Eggs In Nests Research Articles

Importance of Costs in Target Date Fund Selection Using Three Morningstar Ratings

Although target date mutual funds (TDFs) have only been around since the mid-1990s, they are now common vehicles for retirement investing. Sixty percent of US companies now automatically funnel employees’ non-directed retirement funds into TDFs, which account for nearly one-quarter of all savings US workers have in 401(k)s. Helping investors pick among TDFs, Morningstar rates past risk-adjusted performance using a star system and provides forward-looking evaluations of more than 2,500 TDFs using either Analyst Ratings or a newly implemented machine-learning-based Quantitative Ratings. Morningstar assigns Analyst Ratings to a smaller subset of TDFs that tend to have been in existence the longest and have the largest size. We find that TDFs with lower fees have significantly higher star ratings than their higher expense counterparts. No-load TDFs have significantly higher star ratings than their load-charging counterparts. In assessing future fund prospects, TDFs with low expense ratios are favored by both analysts and artificial intelligence. TDFs without load charges have significantly better Quantitative Ratings than their load charging counterparts. TDFs with Quantitative Ratings tend to be smaller, younger, and have poorer prior performance than TDFs with Analyst Ratings. <b>TOPICS:</b>Long-term/retirement investing, mutual funds/passive investing/indexing, information providers/credit ratings <b>Key Findings</b> ▪ Target date funds (TDFs) with low expenses and without load charges have significantly higher Morningstar star ratings of past risk-adjusted performance. These same low-cost funds have higher Morningstar Analyst ratings and Quantitative ratings, which estimate future fund prospects of performance. ▪ Regression results suggest Morningstar’s two forward-looking fund ratings are not perfect substitutes. Analyst ratings weight fund expense and fund age more heavily (both negatively) while the computer-generated Quantitative ratings are more positively influenced by past fund performance. ▪ Morningstar’s star ratings, Analyst ratings, and Quantitative ratings all suggest that retirement investing will result in a larger nest egg when attention is restricted to no-load, low-expense TDFs. Additionally, the ratings suggest investors should favor larger but relatively younger funds.

Carcasses attract invasive species and increase artificial nest predation in a desert environment

In addition to feeding on animal remains, many scavengers also function as predators. Carcasses may therefore affect local animal communities by attracting facultative scavengers and increasing predation risk for other species in the vicinity of the carcasses. This risk may be elevated in low productivity environments, especially where humans increase carcass production and where facultative scavengers include invasive species. In June and October 2018, we monitored experimentally placed red kangaroo (Osphranter rufus) carcasses and artificial bird nests in two different habitats in the Simpson Desert, Australia, to identify the nest predators attracted to the carcasses, and to determine how carcasses affect overall and predator-specific nest predation. We modelled our nests to approximate those of the ground nesting little buttonquail (Turnix velox) and the endangered night parrot (Pezoporus occidentalis). Native Corvus spp. and then invasive red foxes (Vulpes vulpes) were the top carcass visitors and nest egg predators. Carcass presence and open habitat increased overall nest predation and fewer artificial parrot nest eggs were depredated compared to those of quail. Open habitat and carcass presence only increased predator-specific nest predation by foxes, but corvid nest predation was highest in June 2018, and for the artificial quail nest types. Foxes were the main predator of eggs from night parrot nests. Our study shows that carcass provisioning by humans may have indirect, deleterious effects on ground nesting birds, and indicates that foxes might pose a greater threat to night parrot populations than previously recognised.

Cryptic eggs are rejected less frequently by a cuckoo host.

