High Density Of Birds Research Articles

Reproductive traits of marine terns (Sternidae): evidence for food limitation in the tropics?

Marine terns breed between 80°N and 70°S, making them a suitable group for examining links between latitude and reproductive traits. We investigated such traits for 34 taxa in seven genera, using analyses of residuals to correct for effects of e.g. female body mass and egg mass on other life history traits. Both tree- and K-means clustering, based on four traits excluding chick provisioning mode, identified two groups of terns—those that breed on tropical oceanic islands and those that breed along mainland coasts and at temperate islands (>40° from the Equator). Among mainland terns, there is a tendency for reduced clutch investment at low latitudes both between and within species. There is no interspecific latitudinal variation in incubation or fledging period of these terns, but intraspecific variation in fledging period (longer in the tropics) has been reported for one species. Tropical island terns, which mostly breed at sites lacking native ground predators, show extreme clutch reduction and lay a single, relatively large egg that has a long incubation period. Fledging periods are also long, despite the fact that these are the only terns to use multiple prey loading or regurgitation to feed their chicks. These patterns are interpreted as responses to low food availability stemming from a combination of low oceanic productivity, high bird densities because of breeding space limitation and localised prey depletion associated with central place foraging.

Estimate of the Ipswich Sparrow population on Sable Island, Nova Scotia, in 1998, using a random-transect survey design

The Ipswich Sparrow (Passerculus sandwichensis princeps) population on Sable Island, Nova Scotia, has been designated as "vulnerable" by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC). Previous surveys of this population during the nesting season have varied in coverage and the rigour of statistical-survey design. In 1998 we surveyed the population using a stratified random-transect design. Estimated total numbers (±SE) were obtained along with confidence intervals calculated using bootstrap methods. The precision of our survey estimates would permit detection of population differences on the order of 20%. Higher densities of birds were observed in areas with heath, grass (fescue), and beach grass and pea vegetation types than in areas with other vegetation types. However, densities within these favoured vegetation types were constant with increasing transect length, which appears to be contrary to patterns expected from using published models of the effects of breeding habitat patch size on bird population density. Topographical constraints characteristic of Sable Island may impose limits on the birds' territorial boundaries and constrain density, independently of patch size.

Value of fallow farmlands as summer habitats for waterbirds in a Japanese rural area

Flooded rice fields, which occupy half of the total agricultural land in Japan, are known to be foraging habitats for waterbirds. We investigated the use of various fallow fields by birds in midsummer, when rice fields are generally full of grown rice plants and are of little use for foraging waterbirds. We distinguished four types of fallow fields based on the ground cover and vegetation: (i) tall‐grass fields; (ii) wet short‐grass fields; (iii) dry fields; and (iv) flooded open fields. In August 1998 we counted birds four times in 19 survey plots of fallow fields and in seven plots of rice fields in Ibaraki Prefecture, Japan, where 82% of the farmlands are devoted to rice production. We observed 590 individual birds of 22 species, of which 15 species were waterbirds, mostly herons and shorebirds. Flooded open fields supported the largest number of species and the highest bird density, while rice fields supported the fewest. Within flooded open fields, herons preferred open‐water areas, while shorebirds used bare ground most often. Wet short‐grass fields looked similar to flooded open fields, except for the amount of short grass, but supported far fewer birds than flooded open fields. The number of birds in dry fields was comparable to that in flooded open fields, but most of the birds were ground‐foraging passerines. Our limited dataset suggests that fallow fields can serve as valuable supplemental habitats for waterbirds during summer, if they are appropriately managed to preserve flooded open fields and smaller areas of other habitats.

