Artificial Nest Predation Research Articles

Artificial Nest Predation and Abundance of Birds along an Urban Gradient

Artificial Nest Predation and Abundance of Birds along an Urban Gradient

Artificial Nest Predation and Abundance of Birds Along an Urban Gradient

Abstract We studied nest predation pressure on birds along an urban gradient in urban parks in three Finnish towns. Artificial ground nests with Japanese Quail (Coturnix coturnix japonicus) eggs were depredated more in the urban area than in the adjacent forest area. Within each town, the nest predation rate was higher in the town center than in the less urbanized area of detached houses. Predation rates did not vary from year to year or between study towns. Abundances of generalist avian predators were higher in the town center than in the area of detached houses and in the surrounding forest area. Most of the nests in the town center were destroyed by avian predators. Predation rate of artificial nests in each of the town areas was higher in managed parks than in unmanaged parks, presumably due to the less dense vegetation in the managed than the unmanaged parks. A test involving covering nests revealed that artificial nests covered by adjacent vegetation survived better than nests with less cover. In our study, artificial nest loss reflected the distribution of avian nest predators. Ground nesters were present at lower abundances in areas where concealing vegetation was missing and avian nest predation was high. Apparently, nest predation is one of the several possible mechanism affecting urban bird assemblages.

Predation of Natural and Artificial Nests in a Southern Pine Forest

Abstract We compared predation of artificial open-cup nests baited with Japanese Quail (Coturnix coturnix) eggs with predation of natural open-cup nests during 1997 and 1998 in a Louisiana pine forest to assess the assumption that predation of artificial nests is an index to that of natural nests. Cameras were placed at randomly selected natural and artificial nests in shrubs to document predators. Predation at artificial-nest plots was positively correlated with predation at adjacent natural-nest plots overall, although inconsistently by year. Artificial nests were almost exclusively depredated by corvids, but quail eggs were too large to be broken by small-mouthed mammalian predators. American Crows (Corvus brachyrhynchos) appeared to be important predators of natural nests. Predation of natural nests was independent of predation at other nests, but predation of artificial nests by crows was spatially and temporally clumped. Crows may have learned the location of artificial-nest plots, and predation of artificial nests increased significantly between years, contrary to predation of natural nests. Predation of artificial nests did not exhibit seasonal variation like that of natural nests. Overall, predation of artificial shrub nests did not accurately mimic that of natural shrub nests. Changes in procedures for artificial-nest studies that reduce spatially and temporally clumped predation and prevent the exclusion of small-mouthed predators could increase the suitability of such studies as a model for predation at natural nests. However, the difference in labor effort between studies of natural nests versus artificial nests that incorporate the changes we recommend likely would disappear, which would reduce the attractiveness of artificial-nest studies as an experimental model.

Predation of Natural and Artificial Nests in a Southern Pine Forest

Predation of Natural and Artificial Nests in a Southern Pine Forest

Patterns of Nest Predation Contribute to Polygyny in the Great Reed Warbler

According to the polygyny threshold model, females are compensated for the cost of sharing a territory with other females by breeding in territories of higher quality than those of monogamously mated females. In the polygynous Great Reed Warbler (Acrocephalus arundinaceus), the variation in territory quality may be associated with nest site characteristics or food supply. In this study, we examined the probability of nest predation in Great Reed Warblers in relation to an indirect measure of territory quality (territory attractiveness rank as indexed by settlement order) and to several variables of nest site structure. Artificial nests with attached soft plasticine model eggs were placed in Great Reed Warbler territories of different attractiveness. Marks in the soft model eggs were compared to marks from possible predator species. Both inter- and intraspecific predators were found to prey upon eggs in artificial nests. Marsh Harriers (Circus aeruginosus) predominantly preyed upon artificial nests located in territories of low attractiveness, in low-density reed beds, and early in the season. Bitterns (Botaurus stellaris) and Water Rails (Rallus aquaticus) showed a preference for artificial nests located inside the reeds. When all types of predators of artificial nests were pooled, the probability of nest predation was lower in more attractive territories. This pattern was corroborated in an analysis of predation on real nests. In general, polygyny occurred in territories with a low rate of nest predation, whereas unmated males held territories where the risk of predation was high. The low rate of nest predation in attractive territories on average compensated secondary females for the cost associated with sharing a male (i.e., reduced male assistance when feeding nestlings). The polygyny threshold model has been around for several decades, however, only few studies have identified the factors that may compensate secondary females for the cost of sharing a mate. In the present study we were able to show that the patterns of nest predation can be an important territory quality parameter that compensate secondary females, and, hence, contribute to the occurrence of avian polygyny.