Obligate brood parasitism is associated with huge reproduction costs, forcing hosts to evolve various anti-parasitic strategies against brood parasites, among which egg recognition and rejection is the most effective defense strategy. According to the crypsis hypothesis, non-mimetic yet cryptic eggs in a nest can also deceive their hosts and eventually be accepted. To validate this hypothesis, we conducted field experiments on Oriental reed warblers (Acrocephalus orientalis), a common host for common cuckoos (Cuculus canorus). We firstly tested the egg recognition and rejection abilities of Oriental reed warblers, using black and white model eggs in natural nests. Then we designed a comparison test where the cryptic effects of the two groups of experimental eggs were different. We manipulated the nest lining color and added relatively cryptic and bright model eggs to test warblers' rejection behaviors against cryptic and bright foreign eggs. The results showed that warblers have strong egg recognition and rejection abilities. There is a significant tendency for warblers to prefer to peck and reject relatively distinguishable foreign eggs, which supports the crypsis hypothesis. These findings indicate that even in the host-parasite system of open nests, parasitic eggs that are cryptic enough are prevented from being discovered and rejected by the host, and thus obtain the possibility of successful parasitism.

Does experimentally simulated presence of a common cuckoo (Cuculus canorus) affect egg rejection and breeding success in the red-backed shrike (Lanius collurio)?

Providing artificial eggs is a commonly used technique to understand brood parasitism, mainly by the common cuckoo (Cuculus canorus). However, the presence of a cuckoo egg in the host nest would also require an earlier physical presence of the common cuckoo within the host territory. During our study of the red-backed shrike (Lanius collurio), we tested two experimental approaches: (1) providing an artificial “cuckoo” egg in shrike nests and (2) additionally placing a stuffed common cuckoo with a male call close to the shrike nest. We expected that the shrikes subject to the additional common cuckoo call stimuli would be more sensitive to brood parasitism and demonstrate a higher egg rejection rate. In the years 2017–2018, in two locations in Poland, a total of 130 red-backed shrike nests were divided into two categories: in 66 we added only an artificial egg, and in the remaining 64 we added not only the egg, but also presented a stuffed, calling common cuckoo. Shrikes reacted more strongly if the stuffed common cuckoo was present. However, only 13 incidences of egg acceptance were noted, with no significant differences between the locations, experimental treatments or their interaction. Analysis of breeding success revealed significant differences between the locations, between experimental treatments and their interaction, which suggests a strong location effect. The red-backed shrike is an efficient rejector of foreign eggs. It would be interesting to see how similar tests affect hosts that have much higher rates of brood parasitism and egg acceptance.

Pairing status moderates both the production of and responses to anti‐parasitic referential alarm calls in male yellow warblers

AbstractDefending offspring incurs temporal and energetic costs and can be dangerous for the parents. Accordingly, the intensity of this costly behavior should reflect the perceived risk to the reproductive output. When facing costly brood parasitism by brown‐headed cowbirds (Molothrus ater), where cowbirds lay eggs in heterospecific nests and cause the hosts to care for their young, yellow warblers (Setophaga petechia) use referential “seet” calls to warn their mates of the parasitic danger. Yellow warblers of both sexes produce this call only in response to cowbirds or seet‐calling conspecifics. Seet calls are mainly produced during the laying and incubation stages of breeding, when risk of brood parasitism is highest, rather than during the nestling stage. On the other hand, general alarm calls (chips) are produced throughout the nesting cycle and are also used in conspecific interactions unrelated to nesting. We hypothesized that context shapes responses prior to breeding as well, such that yellow warblers without a mate and active nest would be less likely to respond to playbacks that simulate brood parasitism risk. To test this hypothesis, we presented playbacks of two nest threats, cowbirds (brood parasite) and blue jays (Cyanocitta cristata; nest predator), on territories of unmated male warblers (unpaired) and male warblers with a known mate (paired). We found that unpaired males were unresponsive toward playbacks indicating nest threats, whereas paired males were significantly more aggressive and vocal toward these playbacks compared to control playbacks. However, both paired and unpaired males were vocally responsive toward chip calls, which are informative for males regardless of pairing status. Male yellow warblers appear to adjust their responses during the earliest stages of breeding depending on the contextual relevance of specific threat stimuli, and together with prior studies, our work further supports that referential seet calls are associated with stage‐specific risk of brood parasitism.

