Validating the use of temperature data loggers to measure survival of songbird nests

ABSTRACT.   Accurate determination of nest fates and nest predators is possible through continuous video monitoring, but such monitoring is relatively expensive and labor intensive. If documenting of the timing of nest termination events is sufficient, then data loggers (DL) may allow more extensive sampling and may represent a viable alternative. I validated temperature DL records of nest survival time by simultaneous videotaping and compared results derived from DL records with those obtained by regular nest visits by an observer. I estimated the fate of 937 nests of nine species of open cup-nesting songbirds, including 673 nests monitored using DL, 165 monitored using video cameras, 33 validation nests monitored simultaneously using both DL and video cameras, and 132 control nests monitored only by observer visits. Deployment of DL did not negatively influence nest survival rate. DL reliably recorded survival time and allowed classification of nest fates based on the potential fledging age, regardless of the frequency of nest visits by an observer. The true fate of nests that survived beyond the potential fledging age can not be safely determined from time of failure, except for nocturnal events that suggest partial predation. Video revealed frequent partial or complete predation on nests with old nestlings that would have been categorized as successful by other methods. I conclude that temperature DL are efficient, reliable, and relatively inexpensive tools for recording exact nest survival times and classification of nest fates, with implications for nest survival modeling and discriminating between diurnal and nocturnal predation.     

No evidence for observer effects on Lark Sparrow nest survival

ABSTRACT Methods for monitoring bird nests might influence rates of nest predation, but the effects of various methods (e.g., visual markers and observer visitation rates) are often separately investigated among disparate avian taxa and geographic regions. Few investigators have explored the potential effects observers might have on nest success of grassland birds, despite concerns regarding population declines of these species in North America. We examined the possible effects of three monitoring techniques on daily nest survival of Lark Sparrows (Chondestes grammacus): (1) presence or absence of visible markers near nests, (2) observer visitation frequency, and (3) presence or absence of data loggers in nests. We monitored 113 Lark Sparrow nests during the 2009 breeding season. Of these nests, 88.5% failed due to predation, abandonment, weather, or unknown causes, yielding an overall nest success estimate of 9.8% based on daily survival estimation. Main effects of each monitoring technique appeared in top (ΔAICc <2) logistic exposure models. However, 95% confidence intervals around parameter estimates for each technique included zero, indicating no significant effects on daily nest survival. Our results suggest that the nest‐monitoring techniques we used had no effect on Lark Sparrow nest success and, if true, nest survival of other songbirds in arid grasslands of the Great Plains may also be unaffected by cautious nest monitoring. However, we cannot rule out the possibility that any effects of the various techniques in our study were masked by locally intense nest predation. Therefore, additional study is needed to determine if there may be observable variation in nest survival among various nest‐monitoring treatments in other areas of the southern Great Plains where nest predation is less frequent.     

Effects of leg flags on nest survival of four species of Arctic‐breeding shorebirds

Marking wild birds is an integral part of many field studies. However, if marks affect the vital rates or behavior of marked individuals, any conclusions reached by a study might be biased relative to the general population. Leg bands have rarely been found to have negative effects on birds and are frequently used to mark individuals. Leg flags, which are larger, heavier, and might produce more drag than bands, are commonly used on shorebirds and can help improve resighting rates. However, no one to date has assessed the possible effects of leg flags on the demographic performance of shorebirds. At seven sites in Arctic Alaska and western Canada, we marked individuals and monitored nest survival of four species of Arctic‐breeding shorebirds, including Semipalmated Sandpipers (Calidris pusilla), Western Sandpipers (C. mauri), Red‐necked Phalaropes (Phalaropus lobatus), and Red Phalaropes (P. fulicarius). We used a daily nest survival model in a Bayesian framework to test for effects of leg flags, relative to birds with only bands, on daily survival rates of 1952 nests. We found no evidence of a difference in nest survival between birds with flags and those with only bands. Our results suggest, therefore, that leg flags have little effect on the nest success of Arctic‐breeding sandpipers and phalaropes. Additional studies are needed, however, to evaluate the possible effects of flags on shorebirds that use other habitats and on survival rates of adults and chicks.     