PATTERNS OF NEST PREDATION CONTRIBUTE TO POLYGYNY IN THE GREAT REED WARBLER

According to the polygyny threshold model, females are compensated for the cost of sharing a territory with other females by breeding in territories of higher quality than those of monogamously mated females. In the polygynous Great Reed Warbler (Acrocephalus arundinaceus), the variation in territory quality may be associated with nest site characteristics or food supply. In this study, we examined the probability of nest predation in Great Reed Warblers in relation to an indirect measure of territory quality (territory attractiveness rank as indexed by settlement order) and to several variables of nest site structure. Artificial nests with attached soft plasticine model eggs were placed in Great Reed Warbler territories of different attractiveness. Marks in the soft model eggs were compared to marks from possible predator species. Both inter- and intraspecific predators were found to prey upon eggs in artificial nests. Marsh Harriers (Circus aeruginosus) predominantly preyed upon artificial nests located in territories of low attractiveness, in low-density reed beds, and early in the season. Bitterns (Botaurus stellaris) and Water Rails (Rallus aquaticus) showed a preference for artificial nests located inside the reeds. When all types of predators of artificial nests were pooled, the probability of nest predation was lower in more attractive territories. This pattern was corroborated in an analysis of predation on real nests. In general, polygyny occurred in territories with a low rate of nest predation, whereas unmated males held territories where the risk of predation was high. The low rate of nest predation in attractive territories on average compensated secondary females for the cost associated with sharing a male (i.e., reduced male assistance when feeding nestlings). The polygyny threshold model has been around for several decades, however, only few studies have identified the factors that may compensate secondary females for the cost of sharing a mate. In the present study we were able to show that the patterns of nest predation can be an important territory quality parameter that compensate secondary females, and, hence, contribute to the occurrence of avian polygyny.

PREDATION OF NATURAL AND ARTIFICIAL NESTS IN A SOUTHERN PINE FOREST

Abstract We compared predation of artificial open-cup nests baited with Japanese Quail (Coturnix coturnix) eggs with predation of natural open-cup nests during 1997 and 1998 in a Louisiana pine forest to assess the assumption that predation of artificial nests is an index to that of natural nests. Cameras were placed at randomly selected natural and artificial nests in shrubs to document predators. Predation at artificial-nest plots was positively correlated with predation at adjacent natural-nest plots overall, although inconsistently by year. Artificial nests were almost exclusively depredated by corvids, but quail eggs were too large to be broken by small-mouthed mammalian predators. American Crows (Corvus brachyrhynchos) appeared to be important predators of natural nests. Predation of natural nests was independent of predation at other nests, but predation of artificial nests by crows was spatially and temporally clumped. Crows may have learned the location of artificial-nest plots, and predation of ...

Artificial nest predation in bogs: Does peat harvest increase risk?

Bogs in southern Québec are facing significant and growing industrial pressure. Peat moss harvesting results in bog fragmentation and in edge increase between harvested areas and remaining natural patches. The objective of our study was to assess the effects of harvesting on nesting success of songbirds in adjacent undisturbed sites. We determined whether exposure of nests to predators was edge-dependent in harvested bogs and compared the risk of nest predation in harvested and undisturbed bogs. Over three summers, we placed a total of 480 artificial nests at various distances (£ 450 m) from edges in five harvested and nine unharvested bogs. Mean nest predation rate was significantly higher (62.7%) and more variable in harvested bogs, compared to unharvested bogs (8.6%). However, we found no relation between nest fate and distance to exploitation edge in harvested bogs. We suggest factors associated with harvesting that may attract nest predators to remaining unharvested sites, thereby increasing risk of nest predation and ultimately lowering reproductive success.