High egg rejection and low aggressive responses of Mountain Bluebirds (Sialia currucoides) toward Brown-headed Cowbirds (Molothrus ater)

Hosts of brood parasitic Brown-headed Cowbirds (Molothrus ater) have acquired a suite of behavioral responses against them, including egg rejection and nest defense. Several cavity-nesting species have been shown to exhibit egg rejection, including the Mountain Bluebird (Sialia currucoides). Previous work reported egg rejection rates as low as 20%, under the assumption that they may instead be relying heavily on aggressive interactions to defend their nests from parasitism. In the present study, we evaluated the egg rejection and aggression behaviors of a population of Mountain Bluebirds in western Montana. Results indicate a higher rate of rejection than previously documented, with model cowbird eggs rejected in over 40% of trials (n = 37), compared with 5% rejection of mimetic eggs. In contrast, we found little aggressive response by Mountain Bluebirds toward both an adult cowbird model and a nonthreatening American Goldfinch (Carduelis tristis) model. Aggression patterns were consistent between sexes, with the most common behaviors including sitting and watching from within 5 m and flying past the models (n = 21). Hovering above the model was observed on a few occasions, and physical contact by bluebirds happened on only 3 occasions toward the goldfinch model. In summary, Mountain Bluebirds in western Montana showed relatively high rates of cowbird egg rejection but little aggressive response toward adult heterospecific nest intruders.

Larvae of the blow fly Caiusa testacea (Diptera: Calliphoridae) as egg predators of Polypedates cruciger Blyth, 1852 (Amphibia: Anura: Rhacophoridae)

We investigated the impact of dipteran predators on eggs in foam nests of the Common Hour-glass Tree Frog Polypedates cruciger Blyth, 1852 (Anura: Rhacophoridae) in central Sri Lanka. Foam nests (n=24) of P. cruciger were examined at their natural breeding habitats and infected (n=8) and uninfected spawns (n=16) were identified. Emerging tadpoles were collected in a water container hung under each spawn and the average number of tadpoles (N) hatched from infected spawns (N=0) was compared with that of uninfected spawns (N=354 ± 67). Three severely infected spawns were brought to the laboratory and the fly larvae were reared until they metamorphosed to adults. Morphological and molecular identification of the flies confirmed them as belonging to Caiusa testacea Senior-White, 1923 of the family Calliphoridae. The infected spawns were completely destroyed and an estimated average of 400 P. cruciger eggs per spawn were lost. The results revealed a high impact of Caiusa testacea on egg and embryo mortality of P. cruciger.

Does human hair attract or deter potential ground nest predators?

Abstract The nests of rare and threatened bird and reptile species that breed on the ground are often attempted to be protected from predators with fences, grids, and various repellent materials. Results of some experiments refer to the repellent function of human scent, whereas others suggest that it has an attractive role. We aimed to investigate how effectively ground nests can be protected from predators if human hair is placed around nests. We performed the experiment in a riverine oak-elm-ash forest using 90 artificial nests, each with 1 quail and 1 plasticine egg: 30 nests were protected with a game fence, 30 nests were surrounded with human hair and 30 nests were unprotected (control). During the 24 days, predators damaged 23% of the nests protected by a game fence, 40% of unprotected nests and 47% of the nests surrounded with hair. The daily survival rate of quail eggs in nests protected with a game fence was significantly higher than the ones in the nests surrounded with human hair. Only 18% of the quail eggs and 36% of plasticine eggs were damaged. Such difference can be explained by the fact that small-bodied birds and mammals could pass through the game fence and left traces on plasticine eggs but they were unable to crack the shell of quail eggs. Within the game fence, denser vegetation can provide better nesting conditions and result in greater breeding success. The repellent role of human hair has not been proved, on the contrary, in some cases we have observed signs of its attractant role, such as small-bodied birds took hair away for nest building.

P class="ZootaxaTitle"First description of immature stages of Gastropini, Gastrops willistoni Cresson (Diptera: Ephydridae) preying on eggs in a foam nest of Leptodactylus knudseni Heyer (Anura: Leptodactylidae) in Central Amazon.

