlated with nest-predation in the opposite way. Predation by mustelids accounted for a significant part of female return rate. Females that had returned once were continuously faithful to the former breeding site. Males showed faithfulness only after having returned twice.

Climate change can impact ecosystems by reshaping the dynamics of resource exploitation for predators and their prey. Alterations of these pathways could be especially intense in ecosystems characterized by a simple trophic structure and rapid warming trends, such as in the Arctic. However, quantifying the multiple direct and indirect pathways through which climate change is likely to alter trophic interactions and their relative strength remains a challenge. Here, we aim to identify direct and indirect causal mechanisms driven by climate affecting predator-prey interactions of species sharing a tundra food web. We based our study on relationships between one Arctic predator (Arctic fox) and its two main prey - lemmings (preferred prey) and snow geese (alternate prey) - which are exposed to variable local and regional climatic factors across years. We used a combination of models mapping multiple causal links among key variables derived from a long-term dataset (21years). We obtained several possible scenarios linking regional climate factors (Arctic oscillations) and local temperature and precipitation to the breeding of species. Our results suggest that both regional and local climate factors have direct and indirect impacts on the breeding of foxes and geese. Local climate showed a positive causal link with goose nesting success, while both regional and local climate displayed contrasted effects on the proportion of fox breeding. We found no impact of climate on lemming abundance. We observed positive relationships between lemming, fox and goose reproduction highlighting numerical and functional responses of fox to the variability of lemming abundance. Our study measures causal links and strength of interactions in a food web, quantifying both numerical response of a predator and apparent interactions between its two main prey. These results improve our understanding of the complex effects of climate on predator-prey interactions and our capacity to anticipate food web response to ongoing climate change.

(1) Shoots of the circumpolar species Cassiope tetragona were collected on brief visits to three remote arctic and subarctic sites, two in Svalbard and one in Swedish Lapland. The shoots were subsequently analysed by measuring leaf lengths in strict sequence along individual shoots. (2) This evergreen species retained up to 232 leaves per shoot. Leaf lengths, plotted against leaf position on the shoots, revealed two trends: (i) more or less regular waves caused by the alternation of short spring and autumn leaves with long summer leaves, and (ii) an ontogenetic trend represented by a general increase in leaf length with increasing distance between the point of origin of the leaf and the origin of the shoot. (3) The seasonal trend of leaf length was used to delimit annual complements of leaves, of which up to twenty persisted. The number of leaves was counted for each year and the ontogenetic trend of leaf length was removed by statistical methods so that leaf length indices could be calculated and relative lengths compared, both between years within populations and between populations. Three indices of leaf length were derived: maximum, minimum and the total of all leaf length indices for each year. (4) Correlation analysis between the four measures of annual leaf performance showed several similarities between the two Svalbard populations, a few between the low altitude population from Svalbard and that from Swedish Lapland and none between the higher altitude Svalbard population and that from Swedish Lapland. (5) Correlation analysis between annual leaf performance and mean monthly temperature and monthly total precipitation showed that July temperatures and precipitation during May were particularly important for leaf development in the Svalbard populations. July temperatures represent mid-summer conditions during a very short growing season in Svalbard, whereas May is normally the driest month in this region of generally low precipitation. Ambient temperature is usually sub-zero for most of May and precipitation as snow is probably important in protecting the sensitive shoot apices of C. tetragona which lack true buds. (6) In Swedish Lapland, the number of leaves per year was correlated with summer temperatures but only negatively with precipitation which was greater at the Swedish site than in Svalbard. At the Swedish site, therefore, the protection of leaf primordia from frost is probably greater than in Svalbard because of a more persistent snow cover. (7) Correlations between the number of leaves per year and leaf length indices in the previous year, together with correlations between leaf performance and weather conditions in the previous year, were often significant. In general, the same weather variables were correlated with leaf performance as in the within-year comparisons. (8) The correlations between the number of leaves per year and the other measures of leaf performance and weather in the previous year were particularly strong in the Svalbard populations. This demonstrates the preformation of an annual leaf complement by the High Arctic Svalbard populations. This may be an important mechanism to buffer

Newly laid eggs of Pied Flycatchers Ficedula hypoleuca breeding in subalpine birch forest in Swedish Lapland were weighed in the field in 1965–1976. The main objective of the study was to get knowledge of the egg production capacity and its relation to the environmental conditions in the northern periphery of the breeding range of the species. The eggs were on average smaller than what is known from other Pied Flycatcher populations. Egg mass was non-linearly related to ambient temperature, and smallest at temperatures <10°C. About 70% of the eggs were laid at those temperatures. Variation in temperatures during the egg formation contributed to a significant egg mass variation between years. Average egg mass was lowest in the biggest clutches (7 or 8 eggs). Egg mass did not vary significantly within clutches, was not significantly related to the female mass, and did not vary between years in the same female. Hatching and fledging success were non-significantly related to the mean egg masses, indicating that egg sizes were not decisive for the breeding output.