Do alien predators pose a particular risk to duck nests in Northern Europe? Results from an artificial nest experiment

Several alien predator species have spread widely in Europe during the last five decades and pose a potential enhanced risk to native nesting ducks and their eggs. Because predation is an important factor limiting Northern Hemisphere duck nest survival, we ask the question, do alien species increase the nest loss risk to ground nesting ducks? We created 418 artificial duck nests in low densities around inland waters in Finland and Denmark during 2017–2019 and monitored them for seven days after construction using wildlife cameras to record whether alien species visit and prey on the nests more often than native species. We sampled various duck breeding habitats from eutrophic agricultural lakes and wetlands to oligotrophic lakes and urban environments. The results differed between habitats and the two countries, which likely reflect the local population densities of the predator species. The raccoon dog (Nyctereutes procyonoides), an alien species, was the most common mammalian nest visitor in all habitats and its occurrence reduced nest survival. Only in wetland habitats was the native red fox (Vulpes vulpes) an equally common nest visitor, where another alien species, the American mink (Neovison vison), also occurred among nest visitors. Although cautious about concluding too much from visitations to artificial nests, these results imply that duck breeding habitats in Northern Europe already support abundant and effective alien nest predators, whose relative frequency of visitation to artificial nests suggest that they potentially add to the nest predation risk to ducks over native predators.

     

Ineffectiveness of plastic mesh for protecting artificial freshwater turtle nests from red fox (Vulpes vulpes) predation

Invasive mammalian predators are efficient at driving native animal declines. The red fox (Vulpes vulpes) kills millions of endemic reptiles in Australia each year. In areas of south-eastern Australia, the eastern long-necked turtle (Chelodina longicollis) and Murray River turtle (Emydura macquarii) have declined by more than 50%. High rates of nest predation by foxes limit the recruitment of young turtles in these populations, but previous methods of fox control have been ineffective at protecting turtle nests. Here, we tested the effectiveness of plastic mesh for protecting artificial turtle nests from predation by foxes, in the mid-Murray catchment, Victoria. We also tested whether protecting a large number of artificial nests in a given area encourages foxes to give up foraging following predictions from giving-up density theory. We made a series of plots, each containing 32 artificial turtle nests. In each plot, we covered a percentage (0%, 25%, 50%, 81% or 100%) of the nests with either 1 or 2 sheets of plastic mesh. We used remote cameras to photograph and identify any predator that attacked nests in the plots. The cameras also allowed us to estimate the amount of time a fox was visible on each plot, as a metric of how much effort foxes expended on protected nests. Nest survival rate was not increased by either 1 or 2 sheets of mesh, and increasing the number of protected nests on a plot did not reveal a giving-up density (GUD) value for fox foraging behaviour. Our study demonstrates that plastic mesh is not effective for protecting artificial turtle nests from foxes in this region.     

Predation on artificial and natural nests in the lowland rainforest of Papua New Guinea

Capsule: Although survival of nests was similar between forest fragments and continuous forest, the range of predators differed. Artificial nests provide an under-estimate of nest predation by snakes.

Aims: To estimate the natural nest predation rate in continuous primary forest, compare it with predation rates in forest fragments. To assess the reliability of nest survival rates determined by the use of artificial nests with clay eggs and identify the main nest predators.

Methods: We observed survival of natural nests during the incubation period in continuous primary forest in Papua New Guinea. Some nests were monitored with infrared cameras. We also used artificial nests deployed with clay eggs to identify predators.

Results: There was a predation rate of 50% for natural nests and snakes were major predators of nest contents. Clutch daily survival rates (DSRs) differed among nest types. The DSR of artificial nests (0.977) was not significantly different to that of natural cup nests (0.969). Survival rates of artificial nests were similar in forest fragments and continuous forest. Forest fragments had, however, a higher proportion of avian predators than continuous forest.