The third instar larva and puparium of Gastrops willistoni Cresson (Diptera: Ephydridae), preying on eggs in a foam nest of Leptodactylus knudseni Heyer (Anura: Leptodactylidae), in a central Amazonian dryland forest (Brazil) are described for the first time. The fusiform larva has a short breathing tube, its anterior spiracles are fan-shaped and posterior spiracles with three spircular openings. Pupa is ovoid with a broad anterior margin and bifurcate posterior tip. The taxonomic relationship of the frog egg predators, Gastrops Williston and Typopsilopa Cresson, are discussed.

Validating an Unmanned Aerial Vehicle (UAV) Approach to Survey Colonial Waterbirds

Unmanned aerial vehicles (UAVs) can improve detection and count accuracy of avian species and provide an inexpensive alternative to surveying waterbirds compared to ground counts and other aerial methods. To validate this method for surveying colonial waterbirds in logistically challenging areas, we compared counts from images collected with a fixed-wing UAV to ground counts using a marked-subsample method or direct counts at three study sites: 1) in an open field using decoys that represented three colonial waterbird species; 2) constructed platforms in a swamp with colonial nesting Great Egrets (Ardea alba); and 3) an island with a large nesting colony of Brown Pelicans (Pelecanus occidentalis). Estimates or direct counts from UAV images were not significantly different from a known number of decoys or ground counts for Great Egrets but were almost twice as high compared to ground counts for juvenile Brown Pelicans. UAV flights did not cause either Great Egrets or Brown Pelicans to flush from nesting areas while ground surveys flushed the majority of adult Brown Pelicans from the survey area. UAV surveys captured images of eggs in nests that could not be observed by ground surveyors. Our results indicate that UAVs can provide a cost-effective and efficient method of surveying waterbirds with similar or improved results and little disturbance of colonies compared to ground counts.

Genetic patterns of repeat and multiple parasitism by screaming cowbirds, a specialist brood parasite

Avian brood parasites lay their eggs in the nests of other species, leaving the hosts to care for the parasitic offspring. The bookkeeping hypothesis predicts that, in order to reduce competition between parasitic nestlings, female parasites should keep a mental inventory of host nests that they have already parasitized and avoid laying multiple eggs in the same host nest. However, selection against repeat parasitism should be weaker when host nests are limited, or when hosts are able to rear more than one parasitic nestling. Here we use microsatellite genotyping of parasitic eggs to test whether female screaming cowbirds, Molothrus rufoaxillaris, avoid repeatedly parasitizing nests of their primary host, the greyish baywing, Agelaioides badius, in Argentina. Parasitism rates were extremely high (96.5% of 57 host clutches were parasitized with an average of 5.7 cowbird eggs each), indicating that host nests are limited. Although eggs laid by the same female showed moderate spatiotemporal clustering, individual females rarely laid more than one egg in the same host clutch (2 of 57 clutches, 26 of which contained multiple genotyped cowbird eggs). Females were much more likely to lay subsequent eggs in different host nests than to return to the same host nest. We found no evidence for kin structure among female cowbirds parasitizing the same host nest, which were no more closely related than chance would predict. These results suggest that female screaming cowbirds frequently lay eggs in host nests that have already been parasitized by unrelated females. However, they typically lay just one egg per host clutch, even though greyish baywings are capable of rearing several nestlings. Since screaming cowbird laying is often poorly synchronized with that of their host, avoidance of repeat parasitism may be adaptive if it allows females to spread the risk of failure among multiple host nests.

Regulation of Folliculogenesis by Growth Factors in Piglet Ovary Exposed Prenatally to β-Hydroxy-β-Methylbutyrate (HMB)

Abstract Β-hydroxy-β-methylbutyrate (HMB) is one of the leucine metabolites with protein anabolic effects which makes it very popular among athletes. Previously, it was shown that HMB administered during the prenatal period reduced the pool of primordial follicles and increased the proportion of developing follicles in newborn piglets. This work is a further step to understand these morphological alterations. Therefore, the aim of this study was to examine the effect of prenatal HMB treatment on the expression of the Kit ligand, BMP-4, bFGF, and the IGF-1/IGF-1R system which are the main growth factors controlling follicular development. Excised ovaries from 12 newborn piglets, originated from the control (n=6) and HMB-treated (n=6) sows were used for immunohistochemical and western-blot analysis. The tested proteins were localized within egg nests and ovarian follicles. Furthermore, the western-blot assay indicated higher BMP-4, Kit ligand, and IGF-1R expression, while the level of bFGF and IGF-1 proteins decreased after HMB dietary treatment. These findings show that HMB included into sow diet can modulate the expression of growth factors and thereby alter ovarian morphology in offspring. Therefore, this study opens a discussion about the benefits and risks of the diet supplemented with HMB and its potential application in medicine and animal husbandry, and further research is necessary in this area.

