High Nest Predation Research Articles

EDGE AVOIDANCE BY NESTING GRASSLAND BIRDS: A FUTILE STRATEGY IN A FRAGMENTED LANDSCAPE

Abstract Some grassland passerine species are considered area-sensitive, but the mechanisms underlying that phenomenon are not understood, particularly on grazed grasslands. Area sensitivity may result from edge avoidance or higher nest predation near edges, both of which may be influenced by predator activity or cattle-induced vegetational differences between pasture edge and interior. We assessed the effect of distance to edge on nest density and predation Savannah Sparrows (Passerculus sandwichensis), Grasshopper Sparrows (Ammodramus savannarum), Bobolinks (Dolichonyx oryzivorus), and meadowlarks (Sturnella spp.) along wooded and nonwooded edges of Wisconsin pastures in 1998-2000 and the activity of potential mammalian nest predators along those edges in 2000-2001. We found a positive relationship between nest density and distance from edge for all edge types combined, but that was not the result of effects of wooded edges: we found no difference in density between nests located <50 or <100 m from wood...

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.

Competing Females and Caring Males. Polyandry and Sex‐Role Reversal in African Black Coucals,Centropus grillii

AbstractMost species of birds show bi‐parental or female‐only care. However, a minority of species is polyandrous and expresses male‐only care. So far, such reversals in sex roles have been demonstrated only in precocial bird species, but there was suggestive evidence that such a mating system may occur in one altricial bird species, the black coucal,Centropus grillii. In a field study in Tanzania we investigated whether black coucals are sex‐role reversed and polyandrous. We found that males were mated to one female, rarely vocalized and provided all parental care from incubation of eggs to feeding of young. In contrast, female black coucals were about 69% heavier and 39% larger than males and polyandrous. They spent a large proportion of time calling from conspicuous perches, defended breeding territories, did not help in provisioning young and had a higher potential reproductive rate than males. We conclude that the black coucal currently represents the only altricial bird species with sole male parental care and a classical polyandrous mating system. High nest predation pressure and small territory sizes due to high food abundance may have been important factors in the evolution of sex‐role reversal and polyandry in this species.

Effect of Prey Biomass on Reproductive Success and Mating Strategy of Bicknell's Thrush (Catharus Bicknelli), a Polygynandrous Songbird

Abstract Resource availability and distribution are hypothesized to be the primary ecological mechanisms driving variation in avian mating systems. Although food supplementation experiments have been used to examine plasticity in mating strategies, variation in avian mating strategies across naturally occurring gradients of prey availability has rarely been examined. Here, we test the hypothesis that the polygynandrous mating system of Bicknell's Thrush (Catharus bicknelli) results from food limitation on female home ranges in the species' harsh montane breeding environment. In 2000, number of chicks fledged per nest was significantly positively correlated with prey biomass on a female's home range, and number of male feeders at a nest was significantly negatively correlated with prey biomass. Neither relationship was significant in 2001, a year with high nest-predation rates, which suggests that nest predation may ultimately limit the species' productivity. These results are consistent with the hypothesis that (1) female productivity is limited by prey biomass, and (2) female mating decisions may be influenced by their assessment of home-range food abundance prior to egg laying.

Nest site selection and nesting success of five species of passerines in a South American open Prosopis woodland

I analyzed nest site preferences and whether these preferences were linked to nest success of five bird species breeding in an arid area of southern South America. Most nests (90%) were located in three plant species (Geoffroea decorticans, Capparis atamisquea, and Atriplex lampa). Serpophaga griseiceps, Poospiza ornata, and P. torquata nested in plants with size significantly different from randomly selected plants. At the mesohabitat scale (i.e., habitat patch surrounding the nest), four species showed clear differences from random patches within the general habitat, and the remaining species (Saltatricula multicolor) showed a non-significant trend. The daily survival rate of S. griseiceps nests placed in the preferred plant species (i.e., G. decorticans) was lower than those in the other nest-plants. In the other four bird species, nest survival did not differ between preferred and other plants used for nesting. At the scale of microhabitat (i.e., plant size and location of the nest inside the plant), no significant differences were detected between unsuccessful and successful nests. Similarly, unsuccessful nest patches did not differ significantly in habitat features from those that were successful. High nest predation rates found in this habitat (around 85% for the total assemblage) and a relatively high diversity of predators (and of predation tactics) appear to impede the presence of “safe” sites for nesting (i.e., there are trade-offs between avoidance strategies).