Habitat use and diet of skylarks Alauda arvensis wintering on lowland farmland in southern Britain

Summary The habitat use and diet of skylarks wintering on lowland farms were studied to assess whether changes in agricultural practice could have reduced their most favoured wintering habitats or foods. Faecal samples were collected and soil seed densities were estimated. Skylarks in 122 cereal stubble fields in Oxfordshire were counted monthly to examine habitat use. Cereal stubble fields were more likely to be occupied than other crops, and densities of birds in occupied fields were high. Barley stubbles were significantly more likely to be occupied than wheat stubbles. Growing cereals were weakly selected. Sugar beet stubbles held high densities of birds. Rotational set‐aside was occupied more frequently and held higher densities than non‐rotational set‐aside. Field size affected field occupancy independently of crop type, with larger fields more likely to be occupied. Fields enclosed by hedges or trees tended to be avoided. Cereal and set‐aside fields that were occupied by skylarks in at least 1 month held significantly higher soil seed densities than fields that were not occupied. Differences in occupancy between crops could be explained by diet. Birds in cereal stubbles fed largely on cereal grain, whereas those in winter cereals fed largely on cereal leaves. Broad‐leaved weed leaves were strongly selected as food in cereal crops and farmland grass fields. In grass fields, the proportion of the diet made up by broad‐leaved weeds was positively correlated with their availability. Broad‐leaved weed seeds did not make up a significant dietary component in any crop. Our results show that the shift from spring to autumn sowing of cereals has led to a loss of the skylark’s most strongly selected wintering habitat and best food source. In winter cereals and in grass there was a high selectivity for relatively scarce, and probably declining, food resources. Our results suggest that the retention of weed‐rich cereal (particularly barley) and sugar beet stubbles through the winter, particularly in large open blocks, will improve conditions for skylarks in winter. Whole‐field rotational set‐aside, particularly as naturally regenerating cereal stubbles, provides good winter food resources for skylarks.

Effects of Habitat Fragmentation on Pairing Success of Ovenbirds: Importance of Male Age and Floater Behavior

AbstractBetween 1996 and 1998, we compared pairing success of territorial male Ovenbirds (Seiurus aurocapillus) in forest fragments created by forestry (n = 3) and agriculture (n = 10) to contiguous forest plots (n = 3) in the southern boreal mixedwood forest of central Saskatchewan. The percentage of Ovenbird males paired per site was lower in fragments created by agriculture (86 ± 3%) and forestry (87 ± 3%) than in contiguous forest (97 ± 3%). At the individual level, second-year males (82%) were less likely to be paired than after-second-year males (94%), whereas males closer to edges were less likely to be paired than those in forest interiors. Although pairing success differed among landscapes, those differences were smaller than reported in studies conducted in eastern North America. The high density of birds in our study area may have resulted in intense intraspecific competition, which could have prevented unpaired individuals from maintaining territories. Removal experiments in 1997 and 1998 demonstrated floaters occurred in contiguous forest, but rarely occurred in fragments created by agriculture. The presence of floaters in contiguous forest suggests the ratio of breeding to nonbreeding males in forest fragments and contiguous forest may be similar, but that the strategy (i.e. floater vs. territorial) used by unpaired birds may differ among landscapes.

EFFECTS OF HABITAT FRAGMENTATION ON PAIRING SUCCESS OF OVENBIRDS: IMPORTANCE OF MALE AGE AND FLOATER BEHAVIOR

Abstract Between 1996 and 1998, we compared pairing success of territorial male Ovenbirds (Seiurus aurocapillus) in forest fragments created by forestry (n = 3) and agriculture (n = 10) to contiguous forest plots (n = 3) in the southern boreal mixedwood forest of central Saskatchewan. The percentage of Ovenbird males paired per site was lower in fragments created by agriculture (86 ± 3%) and forestry (87 ± 3%) than in contiguous forest (97 ± 3%). At the individual level, second-year males (82%) were less likely to be paired than after-second-year males (94%), whereas males closer to edges were less likely to be paired than those in forest interiors. Although pairing success differed among landscapes, those differences were smaller than reported in studies conducted in eastern North America. The high density of birds in our study area may have resulted in intense intraspecific competition, which could have prevented unpaired individuals from maintaining territories. Removal experiments in 1997 and 1998 dem...