Cuckoos use host egg number to choose host nests for parasitism.

To maximize their offspring success common cuckoo (Cuculus canorus) females should lay their eggs into host nests before incubation has begun. This ensures that the parasite chick hatches before all host chicks and can evict its foster siblings to monopolize host parental care. Many studies have demonstrated that most cuckoo eggs are indeed laid before the onset of host incubation. But cues used by female cuckoos to choose the right nest at the right time remain unclear. Here, we combine field observations with a field experiment to test whether female cuckoos use the number of eggs in the nests of their Oriental reed warbler (Acrocephalus orientalis) hosts to direct their choice. Over 8 years of field observations and 5 years of experiments, cuckoo females placed the majority of their eggs in nests with fewer than three host eggs, i.e. early in the laying sequence. For natural nests, the cuckoos may use information gleaned from the activity and behaviour of the host parents to make their choice. In our sets of experimental nests containing different numbers of model eggs, the vast majority of parasitism events occurred in nests containing a single egg. To our knowledge, this is the first field experiment showing that cuckoos choose host nests for parasitism based on the number of host eggs they contain. It appears that cuckoo females use the egg number to estimate the appropriate host nest stage for timely parasitism.

A Novel Network Flow Prediction Method based on Cuckoo Search Algorithm Optimizing BP Neural Network

Network traffic modeling and forecasting is the basis of network management and security warning. According to the characteristics of the nonlinear network flows, chaos, polygon, etc., in order to improve the prediction accuracy of network traffic, and puts forward the a cuckoo search cable calculation method and BP neural network by network traffic prediction model, BP neural network is used by the network of the learning sample book training, die quasi cloth Valley bird found nest eggs to find the optimal model parameters and the mining network flow number in simulation experiment according to measure the trial model of can. Simulation results show that compared with the reference model, CS-BPNN improves the prediction accuracy of network traffic, network traffic trends are described more accurately, provides a new research tool with network traffic prediction.

Communal egg‐laying behaviour and the consequences of egg aggregation in the brown anole (Anolis sagrei)

AbstractCommunal nesting is a behaviour that involves multiple females laying eggs in the same nest or nesting site. This behaviour may be a consequence of a shortage of preferable nest sites (constraint hypothesis) or an adaptation generated by fitness benefits associated with egg aggregation (adaptive hypothesis). Experimental tests of these hypotheses require information about maternal nest site choice and its fitness consequences. To address these, we studied a lizard (brown anole; Anolis sagrei) that produces single‐egg clutches, but often aggregates eggs in nest sites. In a lab study, females were given the option of nesting in (a) soil previously used as nest substrate vs. fresh soil and (b) soil with eggshells vs. without eggshells. We also experimentally examined the effects of egg aggregation by incubating eggs singly, in groups of four, and in groups of nine. We recorded egg surface temperature, water uptake, and hatchling morphology. Females were more likely to nest in pots with used soil and with eggshells than in pots with fresh soil or without eggshells. We observed no effects of egg aggregation on egg survival, egg temperature, or most measures of hatchling morphology. However, singly‐incubated eggs absorbed more water than eggs incubated in the four and nine egg aggregations and this resulted in offspring with greater body condition (i.e. heavier for their length) at hatching. The behavioural experiment demonstrates that females actively choose nest sites that have been used previously (as expected under the adaptive hypothesis), but the egg‐aggregation experiment shows no benefits to offspring based on the variables measured. Thus, results of the behaviour study support the adaptive hypothesis; however, results from our egg‐incubation study do not. Likely, the adaptive and constraint hypotheses are not mutually exclusive, and a diversity of factors influence the evolution of communal nesting behaviour.

