Nest Site Use Research Articles

Duck nests and predators: interaction, specialisation and possible management

Low hatching success due to nest depredation has frequently been reported from waterfowl breeding sites, but current knowledge on relationships between duck nests and their predators, which should form a basis for successful management, remains incomplete. We used a 13‐year data set to test whether specific predator species are more successful in finding certain types of natural duck nests and whether there are interspecific differences in nest characteristics. Multinomial logistic regression allowed simultaneous evaluation of the effects of different factors, including their interactions. Significant predictors of duck nest fate were the presence of water edge and 3‐way interaction among presence of gull colonies, island type and clutch initiation date. Significant predictors of nest site use by duck species were: 3‐way interaction among presence of gull colonies, island type and clutch initiation date, 3‐way interaction among presence of gull colonies, island type and presence of water edge and 2‐way interaction between presence of water edge and clutch initiation date. The above interactions led to certain associations between duck species and predator species. Corvids (hooded crow Corvus corone cornix and raven Corvus corax) were responsible for depredating more mallard Anas platyrhynchos nests, but fewer common pochard Aythya ferina and tufted duck Aythya fuligula nests than expected. American mink Mustela vison was responsible for destroying more small Anas species (northern shoveler Anas clypeata, garganey Anas querquedula and gadwall Anas strepera) and tufted duck nests, but fewer mallard nests than expected. Marsh harrier Circus aeruginosus was apparently a generalist predator since we were not able to detect significant associations between this predator and nests of any specific duck species. We believe that examination of interactions between different factors affecting the probability that nests will be either successful or depredated by certain predator species may help waterfowl managers increase management success.

Nest use by the common goby Pomatoschistus microps in Camargue (France)

Nest site use by the common goby, Pomatoschistus microps was investigated in the Malagroy lagoon (France, Camargue) during a complete breeding season. Male common gobies seemed to select their nests in relation to their size, as a positive relationship between male total length and nest area was found. No significant relationship was found between the number of eggs in a nest and the size of nesting male, suggesting that female common goby did not show a preference for larger males. Nests containing two distinct eggs clutches were observed for the first time. The percentage of double clutched nests was relatively high in June-July, when only young-of-the-year common gobies were observed to reproduce. Large nesting males reproduced first in the season (in February- March), but they were not observed to reproduce again in July. Instead they were replaced by small males born early in spring.

Occurrence of pygmy possums, Cercartetus lepidus and C. nanus, and their nest sites in logged and unlogged dry and wet eucalypt forest in Tasmania

Summary Occurrence and nest site use by pygmy possums were investigated in dry and wet sclerophyll forest in Tasmania. There were four silvicultural treatments in the dry sclerophyll forest (a clearfelled coupe with 17-year-old regrowth, two partially logged coupes and old-growth forest) and four in the wet sclerophyll forest (4- and 20-year-old regrowth resulting from clearfelling, 80-year-old natural regrowth and old-growth forest). Cercartetus lepidus was captured in all ages of regrowth and in both partially logged and old-growth forest. C. nanus was captured only in 20- and 80-year-old regrowth in wet sclerophyll forest. Partially decayed logs were important nest sites for C. lepidus. Fissures in live trees associated with fire scars and hollows in stumps were also used as nests. All three nests of C. nanus were located in stumps. The amount of suitable nesting substrate did not appear to be a factor limiting populations in either the dry or wet sclerophyll forest.

Predator Responses to Similarity and Dispersion of Artificial Nest Sites: Implications for the Structure of Boreal Forest Songbird Communities