Breeding songbird abundance related to secondary succession in the subarctic forests of western Labrador

To describe the effects of natural disturbance on birds in western Labrador, we mapped songbird territories in fourteen 10-ha plots originating by natural fire. Plots were 2, 18, 40, < 70 (young conifer) and < 135 years old (mature conifer and mature white birch, Betula papyrifera, forests). Three species, dark-eyed junco, white-throated sparrow and ruby-crowned kinglet, accounted for 50% of all bird records. Bird density and species richness peaked in 2-year-old burns and mature forest stages. High bird densities in 2-year-old burns were likely due to high snag densities. Most species were not unique to a particular age since disturbance, but there were different species in early, < 40-years-old burns, and later stages. Some birds such as yellow-bellied flycatcher and Swainson’s thrush were exclusive to white birch forests, a rare forest type in western Labrador.

Associations of Grassland Birds with Landscape Factors in Southern Wisconsin

We investigated the association of grassland birds with field- and landscape-level habitat variables in south-central Wisconsin during 1985–1987. Landscape-level variables were measured and digitized at 200, 400 and 800 m from the perimeter of 38 200 m × 100 m strip transects. A mixture of field and landscape variables was associated with the density of savannah sparrow (Passerculus sandwichensis) and grasshopper sparrow (Ammodramus savannarum). Only landscape variables were associated with the density of bobolink (Dolichonyx oryzivorus), eastern meadowlark (Sturnella magna) and all birds that were grassland species of management concern. Field size was not an important predictor of bird density. Cover-type diversity of the surrounding area was commonly selected in the models for three species and all birds that were grassland species of management concern. Higher bird densities in the transects were associated with landscapes where the cover types were less diverse. Landscapes with low cover type diversity were dominated by grassland, pasture and hay. Field habitat, mean patch size of cover types and distance to woody vegetation were the next most common predictors of avian density. The density of some grassland birds increased as nonlinear woody features such as woodlots and shrub carrs decreased in patch size, decreased in total amount in the landscape and increased in distance from a transect. However, density of other species was positively associated with linear woody features such as the total amount and nearness of hedgerows. The composition of the surrounding landscape, at least out to 800 m, is important in grassland bird management.

Seasonal changes in bird assemblages of coastal woodlands in east-central Argentina

We studied seasonal variation in bird assemblages during two years in the coastal woodlands of the reserve, 'El Destino', Buenos Aires Province, Argentina. Higher bird density was recorded during spring, and lower one during autumn, but species richness did not show changes during the annual cycle. Seasonal variation in abundance and species composition was recorded for the frugivore-insectivore and the granivore guilds, however, not for the insectivores. As winter is not harsh, insectivorous species might not be faced with food shortage. In contrast, the abundance of frugivorous-insectivorous and granivorous species appeared to be related with fluctuations in their food resources.

Summer bird abundance and distribution on set‐aside fields on intensive arable farms in England

The abundance and distribution of breeding birds were compared on paired fields comprising one set‐aside field and one crop field, on 11 intensive arable farms in eastern and western England. A single observer made four visits to all set‐aside and crop fields between April and July and recorded all birds seen during standardised counts and transects.Rotational and non‐rotational set‐aside supported higher densities and more species of birds than fields of wheat, brassicas, root crops and seed rye. These differences in density, between set‐aside and crops, were evident across a suit of species including waders, gamebirds, pigeons and passerines and were particularly marked on rotational set‐aside. The majority of species recorded in fields away from boundaries would have been feeding rather than nesting there and higher bird densities on set‐aside compared with adjacent arable crops probably reflects greater food abundance in the former.The study is the first to demonstrate a clear habitat preference for set‐aside by a wide range of bird species throughout the breeding season and it allows a number of recommendations to be made concerning the development of cost‐effective agri‐environment measures. The fact that the majority of birds utilised the outer 5 m, or in some cases 20 m, margin of the field suggests that many of the benefits of whole field set‐aside may be derived from marginal strips. A slight, but not significant preference for rotational over non‐rotational set‐aside suggest such margins should be managed to maintain a patchy, relatively diverse sward of arable plants. A key feature of set‐aside is the scale at which it has been incorporated into the arable landscape. Agri‐enviromental schemes will only provide similar national benefits if they are implemented on a wide scale in such as way as to promote high uptake by farmers.