EFFECT OF PREY BIOMASS ON REPRODUCTIVE SUCCESS AND MATING STRATEGY OF BICKNELL'S THRUSH (CATHARUS BICKNELLI), A POLYGYNANDROUS SONGBIRD

Abstract Resource availability and distribution are hypothesized to be the primary ecological mechanisms driving variation in avian mating systems. Although food supplementation experiments have been used to examine plasticity in mating strategies, variation in avian mating strategies across naturally occurring gradients of prey availability has rarely been examined. Here, we test the hypothesis that the polygynandrous mating system of Bicknell's Thrush (Catharus bicknelli) results from food limitation on female home ranges in the species' harsh montane breeding environment. In 2000, number of chicks fledged per nest was significantly positively correlated with prey biomass on a female's home range, and number of male feeders at a nest was significantly negatively correlated with prey biomass. Neither relationship was significant in 2001, a year with high nest-predation rates, which suggests that nest predation may ultimately limit the species' productivity. These results are consistent with the hypothesi...

CLUTCH SIZE REDUCTION AS A RESPONSE TO INCREASED NEST PREDATION RATE IN THE COLLARED FLYCATCHER

Nest predation has been hypothesized as a major factor influencing clutch size in birds. Indirect and correlative evidence for clutch size reduction under high nest predation risk is accumulating, but such a reduction has never been shown experimentally. We experimentally tested this “nest predation hypothesis” by manipulating nest predation rate in the Collared Flycatcher, Ficedula albicollis. As predicted, clutch size decreased in the year following the experiment in “depredated” areas (in which 20–35% of the nests were totally depredated) compared to control ones (no predation). This could result from (1) phenotypic plasticity in clutch size, or (2) differential breeding habitat selection, with dominant individuals or individuals laying large clutches preferentially leaving depredated areas and settling in control ones. There was no evidence for differential dispersal from areas of the two treatments, nor differential competitive abilities of breeders in areas of the two treatments. Conversely, all ind...

Predation of Songbird Nests Differs by Predator and between Field and Forest Habitats

Our understanding of factors affecting nest predation and ability to mitigate high nest predation rates is hampered by a lack of information on the importance of various nest predator species in different habitats and landscapes. We identified predators of songbird nests in old-field and forest habitats in central Missouri, USA, with miniature video cameras. We used an information-theoretic approach to evaluate support for hypotheses that the importance of predator species varied among habitats and nest stage. We monitored 165 nests with cameras and 272 nests without cameras during 1997-1999, and identified predators at 61 of 74 depredated nests monitored by cameras. Model selection indicated the most support for a model with seperate rates for predation by birds, mammels, and snakes in field and forest habitats. Predation by snakes was greater than predation by mammels and birds in old fields; predation by mammels (mostly rccoons [Procyon lotor]) was greater than by snakes and birds in forest. We found little support for the hypothesis that monitoring nests with cameras effects predation. Nests could not be assigned reliably to a predator group based on condition of the nest. We believe that knowledge of the identity and abundance of dominant predators in a habitat or landscape is neccessary to target conservation efforts to reduce nest predation or to interpret results of research on factors affecting nest success.

SONGBIRD POPULATIONS IN FLUCTUATING ENVIRONMENTS: PREDATOR RESPONSES TO PULSED RESOURCES

In response to mast production of acorns, populations of small mammals, such as the white-footed mouse and eastern chipmunk, greatly increase and, in turn, initiate cascades of direct and indirect effects that permeate throughout forest communities. To examine the strength of the effects stemming from acorn crops, we conducted studies in oak-dominated deciduous forest of the Hudson Valley, New York, documenting the connections between predator abundance (small mammals and raptors) and the abundance and reproductive success of five woodland songbirds. Nest predation rates increased at high rodent densities for Veeries, Red-eyed Vireos, and Wood Thrushes. Analysis of Breeding Bird Survey (BBS) data from surrounding counties demonstrated a unimodal relationship between rodent density (year t) and songbird abundance (year t + 1), rather than a monotonic decline. Regional Christmas Bird Count data for Sharp-shinned and Cooper's Hawks showed a positive correlation between rodent density and accipiter abundance the following winter, suggesting that hawks exhibit a numerical response to rodents. Taken together, we suggest that predation by accipiters when rodents are scarce, in combination with high nest predation when rodents are abundant, may explain the unimodal relationship between rodents and songbirds. Nonlinear relationships between predator and prey abundance and indirect interactions appear to characterize this system. Corresponding Editor: J. R. Walters.

