Non-parasitized Nests Research Articles

Owens Valley nesting willow flycatcher under pressure

Willow flycatchers (Empidonax traillii; WIFL) nest along the Owens River and Horton Creek in the Owens Valley. Migrating WIFL visit these sites as well as many other tributaries to both the Owens River and Mono Lake. We estimate there are approximately 35 WIFL territories in the Owens valley, or 5% of territories in California. Nesting WIFL in the Owens Valley are likely the federally endangered southwestern subspecies (E. t. extimus; SWIFL). The Chalk Bluff nesting site is particularly important as large nesting areas tend to be both rare and important for SWIFL and it contains more than half (63%) of all known WIFL territories in the region, which also represents 12% of all nesting SWIFL in California. Between 2014 and 2016, WIFL territory numbers declined from 37 to 27 across the three largest breeding sites. Territory numbers may have been influenced by drought conditions or brown-headed cowbird (Molothrus ater; BHCO) nest parasitism. In 2015 and 2016, comprehensive nest monitoring found nest parasitism rates were >40%, and nest success was lower in parasitized nests (16%; N = 5/31) compared with non-parasitized nests (60%; N = 31/52). BHCO management could potentially improve nest success for WIFL as well as many other open-cup nesting riparian birds in the Owens Valley.

Effect of introduced parasites on the survival and microbiota of nestling cactus finches (Geospiza scandens) in the Galápagos Islands

Introduced parasites and pathogens have colonized the Galapagos Islands of Ecuador. For example, a parasitic nest fly, Philornis downsi, was introduced to the Galapagos and has since caused significant nestling mortality for some endemic Darwin’s finches. However, some larger bodied species of birds in the Galapagos, including vegetarian finches (Platyspiza crassirostris) and Galapagos mockingbirds (Mimus parvulus), can be less affected by the parasite. Our study explores the effects of P. downsi on a small population of common cactus finches (Geospiza scandens) across two breeding seasons on San Cristobal Island, Galapagos. Specifically, we experimentally manipulated P. downsi abundance and characterized the gut and skin microbiota, and survival of nestling finches. Because cactus finches are medium-sized birds and small- and medium-sized birds are generally negatively affected by P. downsi, we predicted that the parasite would have a similar detrimental effect on fledging success. We also determined the effect of P. downsi on the microbiota because other studies have shown that the bacterial community can be beneficial for host health (e.g., conferring immunity and nutrient absorption). Although the overall skin and gut microbiota differed, we found that parasite treatment did not affect the microbiota in either tissue. However, nestlings from parasitized nests had significantly lower fledging success (25%, on average) compared to nestlings from non-parasitized nests (79%). We found that, similar to other medium-sized species, cactus finches are negatively affected by P. downsi, which could have implications for their risk of extirpation from the island. The results of this study should be considered when managing this population of concern.

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).

Contrasting impacts of invasive plants and human-altered landscape context on nest survival and brood parasitism of a grassland bird

Humans have altered grasslands in recent decades through crop conversion, woody encroachment, and plant invasions. Concurrently, grassland birds have experienced range-wide declines. Studies have reported effects of plant invasions and land conversion on nest ecology, but few have assessed relative impacts of these changes. We compared impacts of invasive plants and landscape context on nest survival of a grassland songbird, the dickcissel (Spiza americana). We also compared effects on parasitism by brown-headed cowbirds (Molothrus ater) and tested whether parasitism affects survival. From 2013–2016, we monitored 477 dickcissel nests. We measured nest-site vegetation (including woody plants, tall fescue Schedonorus arundinaceous, and other invasive grasses) and measured landscape context at broad scales. Nest survival declined with increasing tall fescue cover at nest sites, and parasitism was more common at nests with greater fescue and woody cover. Some evidence suggested a negative effect of row-crop cover within 1000 m on nest survival, but no landscape patterns unambiguously affected survival. Woodland cover and wooded-edge prevalence were associated with reduced parasitism risk. Parasitized nests had smaller clutches, failed more frequently, and produced fewer fledglings than non-parasitized nests. Determining the impacts of invasive plants and other anthropogenic changes on grassland birds will aid in prioritizing management to improve habitat quality. Our results indicate that optimizing landscape context around habitats may not affect dickcissel nest survival strongly, except perhaps through effects on parasitism. In contrast, controlling tall fescue and shrubs within grasslands could benefit birds by increasing nest success and reducing parasitism.