Composition, seasonal occurrences and habitat use of bird assemblages in wet forests on the Central Plateau ofTasmania

Bird communities in montane wet forest at three sites (altitudes 700,750 and 880 m) on the Central Plateau of Tasmania were surveyed over a 12-month period between December 1991 and November 1992. Monthly transect counts were carried out at each site. Snowf:,lls are common at all three sites during winter and snow can remain at the highest site for several weeks. Bird communities at the study sites showed significant differences in densities and seasonal patterns even though species composition was similar. These differences were influenced by the variation in habitats and the environments at the sites. Butlers Road, the lowest site with the mildest winters and greatest proportion of drier habitat, had the highest bird densities, while D'Arcys Bluff, at the highest altitude, had the lowest. The degree of seasonal changes of birds was similar to mainland montane wet forests, with over half the species moving either locally or to the mainland, However, there was variation in seasonal occurrences between the study sites, with proportionally more species moving from the highest site during the winter, Within the study sites, the wet forest habitats with a diverse shrub and/or fern understorey supported higher bird populations than did mixed forest and damp forest. Species richness is lower at these sites compared with equivalent montane forests on mainland southeastern Australia.

The effects of management regimes and location in landscape on the conservation of farmland birds breeding in semi-natural pastures

Semi-natural dry grasslands have almost disappeared in the modern farmland of southwestern and central Europe. In the northern and eastern parts of Europe, however, this species-rich habitat is still relatively common, albeit in a phase of rapid loss. To halt this decline the Swedish government started a large-scale subsidy scheme for the management and restoration of semi-natural pastures mainly aimed at increasing botanical values. We compared and contrasted the current management prescriptions with habitat preferences of 23 farmland bird species breeding in 88 dry semi-natural pastures in south-central Sweden. Semi-natural pastures showed very high breeding densities of several farmland birds underlining the importance of this habitat to the conservation of farmland birds. A TWINSPAN classification of all birds identified two groups of pastures with different bird communities. Eleven (48%) of the bird species were significantly more common in a group of pastures situated in open farmland, while only five (22%) species occurred in higher densities in pastures characterised by a high proportion of forest along the borders. Fifteen (83%) of the 18 species occurring in both pasture groups showed significant habitat-abundance relationships related to the management of semi-natural pastures, although in different directions and to different extents. Our results suggest that many farmland bird species require two important factors for their choice of breeding habitat, namely safe nest sites close to good foraging areas. Both factors are partly under the control of farmers and should be invoked in conservation strategies since many farmland birds are declining across Europe. To benefit the conservation of farmland birds in Sweden one should, in contrast to the present botanical-based subsidy scheme, retain ⩾10% cover of shrubs within pastures and preferentially select pastures in open farmland (i.e. potentially safer nesting sites with better food conditions) for restoration and management plans.

