No description available.

I studied bird and rodent nesting in woodpecker-excavated cavities in pifion-juniper (Pinus edulis-Juniperus monosperma) (P-J) woodland in southeastern Colorado during the spring and summer of 1987 and 1988. Two related investigations were conducted: one described characteristics of habitat used by birds and rodents nesting in woodpecker-excavated cavities and the other evaluated whether or not birds and rodents were competing for the nest-cavity resource. Seven species of birds and 4 species of rodents were included in the study: American kestrel (Falco sparverius), western screech-owl (Otus kennicottii), northern flicker (Colaptus auratus), ash-throated flycatcher (Mviarchus cinerascens), plain titmouse (Parus inornatus), Bewick's wren (Thrvothorus bewickii), mountain bluebird (Sialia currucoides), white-footed mouse (Peromvscus leucopus), deer mouse (P. maniculatus), pition mouse (P. truei), and woodrat (Neotoma spp.). 1987 was a preliminary year. In 1988, 248 nests were located in 433 cavities monitored, and cavity density averaged 1.5/ha. Western screech-owls nested earlier than all other species (P < 0.001), plain titmice nested earlier than ash-throated flycatchers (P = 0.033), and other species of birds and rodents nested at the same time (P < 0.05). Seven of 19 characteristics associated with nests differed (P < 0.05) among species: 4 of 5 at the cavity-level, 2 of 5 at the cavity-tree level, and 1 of 9 at the cavity-site level. Generally, larger species (kestrels, screech-owls, and flickers) nested in larger cavities and smaller species (white-footed, deer, and pitlon mice, and Bewick's wren) nested in smaller cavities. Characteristics of cavities used for nesting by secondary cavity-nesting species also differed from characteristics of all cavities monitored most frequently on characteristics associated with cavity size. Differences were demonstrated using univariate analysis (Kruskal-Wallis ANOVA) because with the considerable overlap among species, multivariate analysis (discriminant function analysis [DFA]) could not discriminate among species. Management implications include the need to evaluate impacts to the P-J woodland cavity-nesting community before converting the woodland to rangeland, evaluate impacts of logging in higher elevation forests where many of the cavity-excavating woodpeckers breed, and evaluate the influence of the nest-parasitic brown-headed cowbird (Molothrus ater) and the highly competitive European starling (Sturnus vulqaris). In 1988, 95 cavities were manipulated to yield 47 rodent exclusions and 48 bird exclusions. Proportions of these manipulated cavities used for nesting by birds and rodents were compared to the proportions of 83 control cavities used for nesting by the appropriate group of species. Cavities were revisited at 10-day intervals 4 May - 6 August 1988 and evidence of use recorded. The proportions of cavities used as nests by rodents was significantly greater in manipulated cavities than in control cavities (P = 0.0083). Thus, interspecific competition was experimentally demonstrated between birds and rodents for nest-sites in woodpecker-excavated cavities. / Graduation date: 1991

Graduation date: 1994

No description available.

No description available.

This study was restricted to birds using tree-holes as nest-sites. Of a total of 20 species in the study area, only 13 were sufficiently abundant to merit consideration. These fell into three natural groups on the basis of hole size, with only one euryoecious species (Iridoprocne bicolor) nesting in all three groups. Only the group based on holes made by the Colaptes woodpeckers (Flickers) can presently be construed as showing evidence of nest-site competition. Physical and ecological characteristics of nest-sites are analyzed in terms of intensification or amelioration of nest-site competition. The competing species, all using holes made by Colaptes cafer, are Sturnus vulgaris, Sialia currucoides, Bucephala albeola, Iridoprocne bicolor and Falco sparverius. The data suggest that although competition is now present in this group, it may have been absent before the advent of Sturnus in the avifauna. Neither selection for different sites nor competitive exclusion seem to have occurred before the appearance of Sturnus, which now occupies roughly 25% of all available nests, but one or both of these may now be going on. / Science, Faculty of / Zoology, Department of / Graduate

No description available.

No description available.

No description available.

Aggregations of the ground-nesting bee Halictus rubicundus were found at several locations across the UK. The phenology, social organisation, nest architecture and foraging behaviour of this bee were described for the largest of these aggregations (Invergowrie, Scotland). This site was unusual in having an extremely high brood mortality due to the impact of an anthomyiid fly. Nest parasitism was found to be directly density-dependent and it lead to a marked decline in nest numbers over the period of this study, indicating the possible forthcoming extinction of the aggregation. The other sites contained smaller nesting aggregations and the level of parasitism was considerably less. There was a marked variation in size across UK populations and this was explained by a temperature rather than a latitudinal cline. There was no evidence from field or laboratory studies to suggest that this species is endothermic; H. rubicundus is purely a behavioural thermoregulator. The effect of size upon various rates of heat exchange were examined in the laboratory for both sexes, and related to behaviours observed at the nest-site. Thus the microclimatic windows for different activities were established. The abundance of flying individuals at the nest-site was highly predictable from ambient temperature and light intensity; with predictions during a single day being more accurate than those combining several days throughout the season. Furthermore the usefulness of standard operative temperatures in predicting flight activity was assessed. The thoracic temperature of both sexes depended on the prevailing ambient temperature and also on the size of the individual while either basking or flying. Body temperatures increased with both ambient temperature and head width. However when both these predictors were combined into a single model, then size was only a strong predictor at lower temperatures. These findings were used to explain many of the behavioural patterns observed at Invergowrie. The nest site selection behaviour of females was examined both within and across sites. H. rubicundus was able to utilise a range of edaphic and microclimatic conditions when choosing a site to excavate a nest. There were some factors with broad tolerances such as slope and hardness, and others with much narrower limits such as aspect, soil humidity and particle composition. The thermal advantages of having a warm nest meant that the most suitable areas were those with a southern aspect and a slope which maximised the absorption of solar radiation. Limited areas of substrate with the most desirable characteristics resulted in gregarious nesting ('limited substrate' hypothesis). There was a preference for softer soils, that were easier to dig, within a site with a low overall density; but in much denser aggregations problems of maintaining the structural integrity of a nest lead to the favouring of harder soils. The tendency to nest in close proximity to the natal nest (philopatry) complemented the 'limited substrate' hypothesis in producing an aggregation of nests. The spatial distributions of nests within aggregations were examined using nearest neighbour distance analyses; at low densities, microscale variation in substrate quality produced clumped patterns, whereas at high densities the risk of adjacent nests collapsing into one another forced nest spacing to be more regular. Findings concerning temperature dependence of nesting and foraging activities, and broader environmental controls on nest-site selection, are considered in relation to key aspects of bee biology: the origins and function of social behaviours, the conservation of, or provision of, nest-sites, and the utility of solitary bees as crop pollinators.