Practical Applications of The Unrealistic Optimism That Threatens Retirement Security

<h3>Practical Applications Summary</h3> In <b><i>The Unrealistic Optimism That Threatens Retirement Security</i></b>, from the Fall 2019 issue of <b><i>The Journal of Retirement</i></b>, author <b>Alfred Rappaport</b> of <b>Northwestern University</b> details the retirement crisis facing Americans today. Fewer employers are offering lifetime pensions, and nearly half of American families have no retirement savings—but most Americans believe they are on track to a comfortable retirement. This unrealistic optimism comes from the fact that Americans underestimate their expenses in retirement while overestimating how much their investments will grow once they start saving. Investors often assume they will realize high rates of return in line with historical growth rates. However, they often sabotage their retirement nest egg’s potential by failing to reinvest dividends, and by investing when the market is high and selling when the market is low. Investors also often fail to factor in investment fees, inflation, and taxes. The author gives investors a reality check, providing tools that show how these factors cut into retirement savings over time. Financial advisors can use these tools to educate their clients and create retirement savings plans that are free of unrealistic optimism. <b>TOPICS:</b>Wealth management, retirement, pension funds, portfolio theory

The effect of parachlorophenylalanine treatment on the activity of gonadal and lactotrophic axes in native Polish crested chickens stimulated to broodiness

Brooding behavior, a common characteristic of native breeds of the domestic chicken, is marked by elevated prolactin (PRL) levels, which is necessary for incubation and connected with changes in hypothalamic–pituitary–gonadal axis activity. Evidence indicates the serotoninergic system is a potent modulator of PRL secretion. The objective of this study is to investigate whether blocking serotonin synthesis with parachlorophenylalanine (PCPA) prevents incubation behavior in native Polish crested chickens. In addition, we examined the effect of PCPA on the gene expression of the gonadal and lactotrophic axes. Birds were stimulated to broodiness by artificial eggs in nests. At 34 wk of age (April: spring period), the hens were divided into 2 groups (14 hens in each group): control and PCPA-treated (50 mg/kg BW) group. After 5 wk of treatment, the artificial eggs were removed from the nests. Egg production, incubation activity, and levels of plasma ovarian steroids progesterone (P4), testosterone (T), estradiol (E2), and PRL were examined. At the end of the experiment (45 wk of age, June: summer period), ovarian characteristics and mRNA gene expression of gonadal (gonadotropin-releasing hormone [GnRH] I, luteinizing hormone [LH] ß, follicle-stimulating hormone [FSH] ß) and lactotrophic (vasoactive intestinal peptide [VIP], PRL) axes were measured by quantitative real-time PCR. Incubation activity was observed in the hens of both groups but with lower frequency in PCPA-treated birds. Moreover, the PCPA group had a higher cumulative egg production than the controls. During the first six and 8 wk of the experiment, levels of P4 and E2, respectively, were similar in both groups, but all concentrations increased in the PCPA-treated hens after this period. In addition, increased GnRH-I, LHß, and FSHß and decreased VIP mRNA expression was observed in the PCPA group compared with the controls. There were no differences in PRL mRNA expression, the PRL level, and ovarian morphometry between the 2 groups. These results indicate that blockage of serotonin synthesis by PCPA does not effectively prevent incubation in native Polish crested chickens. However, treatment with PCPA increased gonadal axis activity and improved reproductive performance.