Habitat of the Regent Honeyeater Xanthomyza phrygia and the value of the Bundarra-Barraba region for the conservation of avifauna

Five types of woodland and forest in the Bundarra-Barraba region of northern New South Wales were surveyed for Regent Honeyeaters Xanthomyza phrygia and other birds over two years. Regent Honeyeaters were found in 24 of the 93 transects, at a density of 0.09 birds/ha. Most were found in box-ironbark woodland (34% of 62 sites), with single records from box-gum woodland, box-stringybark woodland and dry plateau complex woodland. No Regent Honeyeaters were found in riparian gallery forest during censuses, but they were found breeding there at other times. All habitats contained a high density of birds, compared to other wooded regions in southern Australia, with riparian gallery forest and box-ironbark woodland being particularly rich in species and numbers. These habitats had greater flowering indices, larger trees and more mistletoes than other habitats. Sites used by Regent Honeyeaters supported significantly more birds and bird species than unoccupied sites. The region supports a total of 193 species, four of which are nationally threatened and seven which are threatened in New South Wales. The richness of the bird community in the region is partly because it retains a higher proportion of native vegetation cover (43%) than many other parts of rural Australia. Protection and rehabilitation of box-ironbark woodland and riparian gallery forest is of high priority in a regional conservation plan. However, all habitats in the Bundarra-Barraba region should be protected from clearing and degradation, because they are also used at times by Regent Honeyeaters and support a wide range of bird species. Wise management should retain many sensitive bird species that have disappeared from or declined in other regions of southeastern Australia.

Density and Reproductive Success of California Towhees

Models of habitat selection commonly asume that higher‐quality source habitats will be occupied at higher densities than sink habitats. We examined an apparent sink habitat for California Towhees (Pipilo crissalis) in which densities are greater than in nearby source habitats. We estimated territory density using spot‐mapping and monitored nests of towhees in grazed and ungrazed oak‐pine woodland habitat. Breeding density of California Towhees was higher in ungrazed oak‐pine woodlands than in grazed areas, yet birds in the ungrazed site experienced lower reproductive success. Predation during the nestling period was primarily responsible for the lower nest success. Clutch size and the number of young fledged were also lower in the ungrazed site. Towhees selected nest sites with high foliage density and cover of live oaks (Quercus wislizenii) in the understory. Grazed sites had greater cover of live oak than ungrazed sites, and successful nests were more often built in live oak than in other plant species. This pattern could not be explained by dominant birds settling in grazed sites and excluding subdominant individuals because a large proportion of adults continued to settle in the ungrazed area. Towhees may have perceived the dense foliage of the ungrazed area as suitable due to abundant nest sites, cover, and food, resulting in an “ecological trap.” The resulting high density of birds there may have contributed to density‐dependent predation. Alternatively, towhees are not ideally adapted to their habitats because of their sedentary habits and site tenacity that is not affected by persistent nest loss. We stress the need to examine the reproductive success and productivity of individual species within specific habitat types.Densidad y Exito Reproductivo del Rascador CalifornianoLos modelos de selección de hábitat comunmente asumen que las fuentes de hábitat de alta calidad estarían ocupadas con densidades mas altas que en los hábitats pobres. Examinamos un hábitat aparentemente pobre para rascadores californianos (Pipilo crissalis) en el cual las densidades son mayores que en las fuentes de hábitat adyacentes. Estimamos las densidades territoriales utilizando mapeo de puntos y monitoreo de nidos en hábitats utilizados para pastoreo, así como en bosques de encino‐pino no pastoreados. La densidad de crianza de los rascadores fue mas alta en los bosques de encino‐pino libres de pastoreo que en las áreas utilizadas para pastoreo, sin embargo, las aves en el sitio sin pastoreo experimentaron un menor éxito reproductivo. La depredación durante el periodo de polluelos fue el motivo principal. El tamaño de puesta y el número de juveniles emplumando por nido fueron mas bajos en sitios libres de pastoreo. Los rascadores escogieron sitios de nidación con alta densidad de follaje y cobertura de encino siempreverde (Quercus wislizenii) en el sotobosque. Los sitios utilizados para pastoreo tuvieron mas encino siempreverde, en los cuales las aves construyeron mas nidos que en caulquier otra especie de planta. No se puede explicar este modelo en base al establecimiento de individuos dominantes en las áreas utilizadas para pastoreo y excluyendo a las aves menos dominantes, puesto que una proporción grande de adultos se estableció en sitios sin pastoreo. Es posible que los rascadores percibieron el follaje denso del sitio libre de pastoreo como apropiado, con abundantes sitios para nidación, cobertura y alimento, resultando en una “trampa ecológica.” La densidad alta de aves en el sitio sin pastoreo posiblemente contribuyó a una depredación denso‐dependiente. Alternativamente, los rascadores no estan idealmente adaptados a sus hábitats debido a sus hábitos sedentarios y a su tenacidad por sitios, misma que no es afectada por una pérdida persistene de nidos. Enfatizámos la necesidad de analizar el éxito reproductivo y la productividad de especies a nivel individual dentro de tipos de hábitat específicos.