Conclusion: Although, we observed similar survival rates in artificial and natural nests, the composition of nest predators was different between natural and artificial nests. Artificial nests were not suitable for estimating the real predation caused by reptiles. Nevertheless, we find that participation of avian nest predators can be estimated correctly with the use of artificial nests.     

Mortality of Wood Warbler Phylloscopus sibilatrix nests in Welsh Oakwoods: predation rates and the identification of nest predators using miniature nest cameras

Capsule Predation was the main cause of nest failure, but predation rates have remained unchanged since the 1980s. Eurasian Jays Garrullus glandarius were the most common predator.

Aims To quantify, and compare, nest predation rates for 1982–84 and 2009–11, and to identify predators of Wood Warbler Phylloscopus sibilatrix nests in Welsh oakwoods.

Methods During 2009–11, 167 Wood Warbler nests were monitored and purpose-built miniature nest cameras deployed at 73 of them. Nest predation rates were compared with 67 nests monitored during 1982–84.

Results Of 167 nests monitored from 2009 to 2011, 62 failed due to predation (32/73 camera nests, 30/94 non-camera nests), giving an overall Daily Survival Rate (DSR?±?se) of 0.979?±?0.003. This was not significantly different from the rate during 1982–84 (0.967?±?0.006). In 2009–11, the DSR of nests declined temporally during the season at both the egg and chick stages. For chick stage nests, DSR varied annually and nonlinearly with age of nestlings. There was no evidence for an effect of cameras at either stage. Of 32 camera nests lost to predation, the predator was identified from 28, resulting in 30 predators being identified. There was one case of multiple predators at a single nest. The majority of nest predation was carried out by birds (28/30), predominantly Eurasian Jays (18/28), but also Common Buzzards Buteo buteo (5/28), Great Spotted Woodpeckers Dendrocopos major (3/28) and Eurasian Sparrowhawks Accipiter nisus (2/28). There was one predation by both a Eurasian Badger Meles meles and a Red Fox Vulpes vulpes. There were no records of Grey Squirrels Sciurus carolinensis depredating nests.

Conclusions Nest predation rates were similar in both periods, suggesting that increased rates of nest predation have not been driving the decline of the Wood Warbler population in Wales. Deployment of nest cameras did not affect nest survival rates and were successful in identifying nest predators, the majority of which were avian, especially Eurasian Jays. Knowledge of the identity of nest predators can aid the development of conservation measures.     

Effects of environmental conditions on reproductive effort and nest success of Arctic‐breeding shorebirds

The Arctic is experiencing rapidly warming conditions, increasing predator abundance, and diminishing population cycles of keystone species such as lemmings. However, it is still not known how many Arctic animals will respond to a changing climate with altered trophic interactions. We studied clutch size, incubation duration and nest survival of 17 taxa of Arctic‐breeding shorebirds at 16 field sites over 7 years. We predicted that physiological benefits of higher temperatures and earlier snowmelt would increase reproductive effort and nest survival, and we expected increasing predator abundance and decreasing abundance of alternative prey (arvicoline rodents) to have a negative effect on reproduction. Although we observed wide ranges of conditions during our study, we found no effects of covariates on reproductive traits in 12 of 17 taxa. In the remaining taxa, most relationships agreed with our predictions. Earlier snowmelt increased the probability of laying a full clutch from 0.61 to 0.91 for Western Sandpipers, and shortened incubation by 1.42 days for arcticola Dunlin and 0.77 days for Red Phalaropes. Higher temperatures increased the probability of a full clutch from 0.60 to 0.93 for Western Sandpipers and from 0.76 to 0.97 for Red‐necked Phalaropes, and increased daily nest survival rates from 0.9634 to 0.9890 for Semipalmated Sandpipers and 0.9546 to 0.9880 for Western Sandpipers. Higher abundance of predators (foxes) reduced daily nest survival rates only in Western Sandpipers (0.9821–0.9031). In contrast to our predictions, the probability of a full clutch was lowest (0.83) for Semipalmated Sandpipers at moderate abundance of alternative prey, rather than low abundance (0.90). Our findings suggest that in the short‐term, climate warming may have neutral or positive effects on the nesting cycle of most Arctic‐breeding shorebirds.     