Shared transcriptional responses to con- and heterospecific behavioral antagonists in a wild songbird

The recognition of and differential responses to salient stimuli are among the main drivers of behavioral plasticity, yet, how animals evolve and modulate functional responses to novel classes of antagonistic stimuli remain poorly understood. We studied free-living male red-winged blackbirds (Agelaius phoeniceus) to test whether gene expression responses in blood are distinct or shared between patterns of aggressive behavioral responses directed at simulated conspecific versus heterospecific intruders. In this species, males defend territories against conspecific males and respond aggressively to female brown-headed cowbirds (Molothrus ater), a brood parasite that commonly lays eggs in blackbird nests. Both conspecific songs and parasitic calls elicited aggressive responses from focal subjects and caused a downregulation in genes associated with immune system response, relative to control calls of a second, harmless heterospecific species. In turn, only the conspecific song treatment elicited an increase in singing behavior and an upregulation of genes associated with metabolic processes relative to the two heterospecific calls. Our results suggest that aspects of antagonistic behaviors to both conspecifics and brood parasites can be mediated by similar physiological responses, suggestive of shared molecular and behavioral pathways involved in the recognition and reaction to both evolutionarily old and new enemies.

Consequences of a changing environment on the breeding phenology and reproductive success components in a long‐distance migratory bird

AbstractMigratory birds have a narrow time window to breed, especially in the Arctic, where early nesting typically yields the highest reproductive success. We assessed temporal changes (1991–2015) in reproductive success components in relation to timing of breeding in greater snow geese (Chen caerulescens atlantica). This species breeds in the Canadian Arctic, a region that has experienced a strong warming trend. We tested the effect of laying or hatching date, year and their interaction on six reproductive components: Total clutch laid, nesting success, egg survival, hatching success, prefledging, and postfledging survival. Over 25 years, mean laying date changed little, even though it advanced 1.8 days in early breeders and was delayed 3 days in late breeders. Likewise, the number of eggs in nests initiated early in the season decreased by 0.6 egg, whereas in late nests it increased by 0.3 egg. Success of nests initiated early and late in the season was lower than nests initiated near the population mean, and consistently increased over time. The proportion of eggs surviving to partial predation and postfledging survival decreased with laying date but the pattern did not change over time. In contrast, prefledging survival was not affected by laying date initially but declined in nests initiated late in the season toward the end of the study. Overall, nests initiated close to the population mean showed little temporal change for most components of reproductive success and seem to be less affected by environmental change than nests initiated early and late in the season.

Conspecific brood parasitism in an upland-nesting bird: cues parasites use to select a nest

Among birds exhibiting conspecific brood parasitism (CBP), parasites demonstrate a variety of intriguing tactics for selecting a host nest, including preference for safe nests (i.e., avoiding nests depredated during the previous season). Brood parasites of birds that do not reuse nest sites, however, are limited to nest-site information available to them during the current breeding season. This study explores cues used by brood parasites in a population of red-breasted mergansers nesting in upland vegetation and sandy substrate that prohibits reuse of nest sites in consecutive years. Nest-site and host traits were measured for 33 parasitized and 23 non-parasitized nests. There was no association between CBP and nest-site traits potentially providing cues about nest safety from avian predators (concealment and density of nesting larids), likely due to very low rates of egg predation. Distance to shore for parasitized nests was slightly greater than for unparasitized nests. Parasites did not select nests in relation to host age, mass, date of nest initiation, or stage of nesting (laying or incubation). Artificial nests were used to simulate natural nests without a host and to assess whether host presence serves as a cue for parasites. The proportion of natural nests receiving ≥ 1 foreign egg (60% of 15 nests) was thrice that for artificial nests (21% of 14 nests). Some aspect of host presence may therefore be an important, but not necessary, cue for brood parasites targeting nests that are heavily concealed in uplands. Whenever brood parasitism is a well-developed component of reproduction, selection is expected to favor brood parasites that make use of environmental or social information allowing them to discriminate among host nests and maximize reproductive success. We assessed cues used by brood parasites in ground-nesting red-breasted mergansers for which conspecific brood parasitism (CBP) is common, and nests are well concealed in upland vegetation. Observations at parasitized and unparasitized nests revealed that nest-site safety and visibility from habitat edges are not central to laying decisions by parasites in this population. Brood parasites, however, were considerably more likely to lay their eggs in natural nests with a host than in artificial nests without a host, suggesting that some aspect of host presence is important in the nest-site selection process for parasites. The ability of brood parasites to discriminate among nests based on host presence is expected to affect parasite success because individuals can avoid nests in which their eggs are doomed to fail (e.g., abandoned nests).