Procellariiformes are one of the most threatened groups of birds of the world so knowledge of nesting habitat and factors affecting breeding rates are vital issues for their conservation. Although Cory's Shearwater Calonectris borealis is a well-studied seabird species on the whole, information on the relationship between its breeding parameters and nest site characteristics is quite limited. To address this gap, during 2017-2019, we conducted a study on its breeding performance on Tenerife, the largest and the most densely populated island of the Canarian archipelago. We constructed generalized linear mixed models to evaluate the potential effects of nest features on breeding performance. Two variables explained breeding success: the distance from the nest to the nearest paved road, and the presence of pebbles at the entrance of the nest-burrow, which correlated negatively and positively with breeding success, respectively. The majority of failures occurred during the incubation period. Breeding failures were mainly related to egg abandonment and rat predation upon eggs or chicks. Effective measures mitigating human-instigated disturbance (e.g. control of dogs, rats and feral cat populations, and reducing light pollution), together with studies on factors affecting demographic parameters, are needed to guarantee the long-term conservation of Cory's Shearwater and other seabird species on the main Canary Islands.—Rodríguez, B., Siverio, F., Acosta, Y. & Rodríguez, A. (2022). Breeding success of Cory's Shearwater in relation to nest characteristics and predation by alien mammals. Ardeola, 69: 115-128.

Seabirds were counted on Michaelmas Cay every month from May 1984 to April 1990. Seven species bred during the study. The major breeding species were Sooty Tern Sterna fuscata, Common Noddy Anous stolidus, Crested Tern S. bergii and Lesser Crested Tern S. bengalensis. Silver Gull Larus novaehollandiae, Black-naped Tern S. sumatrana and Bridled Tern S. anathaetus bred in some years in small numbers. Sooty Terns had a sub-annual breeding cycle of 8.6 months duration, measured between peaks of breeding numbers, while the other species were annual breeders, five in summer and one (Silver Gull) in winter. In successive breeding cycles, the sizes of breeding populations of Sooty Tern and Common Noddy both fluctuated strongly. Crested Tern numbers increased slightly then decreased, and Lesser Crested Tern numbers increased strongly then decreased again. Average Silver Gull numbers remained fairly stable over the study period. Fledging success varied considerably among breeding cycles of Sooty Tern, Common Noddy and Crested Tern. Lesser Crested Terns bred successfully in three cycles and showed increasing fledging success over the study period. Climate had a major influence on breeding populations of Sooty Tern and Common Noddy. Three cyclones were recorded; one altered the periodicity of Sooty Tern breeding cycles and two affected its breeding numbers and success. In mid-year, prolonged periods of strong winds caused breeding failures in Sooty Tern and Common Noddy. Erosion of the cay also caused nest losses. Human disturbance had little effect on breeding populations.

Breeding success plays a crucial role in the dynamics of bird populations and yet is the least-studied avian life-stage. Habitat quality during breeding phase may have important implications for survival and conservation, particularly for declining populations in landscapes that have undergone wide-scale human modification. The European Turtle dove is a widespread but fast declining species both in breeding and wintering zones. Reduced food availability is thought to influence breeding success of this game species, but it is not known how agriculture practices could influence breeding Doves, in its high altitude breeding zones. Here, we monitored Turtle dove nests in apple orchards from early Marsh to the end of October 2015. Nest-tree support, breeding success, and predation were determined and analysed depending on agricultural practices. Compared to prune, cherry and other plantation, apple orchards had the highest overall Turtle doves’ nests (85%). However, 60% of recorded nests were located on Golden delicious, where are noted the highest nesting success rates (respectively 77.6% and 57.9% for eggs and chicks). However, Turtle dove showed high rate of nesting failure in the Midelt region, more especially in apple orchards, and this is mainly due to predation attacks, which caused a loss of 77.8% of broods, both among eggs and chicks. In addition, several farming practices in apple orchards influenced significantly nesting success of this species. In fact, this game bird does not breed in the orchards covered by hail-nets. Similarly, tree pruning disturb doves nesting on apples.

Egg measurements together with calculated volumes are presented for nine passerine species (Prunella modularis, Luscinia svecica, Phoenicurus phoenicurus, Turdus pilaris, Turdus philomelos, Turdus iliacus, Phylloscopus trochilus, Fringilla montifringilla, and Carduelis flammea), breeding in rich subalpine birch forests on a south-faced mountain slope in southern Swedish Lapland. There were no clear regional size trends in comparisons with egg collections from other parts of Europe. There was a significant increase in egg size in the latter part of the laying sequence. The ultimate egg is from 2.1% (F. montifringilla) to 6.5% (Ph. trochilus) larger than the mean of the clutch. According to several years’ measurements of T. pilaris and T. iliacus eggs there was no significant size variation between seasons. This constancy together with the relatively large egg sizes might be a consequence of the productive breeding habitat of the study area.