Do artificial nests reveal relative nest predation risk for real nests?

Present knowledge of the effects of nest predation on spatial distribution, habitat selection and community structure of birds is to a large extent based on results from experiments with artificial nests. Although nest predation risk is likely to differ between artificial and real nests, most previous studies of nest predation using artificial nests have been lacking a proper control. We investigated whether predation rates on artificial nests predicted those on real nests by simultaneously comparing the fate of real and artificial nests (containing quail Coturnix coturnix and plasticine eggs) in 92 territories of the northern wheatear Oenanthe oenanthe in 1996. We also investigated whether risk for artificial nests was related to relative average risk for real nests in these territories (based on data collected two years before and two years after the experiment). Nest predation on artificial nests did predict relative predation risk for real nests only when quail egg depredation was used as the criterion for artificial nest predation. Despite plasticine egg depredation being the most common type of predation it was not associated with predation risk for real nests. Small mice and vole species dominated among cases with only plasticine egg depredation, while predatory mammals and snakes destroyed most quail eggs in artificial nests and most eggs in real wheatear nests. The results suggest that artificial nests may only predict the risk for real nests when the nest predator species are similar among the two types of nest. Furthermore, our data suggest that small mice and vole species rarely depredate nests of mid-sized passerine birds . Our results cast doubt on many previous conclusions based on experiments with artificial nests, since predation risk for such nests is likely to be uncorrelated with risk for real nests due to nest-type-specific differences in nest preying species.     

Effects of Mesopredators on Nest Survival of Shrub-Nesting Songbirds

ABSTRACT Although nest predation is often the single largest source of mortality in avian populations, manipulative studies to determine predator impacts on nest survival are rare, particularly studies that examine impacts of mid-size mammalian predators (hereafter, mesopredators) on nest survival of shrub-nesting birds. We quantified nest survival and identified nest predators of shrub-nesting songbirds within 4 large (approx. 40-ha) exclosures and 4 control sites within a longleaf pine (Pinus palustris) ecosystem. During 2003–2006, we located and monitored 535 shrub nests (222 with videography) for 4,804 nest-days to quantify daily nest survival and document predation events. We found no support for a treatment effect, suggesting mesopredators had little impact on daily nest survival (0.9303 in controls and 0.9260 in exclosures) of shrub-nesting songbirds. For the 5 most commonly monitored species, daily nest survival within species was constant. Our analysis suggested that shrub nests were most vulnerable during the nestling stage and presence of cameras on nests increased survival with the increase in survival being more pronounced during the incubation stage. We filmed 107 nest predation events, identifying predators at 88 nests. Of these 88 nests, snakes caused 33%, red imported fire ants (hereafter fire ants, Solenopsis invicta) 28%, raptors 17%, corvids 8%, mesopredators 6%, and small mammals 8% of nest predations. Cause-specific nest predation in controls and exclosures did not differ from expectation, providing evidence that compensatory predation did not occur. Nest predators differed from expectation with regard to nest stage; fire ants and raptors only depredated nests during the nestling stage. Presence of cameras had no effect on nest abandonment. Fire ants were the most prevalent nest predator, and nest predation by fire ants was only observed on nestlings, potentially reducing likelihood of renesting. Magnitude and timing of fire ant predation suggests that fire ants may be the most influential nest predator of shrub-nesting birds within the longleaf pine ecosystem. Our data suggest that controlling mesopredators will have no effect on nest success of shrub-nesting birds within longleaf pine forests.     

