Perisoreus Infaustus Research Articles

Patch Size and Composition of Social Groups in Wintering Tufted Titmice

Formation of small, non-kin flocks in winter is typical of many resident passerines of the temperate zone (e.g. Ekman 1989). The adaptive significance of such aggregations is usually explained in terms of better predator detection and improved foraging success for flock members (Thorpe 1963, Pulliam 1973). If kin-based aggregations in winter are formed by means of delayed dispersal of young, additional benefits may arise for both adult and first-year group members (Emlen 1997). Ekman and Rosander (1992) suggested that parental control of natal dispersal could be the main factor determining the size and composition of winter groups. According to their model, in the face of limited resources, a territorial mated pair will increase their level of aggression toward non-kin flock members, forcing them to leave. By contrast, subordinate kin (e.g. offspring) will be tolerated to a greater extent by the territorial pair as long as resources are sufficient. When adults cannot afford to share food even with their own offspring, they will exclude such offspring from the flock as well (see Ekman et al. 1994). This model has been supported by studies of Siberian Jays (Perisoreus infaustus; Ekman et al. 1994, 1996) and Gray Jays (Perisoreus canadensis; Waite and Strickland 1997). The Tufted Titmouse (Baeolophus bicolor) is one of few non-corvid, permanent-resident, temperatezone passerines in which offspring are known to spend the winter with their parents (Grubb and Pravosudov 1994). Because cohesive winter units of titmice may include up to eight members (Nice 1930), which may or may not be related, it remains unclear how often offspring are retained in this species and what factors determine the size and composition of winter groups. In our study sites within the agricultural landscape of central Ohio, titmice are permanent residents of forest fragments and often form small wintering groups of three or four birds. We predicted from Ekman and Rosander's (1992) model for offspring retention that under conditions of low resources, a wintering pair of adult titmice would be more likely to tolerate an offspring than a non-offspring flock member. When a pair of titmice is the only territorial pair in a very small woodlot, which presumably affords low levels of food resources, we expected that any juvenile in the same woodlot

Increased lifetime reproductive success for Siberian jay (Perisoreus infaustus) males with delayed dispersal

In a crowded environment the natal territory could serve as a haven for young and inexperienced offspring until a breeding vacancy emerges. Delayed dispersal and association with kin could then offer adaptive benefits through an individual fitness gain. Here we report that delayed dispersal is associated with a higher lifetime individual fitness in Siberian jay (Perisoreus infaustus) males. Sons bred more successfully and had more reproductive events in life when they delayed dispersal. The higher lifetime reproductive success when sons disperse later in life is sufficient to promote postponement of natal dispersal, suggesting that dispersal is delayed due to ecological constraints on access to high-quality habitats. We argue that the maintenance of this variation in the timing of dispersal and reproductive success can be reconciled with non-genetic mechanisms driving dispersal. Social dominance within broods reflecting environmental conditions during growth is such a mechanism.

The influence of kinship on foraging competition in Siberian jays

Foraging competition in Siberian jay groups was examined in relation to dominance and kinship to determine whether juvenile offspring, by associating with adults, gained in food acquisition relative to juvenile immigrants. Members of the adult pair were dominant over juvenile cohort members and males were dominant to females, although an inter-sexual hierarchy, with male juveniles occasionally overlapping adult females, was suggested. Few competitive asymmetries were found between adults and retained offspring or adults and immigrant juveniles when they were competing for food together, but in kin and non-kin foraging groups, respectively. Male offspring visited the bait site more frequently than adult males, and female immigrants spent less time at the bait site than adult females. Under these circumstances, hoarding activities may limit the ability of alpha members to control resources. In mixed groups containing both juvenile offspring and juvenile immigrants, no difference was found in the number of visits made to the bait site, although load sizes and foraging rates were lower for immigrant birds. Retained juveniles obtained greater load sizes and foraging rates when associating with adults. The social dominance of parents suggests that they control juvenile foraging. Although offspring benefit in the presence of adults, adults may incur a cost to their restraint by spending more time at the bait site when competing with immigrants. These results extend conclusions from previous work describing the role of selective tolerance by adults which relaxes competition with retained offspring in Siberian jay winter groups. The present findings suggest that offspring benefit in both immediate and future energy gains, which may have a direct influence on survival.

Selfish long-term benefits of hoarding in the Siberian jay

We followed the consumption of cached food in Siberian jay flocks during winter. Siberian jay flocks contain kin associations composed of parents in company with mature offspring. Further, flocks often contain immigrants not closely related to the group members. We studied the extent to which Siberian jay offspring kept caches to themselves or whether they showed a kin bias and shared cached food mutualistically with relatives (parents/siblings) thus making an inclusive fitness gain. We recorded the retrieval of cached food using radio-ptilochronology, a technique that detects the consumption of a radioactively labeled food item in the growth bar laid down in a growing feather the day of consumption. Food caching entailed a selfish benefit to the hoarder. The hoarding bird showed a substantial recovery advantage and retrieved its own cached food seven times as often as any of its flock mates. There was no evidence for mutualistic sharing of caches among relatives. This selfish benefit persisted throughout the 7-week period for which we could follow the consumption of labeled food.