Parasites favour intermediate nestling mass and brood size in cliff swallows.

A challenge of life-history theory is to explain why animal body size does not continue to increase, given various advantages of larger size. In birds, body size of nestlings and the number of nestlings produced (brood size) have occasionally been shown to be constrained by higher predation on larger nestlings and those from larger broods. Parasites also are known to have strong effects on life-history traits in birds, but whether parasitism can be a driver for stabilizing selection on nestling body size or brood size is unknown. We studied patterns of first-year survival in cliff swallows (Petrochelidon pyrrhonota) in western Nebraska in relation to brood size and nestling body mass in nests under natural conditions and in those in which hematophagous ectoparasites had been removed by fumigation. Birds from parasitized nests showed highest first-year survival at the most common, intermediate brood-size and nestling-mass categories, but cliff swallows from nonparasitized nests had highest survival at the heaviest nestling masses and no relationship with brood size. A survival analysis suggested stabilizing selection on brood size and nestling mass in the presence (but not in the absence) of parasites. Parasites apparently favour intermediate offspring size and number in cliff swallows and produce the observed distributions of these traits, although the mechanisms are unclear. Our results emphasize the importance of parasites in life-history evolution.

Great spotted cuckoo nestlings have no antipredatory effect on magpie or carrion crow host nests in southern Spain.

Host defences against cuckoo parasitism and cuckoo trickeries to overcome them are a classic example of antagonistic coevolution. Recently it has been reported that this relationship may turn to be mutualistic in the case of the carrion crow (Corvus corone) and its brood parasite, the great spotted cuckoo (Clamator glandarius), given that experimentally and naturally parasitized nests were depredated at a lower rate than non-parasitized nests. This result was interpreted as a consequence of the antipredatory properties of a fetid cloacal secretion produced by cuckoo nestlings, which presumably deters predators from parasitized host nests. This potential defensive mechanism would therefore explain the detected higher fledgling success of parasitized nests during breeding seasons with high predation risk. Here, in a different study population, we explored the expected benefits in terms of reduced nest predation in naturally and experimentally parasitized nests of two different host species, carrion crows and magpies (Pica pica). During the incubation phase non-parasitized nests were depredated more frequently than parasitized nests. However, during the nestling phase, parasitized nests were not depredated at a lower rate than non-parasitized nests, neither in magpie nor in carrion crow nests, and experimental translocation of great spotted cuckoo hatchlings did not reveal causal effects between parasitism state and predation rate of host nests. Therefore, our results do not fit expectations and, thus, do not support the fascinating possibility that great spotted cuckoo nestlings could have an antipredatory effect for host nestlings, at least in our study area. We also discuss different possibilities that may conciliate these with previous results, but also several alternative explanations, including the lack of generalizability of the previously documented mutualistic association.

Brood parasitism by the enigmatic and rare Pavonine Cuckoo in Amazonian Peru

ABSTRACT Brood parasitism is an uncommon and understudied strategy in Amazonian bird communities, within which only 5 species are known to be brood parasites. We present data on the brood-parasitic behavior of the Pavonine Cuckoo (Dromococcyx pavoninus) in 3 host species of small-bodied flycatchers in the Peruvian Amazon that construct hanging globular nests with side entrances. During the 7 yr of the study, we encountered 74 nests of these 3 hosts, but parasitism occurred only in 9 nests (12.2%) in 2 yr. Only 1 Pavonine Cuckoo egg was deposited in each host nest (n = 7), and eggs were markedly dissimilar in size and coloration between hosts and parasite. Incubation investment per day was slightly higher (4%) for 1 parasitized nest than for nonparasitized nests. Overall, 33% of parasitic eggs (n = 6) hatched; cuckoo nestlings apparently removed host eggs and killed host nestlings. The nestling period lasted 24 days, and the growth-rate constant based on nestling mass (k = 0.23) was slower for parasite nes...

Relationships between egg-recognition and egg-ejection in a grasp-ejector species.