Predators at bird nests in a northern hardwood forest in New Hampshire

ABSTRACT.   Nest predation is the primary cause of nest failure in most passerine birds, and increases in nest predation associated with anthropogenic habitat disturbance are invoked as explanations for population declines of some bird species. In most cases, however, the identity of the nest predators is not known with certainty. We monitored active bird nests with infrared time-lapse video cameras to determine which nest predators were responsible for depredating bird nests in northern New Hampshire. We monitored 64 nests of 11 bird species during three breeding seasons, and identified seven species of predators during 14 predation events. In addition, we recorded two instances of birds defending nests from predators and, in both cases, these nests were ultimately lost to predation. These results contrast with other studies in terms of the relatively high proportion of nests depredated by raptors and mice, as well as the absence of any predation by snakes. The diverse suite of predators in this and other studies is likely to confound our understanding of patterns of nest predation relative to fragmentation and habitat structure.     

Using egg flotation and eggshell evidence to determine age and fate of Arctic shorebird nests

ABSTRACT.   Egg flotation was used to estimate incubation age and eggshell evidence was collected to determine nest fate at nests of 11 species of shorebirds on the Arctic Coastal Plain of Alaska during 2002–2004. We present egg-flotation schedules for nine species to facilitate the estimation of nest age. We evaluated the predictive ability of an egg-flotation schedule for Semipalmated Sandpipers ( Calidris pusilla ) and were able to estimate incubation age within ∼1–3 d of the assumed age. Patterns of eggshell evidence were similar across species, with eggshell fragments (1–5 mm) present at most successful nests (96%) and eggshell tops or bottoms present only at successful nests. We determined nest fate independently of eggshell evidence and then used discriminant function analysis to predict the probability of correctly classifying a nest's fate using different types of eggshell evidence. The use of eggshell fragment evidence resulted in the correct classification of the fate of all 11 species of shorebirds in 92% of the cases. Both the egg-flotation technique and eggshell evidence can be used in future studies to calculate accurate measures of reproductive success needed for ecological investigations of shorebirds.     

Habitat selection,reproduction and predation of wintering lemmings in the Arctic

Snow cover has dramatic effects on the structure and functioning of Arctic ecosystems in winter. In the tundra, the subnivean space is the primary habitat of wintering small mammals and may be critical for their survival and reproduction. We have investigated the effects of snow cover and habitat features on the distributions of collared lemming (Dicrostonyx groenlandicus) and brown lemming (Lemmus trimucronatus) winter nests, as well as on their probabilities of reproduction and predation by stoats (Mustela erminea) and arctic foxes (Vulpes lagopus). We sampled 193 lemming winter nests and measured habitat features at all of these nests and at random sites at two spatial scales. We also monitored overwinter ground temperature at a subsample of nest and random sites. Our results demonstrate that nests were primarily located in areas with high micro-topography heterogeneity, steep slopes, deep snow cover providing thermal protection (reduced daily temperature fluctuations) and a high abundance of mosses. The probability of reproduction increased in collared lemming nests at low elevation and in brown lemming nests with high availability of some graminoid species. The probability of predation by stoats was density dependent and was higher in nests used by collared lemmings. Snow cover did not affect the probability of predation of lemming nests by stoats, but deep snow cover limited predation attempts by arctic foxes. We conclude that snow cover plays a key role in the spatial structure of wintering lemming populations and potentially in their population dynamics in the Arctic.     

Predation of experimental nests is linked to local population dynamics in a fragmented bird population

Artificial nest experiments (ANEs) are widely used to obtain proxies of natural nest predation for testing a variety of hypotheses, from those dealing with variation in life-history strategies to those assessing the effects of habitat fragmentation on the persistence of bird populations. However, their applicability to real-world scenarios has been criticized owing to the many potential biases in comparing predation rates of artificial and natural nests. Here, we aimed to test the validity of estimates of ANEs using a novel approach. We related predation rates on artificial nests to population viability analyses in a songbird metapopulation as a way of predicting the real impact of predation events on the local populations studied. Predation intensity on artificial nests was negatively related to the species' annual population growth rate in small local populations, whereas the viability of large local populations did not seem to be influenced, even by high nest predation rates. The potential of extrapolation from ANEs to real-world scenarios is discussed, as these results suggest that artificial nest predation estimates may predict demographic processes in small structured populations.     