THE INFLUENCE OF ACORN CROPS ON ANNUAL VARIATION IN RODENT AND BIRD POPULATIONS

I recorded mast production by oaks (Quercus sp.) at 12 forested sites in western Virginia for 6–12 yr and measured its impact on the abundance of small mammals, understory vegetation, and artificial-nest predation. White-tailed deer (Odocoileus virginianus) were excluded from half the 4-ha sites after at least one season of data collection. My hypothesis was that annual variation in acorn crops affected multiple species and that the strength of those interactions is mediated by white-tailed deer. The acorn crop was variable across sites and year, with some of the between-site variability explained by differences in elevation. All sites experienced at least one mast failure, and mast failure years were generally consistent across sites. White-footed mouse (Peromyscus leucopus), eastern chipmunk (Tamias striatus), and gray squirrel (Sciurus carolinensis) populations were significantly correlated with annual fluctuations in the acorn crop. The exclusion of deer had a significant impact on P. leucopus and T. striatus populations by increasing the number of animals captured following low acorn mast years. Annual fluctuations in the acorn crop, but not in rodent densities, were significantly correlated with the rates of predation on artificial nests the next summer. There was no significant interaction between predation rates and the exclusion of deer. An index from the Breeding Bird Survey (BBS) for Virginia was used to measure regional numbers for 11 common species captured at the sites. The index for two understory species was significantly negatively correlated with the mean acorn crop measured 2 yr previously. The effect of white-tailed deer on the forest community was not consistent across all conditions, as sites with large acorn crops were not strongly influenced by deer. These data are consistent with the hypothesis that mast crops from oaks serve as important determinants of community function within Appalachian forests.

No evidence of short-term effects of clear-cutting on artificial nest predation in boreal mixedwood forests

We examined whether nest predation in unharvested blocks of trembling aspen (Populus tremuloides Michx.) would increase when adjacent stands were clearcut in the boreal mixedwood forest of Alberta, in 1993, 1994, and 1998. Artificial nests placed on the ground and in shrubs were baited with Chinese painted quail (Coturnix chinensis L.) and plasticine eggs, which along with cameras, were used to identify nest predators. Fragmented sites were isolated from continuous forest by clear-cutting in 1994, while control sites remained unfragmented. Overall, predation on ground and shrub nests did not increase in isolated forest patches post-harvest (p = 0.056 and p = 0.085, respectively), nor was there a consistent effect of distance from a clearcut edge (p >= 0.050). Predation on ground nests was higher in 1994 and 1998 compared with 1993 levels (p < 0.001), while predation on shrub nests remained relatively constant over the 3 years (p >= 0.073). Mice, voles, and red squirrels (Tamiasciurus hudsonicus Erxleben) were the main identified predators of ground and shrub nests, respectively. Probability of nest predation could not be consistently predicted by nest site vegetation or adjacent land cover, but was related to predator abundance. However, neither predators nor songbirds congregate at recent clearcut-forest edges, and we conclude that elevated nest predation caused by clear-cutting may not occur in the boreal mixedwood, at least not at current levels of harvest and within 5 years of clear-cutting.

Artificial nest predation rates in tropical and temperate forests: a review of the effects of edge and nest site

Nest predation rates are believed to be higher in tropical than in temperate forests. This notion is central in explaining different life history traits of tropical and temperate birds, but it is not known whether this assertion is true for all nest sites, such as ground and shrub nests, and at different distances from forest edge. I reviewed 22 studies using artificial nest experiments which concurrently contrasted predation rates of ground and shrub nests in temperate and tropical forests and found, contrary to the current dogma, no overall difference in predation rates between regions. However, there was a significant interaction between region and nest site. Ground nest predation rates were significantly higher in the tropical region, while predation rates on shrub nests were similar between regions. Within the tropical region, ground nests had significantly higher predation rates than shrub nests. Elevated nest predation rates at forest edges were found in both temperate and tropical forests. The results may have great implications for expected patterns of avian life histories and for the effects of forest fragmentation in temperate and tropical regions. First, if nest predation affects avian life histories, my results predict ground‐nesting species in tropical forests to have shorter nestling periods, more broods and smaller clutch sizes than shrub‐nesting species. Second, vulnerability of ground‐ and shrub‐nesting guilds is suggested to differ between regions due to differences in forest vegetation structure, and the composition of predator faunas and their specific responses to forest fragmentation. Data to test these hypotheses are limited, but agree with the results of this review.

Effects of nest features and surrounding landscape on predation rates of artificial nests

Artificial nest predation experiments were carried out in northern Italy in woods which varied in size, isolation and surrounding landscape structure. Multivariate analyses, including logistic regression, showed that: (1) size and isolation of woods did not significantly affect predation rates; (2) nests on the edge of woods did not suffer higher predation rates than nests inside the wood; (3) nest camouflage greatly influenced predation rates, suggesting that predators were mainly using visual clues to identify nests; (4) the type of habitat that surrounded the woods emerged as a crucial factor in nest survival and the amount of human settlements in the vicinity of the wood was inversely correlated with nest survival, probably due to predators associated with humans; (5) other habitat variables, which were apparently individually unimportant, were found to have an effect on nesting success, if combined in a single ‘suitability index’. It is impossible to generalize about the influence of landscape fragmentation on nest predation because local landscape history and predator guilds, together with the scale of fragmentation, probably interact to determine the suitability of nest sites and their vulnerability to predators.