Brood parasitism frequently leads to a total loss of host fitness, which selects for the evolution of defensive traits in host species. Experimental studies have demonstrated that recognition and rejection of the parasite egg is the most common and efficient defence used by host species. Egg-recognition experiments have advanced our knowledge of the evolutionary and coevolutionary implications of egg recognition and rejection. However, our understanding of the proximate mechanisms underlying both processes remains poor. Egg rejection is a complex behavioural process consisting of three stages: egg recognition, the decision whether or not to reject the putative parasitic egg and the act of ejection itself. We have used the blackbird (Turdus merula) as a model species to explore the relationship between egg recognition and the act of egg ejection. We have manipulated the two main characteristics of parasitic eggs affecting egg ejection in this grasp-ejector species: the degree of colour mimicry (mimetic and non-mimetic, which mainly affects the egg-recognition stage of the egg-rejection process) and egg size (small, medium and large, which affects the decision to eject), while maintaining a control group of non-parasitized nests. The behaviour of the female when confronted with an experimental egg was filmed using a video camera. Our results show that egg touching is an indication of egg recognition and demonstrate that blackbirds recognized (i.e., touched) non-mimetic experimental eggs significantly more than mimetic eggs. However, twenty per cent of the experimental eggs were touched but not subsequently ejected, which confirms that egg recognition does not necessarily mean egg ejection and that accepting parasitic eggs, at least sometimes, is the consequence of acceptance decisions. Regarding proximate mechanisms, our results show that the delay in egg ejection is not only due to recognition problems as usually suggested, given that experimental eggs are not touched significantly more often. Thus, the delay in egg ejection is mainly the consequence of a delay in the decision to eject, probably triggered by mechanical constraints imposed by eggs that are harder to eject (i.e. larger). Our results offer important information on the relationships between recognition and ejection and contribute to a better understanding of host defences against brood parasites.

The common redstart as a suitable model to study cuckoo-host coevolution in a unique ecological context.

BackgroundCo-evolutionary arms-races result in spatio-temporally dynamic relationships between interacting species, e.g., brood parasites and their avian hosts. However, majority of avian co-evolutionary studies are limited to “snap-shots” of a single breeding season in an open-nesting host. In a long-term study (11 breeding seasons), we explored a unique system between the brood parasitic common cuckoo (Cuculus canorus) and its host, the common redstart (Phoenicurus phoenicurus) which is exceptional among all cuckoo hosts due to being a cavity nester. Conditions in cavities are different from open nests, e.g., lower risks of predation, more favourable microclimate, increased risks of unsuccessful eviction of host offspring by the cuckoo nestling. Different conditions in cavities thus can be expected to shape parasite-host coevolution differently from what is typically studied in open nesting hosts.ResultsIn our highly parasitised nest-box population (32.5%, n = 569 nests) only 35.7% of cuckoo eggs were laid into the nest cup and incubated by redstarts. Host nests shifted availability to later into the breeding season from 2006 to 2016 and cuckoos followed this trend by also shifting their timing of parasitism. Although previous studies revealed that redstarts selectively eject experimental non-mimetic eggs (desertion was not a specific response to foreign eggs), the hosts never ejected naturally-laid cuckoo eggs or cuckoo eggs cross-fostered into naturally non-parasitised nests. We solve the long-standing debate about the origin of cuckoo eggs found on the nest rim: we gained the first direct video-recording evidence that eggs found on the nest rim were mislaid by parasites and not ejected by hosts. Naturally-parasitised nests were deserted more often (18.6%) than control non-parasitized nests (5.6%) or nests artificially parasitised by us (1.4%). This suggests that the sight of the laying cuckoo female is the primary cue that triggers egg rejection (by desertion) in this host. Review of data from this and other study sites (10 populations, n = 853 experiments) demonstrates high variability in rejection rates and shows that populations facing higher parasitism rates reject parasitic eggs with higher frequencies. Surprisingly, cuckoo chicks either growing solitarily or with redstart chicks did not differ in their fledging success.ConclusionsWe suggest that the redstart is an ideal model system to study the flexibility and limits of brood parasite-host co-evolution in an extreme ecological setting.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0835-5) contains supplementary material, which is available to authorized users.