Review and Meta-Analysis of Camera Effects on Avian Nest Success

ABSTRACT Identifying nest predators is critical to understanding predation pressures that birds face, and using surveillance cameras appears to be the most reliable method of nest predator identification. However, presence and methods of using camera equipment may introduce bias in predation rates. To summarize potential effects of cameras on nest success we reviewed published and unpublished studies that estimated daily nest predation for bird nests with and without surveillance cameras. We used meta-analyses to quantitatively synthesize the direction and magnitude of these effects from independent studies. We found evidence that, on average, use of camera equipment may reduce nest predation rates, although these differences were not always significant and varied relative to geographic regions, vegetation types, and study duration. Researchers using camera surveillance to monitor nests must be aware that the equipment may be affecting rates of predation and possibly biasing data collected on predator identity. Based on our review and analysis, we provide recommendations for researchers seeking to minimize or control for potential bias when using surveillance cameras to monitor nest predation.     

A predator's perspective of nest predation: predation by red squirrels is learned,not incidental

Nest predation has been used to explain aspects of avian ecology ranging from nest site selection to population declines. Many arguments rely on specific assumptions regarding how predators find nests, yet these predatory mechanisms remain largely untested. Here we combine artificial nest experiments with behavioural observations of individual red squirrels Tamiasciurus hudsonicus to differentiate between two common hypotheses: predation is incidental versus learned. Specifically, we tested: 1) whether nest survival could be explained solely by a squirrel's activity patterns or habitat use, as predicted if predation was incidental; or 2) if predation increased as a squirrel gained experience preying on a nest, as predicted if predation was learned. We also monitored squirrel activity after predation to test for evidence of two search mechanisms: area‐restricted searching and use of microhabitat search images. Contrary to incidental predation and in support of learning, squirrels did not find nests faster in areas with high use (e.g. forest edges). Instead, survival of artificial nests was strongly related to a squirrel's prior experience preying on artificial nests. Experience reduced nest survival times by over half and increased predation rates by 150–200%. Squirrels returned to and doubled their activity at the site of a previously preyed on nest. However, neither area‐restricted searching nor microhabitat search images can explain how squirrels located artificial nests more readily with experience. Instead, squirrels likely used cues associated with the nests or eggs themselves. Learning implies that squirrels could be increasingly effective predators as the density or profitability of nests increases. Our results add support to the view that nest predation is complex and broadly influenced (e.g. by predator experience, motivation), and is unlikely to be predicted consistently by simple relationships with predator activity, abundance or habitat.     

Using artificial nests to predict nest survival at reintroduction sites

Artificial nests are frequently used to assess factors affecting survival of natural bird nests. We tested the potential for artificial nests to be used in a novel application, the prediction of nest predation rates at potential reintroduction sites where exotic predators are being controlled. We collected artificial nest data from nine sites with different predator control regimes around the North Island of New Zealand, and compared the nest survival rates with those of North Island robin (Petroica longipes) nests at the same sites. Most of the robin populations had been reintroduced in the last 10 years, and were known to vary in nest survival and status (increasing/stable or declining). We derived estimates of robin nest survival for each site based on Stanley estimates of daily survival probabilities and the known incubation and brooding periods of robins. Estimates of artificial nest survival for each site were derived using the known fate model in MARK. We identified the imprints on the clay eggs in the artificial nests, and obtained different estimates of artificial nest survival based on imprints made by different potential predators. We then compared the value of these estimates for predicting natural nest survival, assuming a relationship of the form s = αpβ, where s is natural nest survival and p is artificial nest survival. Artificial nest survival estimates based on imprints made by rats (Rattus spp.) and brushtail possums (Trichosurus vulpecula) were clearly the best predictors (based on AICc), and explained 64% of the variation in robin nest survival among sites. Inclusion of bird imprints in the artificial nest survival estimates substantially reduced their predictive value. We suggest that artificial nests may provide a useful tool for predicting the suitability of potential reintroduction sites for New Zealand forest birds as long as imprints on clay eggs are correctly identified.     