AbstractRelatively little is known about the role of predation in shaping patterns of coexistence and nest dispersion of songbird species. It has been hypothesized that predators diversify songbird communities by preying more heavily on individuals and species with greatest similarity in nest-site use. To investigate the importance of predation, we tested how predators responded to assemblages of artificial songbird nests that varied in nest-site placement, vegetation features, and nest dispersion patterns in boreal forest of west-central Alberta, Canada. Variability among nest sites was achieved by deploying wicker nests throughout a gradient of vegetation cover and by deploying nests to simulate two- and three-species assemblages. Two-species assemblages, comprising 20 simulated White-throated Sparrow (Zonotrichia leucophrys) and 3 simulated Hermit Thrush (Catharus guttatus) nests, and three-species assemblages, comprising 10 simulated White-throated Sparrow, 9 simulated Hermit Thrush, and 4 simulated Chipping Sparrow (Spizella passerina) nests, were deployed in eight replicate plots. We hypothesized that predators would be more adept at locating and depredating (1) nests characterized by similar vegetation features in nest patches; (2) nests of similar appearance or nest guild; and (3) clumped versus randomly distributed nests. Contrary to predictions, predation did not increase as variance in vegetation of nest sites decreased across 16 nest-predation plots, nor did variance in vegetation of successful nests increase as predation level increased across 15 nest-predation plots. The addition of one species' nest type to assemblages did not result in lower predation rates. Predators also did not depredate more clumped nests than randomly distributed nests. Overall, predation did not appear to influence patterns of songbird species coexistence or nest dispersion. Abilities of predators to discriminate among less-similar versus more-similar nest sites and nest-dispersion patterns are probably species-specific; that is probably related to the hunting behavior of predators (i.e. use of olfactory and visual cues) and territory size.

Predator Responses to Similarity and Dispersion of Artificial Nest Sites: Implications for the Structure of Boreal Forest Songbird Communities

Relatively little is known about the role of predation in shaping patterns of coexistence and nest dispersion of songbird species. It has been hypothesized that predators diversify songbird communities by preying more heavily on individuals and species with greatest similarity in nest-site use. To investigate the importance of predation, we tested how predators responded to assemblages of artificial songbird nests that varied in nest-site placement, vegetation features, and nest dispersion patterns in boreal forest of west-central Alberta, Canada. Variability among nest sites was achieved by deploying wicker nests throughout a gradient of vegetation cover and by deploying nests to simulate two- and three-species assemblages. Two-species assemblages, comprising 20 simulated White-throated Sparrow (Zonotrichia leucophrys) and 3 simulated Hermit Thrush (Catharus guttatus) nests, and three-species assemblages, comprising 10 simulated White-throated Sparrow, 9 simulated Hermit Thrush, and 4 simulated Chipping Sparrow (Spizella passerina) nests, were deployed in eight replicate plots. We hypothesized that predators would be more adept at locating and depredating (1) nests characterized by similar vegetation features in nest patches; (2) nests of similar appearance or nest guild; and (3) clumped versus randomly distributed nests. Contrary to predictions, predation did not increase as variance in vegetation of nest sites decreased across 16 nest-predation plots, nor did variance in vegetation of successful nests increase as predation level increased across 15 nest-predation plots. The addition of one species' nest type to assemblages did not result in lower predation rates. Predators also did not depredate more clumped nests than randomly distributed nests. Overall, predation did not appear to influence patterns of songbird species coexistence or nest dispersion. Abilities of predators to discriminate among less-similar versus more-similar nest sites and nest-dispersion patterns are probably species-specific; that is probably related to the hunting behavior of predators (i.e. use of olfactory and visual cues) and territory size.

PREDATOR RESPONSES TO SIMILARITY AND DISPERSION OF ARTIFICIAL NEST SITES: IMPLICATIONS FOR THE STRUCTURE OF BOREAL FOREST SONGBIRD COMMUNITIES

Abstract Relatively little is known about the role of predation in shaping patterns of coexistence and nest dispersion of songbird species. It has been hypothesized that predators diversify songbird communities by preying more heavily on individuals and species with greatest similarity in nest-site use. To investigate the importance of predation, we tested how predators responded to assemblages of artificial songbird nests that varied in nest-site placement, vegetation features, and nest dispersion patterns in boreal forest of west-central Alberta, Canada. Variability among nest sites was achieved by deploying wicker nests throughout a gradient of vegetation cover and by deploying nests to simulate two- and three-species assemblages. Two-species assemblages, comprising 20 simulated White-throated Sparrow (Zonotrichia leucophrys) and 3 simulated Hermit Thrush (Catharus guttatus) nests, and three-species assemblages, comprising 10 simulated White-throated Sparrow, 9 simulated Hermit Thrush, and 4 simulated ...