Egg-spot matching in common cuckoo parasitism of the oriental reed warbler: effects of host nest availability and egg rejection

The success of cuckoo parasitism is thought to depend largely on the extent of egg matching between cuckoo and host eggs, since poor-matching cuckoo egg would lead to more frequent egg rejection by the host. In this study, we investigated how egg-spot matching between the Common Cuckoo (Cuculus canorus) and its host, the Oriental Reed Warbler (Acrocephalus orientalis) is affected by the local parasitism rate, nest availability in breeding synchronization and egg rejection. We used the paired design of parasitized and their nearest non-parasitized nests where breeding occurred simultaneously to compare egg-spot matching. The image analysis was used to compare four eggshell pattern variables, namely spot size, density, coverage on the different areas of egg surface, and the distribution on the whole egg surface. Egg recognition experiments were conducted to test the effect of egg spots on egg rejection by the host. Our results show that much better matching in almost all spot parameters tested on the side of the egg and the spot distribution on the whole egg occurred in parasitized nests than in non-parasitized nests. Matching of spot density between cuckoo and host eggs in parasitized nests increased with the synchronization between temporal availability of nests and the egg-laying period of female cuckoos. Egg recognition experiments in which the warbler eggs were deliberately painted with extra spots led to a significantly higher egg rejection rate (78.3%) than of unpainted eggs. Our data suggest that both the high temporal encounter rate between cuckoo and warbler nests as well as the high egg rejection ability of the host are important factors for egg-spot matching of the cuckoos.

Do common cuckoo chicks suffer nest predation more than host nestlings?

Nestlings of brood parasites exhibit more intensive begging than offspring of their hosts to gain sufficient amount of food or competitive advantage over host nestlings. This begging behaviour should be costly because exuberant acoustic begging may more likely attract nest predators. However, to date, nobody has explored the survival of nests with and without chicks of brood parasites in the common cuckoo (Cuculus canorus) host system. Here, we analysed an extensive dataset of 817 great reed warbler (Acrocephalus arundinaceus) and 788 reed warbler (Acrocephalus scirpaceus) nests to explore the relationships between nest predation and parasitism status (parasitized vs. non-parasitized), nest contents (cuckoo chick vs. host nestlings) and age of nestlings. We found that although parasitized nests had higher predation rate than non-parasitized nests in the incubation stage, the effect of original parasitism status almost disappeared in the nestling stage. In both host species, nests with younger cuckoo chicks survived similarly to nests with host nestlings of the same age (till the ninth day of age). Later on, however, nest contents influenced nest predation in each species differently. While nests with older cuckoo chicks (from the ninth to the 17th day of age) did not survive worse that host nestlings in the great reed warbler, older cuckoos survived much worse than host nestlings in reed warbler nests. Finally, nest survival decreased with nestling age in all three species. Thus, it seems that common cuckoo chicks can be penalized for more intensive begging only in nests of smaller reed warbler hosts. Parental feeding of young is in birds frequently accompanied by striking nestlings begging behaviour serving as a signal of their need. Brood parasites exhibit even more intense food solicitation than their hosts which may attract predators to the nest. However, this hypothesis has never been tested in a widely studied brood parasite species—the common cuckoo. Here, we analysed survival of more than 1600 nests of its two main host species. We found that nests containing older common cuckoo chicks were depredated more frequently than nests with host own nestlings only in the smaller reed warbler hosts but not in the larger and more aggressive great reed warblers. This shows that the intensity of begging could be costly in terms of nest predation at least in some common cuckoo host species.

Potential effects of Brown-headed Cowbirds (Molothrus ater) on host postfledging dispersal and survival

ABSTRACT Nest parasitism by Brown-headed Cowbirds (Molothrus ater) negatively affects nest production and nest success of the majority of their hosts. However, it is unclear what effects cowbird fledglings have on host broods during the postfledging period. We monitored 65 nests of Ovenbirds (Seiurus aurocapilla) from 2012–2014 in central Missouri, 49% of which were parasitized by Brown-headed Cowbirds. We used radio-telemetry to track daily movements, survival, and parental care for 13 Ovenbird fledglings from parasitized nests that fledged cowbirds and 21 Ovenbird fledglings from non-parasitized nests. Clutch size and nest productivity were lower in parasitized nests, but mean nestling mass at fledging and total brood size (host and parasite young) did not differ between parasitized and non-parasitized nests. All mortalities occurred within the first 10 days after fledging. Estimated postfledging cumulative survival and observed adult care were similar between parasitism groups. There was no difference ...

