Nest Site Characteristics Research Articles

Breeding-habitat and nest-site characteristics of Scarlet Robins and Eastern Yellow Robins near Armidale, New South Wales

I studied the selection of breeding habitat and nest microhabitat in Scarlet Robins Petroica multicolor and Eastern Yellow Robins Eopsaltria australis, in remnant woodland on the New England Tablelands of New South Wales in 2000?2002. Yellow Robins used breeding territories (n = 10) with significantly higher densities of rough-barked saplings, acacias and other (non-Acacia) shrubs than Scarlet Robin breeding territories (n = 10) and plots lacking Yellow Robins (n = 7). Yellow Robins nested mostly in gully and lower-slope positions, with a southerly aspect, >40 m from the woodland edge, whereas Scarlet Robins nested mostly on upper slopes and ridges, with no preferred minimum distance from the woodland edge. Most Yellow Robin nests (86% of 58) had overhead foliage within 1 m, shielding them from above, whereas over half (58% of 54) of Scarlet Robin nests were in unconcealed positions. Yellow Robin nests had significantly greater density of cover, and the surrounding habitat was more complex, than for Scarlet Robin nests, in 0.13-ha plots centred on the nest. Breeding success and fledgling survival in the Yellow Robin were positively related to the density of acacias, non-Acacia shrubs and rough-barked saplings (but not gum saplings) in breeding territories. Fledging success and juvenile survival in the Yellow Robin were also positively related to habitat complexity around nest-sites (but not distance to nearest cover, or items of cover within 20 m). Scarlet Robins had exposed nests and suffered high nest predation, with too few successful nests for comparison with unsuccessful nests. Habitat conservation for the Yellow Robin should address the complexity of the ground, shrub and sapling layer in woodland remnants; that for the Scarlet Robin may need to address foraging substrate and ecologically based control of nest predators.

Nest site attributes and temporal patterns of northern flicker nest loss: effects of predation and competition

To date, most studies of nest site selection have failed to take into account more than one source of nest loss (or have combined all sources in one analysis) when examining nest site characteristics, leaving us with an incomplete understanding of the potential trade-offs that individuals may face when selecting a nest site. Our objectives were to determine whether northern flickers (Colaptes auratus) may experience a trade-off in nest site selection in response to mammalian nest predation and nest loss to a cavity nest competitor (European starling, Sturnus vulgaris). We also document within-season temporal patterns of these two sources of nest loss with the hypothesis that flickers may also be constrained in the timing of reproduction under both predatory and competitive influence. Mammalian predators frequently depredated flicker nests that were: lower to the ground, less concealed by vegetation around the cavity entrance and at the base of the nest tree, closer to coniferous forest edges and in forest clumps with a high percentage of conifer content. Proximity to coniferous edges or coniferous trees increased the probability of nest predation, but nests near conifers were less likely to be lost to starlings. Flickers may thus face a trade-off in nest site selection with respect to safety from predators or competitors. Models suggested that peaks of nest predation and nest loss to eviction occurred at the same time, although a competing model suggested that the peak of nest loss to starlings occurred 5 days earlier than the peak of mammalian predation. Differences in peaks of mammalian predation and loss to starlings may constrain any adjustment in clutch initiation date by flickers to avoid one source of nest loss.

Nesting success of common eiders Somateria mollissima as influenced by nest-site and female characteristics in the Gulf of the St. Lawrence

In the common eider Somateria mollissima as well as in many other bird species, nesting success has been associated with female reproductive characteristics and predator accessibility to the nest site. In this study, we tested the following predictions on nesting common eiders: 1) female and nest-site characteristics are correlated within a colony, where those with the highest ranked reproductive traits nest where the environment provides best protection, 2) females nesting on forested islands generally exhibit better reproductive traits than females nesting on open islets (hereafter habitats) because the former provide the best nest protection, and consequently, 3) colonies located on forested islands have higher nesting success than those on open islets. During the summers of 1995 and 1996, we recorded nesting success at 270 eider nests on two forested islands and four open islets. Simultaneously, we measured several variables describing nest (nest concealment, vegetation height, distance to shore and density of associated nesting gulls) and female (laying date and clutch size) characteristics. Using factor analysis to relate nest-site and female characteristics, we found a correlation between factor scores within four of the six colonies monitored. This correlation indicated that females with largest clutch size and early laying were associated with nest sites of low concealment that were close to shore. However, female score did not differ with habitat. Nesting success did not differ between habitats when controlled for female and nest scores, but was related to female score, and marginally to nest-site score. Because nesting success was principally related to female characteristics rather than to nest-site characteristics, we suggest that eiders rely on nest attendance rather than on nest concealment to protect their nests. Nesting close to shore may shorten incubation recesses and improve hatchling survival when leaving the nest.