Habitat-related nest predation effect on the breeding success of the Eurasian treecreeper

We studied the impact of habitat structure on the long-term breeding success of an old-growth forest passerine the Eurasian treecreeper (Certhia familiaris) assessed over a period of 7 years in the same forest patches. Breeding success was greaterless variable in areas with a high proportion of mature forest lower more variable in areas with high proportions of young sapling stands. This difference was almost exclusively due to a high degree of nest predation in patches characterized by a low proportion of mature forest. In this study nest predation explained approximately 50% of the between-year variation in breeding success. We found that in patches where the proportion of mature forest in the landscape was over 60% nest predation was considerably lower than in patches below this threshold value. Small mustelids were likely responsible for the high nest predation rate increased year-to-year variability in the breeding success of the treecreeper. Small mustelids that mainly prey on voles may following a crash in the vole populationshift their diet towards alternatives such as bird nests. This can happen especially in environments with a high human impact such as in sapling areas young forests since these habitats can support high numbers of voles their predators.

Mate acquisition in the European blackbird and its implications for sexual strategies

Female European blackbirds, Turdus merula have been shown to engage in mixed reproductive strategies and females do not seem to gain any material benefit from their extra-pair copulation behaviour. To test the hypothesis that such behaviour arises out of constraint on their choice of social mate, I investigate if and how these females are constrained in their choice at mate acquisition. I recorded patterns of territorial distribution and interactions between resident birds both before pairing and during the breeding season. Patterns of observed behaviour agreed with earlier descriptions of winter and breeding territoriality and provided clues to the underlying mechanism of mate acquisition. I conclude that the constraint on breeding success imposed by high nest predation promotes intrasexual competition for high quality nesting habitat between females prior to pair formation. Female distribution promotes intrasexual competition between males for territorial area overlapping females or for habitat likely to be occupied by females. Mate choice during pair formation is constrained by the outcome of this intrasexual competition and, typically, overlapping territorial males and females pair into social monogamy on a shared breeding territory. Although this ultimately leads to assortitive mating by competitive ability, low quality females paired to low quality males may improve upon the quality of their genetic mate by engaging in extra-pair copulations. These data suggest that the process of mate acquisition in urban European blackbirds constrains the choice of social mate and so generates sexual selection pressures to drive mixed reproductive strategies during the breeding season.

PREDATOR ABUNDANCE AND PREDATION OF ARTIFICIAL NESTS IN NATURAL AND ANTHROPOGENIC CONIFEROUS FOREST EDGES IN SOUTHEAST ALASKA

Abstract Creation of forested edges in some landscapes can increase the risk of nest predation and consequently lower the reproductive success of forest passerines. This edge effect has not been well studied in western coniferous forests, particularly in southeast Alaska. In a series of artificial nest predation experiments, conducted in southeast Alaska between 1994 and 1997, we tested the risk of nest predation among open, edge, and interior forest habitats associated with natural (wetland) and anthropogenically created (clearcuts and suburbs) openings in coniferous north-temperate rainforest. We also censused known (Steller's Jays [Cyanocitta stelleri] and red squirrels [Tamiasciurus hudsonicus]) and probable nest predators (Common Ravens [Corvus corax] and Northwestern Crows [C. caurinus]). In general, higher nest predation was seen in habitats with the highest abundance of nest predators. Nests in wetland forest edges, where both jays and squirrels were detected frequently, were depredated more often...

LANDSCAPE FRAGMENTATION AND FOREST COMPOSITION EFFECTS ON GROUSE BREEDING SUCCESS IN BOREAL FORESTS

We examined the breeding success of forest grouse in relation to anthropogenic forest fragmentation in Finland. Employing Geographic Information Systems (GIS) and grouse data derived from Finnish wildlife triangle censuses conducted during 1989–1994, we combined the locations of 2267 Black Grouse (Tetrao tetrix) and 1060 Capercaillie (T. urogallus) females after the breeding season in mid-August with landscape data. The indicators of breeding success were the proportion of grouse hens with a brood and brood size. Two study areas (each 45 000 km2) in the boreal zone were selected for investigation. The breeding success of grouse was negatively correlated with both fragmentation of forest area per se by farmland and the decreasing proportion of older forest as a result of clear-cutting. The extent of landscape accounting best for variation in nesting success was an order of magnitude larger (∼100 km2) than the area most probably used by a grouse female and her brood during the summer, which suggests that landscape-scale factors may override local factors such as track size and distance from edge. The proportion of grouse hens with a brood was lower in heavily fragmented landscapes than in more continuous forest landscapes whereas only minor differences in brood size were detected. We suggest that the most likely cause of the observed spatial correlation was higher nest predation by generalist predators in fragmented forest landscapes. The effects of landscape composition on the breeding success of grouse were more marked in northern than in southern Finland, probably because predator populations are more food-regulated in the north. The diminished breeding success of forest grouse as a result of increased forest fragmentation is a probable cause of population declines in forest grouse species during the past decades in Fennoscandia.