Disappearance of eggs from nonparasitized nests of brood parasite hosts: the evolutionary equilibrium hypothesis revisited

WL was funded by the National Natural Science Foundation of China (Nos. 31071938, 31272328, and 31472013). BGS and FF were funded by the Research Council of Norway (218144). CY was funded by the National Natural Science Foundation of China (Nos. 31101464 and 31260514) and New Century Excellent Talents in University (NCET-13-0761). CM was funded by the Hungarian National Science Fund (OTKA, No. 83217).

Do common cuckoos (Cuculus canorus) possess an optimal laying behaviour to match their own egg phenotype to that of their Oriental reed warbler (Acrocephalus orientalis) hosts?

Received 20 June 2015; revised 6 August 2015; accepted for publication 7 August 2015Optimality theory suggests that parasitic cuckoos should evolve an optimal laying behaviour aiming to positivelyselect host nests in which the eggs match the phenotype of their own eggs, thus minimizing the rejection riskfrom hosts and, in turn, maximizing the cuckoos’ fitness. We tested this hypothesis by investigating cuckoo-eggmatching between parasitized and nonparasitized nests in a common cuckoo (Cuculus canorus) host, the Orientalreed warbler (Acrocephalus orientalis), by use of Vorobyev–Osorio and Nature-Pattern-Match models to quantifythe matching of egg colour and pattern from avian vision, respectively. The results of our study indicated thatcuckoo-egg matching in parasitized nests was no better than that in nonparasitized nests, and thus we found nosupport for the optimal laying hypothesis in cuckoos. The mixed conclusions from all previous studies, includingthe present study, may be explained by (1) the parallel coevolution in different cuckoo–host systems; (2) theinappropriate methodology; and (3) the deficiency of the assumption itself. We suggest that a better methodologyshould be developed to solve the puzzle of whether cuckoos choose to lay eggs matching those of the host. © 2015The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 00, 000–000.

Nesting ecology of grassland songbirds: effects of predation, parasitism, and weather

Understanding the breeding ecology of grassland birds is vital for understanding the mechanisms underlying their widespread population declines. We describe the breeding biology of Sprague's Pipit (Anthus spragueii), Vesper Sparrow (Pooecetes gramineus), Savannah Sparrow (Passerculus sandwichensis), Baird's Sparrow (Ammodramus bairdii), and Western Meadowlark (Sturnella neglecta) and quantify the effects of nest predation, brood parasitism, and weather on the nest survival of these species in southeastern Alberta. Nest predation was the primary cause of nest failure, accounting for 75% of all nest losses. Daily survival rates were higher during incubation than the nestling stage for the three sparrow species, and nest survival of Baird's Sparrows was highest at intermediate temperatures. For all five species, clutch size, hatching success, and fledging success were within the range of values previously reported for these species in other parts of their range. Brown-headed Cowbirds parasitized nests of all species except Sprague's Pipit, with 4–11% of nests containing cowbird eggs. Savannah Sparrow experienced the highest frequency of brood parasitism and was the only species to successfully fledge cowbird young. Parasitized nests of Savannah Sparrows had reduced clutch size and hatching success, and fledged fewer young compared to non-parasitized nests. The overall cost of parasitism to Savannah Sparrows was at least 1.7 young per successful nest.

Experimental test of the effect of introduced hematophagous flies on corticosterone levels of breeding Darwin’s finches

Parasites can negatively affect the evolutionary fitness of their hosts by eliciting physiological stress responses. Parasite-induced stress can be monitored by measuring changes in the adrenal steroid hormone corticosterone. We examined the effect of an invasive parasite on the corticosterone concentrations of a common species of Darwin’s finch, the medium ground finch (Geospiza fortis). Philornis downsi (Diptera: Muscidae) is a parasitic nest fly recently introduced to the Galapagos Islands, where it feeds on the blood of nestlings and breeding adult female finches. Previous work shows that P. downsi significantly reduces the reproductive success of several species of finches. We predicted that the effect of P. downsi on host reproductive success is mediated by stress responses in breeding female finches. High stress levels could reduce the ability of females to invest in offspring, thus decreasing their reproductive success. To test this hypothesis, we experimentally manipulated the abundance of P. downsi in nests, then measured baseline and acute stress-induced corticosterone levels, body condition, and hematocrit (red blood cell content). Acute stress-induced corticosterone levels increased over baseline levels, but this response did not differ significantly with parasite treatment. There was also no significant difference in the body condition or hematocrit of females from parasitized versus non-parasitized nests. Our results suggest that the lower reproductive success of females from parasitized nests is not mediated by a physiological stress response.