Predation risk and nest-site characteristics of the Black-browed Reed Warbler Acrocephalus bistrigiceps: the role of plant strength

ABSTRACT I examined both natural and artificial nests to investigate the relationship between nest-site characteristics and the risk of nest predation in a grassland-nesting passerine, the Black-browed Reed Warbler Acrocephalus bistrigiceps. Although an early-season artificial nest experiment did not detect significant effects because of infrequent predation, a late-season experiment indicated that nests were more likely to be depredated at sites where Phragmites reeds were highly dominant. Stems of the common reed P. communis are extremely thick and strong compared to those of other grasses. The results suggest that strong stems aid the effective search and attack on bird nests by predators. Among natural nests, however, predation was not explained by any nest-site characteristics, suggesting that the activity of parents and nestlings masked the effect of plant strength on nest predation.

Nest-site characteristics and breeding biology of the Black-cheeked Lovebird Agapornis nigrigenis in Zambia

The nest-site characteristics and breeding biology of the Black-cheeked Lovebird Agapornis nigrigenis in their natural habitat and in captivity were investigated as part of a wider study of the ecology of the species. Seventy-eight nests were found. Black-cheeked Lovebirds nested inside naturally formed cavities in live Mopane trees Colophospermum mopane, in localities which were used for roosting during the non-breeding season. Nest-site fidelity was suspected. Most nests were found in a loosely clumped distribution. Nest-site characteristics including cavity dimensions, height from ground, distance to three nearest nest trees, cavity entrance orientation and nest shape are presented. No nesting requirement appeared to be limiting, or to affect the population's reproductive output. Reproductive data were necessary to elucidate factors affecting reproductive success and to assist with the development of a conservation management plan for this Vulnerable species. Breeding occurred from January to May, coinciding with annual maximum rainfall and the early dry season, when a single clutch was raised by most pairs. Nesting chronology was correlated with mean monthly rainfall and major food source availability. Behavioural data on nest building, location, defence and breeding success are presented. Courtship, copulation, parental care and juvenile behaviours are reported, and clutch size, laying intervals and hatching successes of captive birds are discussed.

Warbling Vireo reproductive success and nest-site characteristics in the northern Sierra Nevada, California

Over the past 20 yr Warbling Vireo (Vireo gilvus) populations have declined in California. We monitored Warbling Vireo nests in the high elevations of the northern Sierra Nevada in the Tahoe National Forest near Truckee, California. Nest survivorship was low (29.9% Mayfield estimate) compared to Warbling Vireo populations outside of California, but similar to levels reported for other California populations. Brown-headed Cowbird (Molothrus ater) parasitism in the study population was low (7%). Warbling Vireo nest fate was related to nest-site location; successful nests in lodgepole pine (Pinus contorta) were situated on the west or “warmer” side of the tree, in the outer periphery of the foliage, and in areas with slightly less canopy cover compared to unsuccessful nests. These features of the nest site may help reduce the threat of predation and combat cold stress. Our results argue that Warbling Vireos in the northern Sierra Nevada have low nest survivorship (similar to populations in other areas of the state), and that successful nests are often found on thin branches well removed from the main stem.

Use of large Acacia trees by the cavity dwelling Black-tailed Tree Rat in the Southern Kalahari

Recent extensive harvesting of large, often dead Acacia trees in arid savanna of southern Africa is cause for concern about the conservation status of the arid savanna and its animal community. We mapped vegetation and nests of the Black-tailed Tree Rat Thallomys nigricauda to assess the extent to which the rats depend on particular tree species and on the existence of dead, standing trees. The study was conducted in continuous Acacia woodland on the southern and eastern edge of the Kalahari, South Africa. Trees in which there were tree rat nests were compared with trees of similar size and vigour to identify the characteristics of nest sites. Spatial analysis of tree rat distribution was conducted using Ripley's-L function. We found that T. nigricauda was able to utilize all available tree species, as long as trees were large and old enough so that cavities were existing inside the stem. The spatial distribution of nest trees did not show clumping at the investigated scale, and we therefore reject the notion of the rats forming colonies when inhabiting continuous woodlands. The selection of a particular tree as a nest site was furthermore depending on the close proximity of the major food plant, Acacia mellifera. This may limit the choice of suitable nest sites, since A. mellifera was less likely to grow within a vegetation patch containing a large trees than in patches without large trees.