Home-Range Size, Movements, and Nest-Site Use in the Siberian Flying Squirrel, Pteromys volans

Home-Range Size, Movements, and Nest-Site Use in the Siberian Flying Squirrel, Pteromys volans

Use of Artificial Nest Sites as a Function of Age of Litter in Peromyscus leucopus

Abstract Relocation of nest sites is common among mice of the genus Peromyscus. We documented the occupation of artificial nest boxes by litters of white-footed mice (P. leucopus) at different stages of development to determine if nest relocation by lactating females is related to the developmental stage of the offspring. Three stages of development (neonates, age 0–5 d; nestlings, age 6–14 d; and juveniles, age 15–27 d) were recognized. Although the nest boxes were monitored at approximately weekly intervals, 72% of 134 litters were observed during only one of the stages of development, indicating that movement of young during lactation was common. Comparison of observed use of the boxes at different stages of development of young to expected use indicated that use of boxes was not random. Boxes were used relatively infrequently by dams with neonates and nestlings and most frequently by dams and juveniles. We believe that the suitability of a nest site to a lactating female depends on the age of her litt...

Philopatry and faithfulness to nest site in Cory's Shearwaters Calonectris diomedea at Selvagem Grande

Mougin, J.-L., Granadeiro, J. P., Jouanin, C. & Roux, F. 1999. Philopatry and faithfulness to nest site in Cory's Shearwaters Calonectris diomedea at Selvagem Grande. Ostrich 70 (3&4): 229–232. Nearly fledged Cory's Shearwater Calonectris diomedea chicks at Selvagem Grande occasionally desert their nest sites during the night, but generally return before dawn. The temporary use of other nest sites is rare and lasts less than two days. Almost all chicks from Selvagem Grande return to the island for their first breeding attempt; very few breed at islands outside the archipelago. On Selvagem Grande, almost half the males return to their native colony whereas more than 90% of females recruit to other colonies. Inter-colony movements sometimes exceed 1 km, but, if they return to their native colony, both sexes settle within 20 m of their natal site. From the second breeding attempt onwards, most birds of both sexes are faithful to the nest site. On average, less than 20% of birds desert their former nest site each year, with a shift of about 4 m only. Most nest shifts follow a breeding failure or a temporary respite from breeding, and are accompanied by a switch in partners. Mougin, J.-L., Granadeiro, J. P. Jouanin, C. & Roux, F. 1999. Philopatrie et fidélité au nid chez le Puffin cendré Calonectris diomedea de Selvagem Grande. Ostrich 70 (3&4): 229–232. Le poussin en fin de croissance du Puffin cendré Calonectris diomedea de Selvagem Grande déserte parfois son nid pendant la nuit, mais y revient généralement avant le jour. L'utilisation temporaire d'un autre site de nid est rare et dure moins de deux jours. Les jeunes adultes nés à Selvagem Grande reviennent presque toujours nicher sur l'île et extrêmement rarement en dehors de l'archipel. A Selvagem Grande, près de la moitié des mâles reviennent à leur colonie de naissance, mais moins de 10% des femelles. Le déplacement est parfois supérieur à 1 km mais, s'ils reviennent à leur colonie natale, les deux sexes s'établissent à moins de 20 m du nid où ils sont nés. A partir de leur deuxième reproduction, les deux sexes sont fidèles à leur nid. Moins de 20% des oiseaux changent de nid d'une année à l'autre, avec un déplacement de 4 m seulement, le plus souvent à la suite d'un échec ou d'une interruption temporaire de la reproduction, ce déplacement étant le plus souvent accompagne d'un changement de partenaire.

Avian Habitat Selection: Pattern from Process in Nest-Site Use by Ducks?