Differences in the avian communities of natural and createdSpartina alterniflora salt marshes

Birds were surveyed by censusing strip transets, monthly from October 1990 through September 1991 in seven created and seven natural salt marshes located in lower Galveston Bay. All birds observed using the transect, the airspace above the transect, and 5m of bay bottom adjacent to the transect were recorded. Species richness and species diversity were calculated for each salt marsh and compared between natural and created sites. Species richness and diversity were greater in natural salt marshes due to the occurrence of migratory waterfowl, wintering shorebirds, and typical marsh species such as rails and marsh sparrows. Birds using created salt marshes consisted primarily of gulls and terns, especially during the nesting season. Bird density was greater in natural marshes during fall and winter months, while created marshes had higher bird density from March through July. Created salt marshes provided bird habitat, however not necessarily for the same species assemblage as natural salt marshes.

Bird Communities and Habitat Relationships in a Residential Area of Tokyo.

Conserving birds in urban environments requires ecological information that can be applied to city planning and designing, but few ecological studies on bird communities in residential area have so far been made. I conducted surveys of the terrestrial bird communities at 12 locations in a residential area of Tokyo, Japan in both the breeding and wintering seasons in 1990-91, and identified habitat features associated with bird communities. In both seasons, the residential areas with abundant vegetation supported more species and higher densities of birds. Number of trees (>8m in height) and average tree height were the most significant variables for explaining variances of diversity of bird species among study plots. Abundance and height of buildings were negative factors for diversity in the wintering season, conversely they were positive in the breeding season. Most bird species preferred to use land covered by vegetation. Land occupied by buildings and bare land tended to be avoided by birds and used by fewer species than expected. It was confirmed that vegetation, especially trees, was the key element for bird conservation in residential areas. I present environmental guidelines required for bird conservation in residential areas.

The intensity of interference varies with food density: support for behaviour-based models of interference.

Dolman (1995) measured the intake rates of snow buntings feeding on seed patches at difference bird densities, for each of two different seed densities. Interference occurred in the low food density treatment, with intake rate declining at high bird densities, but did not occur in the high food density treatment. Dolman states that existing models of the interference process assume that the intensity of interference is independent of food density. While this statement is true for the model of Hassell and Varley (1969), we show that behaviour-based models of interference do not assume that interference is independent of food density. We examine two simple analytic behaviour-based models of interference and show that, in agreement with Dolman's observations, intensity of interference is predicted to decrease with increasing food density. Dolman plotted log (intake rate) against log (bird density). Rather than obtaining a linear relationship predicted by the Hassell and Varley model, the results from the low seed density treatment indicated a curvilinear relationship consistent with those produced by our behaviour-based models. These results provide support for the use of behaviour-based models of interference over the model of Hassell and Varley.