No evidence of short-term effects of clear-cutting on artificial nest predation in boreal mixedwood forests

No evidence of short-term effects of clear-cutting on artificial nest predation in boreal mixedwood forests

Predation of Artificial Ground Nests on White-Tailed Prairie Dog Colonies

Prairie dog (Cyuomys spp. 1 colonies are unique to prairie and shrub-steppe landscapes However, widespread eradication, habitat loss, and sylvatic plague (Yersinia pestis) have reduced their numbers by 98% since historical times. Birds associated with prairie dogs also are declining. Potential nest predators, such as coyotes (Canis latrans), swift foxes (Vulpes velox), and badgers (Taxidea taxus), may be attracted to colonies where a high concentration of prairie dogs serve as available prey, Increased abundance of small manimals, including prairie dogs, also may increase the risk of predation for birds nesting on colonies. Finally, because grazing by prairie dogs may decrease vegetation height and canopy cover, bird nests may be easier for predators to locate. In this study we placed 1.444 artificial ground nests on and off 74 white-tailed prairie dog (C. leucurus) colonies to test the hypothesis that nest predation rates are higher on colonies than at nearby off sites (i.e., uncolonized habitat) We sampled colonies from 27 May to 16 July 1997 at the following 3 complexes: Covote Basin, Utah and Colorado: Moxa Arch, Wyoming; and Shirley Basin, Wyoming, Differences in daily predation rates between colonies and paired off sites averaged 1.0% ( P = 0.060). When converted to a typical 14-day incubation period, predation rates averaged 14% higher on colonies (57.7 ± 2.7%, x ± SE) than at off sites (50.4 ± 3.1%) Comparisons of habitat variables on colonies to off sites showed percent canopy cover of vegetation was similar (P = 0.114) percent bare ground was highe on colonies (P 0.288), Although we found the risk of nest predation was higher on hite-tailed prairie dog colonies than at off sites, fitness of birds nesting on colonies might depend on other factors that influence foraging success, reproductive success, or nestling survival.

Different nest predator faunas and nest predation risk on ground and shrub nests at forest ecotones: an experiment and a review.

This study examined predator faunas of artificial ground and shrub nests and whether nest predation risk was influenced by nest site, proximity to forest edge, and habitat structure in 38 grassland plots in south-central Sweden. There was a clear separation of predator faunas between shrub and ground nests as identified from marks in plasticine eggs. Corvids accounted for almost all predation on shrub nests whereas mammals mainly depredated ground nests. Nest predation risk was significantly greater for shrub than for ground nests at all distances (i.e. 0, 15 and 30 m) from the forest edge. However, nest predation risk was not significantly related to distance to forest edge, but significantly increased with decreasing distance to the nearest tree. Different corvid species robbed nests at different distances from the forest edge, with jays robbing nests closest to edges. We conclude that the relationship between the predation risk of grassland bird nests and distance to the forest edge mainly depends on the relative importance of different nest predator species and on the structure of the forest edge zone. A review of published articles on artificial shrub and ground nest predation in the temperate zone corroborated the results of our own study, namely that shrub nests experienced higher rates of depredation in open habitats close to the forest edge and that avian predators predominantly robbed shrub nests. Furthermore, the review results showed that predation rates on nests in general are highest <50 m inside the forest and lower in open as well as forest interior habitats (≥50 m from the edge).

Predation of Artificial Nests in Hardwood Fragments Enclosed by Pine and Agricultural Habitats

Nesting success of songbirds often is poor in edge-dominated habitats. Because the spatial juxtaposition of forest fragments relative to other habitats may influence nest success, we tested the hypothesis that the depredation rate for bird nests in small hardwood forests would decrease if the degree of edge contrast with adjoining habitats was reduced. Over 4 trials, we placed 672 artificial nests (336 each at shrub and ground levels divided equally between edge and interior locations) in small (range = 0.5-5.0 ha) hardwood forest stands enclosed by either agricultural fields (n = 7) or mature pine forest (n = 7). Nest predation was greater (P = 0.001) in field-enclosed stands (35%) than in pine-enclosed stands (20%) because of greater (P = 0.03) predation of shrub nests. No differences (P > 0.05) in predation rates were detected between stand types for ground nests or between strata (i.e., ground nests vs. shrub nests) within field-enclosed stands. Predation rates did not differ (P > 0.05) between edge and interior nests between or within stand types. Nest predation by avian species was not suspected in pine-enclosed stands (0%). but 18% of the nests depredated in agriculture-enclosed stands was attributed to birds. The low edge contrast associated with pine-enclosed stands appeared to attract fewer nest predators, especially those that preyed on shrub nests. However, the value of lower predation rates for shrub nests in pine-enclosed stands may be offset by the presence of fewer shrub-nesting sites relative to similar-sized field-enclosed stands, because understory development was impoverished, probably as a result of reduced sunlight penetration.