Patterns of habitat use in animals presumably have evolved in response to diverse selective processes, so we first examined whether the theory of natural selection formed the conceptual framework for published studies (N = 270) of nest-site selection by birds. Most (61%) studies of nest-site selection tested for pattern arising from natural selection (whether used nest habitat differed from available nesting habitat), many (54%) tested for evidence of the process of natural selection (whether unsuccessful nests differed from successful nests), some (10%) tested whether the process of natural selection caused subsequent adaptation, but remarkably few conceptually linked these elements or used the theory of natural selection as the rationale for their questions. We then tested for evidence of natural (phenotypic) selection with data for six species of ducks. At nests, we used six variables to describe vegetation structure/nest position and categorized patch types (pond edge, native grass, planted cover, shrubs, or trees) in which nests were found; nest fates (abandoned, depredated, or successful) were also determined. For Blue-winged Teal (Anas discors), Northern Shoveler (A. clypeata), and Mallard (A. platyrhynchos), there were significant patterns of nonrandom nest-site placement within a gradient of vegetation structure/nest position. For Blue-winged Teal and Gadwall (A. strepera), nest success varied within these gradients in a way that could exert directional selection. Several tests for adaptive nest-site choice were conducted. Nest fate did not influence fidelity of females to patch types. However, Mallards with previously unsuccessful nests dispersed farther than females with previously successful nests. Nonetheless, neither fidelity to patch type nor dispersal distance influenced subsequent nest success. In the long term (over 8 yr), there was a weak tendency within species for nest density to be higher among patch types where relative nest success was higher. In the short term (from year t to year t + 1), this pattern was not observed in a vegetation-structure/nest-position gradient for any species. The strongest evidence of adaptive response to nest fate was higher nest density on an island where nest success was relatively high.

Competition for Nest Sites between Kelp Gulls (Larus dominicanus) and Terns (Sterna maxima and S. eurygnatha) in Patagonia

Seabirds frequently nest in mixed-species colonies (Burger 1985). Several studies have shown differences in habitat and nest-site use among seabirds (Buckley and Buckley 1980, Croxall and Prince 1980, Fasola and Canova 1992). However, some degree of overlap in habitat and nest-site requirements may exist between species, resulting in interspecific competition that often leads to nest-site displacement or even the replacement of one species by another (Buckley and Buckley 1980, Burger 1985). Spatial interactions between seabirds can be more intense in areas where habitat is limited or when the population of one of the species is expanding (Burger and Shisler 1978, Trivelpiece and Volkman 1979, Duffy 1983, Ainley 1990). At many mixed colonies of larids, larger species often displace smaller species from their territories, occasionally forcing them to abandon the breeding area (Burger and Shisler 1978, Burger 1985). In addition, larger larids generally arrive at breeding sites earlier (Morris and Hunter 1976, Burger 1985), which gives them a competitive advantage over smaller species. Gulls (Larus spp.) frequently have been involved in the displacement of other species from breeding habitats (Thomas 1972, Burger 1979, Bradley and Monaghan 1986, Furness and Monaghan 1987). Terns appear to be one of the most affected seabirds, and some tern populations have decreased as a result of population expansion by gulls (Thomas 1972, Nisbet 1973, Greenhalgh 1974, Courtney and Blokpoel 1983, Parnell et al. 1988, Ainley and Hunt 1991, Blokpoel and Scharf 1991). At Punta Le6n, Argentina, Royal Terns (Sterna maxima) and Cayenne Terns (S. eurygnatha) breed intermingled in a dense cluster of nests within a Kelp Gull (Larus dominicanus) colony. The Kelp Gull colony increased in size from 3,200 pairs in 1982 to 6,500 in 1995, and gulls currently occupy almost all of the available nesting space (Yorio et al. 1994). Given the overlap in nest-site use and the current expansion of Kelp Gulls, we expected that competition for nesting space could result in negative effects on both species of terns. In this paper, we document spatial interactions between Kelp Gulls and Royal and Cayenne terns at Punta Le6n, Patagonia. We

Nest site use and changes in habitat of the Seychelles Black Paradise Flycatcher

The population size and extent of habitat for the Seychelles Black Paradise Flycatcher are compared with earlier investigations. The estimated world population is 90 individuals (1992). Deforestation on the western plateau of La Digue is estimated to have resulted in a 24% decline in Takamaka Calophyllum inophyllum and Indian Almond Terminalia catappa woodland since 1978. Monitoring of nest site use supports previous associations of the Flycatcher 's dependence on Takamaka and Indian Almond woodland (Collar and Stuart, 1985; Watson, 1991). Preliminary observations suggest that land management practices (clearing Takamaka and Indian Almond woodland for development) should be mitigated in view of the potential impact on nest site use by the flycatcher.