Nest-site Characteristics of Hole-Nesting Birds in a Primeval Boreal Forest of Mongolia

Nest sites of nine common hole-nesting bird species were studied in the West Khentey Mountains, NE Mongolia. Among three excavators, the Great Spotted Woodpecker used more aspens, larger trees, and more living or intact dead trees than the Lesser Spotted Woodpecker or the Willow Tit. Among non-excavators, the Nuthatch used mainly old holes of the Great Spotted Woodpecker, and the Red-throated Flycatcher frequently used those of the Willow Tit. Thus, the nest site characters of these two species resembled those of the original excavators, and their nests were placed higher than those of other non-excavators. The Coal Tit and the Great Tit used mostly branch holes in living trees. With respect to nest site use, the Daurian Redstart behaved as a generalist while the Common Treecreeper specialized in long slits. The nest site selection of excavators might be governed by body size, territory size and their different abilities of excavation. The non-excavators were best differentiated by their preferred hole type, and their tree use and nest site characters were mainly a consequence of the location of such holes. Interspecific competition did not appear to be important in the nest site use of hole-nesting birds in the study area.

Spatial and Temporal Distribution and Nest Site Characteristics of Feral Honey Bee (Hymenoptera: Apidae) Colonies in a Coastal Prairie Landscape

We evaluated the distribution and abundance of feral honey bee, Apis mellifera L., colonies in a coastal prairie landscape by examining nest site characteristics, population trends, and spatial and temporal patterns in cavity use. The colony densities of up to 12.5 colonies per km2 were the highest reported in the literature for an area including both suitable and unsuitable patches of nesting habitat. The measured cavity attributes were similar to those reported from other areas. The time occupied and turnover indices provided useful information about cavity quality, although none of the measured cavity attributes were correlated with these indices. Unmeasurable cavity characteristics, such as cavity volume, may provide a better estimate of cavity quality. Spatial patterns existed in cavity use by the feral colonies, with the colonies showing an aggregated pattern of distribution throughout the study. Colony aggregations probably resulted from the distribution of resources, especially cavities. Two years after the arrival of Africanized honey bees, cavities used by Africanized and European colonies were aggregated in distribution. During what seemed to be a transition period, both Africanized and European colonies were randomly distributed. After that time, European colonies remained randomly distributed, whereas Africanized colonies were aggregated. Therefore, the invasion of Africanized honey bees seemed to fragment the existing European population, corresponding to a decrease in the overall number of European colonies in the study area.

Bald eagle nest site and nest tree characteristics in select biogeoclimatic zones of the 100 Mile House Forest District, British Columbia

Bald eagle (Haliaeetus leucocephalus) nest site and nest tree characteristics were studied in the Sub-Boreal Spruce (SBS), Interior Cedar–Hemlock (ICH), Sub-Boreal Pine–Spruce (SBPS), and interior Douglas-fir (IDF) biogeoclimatic zones in the 100 Mile House Forest District, British Columbia. Dominant or codominant Douglas-fir (Pseudotsuga menziesii) containing large trunk forks or multiple forks of the trunk comprised 85% of 121 bald eagle nest trees. Black cottonwood (Populus trichocarpa) comprised 11% of known nest trees, and trembling aspen (Populus tremuloides), lodgepole pine (Pinus contorta), Ponderosa pine (Pinus ponderosa), and hybrid white spruce (Picea glauca x engelmannii) each contained 1% of known bald eagle nests. Tree height and diameter at breast height (DBH), nest height, and distance of nest to fish-bearing water were less for island nests compared to non-island nests. The mean distance of nests to fish-bearing water, by biogeoclimatic zone, was 78 m in the SBS, 104 m in the ICH, 241 m in the SBPS, and 368 m in the IDF. Ground slope and aspect were not factors in nest site location. The bald eagle nest trees studied were generally of low economic value to the forest industry as they contained less recoverable lumber than similar-sized trees with better form. To maintain bald eagle nesting habitat, large diameter, dominant or codominant trees containing large trunk forks, or multiple forks or leaders of the trunk and (or) large limbs should be identified and retained in groups, patches, or forest stands.