Habitat associations of coastal wintering passerines

The species composition, relative abundance and vegetation community associations of a wintering passerine assemblage were studied on 7 sites in north Norfolk between 1989 and 1994. A total of 20 species was recorded including coastal specialists as well as habitat generalists; relative abundance varied greatly from Chaffinch and Great Tit with single records, to Twite and Skylark with many hundreds. Most species showed strong association with, and aversion to, particular vegetation community types, but the relationships with vegetation communities varied between species. The communities with the higher bird densities were Limonium, Suaeda vera and Suaeda/Salicornia saltmarshes. Amongst the least used vegetation communities were Halimione saltmarsh and mobile dunes. There was little evidence of any seasonal change in habitat associations. The findings are discussed both in terms of vegetation community availability in north Norfolk and in the wider context of coastal zone planning and the threats and opportunities open to wintering passerines by differing responses to sea-level rise in eastern England.

Songbird Use of Gallery Woodlands in Recently Cleared and Older Settled Landscapes of the Selva Lacandona, Chiapas, Mexico.

Many regions of Central America have undergone wide-scale habitat change as land has been converted for cultivation or grazing. Clearing for agriculture often leaves a variety of regenerating and remnant patches of wooded vegetation. Of particular importance is arroyo vegetation, or strips of trees or tall shrubs growing along streams. Although it is widely acknowledged that tropical arroyo vegetation supports high densities of birds, as avian habitat it remains poorly studied. We used point counts to study populations of migrant and resident songbirds in the arroyo vegetation of settled areas of the Selva Lacandona adjacent to the Montes Azules Biosphere Reserve of southeastern México. Two study areas were established on lands that had been cleared and settled 20-35 and 10 years previously. Our objectives were to asses the value of arroyo vegetation to the conservation of avian species diversity and abundance in agricultural landscapes and to compare the composition and abundance of songbirds in cleared areas settled at different times over a 35-year period. Arroyo vagetation had a wide diversity of songbird species that, in overall terms, differed little between those landscapes cleared recently and those cleared up to 35 years previously. In both areas we found a high abundance of habitat generalists and a smaller number of forest-dependent species, particularly migrants. Loss of forest specialists occurs rapidly, with little further loss as the arroyos become increasingly isolated. Our data also suggest that birds do not crowd into limited habitat as the surrounding vegetation is eliminated, implying that the overall carrying capacity of the agricultural landscape is greatly enhanced as larger areas of arroyo vegetation are protected. Protection of arroyo vegetation will increase the diversity of birds living in agricultural areas and can be achieved simply by expanding upon land-use practices currently in use. Use de galerías boscosas por aves cantoras en paisajes recientemente clareados y en paisajes poblados con anterioridad de la Selva Lacandona en Chiapas, México.

Non-Territorial Behaviour and Habitat Selection in the Jay Garrulus glandarius in a Mediterranean Coastal Area during the Reproductive Period

Spring territorial behaviour and habitat selection of the Jay Garrulus glandarius were investigated in two study areas in the Maremma Natural Park (Central Italy). Seven birds in 1990 and seven in 1991 were trapped and subsequently radio-tracked. Incremental area plots and the analysis of auto-overlap showed that most of the Jays did not have fixed home ranges, and that these overlapped greatly. Furthermore, many untagged Jays were seen inside the home ranges of the tagged ones and one pair of Jays successfully reproduced in 1991 inside other Jays' home ranges. No aggressive interactions were observed. These data seem to suggest that the Jays in Maremma do not show territorial behaviour. Home range sizes at one study area (Faunistico) were larger than in the other area (Pratini) (on average 36 ha versus 5 ha). This could depend on the higher habitat diversity or lower habitat quality of the first area. Habitat use differed between the areas. At Pratini the maquis scrub was positively selected whereas the olive grove was avoided; at Faunistico the maquis, the olive grove and the cultivated fields were avoided whereas the meadows with scattered trees and the open scrub were positively selected. The non-territorial behaviour of the Jays in the Maremma Natural Park may be determined by several local factors, such as resource abundance, high density of birds, low reproductive rates and food partly being collected outside the maquis. In particular, both in the case of resource abundance and in that of high density of birds, the cost of sharing resources would be less than the cost of defending the territory against all intruders and a non-territorial system would indeed be expected.