Geographical Trends in Clutch Size: A Range-Wide Relationship with Laying Date in American Pipits

ODUM, E. P. 1941. Annual cycle of the Black-capped Chickadee. 2. Auk 58:518-535. OJANEN, M., AND M. ORELL. 1985. Changes in the breeding parameters of the Crested Tit Parus cristatus. Ornis Fennica 62:161-167. PETERSON, B., AND G. GAUTHIER. 1985. Nest site use by cavity-nesting birds of the Caribou Parkland, British Columbia. Wilson Bulletin 97:319-331. RAPHAEL, M. G., AND M. WHITE. 1984. Use of snags by cavity-nesting birds in the Sierra Nevada. Wildlife Monographs No. 86. RENCHER, A. C. 1995. Methods of multivariate analysis. John Wiley and Sons, New York. RICKLEFS, R. E. 1969. An analysis of nesting mortality in birds. Smithsonian Contributions to Zoology 9:1-48. RUNDE, D. E., AND D. E. CAPEN. 1987. Characteristics of northern hardwood trees used by cavitynesting birds. Journal of Wildlife Management 51:217-223. SEDGWICK, J. A., AND F. L. KNOPF. 1990. Habitat relationships and nest site characteristics of cavity-nesting birds in cottonwood floodplains. Journal of Wildlife Management 54:112-124. SMITH, S. M. 1991. The Black-capped Chickadee. Cornell University Press, Ithaca, New York. SONERUD, G. A. 1989. Reduced predation by pine martens on nests of Tengmalm's Owl in relocated boxes. Animal Behaviour 37:332-334. SONERUD, G. A. 1993. Reduced predation by nest box relocation: Differential effect on Tengmalm's Owl nests and artificial nests. Ornis Scandinavica 24:249-253. STAUFFER, D. F., AND L. B. BEST. 1982. Nest site selection by cavity-nesting birds of riparian habitats in Iowa. Wilson Bulletin 94:329-337. SWALLOW, S. K., R. J. GUTIARREZ, AND R. A. HOWARD, JR. 1986. Primary cavity-site selection by birds. Journal of Wildlife Management 50:576-583.

Fitness costs of resource overlap among coexisting bird species

NATURAL selection is thought to favour differences in resource use (resource partitioning) among coexisting species because overlap is assumed to incur fitness costs1–5. However, studies of resource partitioning in animal systems in the wild have ignored or had difficulty demonstrating fitness costs of overlap, particularly at the level of individuals. Here I report manipulative and observational tests demonstrating individual-level fitness costs of resource overlap. Based on an extensive data set (2,400 experimental nests and 1,408 natural nests), I show that seven coexisting bird species differ in nesting microhabitats, and that overlap in use of nest sites increases nest predation rates (fitness costs). Moreover, predation risk is greater for individuals within species that use nest sites that overlap with coexisting species. Such intraspecific variation can allow natural selection to shape species differences and patterns of species coexistence.

Factors Influencing Wood Duck Use of Natural Cavities

The lack of suitable cavities is a primary limiting resource for wood ducks (Aix sponsa). We studied wood duck nest site selection, nest success, and use of cavities by other vertebrates at Muscatatuck National Wildlife Refuge (NWR), southcentral Indiana, in 1984-85. Of 789 surveyed tree cavities, 15% (122) were suitable for wood duck nesting. Minimum nest densities were 0.13 ± 0.08 (SE) nest/ha in 1984 and 0.08 ± 0.03 in 1985; 7-9% of the suitable cavities were used by wood ducks. Density of suitable cavities was higher (P < 0.001) in areas with mature or sawlog trees (1.69 ± 0.22 cavities/ha) than in areas with smaller trees (0.31 ± O.11 cavity/ha). American beech (Fagus grandifolia), red maple (Acer rubrum), and American sycamore (Platanus occidentalis) produced 72% of suitable cavities, but composed only 28% of the basal area. We estimated an annual survival probability of 0.91 for suitable cavities during the study. Cavities with vertically facing entrances were used in greater proportion than other cavity types (P = 0.006). Cavity volume, entrance area, and diameter of the bole at entrance were important in distinguishing cavities used by wood ducks (n = 21), fox squirrels (Sciurus niger; n = 29), and raccoon (Procyon lotor; n = 22) in 1985. Distance to nearest water in early spring was greater for successful nests (P = 0.017) than for unsuccessful nests, probably because of raccoon foraging behavior. Daily survival rate for nests was 0.963 ± 0.01 and estimated nest success was 0.22. Wood duck production at Muscatatuck NWR was limited by raccoon predation and not by nest site availability