The influence of nest-site characteristics on the nesting success of the Karoo Prinia (Prinia maculosa)

Choice of nest site has important consequences for nest survival. We examined nest-site characteristics relative to nest success in Karoo Prinias breeding in coastal dwarf shrubland, where high nest predation is the main cause of nest failure. Initially, we compared nests that failed during the building, laying, incubation and nestling stages and those from which young were successfully raised, to test whether nests that survived to progressive stages in the nesting cycle differed in their nest-site characteristics. Subsequently, we compared the characteristics of successful nests with those of unsuccessful nests. The nest-site characteristics considered included nest height, nest-plant height, nest-plant species, distance from lateral foliage edge, nest concealment, nest-patch heterogeneity and vegetation cover at four different heights. We were unable to distinguish between the nest-site characteristics of nests that failed during the various stages of the nesting cycle. Concealment was the main nest-site characteristic that differentiated successful nests from unsuccessful nests, with successful nests being located in more concealed sites. The other variables that contributed to the discrimination between successful and unsuccessful nests by discriminant function analysis included nest-plant type and distance from edge, which are also directly related to concealment. This suggests that nest concealment is the most important variable influencing nesting success at this site, which has a preponderance of visually-oriented predators.

Nest-site partitioning in a strandveld shrubland bird community

Nest-site selection may vary adaptively among co-existing species as a result of competitive interactions among the species or in response to density-dependent nest predation. We examined nest-site characteristics and degree of partitioning among 14 co-existing bird species breeding in dwarf strandveld shrubland at Koeberg Nature Reserve, South Africa. Habitat characteristics of nest sites differed significantly among species, indicating strong nest-site partitioning. The principal variables distinguishing nest-site characteristics among species (substrate height, cover at 1m, cover at 2m) were features that distinguish tall-shrub species which are strongly associated with patches of Dune Thicket from shorter-shrub species which are strongly associated with more open Sand Plain Fynbos. Two groups of species which differ primarily in their selection of habitat patch type within the patchy nesting landscape were identified. One group nested predominantly in low shrubs associated with open Sand Plain Fynbos. A second group nested at a variety of heights within tall-shrub species associated with Dune Thicket. Species within each of these groups differed from each other in their relative nest height (ratio of nest height to substrate height), distance of nest from foliage edge, nest concealment and choice of particular substrate plant species. On average, stepwise discriminant function analysis classified 52.6% of the nest sites correctly as belonging to one of the 14 species, considerably better than the expected random classification of 11.8%. Individual species' classifications were 2–12 times better than a random classification. We suggest that high levels of nest predation may have selected for strong nest-site partitioning in this community.

BREEDING BIOLOGY OF THE ENDANGERED ROTA BRIDLED WHITE-EYE

Little is known about the breeding biology of Bridled White-eyes (Zosterops conspicillatus), especially the federally endangered Rota Bridled White-eye (Z. c. rotensis). Here, we report on the breeding behavior, nest-site characteristics, and nest dimensions of Rota Bridled White-eyes. From 1997 to 1999, we found 20 Rota Bridled White-eye nests in Elaeocarpus joga (35%), Hernandia labyrinthica (30%), Merrilliodendron megacarpum (20%), and introduced Acacia confusa (15%) trees between 320 and 460 m in elevation. Nests were 2.5–12.8 m above the ground (n = 18) in trees 3.3–14.6 m tall (n = 16). Clutch size ranged from one to two eggs (n = 7) and the breeding season was from at least December through August. Nest dimensions (n = 4) were 36–44 × 57.7–60.8 mm (outer height × diameter) and 25–29 × 44.6–47.7 mm (cup depth × diameter).

Relative effects of nest size and site on the risk of predation in open nesting passerines

Large nests may incur fitness cost in terms of conspicuousness to predators, but the effect of nest size on predation risk can be confounded by effects of nest site and parental characteristics. I examined relative effects of nest size and placement by experimentally exchanging subsets of inactive nests baited with artificial clutches, among three open‐cup nesting passerine species characterized by different nest size, placement and predation rate. The prediction that increasing nest size (original nest replaced by nest of the larger species) would increase predation, while decreasing nest size (replacement by nest of the smaller species) would decrease predation, relative to control (replacement by conspecific nest) was not supported in any species. The prediction that predation should be higher for large nests compared to small ones, even after exchanging nests among species‐specific sites, was not supported. Predation rate differed among species (combined site/nest effect) before manipulation, whereas only the effect of nest site was significant after manipulation. This means that predation differed between species‐specific nest sites, irrespective of the nest placed at these sites, but not between large (thrush) and small (warbler) nests, irrespective of their placement. Results do not suggest that nest predation selects directionally for smaller nest size. This conclusion could be specific to the study system characterized by high nest densities and high predation rate.