Conflict of interest between the sexes in Siberian jay winter flocks

Conflict of interest between the sexes in Siberian jay winter flocks

The Significance of Protected Areas for the Land Birds of Southern Finland

Protected areas (nature reserves) cover 0.7% of the land area in southern Finland (162,000 km2), which belongs to the south- and mid-boreal coniferous forest zones. The value of these areas in preserving land birds was studied on the basis of quantitative censuses. The numbers of bird pairs were estimated in nature reserves and in the whole of southern Finland, and the significance of the reserves was evaluated based on how large a proportion of the total population in southern Finland was found in them. Forest habitat generalists and species of coniferous forests occurred in protected areas as expected by the proportion of these areas in southern Finland. Specimens of these species groups comprise two thirds of all the country’s land birds. Species of old-growth forests and open peatlands clearly preferred protected areas, whereas species of bushes, and lush and deciduous forest were scarcer in protected areas than elsewhere in southern Finland. The latter fertile habitats are poorly represented in protected areas, even though due to their disappearance or alteration elsewhere several species confined to these habitats have declined and are even threatened. Drainage of open peatlands and clearcutting of old-growth forests has caused a decrease in the area of these habitats in southern Finland during the past decades. Therefore, protected areas have a high significance in preserving bird species preferring these habitats. Protected areas are particularly important for decreased species of old-growth forests, such as the Three-toed Woodpecker Picoides tridactylus and the Siberian Jay Perisoreus infaustus, as about 10% of their total population in southern Finland was estimated to breed in protected areas. The future protection of both old-growth and deciduous forests is important if we are to preserve bio-diversity of land birds in Finland. Las areas protegidas (reservas naturales) cubren 0.7% del area del sur de Finlandia (tamano 162.000 km2) que pertenece a las zonas de forestas de coniferas sud- y mesaboreales. Se estudio el valor de estas areas en la preservacion de aves terrestres sobre la base de sensos cuantitativos. Se estimaron los numeros de parejas de aves en las reservas naturales y en todo el sur de Finlandia, y se evaluo la importancia de las reservas basandose en la proporcion de la poblacion total del sur de Finlandia que representaban las aves que se encontraban en las reservas. Generalistas de habitats de forestas y especies de bosques de coniferas se encontraron en areas protegidas tal como era esperado en base a la proporcion de estas areas en el sur de Finlandia. Los especimenes de estos grupos de especies comprenden dos tercios de todas las aves terrestres del sur de Finlandia.

Population trends of forest birds in a Finnish Lapland landscape of large habitat blocks: Consequences of stochastic environmental variation or regional habitat alteration?

Birds were counted in Northern Finnish Lapland in an area situated 200 km north of the Arctic Circle in virgin forests in the 1940–1950s, and both in virgin and managed forests in 1982–1989. The area consisted of very large habitat patches: blocks of virgin and managed forests were separated and covered hundreds of square kilometers. The most abundant species fluctuated similarly both in virgin and managed forests in the 1980s. The yearly total density of tropical migrants (insectivores) was negatively correlated with the number of cold days in spring. Short-distance migrants were probably more affected by weather conditions during migration and wintering area. Species which increased and those which decreased in Northern Finland due to habitat alteration had no such trends in large virgin forests, either from the 1940–1950s to the 1980s or during the 1980s. The brambling Fringilla montifringilla was the only species having a significant within-habitat trend: it increased from 1940 to the 1950s but decreased in the 1980s. The brambling is a forest-habitat generalist, and therefore its trends are not likely to be explained by habitat alterations caused by forestry. Year-to-year variations in densities of species seem to reflect stochastic environmental changes, such as in weather conditions and seed crop. Regional population changes caused by habitat alteration are not reflected in population densities in large virgin forests. The northern taiga species preferring virgin forests ( Tetrao urogallus, Picoides tridactylus, Parus cinctus, Perisoreus infaustus and Pinicola enucleator) have drastically declined in the whole of Northern Finland due to habitat loss caused by forest management. These decreased species seem to survive in large, virgin forest, and therefore the protection of these old-aged coniferous forests is essential.

Population Trends of North Finnish Land Birds in Relation to Their Habitat Selection and Changes in Forest Structure

Long-term trends in the 22 most abundant land bird species breeding in northern Finland were related to their habitat selection patterns. Independent data sets were used to describe long-term population trends (POP), edge preferences (EDGE) and the effects of the changing age structure of the forests on bird density (AGE). AGE combined the present age preferences of birds with data on the changing age structure of North Finnish forests from the 1950s to the 1970s. EDGE and AGE correlated positively though not significantly with POP. When EDGE and AGE were taken into account simultaneously, a significant correlation with POP emerged (67% of the variance accounted). Southern species were an exception; their population trends seem to depend on changes in southern Finland. The sedentary species of old forests have plummeted during the recent decades in northern Finland. The results for this group (Parus montanus, P. cristatus, P. cinctus, Certhia familiaris, Perisoreus infaustus) agreed well with the finding that fragmentation and changes in the age structure of the forests are mainly responsible for the recent trends among the abundant forest birds in the north. Our results seemingly indicate a close tracking of the environmental resources by the bird community. However, as the geographical scale of the study is broad (northern Finland as opposed to one population site) and the temporal scale decades rather than years, a simple saturation hypothesis is not an inevitable inference from the data; and if there is close tracking of the environmental resources, it is rather in terms of populations and not of the whole community. An alternative hypothesis is provided by changing numbers of high-quality and low-quality population sites; in this view, the regional pattern is a result of complicated dynamics in a mosaic of local populations.

The Meaning of Nepotism

The Meaning of Nepotism