Describing Willow Flycatcher Habitats: Scale Perspectives and Gender Differences

We compared habitat characteristics of nest sites (female-selected sites) and song perch sites (male-selected sites) with those of sites unused by Willow Flycatchers (Empidonax traillii) at three different scales of vegetation measurement: (1) microplot (central willow [Salix spp.] bush and four adjacent bushes); (2) mesoplot (0.07 ha); and, (3) macroplot (flycatcher territory size). Willow Flycatchers exhibited vegetation preferences at all three scales. Nest sites were distinguished by high willow density and low variability in willow patch size and bush height. Song perch sites were characterized by large central shrubs, low central shrub vigor, and high variability in shrub size. Unused sites were characterized by greater distances between willows and willow patches, less willow coverage, and a smaller riparian zone width than either nest or song perch sites. At all scales, nest sites were situated farther from unused sites in multivariate habitat space than were song perch sites, suggesting (1) a correspondence among scales in their ability to describe Willow Flycatcher habitat, and (2) females are more discriminating in habitat selection than males. Microhabitat differences between male-selected (song perch) and female-selected (nest) sites were evident at the two smaller scales; at the finest scale, the segregation in habitat space between male-selected and female-selected sites was greater than that between male-selected and unused sites. Differences between song perch and nest sites were not apparent at the scale of flycatcher territory size, possibly due to inclusion of (1) both nest and song perch sites, (2) defended, but unused habitat, and/or (3) habitat outside of the territory, in larger scale analyses. The differences between nest and song perch sites at the finer scales reflect their different functions (e.g., nest concealment and microclimatic requirements vs. advertising and territorial defense, respectively), and suggest that the exclusive use of either nest or song perch sites in vegetation analyses can result in misleading, or at least incomplete, descriptions of a species' habitat. Habitat interpretations for Willow Flycatchers (and perhaps for many passerines) are a function of the gender-specific behavior of the birds observed and the scale of vegetation measurement.

Effects of Plant Litter on Foraging and Nesting Behavior of Prairie Rodents

Interspecific differences in seed use and location of nest sites of Peromyscus leucopus, P. maniculatus, Reithrodontomys megalotis , and Microtus ochrogaster were found among experimental patches of habitat that differed only in amount of plant litter. P. leucopus and P. maniculatus foraged selectively in patches with sparse litter and used nest boxes in these patches more than expected. R. megalotis and M. ochrogaster foraged selectively and nested in patches with moderate litter; both nested more in litter than in nest boxes. All species consumed more seeds in patches with moderate litter on bright than dark nights. P. leucopus consumed fewer seeds and P. maniculatus tended to reduce consumption from dark to bright nights; however, R. megalotis and M. ochrogaster consumed similar amounts of seeds under both light conditions. P. leucopus and P. maniculatus forage in open habitats and may perceive changes in light intensity more readily than either R. megalotis or M. ochrogaster that forage in structurally complex habitats. Interspecific differences in activity between dark and bright nights may be related to the ability of each species to detect changes in risk of predation related to variation in light intensity.