Clutch size and the number of young, 8 d old, were determined for 23 individually ringed females of the Willow Warbler Phylloscopus trochilus in a study plot in the subalpine birch forest (550 m a.s.l.) at Ammarndis (660N), Swedish Lapland. Predation caused loss of nests and eggs for 17 of the females. Eleven of them laid a replacement clutch. Two of the latter laid a second replacement clutch after a second exposure of predation. Size of first clutches was 6.4 eggs compared with 5.2 eggs of replacement clutches. The average production of young was 1.3 in first clutches compared with 2.6 with both first and replacement clutches included. The study shows that the Willow Warbler is normally ready to replace lost clutches also at this high latitude and altitude, at least before hatching, delaying breeding up to two weeks. However, it is also shown, by argument, that the length of the breeding season does not allow two successful broods to be raised before the time of adult moult in late July and the decline of invertebrate food in August.

The postnuptial wing moult of the Brambling was studied in a subalpine birch forest near Ammarnäs (65°58'N, 16°07'E) in Swedish Lapland. 580 moult cards were collected during an annual ringing scheme in the years 1984—1989. Regression analysis of moult data, with date as the independent value, showed an average moult duration for males and females of 47 days. Raggedness values support the moult speed estimated from the regression analysis. The moult speed shown here for the Brambling is much faster than for the Chaffinch and might be due to some constraint for moulting during early autumn.

Dramatic declines of some arthropod populations have recently received a lot of attention. Identified declines have mainly been attributed to changes in agriculture, climate, pathogen prevalence and light pollution, as well as cross‐regional effects of, e.g., drifting pesticides. However, the overall picture is complex and debated, and there is a need for systematically collected long‐term data, not least from areas relatively unaffected by humans. We monitored the abundance of arthropods (mainly insects) in subalpine birch forest in Swedish Lapland over a period of 53 years (1968–2020), in an area comparatively unaffected by human activities. Arthropod abundance was assessed by yearly systematic counts on 24,000 birch shoots, in the second half of June. Animals were categorised into 17 different groups directly upon counting, dependent on taxonomy and life stage (imago, larva). Overall, there was no significant change in arthropod numbers. Nor did estimates of the total biomass of arthropods (using group‐specific indices of the mass of individuals) show any significant trend. Accordingly, there are no signs that the arthropod abundance or biomass on birch in this subarctic study site has gone through the same declines as have been reported from sites in other habitats. The reason may be that the impact of factors identified worldwide as drivers of arthropod declines so far are small or non‐existent because of the low human population density in this area.

When a limiting resource (e.g. food) varies drastically between years, and population density is measured in the conventional way as individuals per area, demographic processes such as productivity and survival may erroneously be considered density‐independent. We tested the hypothesis that if the variation in a limiting resource is not taken into account in the density measure, this may lead to erroneous conclusions about the density‐dependence of demographic variables. We studied the food‐related variation in productivity of bramblings Fringilla montifringilla, an insectivorous passerine bird, using 19 years of standardised insect censusing, bird censusing and mist‐netting of birds in subalpine birch forest in Swedish Lapland. The yearly variation in our measure of brambling per capita productivity (numbers of juveniles per adult trapped) was explained to 30–40% by the larvae abundance of the moth Epirrita autumnata. Taking larvae density into account, no other environmental variable (inferred predation pressure, breeding phenology, and summer temperature) was significantly related to variation in reproductive output. There was no effect of brambling population density on per capita productivity, that is, when density was measured the conventional way, productivity seemed density‐independent. However, per capita productivity was significantly and negatively correlated to the food‐related population density (population density divided by larval density), supporting the hypothesis that not including a limiting resource into the density measure may indeed lead to erroneous conclusions about the density‐dependence of demographic variables.

Survival, Experience, and Age in Relation to Breeding Success of Canada Geese

1. In incipient termite colonies, biparental brood care rapidly shifts towards alloparental brood care. This transition was suggested to recapitulate the evolutionary trajectory from subsocial wood roach ancestors to eusociality in termites.2. Incipient colonies of the subterranean termite Coptotermes gestroi (Wasmann) were investigated to determine if this transition was irreversible and if the burden of brood care on the first alloparents could be measured. To do so, the initial size of the work force necessary for an incipient colony to survive once the brood care became alloparental was determined.3. The results of the study show that within 5 months after foundation, brood care duties were fully transferred to workers and the primary reproductives became irreversibly dependent on these workers for survival, reproduction, and colony growth.4. Once the brood care became strictly alloparental, the presence of a single worker was enough to maintain the survival of the king and queen, confirming that ‘reversed parental care’ was also achieved. However, major brood loss and suppressed egg‐laying activity from the queen was observed, suggesting that the burden of brood care was too high for a single worker to absorb. Therefore, once brood care has shifted to alloparents, a critical number of workers is necessary to prevent brood loss and initiate colony growth.5. As the initial cost of brood care is rapidly absorbed with colony growth in termites, the performance in brood care of the first few alloparents in a subsocial wood roach ancestor may have contributed to the emergence of eusociality in this clade.