The possible function of stone ramparts at the nest entrance of the blackstart

Blackstarts,Cercomela melanura, Turdidae, construct a rampart of stones at the entrance to their nests. These ramparts may reach remarkable proportions, containing hundreds of flat rocks. We investigated several hypotheses regarding the function of stone ramparts, by monitoring individually marked blackstarts at the En-Gedi Nature Reserve, Israel. Stones were collected solely by females, who carried them in their beaks, while flying to the nest, at a rate of up to one stone per min, after pair formation had occurred. The number and total weight of stones as well as rampart height showed a highly positive correlation with the size of the nest cavity opening. The rampart decreased the size of the cavity entrance to some nests by as much as 67%, which suggests an antipredator barrier function. Survival rates of eggs and chicks were extremely low and the major cause of reproductive failure was predation. Successful nests tended to be located higher off the ground than predated nests, and often contained fewer stones. Furthermore, larger females in terms of wing and tail length nested in cavities higher off the ground and built smaller ramparts containing lighter stones. An artificial nest predation experiment did not reveal a difference in predation rates between nests with and without stone ramparts. Spiny mice,Acomyssp., were the main egg predators. However, in 37% of nests with ramparts that were predated, the perpetrator flattened the rampart, suggesting that they may serve as a barricade, forcing the predator to invest time in clearing the stones in order to gain access to the nest, and perhaps allowing the nesting female sufficient time to escape. We propose, therefore, that owing to such high nest predation rates, females nesting close to the ground build stone ramparts as an ‘early warning’ mechanism to prevent themselves from being trapped inside nest cavities and predated.

A Meta‐Analysis of Forest Cover, Edge Effects, and Artificial Nest Predation Rates

Landscape fragmentation has been among the most intensely studied topics in conservation biology for decades (Gates & Gysel 1978; Murcia 1995). The influence of habitat edge has often been investigated as an important feature in fragmented areas, especially with respect to bird nesting success, as evidenced by three recent reviews. Paton (1994) concluded that current evidence, although equivocal, suggests that predation and parasitism rates are often significantly greater within 50 m of an edge. Andren (1995) examined edge (or patch size) effects in a review of 40 papers and concluded that edge-related increase in predation seems to be most commonly found inside forests surrounded by farmland and was rarely found in forest mosaics. Major and Kendal (1996) showed that a preponderance of studies demonstrated a positive correlation between predation rate and the degree of habitat fragmentation, but found more variable results regarding edge effects. We believe that none of these papers adequately addressed the issue of whether or not predation rates and edge effects differ between deforested versus forested landscapes. Thus, we decided to evaluate relationships between degree of forest cover in a landscape and (1) avian nest success rates and (2) the existence of elevated predation rates near habitat edges. We combined data from 13 previous studies in 33 U.S. landscapes to explore patterns of nest predation and landscape composition.

A Meta-Analysis of Forest Cover, Edge Effects, and Artificial Nest Predation Rates

A Meta-Analysis of Forest Cover, Edge Effects, and Artificial Nest Predation Rates

Predation of artificial nests in a fragmented landscape on the New England Tablelands of New South Wales

Artificial, cup-shaped nests containing one quail egg and one plasticine egg were placed in small (20 ha), medium-sized (90 ha) and large (350 ha) remnants of eucalypt woodland. Nests were placed near edges and centres of the two larger sites; the small site was considered all edge. Overall, 69% (659/960) of nests were preyed upon within 4 days, reflecting a high predation pressure. More nests were preyed upon in the medium-sized than in the larger or smaller sites. Loss of nests was no higher at the edge than in the centre overall, though it was significantly higher at the edge than the centre of the largest site. The main predators were identified (from beak marks on plasticine eggs) as large and medium-sized birds. Our results provide only weak support for the hypothesis that habitat fragmentation has increased predation on open nests. It is possible that nest predators and their impact have increased regionally, rather than locally. Habitat degradation may also lead to higher predation of nests, due to loss of understorey and an increase in nest predators.