INFLUENCE OF LANDSCAPE AND HABITAT CHARACTERISTICS ON OVENBIRD PAIRING SUCCESS

We investigated the influence of disturbance type (agriculture and silviculture) within forested landscapes, amount of forest cover within 1 km of the site, and local habitat characteristics on the pairing success of Ovenbirds (Seiurus aurocapillus) in central Pennsylvania during May and June 1998. Because areas with low pairing success often are inferred to have high nest predation, we also examined whether pairing and nesting success were correlated across sites. We determined the pairing status of 116 male Ovenbirds on 10 sites within contiguous mature forest. Percent of males that were paired on each site ranged from 54–92% (mean = 78%). Pairing success was negatively associated with forest cover within 1 km and positively associated with leaf litter depth. Percent bare ground also was positively correlated with forest cover within 1 km of the site. Estimates of pairing success were unrelated to Ovenbird nesting success at each site (based on 48 nests), which suggests that site-level differences in nest predation or reproductive potential are not necessarily associated with the ability of males to acquire mates. Our data suggest that pairing success of Ovenbirds in forested landscapes is not reduced by the amount of habitat loss within 1 km and is determined by local habitat rather than landscape characteristics.

Evolution of passerine incubation behavior: influence of food, temperature, and nest predation.

Incubation behavior is one component of reproductive effort and thus influences the evolution of life-history strategies. We examined the relative importance of body mass, frequency of mate feeding, food, nest predation, and ambient temperature to explain interspecific variation in incubation behavior (nest attentiveness, on- and off-bout durations, and nest trips per hour) using comparative analyses for North American passerines in which only females incubate. Body mass and frequency of mate feeding explained little variation in incubation behavior. We were also unable to detect any influence of foot; diet and foraging strategy explained little interspecific variation in incubation behavior. However, the typical temperature encountered during reproduction explained significant variation in incubation behavior: Species breeding in colder environments take shorter bouts off the nest, which prevents eggs from cooling to temperatures below the physiological zero temperature. These species must compensate for shorter off-bouts by taking more of them (thus shorter on-bouts) to obtain needed energy for incubation. Nest predation also explains significant variation in incubation behavior among passerines: Species that endure high nest predation have evolved an incubation strategy (long on- and off-bouts) that minimizes activity that could attract predators. Nest substrate explained additional variation in incubation behavior (cavity-nesting birds have shorter on-bouts and make more frequent nest trips), presumably because nest predation and/or temperature varies among nest substrates. Thus, nest predation can influence reproductive effort in a way previously not demonstrated--by placing a constraint on parental activity at the nest. Incubating birds face an ecological cost associated with reproductive effort (predation of entire brood) that should be considered in future attempts to explain avian life-history evolution.

Determinants of local recruitment in a growing colony of Audouin's gull

1. Local recruitment of Audouin's gull (Larus audouinii Payraudeau) was studied between 1988 and 1997 at the Ebro Delta colony (north‐western Mediterranean). Since its establishment in 1981, the colony has dramatically grown to include, in 1997, 65% of the total world population. Several hypotheses were tested, involving the effects of a badger predatory event in 1994, and sex, age and cohort (year of birth) on recruitment. 2. Results supported the prediction that colony size influenced recruitment: the probability for any individual to have previously bred increased throughout the study, together with colony size. At the end of the study, 90% of breeders aged 4 years had already been recruited at age 3, the age of first reproduction by Audouin's gulls. As expected by the dramatic increase of breeding numbers, most local recruitment occurred at very young ages, especially when compared with other Laridae. 3. Neither food availability nor reproductive success affected recruitment. Recruitment was not affected by high nest predation by the badger, although after the event, the proportion of Ebro Delta birds nesting on the nearby Columbretes Islands tripled. 4. Probability of first reproduction depended on age: it was the highest at ages 3 and 4, and then decreased sharply with age to stabilize beyond age 6 to a value depending on the year and cohort but always very low (&lt; 5%). Cohort and sex did not influence local recruitment. 5. Annual resighting rates ranged between 35% and 82%, and were higher for females. This may represent a sex‐dependent suspension of breeding, probably as a trade‐off between early recruitment and future survival.