Sage Grouse Use of Nest Sites in Southeastern Idaho

We investigated nest site selection by sage grouse (Centrocercus urophasianus) in southeastern Idaho from 1987 to 1989. During 3 breeding seasons, 79% of 84 nest sites were found under sagebrush (Artemisia spp.). Nest success averaged 53% for grouse that used sagebrush and 22% for birds that used nonsagebrush nest sites. Total vegetative cover for sagebrush and nonsagebrush nest sites was similar. However, grass height was shorter (P = 0.01) at sagebrush compared to nonsagebrush nest sites. Herbaceous cover was important to nesting sage grouse but the relatively low nest success of nonsagebrush nest sites indicated they might provide less than optimal nesting habitat. J. WILDL. MANAGE. 55(3):521-524 Most studies that have examined sage grouse nest site selection reported that >90% of nests were found under sagebrush (Patterson 1952: 114, Gill 1965, Wallestad and Pyrah 1974, Braun et al. 1977, Gates 1983). Other species of shrubs commonly grow in sagebrush habitats (Tisdale and Hironaka 1981) but are seldom used by nesting sage grouse. Only Hulet et al. (1984) reported a relatively high incidence (34%) of sage grouse use of shrubs other than sagebrush (hereafter called nest shrub species) for nest sites. Unfortunately, Hulet et al. (1984) did not address the relationship of nest shrub species to habitat quality and nesting success. Our purpose is to describe the use of nest shrub species by sage grouse in southeastern Idaho and to test the hypothesis that nesting success for grouse nesting under sagebrush is greater than that of grouse nesting under other plant species. We thank E. F. Cassirer, J. F. Kennedy, R. R. Spahr, C. M. Stinson, and D. W. Stinson for aid in collecting nest data. We also acknowledge the support of the Bureau of Land Management, U.S. Forest Service, and Idaho Department of Fish and Game. This manuscript was improved by reviews provided by J. J. Beecham, C. E. Braun, J. A. Crawford, R. L. Eng, T. P. Hemker, J. W. Hupp, T. E. Remington, and an anonymous referee. This paper is a contribution from Idaho Federal Aid in Wildlife Restoration Project W-160-R and contribution No. 560 of the Idaho Forest, Wildlife, and Range Experiment Station.

Microhabitat use by Blennius fluviatilis in the Río Matarraña, Spain

SUMMARY. Microhabitat use by Blennius fluviatilis in the Río Matarraña, Spain, varied significantly among dates during a 19‐month study. Most temporal variation, however, was attributable to changes in microhabitat availability. B. fluviatilis demonstrated non‐random use of available microhabitats during each sampling period, and generally occupied deeper microhabitats with higher average current velocities dominated by rubblegravel substrates. B. fluviatilis also demonstrated non‐random use of available nest sites; males generally nested under the largest available pieces of rubble, in areas with less gravel or sand. Water column depth influenced nest site use in two of four study areas. We found few microhabitat differences between spawning and nonspawning periods, or between males and females. In addition, microhabitat use was similar among B. fluviatilis size‐groups. Although B. fluviatilis often were over‐represented in deeper, erosional areas, blennies necessarily inhabited a wide range of microhabitats because average current velocities and water depths fluctuated greatly during the study. Tolerance of a broad range of environmental conditions may contribute to the species' persistence in habitats that exhibit extreme seasonal changes in discharge such as the Matarraña.

Behaviorally mediated spatial and temporal refuges from a cleptoparasite, Argochrysis armilla (Hymenoptera: Chrysididae), attacking a ground-nesting wasp, Ammophila dysmica (Hymenoptera: Sphecidae)

It has been suggested that parasite pressure favors the evolution of sociality within the Hymenoptera. I analyzed the impact of a chrysidid nest parasite, Argochrysis armilla, on its host, the solitary ground-nesting wasp, Ammophila dysmica, to assess the role of parasitism in favoring two steps towards sociality: aggregated nesting and delayed nest provisioning. The foraging strategy of Argochrysis armilla involves discovering host nests during excavation, learning the locations of discovered nest, and returning to oviposit in nests during nest provisioning; I therefore assessed the influence of host behavior on (1) parasite discovery of nests and (2) parasite oviposition in nests. Significantly fewer parasites discovered host nests that were excavated during the early morning and late afternoon, due to partial asynchrony of host and parasite activity. Nests excavated in areas of low nest density were also less likely to be discovered; use of low density nest sites increased during periods of high parasite activity. Due to a rapidly decelerating rate of parasite recruitment to nests under excavation, the duration of nest digging had only a limited influence on nest discovery by parasites. The probability of parasite oviposition in a host nest was determined by the number of parasites discovering the nest during excavation and by the time between nest excavation and provisioning; delaying nest provisioning reduced the risk of parasite oviposition. Delayed provisionings primarily appeared to be a result of the stochastic process of hunting and prey encounter. The number of provisions placed in a nest (one vs two) had no effect on the probability of nest parasitism. Spatial patterns of parasitism were directly density dependent in 1984 and density independent in 1986. In this system parasite pressure acts against the formation of nesting aggregations and in favor of delayed nest provisioning. The dependence of these results on species-specific aspects of the parasite's foraging strategy and the host's defensive strategy suggests, however, that different parasite species may generate qualitatively different selection pressures, potentially contributing to the diversity of nesting behavior in the Hymenoptera.