Do seasonal patterns of rat snake (Pantherophis obsoletus) and black racer (Coluber constrictor) activity predict avian nest predation?

Avian nest success often varies seasonally and because predation is the primary cause of nest failure, seasonal variation in predator activity has been hypothesized to explain seasonal variation in nest success. Despite the fact that nest predator communities are often diverse, recent evidence from studies of snakes that are nest predators has lent some support to the link between snake activity and nest predation. However, the strength of the relationship has varied among studies. Explaining this variation is difficult, because none of these studies directly identified nest predators, the link between predator activity and nest survival was inferred. To address this knowledge gap, we examined seasonal variation in daily survival rates of 463 bird nests (of 17 bird species) and used cameras to document predator identity at 137 nests. We simultaneously quantified seasonal activity patterns of two local snake species (N = 30 individuals) using manual (2136 snake locations) and automated (89,165 movements detected) radiotelemetry. Rat snakes (Pantherophis obsoletus), the dominant snake predator at the site (~28% of observed nest predations), were most active in late May and early June, a pattern reported elsewhere for this species. When analyzing all monitored nests, we found no link between nest predation and seasonal activity of rat snakes. When analyzing only nests with known predator identities (filmed nests), however, we found that rat snakes were more likely to prey on nests during periods when they were moving the greatest distances. Similarly, analyses of all monitored nests indicated that nest survival was not linked to racer activity patterns, but racer‐specific predation (N = 17 nests) of filmed nests was higher when racers were moving the greatest distances. Our results suggest that the activity of predators may be associated with higher predation rates by those predators, but that those effects can be difficult to detect when nest predator communities are diverse and predator identities are not known. Additionally, our results suggest that hand‐tracking of snakes provides a reliable indicator of predator activity that may be more indicative of foraging behavior than movement frequency provided by automated telemetry systems.     

Testing the importance of nest concealment: does timing matter?

ABSTRACT.   Nest concealment by vegetation is considered an important factor affecting predation rates for many passerines and, therefore, is frequently measured in studies examining nest predation. However, the time when concealment measurements are made may affect the results of such studies, particularly in highly seasonal ecosystems where characteristics of the vegetation later in the breeding period may differ considerably from those at the time of nest-site selection. We used artificial nests baited with quail ( Coturnix sp.) eggs in a highly seasonal tropical dry forest in Jalisco, western Mexico, to test the effects of seasonal change in concealment on nest predation. We placed 40 open-cup, artificial nests in shrubs at the end of the dry season and again at the beginning of the rainy season in 2007, and monitored the fate of the nests and the degree of concealment by vegetation during both periods. Nest concealment was significantly greater during the wet season than during the dry season. The percentage of nests predated was marginally higher during the dry (100%) than the wet (72.5%) season, and daily nest survival was lower during the dry than the wet season. Our results suggest that, in highly seasonal environments such as tropical dry forests, delayed measurement of nest concealment after nest completion rather than during nesting may constitute a significant source of error.     

Nest predators of Lance-tailed Manakins on Isla Boca Brava, Panamá

ABSTRACT.   Nest predation is often the primary cause of nest failure for passerines. Despite this, little is known about predation rates and the nest predators of birds in the tropics. I used video cameras to monitor seven Lance-tailed Manakin ( Chiroxiphia lanceolata ) nests on Isla Boca Brava, Panamá. One nest fledged young and six nests failed due to predation. I recorded five predation events involving four avian predators and one mammalian predator. Crested Oropendolas ( Psarocolius decumanus ) predated two nests and a Roadside Hawk ( Buteo magnirostris ) and a Black-chested Jay ( Cyanocorax affinis ) each predated one. The mammalian predator was a common opossum ( Didelphis marsupialis ). All avian predation was diurnal; the mammalian predation was nocturnal. My results suggest that tropical birds are subject to a diverse suite of nest predators, and that avian predators may be an important cause of nest failure at my study site.