EVOLUTION OF PASSERINE INCUBATION BEHAVIOR: INFLUENCE OF FOOD, TEMPERATURE, AND NEST PREDATION

Incubation behavior is one component of reproductive effort and thus influences the evolution of life-history strategies. We examined the relative importance of body mass, frequency of mate feeding, food, nest predation, and ambient temperature to explain interspecific variation in incubation behavior (nest attentiveness, on- and off-bout durations, and nest trips per hour) using comparative analyses for North American passerines in which only females incubate. Body mass and frequency of mate feeding explained little variation in incubation behavior. We were also unable to detect any influence of food; diet and foraging strategy explained little interspecific variation in incubation behavior. However, the typical temperature encountered during reproduction explained significant variation in incubation behavior: Species breeding in colder environments take shorter bouts off the nest, which prevents eggs from cooling to temperatures below the physiological zero temperature. These species must compensate for shorter off-bouts by taking more of them (thus shorter on-bouts) to obtain needed energy for incubation. Nest predation also explains significant variation in incubation behavior among passerines: Species that endure high nest predation have evolved an incubation strategy (long on- and off-bouts) that minimizes activity that could attract predators. Nest substrate explained additional variation in incubation behavior (cavity-nesting birds have shorter on-bouts and make more frequent nest trips), presumably because nest predation and/or temperature varies among nest substrates. Thus, nest predation can influence reproductive effort in a way previously not demonstrated—by placing a constraint on parental activity at the nest. Incubating birds face an ecological cost associated with reproductive effort (predation of entire brood) that should be considered in future attempts to explain avian life-history evolution.Corresponding Editor: E. Ketterson

The Relative Impacts of Nest Predation and Brood Parasitism on Seasonal Fecundity in Songbirds

The impacts of nest predation and brood parasitism on the seasonal fecundity of birds are strongly dependent on the number of nesting attempts, and thus seasonal fecundity is responsive to behavioral traits that increase the number of opportunities to nest. We developed simple models to investigate the relative impacts of nest predation and brood parasitism on seasonal fecundity in songbirds. In particular, we asked to what extent songbirds can ameliorate the negative effects of high nest predation and brood parasitism often typical of fragmented, urbanized, and agricultural landscapes through (1) renesting following predation, (2) abandoning and renesting following parasitism, and (3) double brooding—renesting following a successful brood. Our model assigned probabilities to all possible fates of breeding females and calculated seasonal fecundity by summing up the individual probabilities. We analyzed the model through the use of fecundity isopleths, which allow one to visually determine the impact of predation and parasitism simultaneously over the entire range of probabilities. Our analysis indicates that (1) nest predation has a greater impact on seasonal fecundity over a larger range of parameter space than does parasitism, especially when brood loss due to parasitism is low; (2) songbird populations experiencing nest predation probabilities typical of fragmented landscapes (&gt;0.65) are unlikely to be self‐sustaining; and (3) amelioration of nest predation through frequent renesting or double brooding may be insufficient to establish self‐sustaining populations. These results suggest that predator control should be at least as high a priority as parasitism control, particularly for species that suffer moderate to low brood reduction due to parasitism and that are single‐brooded. Programs aimed solely at managing cowbirds likely will be of limited success.

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.

Nistplatzwahl, Legeperiode und Bruterfolg des Rotkopfwürgers (Lanius senator) in Südfrankreich

Breeding habitats in Mediterranean France consist in open, dry grasslands with a low and discontinuous grass layer and scattered bushes and trees. The choice of nest supports was largely opportunistic, the most abundant suitable nest support type (bush or tree) and the most abundant species being present at each study site have been used. About 75% of the nests were placed at heights between 1 and 3 m. Laying period lasted from 9 May until 6 July (peak of first clutches: 21–30 May). Mean clutch size was 5.14±0.82 eggs (n=114). Breeding success was independent from the site, the height and the concealment of nests. Mean survival rate of nests from laying to fledgling was 0.365. The main cause of low breeding success was high nest predation exerted by a rich guild of predators. The species is mainly threatened through dramatic habitat shrinkage due to pastoralism reduction leading to closures of lightly bushed grasslands in Mediterranean France.