Renesting Decisions and Annual Fecundity of Female Dickcissels (Spiza Americana) in Illinois

Abstract Renesting decisions and annual fecundity are crucial for interpreting other demographic information, yet are infrequently reported. We used radiotelemetry to monitor female Dickcissels (Spiza americana) throughout the 1999 and 2000 breeding seasons in southeastern Illinois. Overall fecundity (regardless of whether females remained in the study area throughout the breeding season) was 0.61 ± 0.13 female fledglings per year. Of females that remained within the study area, 94% fledged young (1.25 ± 0.15 female fledglings per year). Most females (62%) that experienced nest failure emigrated from the study area (moved >10 km) in 2.8 ± 0.6 days; others (36%) initiated subsequent nests in 8.5 ± 0.8 days. After fledging ≥1 young, 95% of females ceased breeding for the season. Successful and failed nest sites were indistinguishable on the basis of vegetative characteristics. Moreover, replacement nests had similar vegetative characteristics and were similar distances from habitat edges, compared with initial nests, which suggests that female Dickcissels do not or cannot “improve” nest-site characteristics in response to nest failure. We observed two behaviors unusual in female Dickcissels: one bird that fledged two broods in one season, and the return of five females banded in 1999 to the study site in 2000.

Microhabitat selection by Kelp Gulls, Larus dominicanus, in Patagonia, Argentina

We studied the microhabitat selection of Kelp Gulls, Larus dominicanus, at 16 colonies along 2500 km of coastline in Patagonia, Argentina, between 1998 and 2001. We quantified 15 habitat variables at 553 nest-sites and at 422 random points. Kelp Gulls selected particular nest-sites from the available habitat. They selected sites with higher cover within 1 m of the nest, closer to the nearest vegetation, but further from the nearest clearing than random points. Slope also showed a clear pattern, where in most colonies, mean nest values were lower than at random points. The variability and diversity of the selected nest-site features indicate that Kelp Gulls are generalists with respect to nest-site habitat selection. Although Kelp Gulls have preferences for certain nest-site characteristics, these preferences are flexible enough to allow them to take advantage of different microhabitats within the diversity of habitat types observed in their colonies.

Nest Site Characteristics of Eastern Wild Turkeys in Central Ontario

Abstract We studied nest site selection by Eastern Wild Turkeys (Meleagris gallopavo silvestris) to compare successful and unsuccessful nests at the northern edge of the species' range in central Ontario during 2000. Six of 16 (38%) nests that we studied were successful. Successful nest sites had greater percent vertical obstruction than unsuccessful nest sites. However, both percent vertical and horizontal obstructions were the best predictors of nest success, suggesting that no single set of habitat characteristics may offer protection from a diverse predator community.

Breeding success in a Red Bishop (Euplectes orix) colony in the Eastern Cape, South Africa, and its relation to nest site characteristics

Data are presented on breeding success of Red Bishops (Euplectes orix) collected over four breeding seasons at a colony in the Addo Elephant National Park, Eastern Cape, South Africa. Overall hatching and fledging success were 53.8% and 26.0% of all eggs laid, respectively, and the overall mean number of fledglings per breeding attempt was 0.77. Hatching and fledging success varied significantly among seasons, with both clutch and brood losses due to predation being the main reason for the observed differences. Hatching success also differed significantly among clutch sizes, being highest for four-egg clutches (63.2%), intermediate for three-egg clutches (55.5%) and lowest for two-egg clutches and five-egg clutches (33.2% and 34.3%, respectively). However, fledging success was not significantly different among clutch sizes. The mean number of fledglings per breeding attempt was 0.44 for two-egg clutches, 0.80 for three-egg clutches, 1.10 for four-egg clutches, and 0.57 for five-egg clutches. The height of accepted nests (i.e.nests in which at least one egg was laid) was significantly lower than the height of nests not accepted. In addition, accepted nests in which eggs hatched and young fledged were significantly lower than accepted nests in which no eggs hatched and no young fledged. These overall effects of nest height on nest acceptance and hatching and fledging success were, however, due only to nests built above water, since no such effects were found when nests built above ground (i.e.on dry land) were analysed separately. I detected no effect of nest coverage on the probability of a nest being accepted, nor was there any effect of nest coverage on hatching or fledging success. Nests above water were significantly more likely to be accepted than nests above ground; however, hatching and fledging success of nests that were accepted did not differ significantly between nests built above water and those built above ground.

Breeding and nest site characteristics of the Black-casqued Hornbill Ceratogymna atrata and White-thighed Hornbill Ceratogymna cylindricus in south-central Cameroon

The reproductive biology of two species of African hornbill, the Black-casqued Hornbill, Ceratogymna atrata, and the Whitethighed Hornbill, Ceratogymna cylindricus, was investigated over a four-year period (1994–1997) on a 25km 2 site in lowland rainforest in south-central Cameroon. Nesting attempts varied considerably among years, with the percentage of successful nests highest in 1995, with 64% and 54% of Black-casqued and White-thighed Hornbill fledging offspring, respectively. There were no nesting attempts in 1994, despite the fact that hornbills were present in the study area. Large differences in fruit availability were also noted across years, suggesting that reproductive activity and success are related to fruit availability. Data collected from 38 nests, over four breeding seasons (1994–1997), showed a preference for nest cavities in larger trees within areas of the forest containing larger trees. Hornbills did not show preferences for particular tree species, with the possible exception of Petersianthus macrocarpus, in which nine of the active nest cavities were found. Comparisons showed few significant differences in cavity characteristics between the two species . While cavities may have been a limiting factor in nesting in 1995, the year with the highest fruit availability, cavities were not limiting during other years when fruit availability was lower. Hornbill diets, as determined from seed traps at cavities, showed significant year-to-year variation. Although courtship and exploratory behaviour of cavities by pairs took place in most years, females did not wall themselves into cavities unless fruit was plentiful. Hornbills appear to time reproduction to coincide with peak food supply and successfully reproduce only when food is plentiful, and may curtail or forego nesting in years when fruit availability is low.

NESTING BIOLOGY OF THREE GRASSLAND PASSERINES IN THE NORTHERN TALLGRASS PRAIRIE

Basic nesting information on grassland passerines is needed for improving grassland bird management. Among the information needs are (1) the suitability of nesting habitat, (2) periods during the breeding season in which birds are most vulnerable to disturbances, and (3) how to fit grasslands into a prioritization scheme for conservation. Comparisons of nesting parameters among grassland species will help identify important management considerations. We describe and compare nest-site characteristics, nesting phenology, clutch size, hatching and fledging success, and brood parasitism by Brown-headed Cowbirds (Molothrus ater) for three grassland passerine species nesting in tallgrass prairie of northwestern Minnesota and southeastern North Dakota. During 1998–2002, we found 793 Clay-colored Sparrow (Spizella pallida), 687 Savannah Sparrow (Passerculus sandwichensis), and 315 Bobolink (Dolichonyx oryzivorus) nests. These species differed in many aspects of their breeding ecology. Clay-colored and Savannah sparrows initiated their nests almost 2 weeks earlier than Bobolinks, with peak nesting occurring in June. Clutch size was lower (3.77 ± 0.03 SE) for Clay-colored Sparrows than Savannah Sparrows (4.13 ± 0.05) and Bobolinks (5.25 ± 0.08). The number of host eggs hatched per nest was higher in Bobolinks (3.46 ± 0.20) than in Clay-colored Sparrows (2.52 ± 0.09) and Savannah Sparrows (2.41 ± 0.11), but the number of young fledged per Bobolink nest (1.97) was similar to that of Savannah Sparrows (2.01). Clay-colored Sparrows fledged only 1.35 host young per nest. Mayfield nest success was higher for Savannah Sparrows (31.4%) than for Clay-colored Sparrows (27.4%) or Bobolinks (20.7%). The main cause of nest failure was nest predation: predation in Clay-colored Sparrows (47.9%) was higher than in Savannah Sparrows (33.5%) but similar to Bobolinks (41.8%). Brood parasitism was lower in Clay-colored Sparrows (5.1%) than in Bobolinks (10.8%), and intermediate (6.7%) in Savannah Sparrows. Compared with most other studies, grassland bird nests in our study area were more successful and less frequently parasitized; thus, northwestern Minnesota and southeastern North Dakota appear to provide important breeding habitat for grassland birds.