Experimental demonstration of a parasite‐induced immune response in wild birds: Darwin's finches and introduced nest flies

Ecological immunology aims to explain variation among hosts in the strength and efficacy of immunological defenses. However, a shortcoming has been the failure to link host immune responses to actual parasites under natural conditions. Here, we present one of the first experimental demonstrations of a parasite-induced immune response in a wild bird population. The recently introduced ectoparasitic nest fly Philornis downsi severely impacts the fitness of Darwin's finches and other land birds in the Galápagos Islands. An earlier study showed that female medium ground finches (Geospiza fortis) had P. downsi-binding antibodies correlating with presumed variation in fly exposure over time. In the current study, we experimentally manipulated fly abundance to test whether the fly does, in fact, cause changes in antibody levels. We manipulated P. downsi abundance in nests and quantified P. downsi-binding antibody levels of medium ground finch mothers, fathers, and nestlings. We also quantified host behaviors, such as preening, which can integrate with antibody-mediated defenses against ectoparasites. Philornis downsi-binding antibody levels were significantly higher among mothers at parasitized nests, compared to mothers at (fumigated) nonparasitized nests. Mothers with higher antibody levels tended to have fewer parasites in their nests, suggesting that antibodies play a role in defense against parasites. Mothers showed no behavioral changes that would enhance the effectiveness of the immune response. Neither adult males, nor nestlings, had P. downsi-induced immunological or behavioral responses that would enhance defense against flies. None of the parasitized nests fledged any offspring, despite the immune response by mothers. Thus, this study shows that, while the immune response of mothers appeared to be defensive, it was not sufficient to rescue current reproductive fitness. This study further shows the importance of testing the fitness consequences of immune defenses, rather than assuming that such responses increase host fitness.Host immune responses can protect against the negative fitness consequences of parasitism; however, the strength and effectiveness of these responses vary among hosts. Strong host immune responses are often assumed to correlate with greater host fitness. This study investigates the relationship between host immune response, parasite load, and host fitness using Darwin's finches and an invasive nest parasite. We found that while the immune response of mothers appeared defensive, it did not rescue current reproductive fitness.

Repeated Brood Parasitism by Brown-Headed Cowbirds (Molothrus ater) at Nesting Sites of Eastern Phoebes (Sayornis phoebe) across Non-consecutive Years

Abstract The temporal and spatial patterns of avian brood parasitism can critically influence host fitness, the coevolution of parasitic strategies and host resistance, and their reciprocal effects on population dynamics. This study examined spatial patterns of Brown-headed Cowbird (Molothrus ater) parasitism on Eastern Phoebe (Sayornis phoebe) hosts in 2009–2011 near Ithaca, NY, USA, and compared them with published data from 1999–2002 at the same nest sites, encompassing a period long enough for a turn-over of most of the breeding adult host and parasite populations. Relative to non-parasitized nests, host nests, that were more likely to be parasitized annually in 2009–2011, had also been parasitized more often during years 1999–2002. These findings are consistent with the hypothesis that Brown-headed Cowbirds, even across generations, show a consistent preference for particular Eastern Phoebe nest sites, although it remains unclear what the relative roles of the biological traits of the hosts occupying...

Protocalliphora (Diptera: Calliphoridae) Infestations of Nestling Red-shouldered Hawks in Southern Ohio

Abstract We examined nestling Red-shouldered Hawks (Buteo lineatus) in 56 nests (147 nestlings) in suburban southwestern Ohio and in 25 nests (67 nestlings) in rural forested Hocking Hills in south-central Ohio, ∼180 km east of southwestern Ohio. Fifteen of 25 nests in Hocking Hills had Protocalliphora avium larvae on one or more nestlings and/or pupae in the nest material. Nineteen nestlings had larvae in one or both ears, an additional 14 had evidence of larvae outside the ears, 32 were not visibly parasitized, and two were not examined or their status was not reported; in contrast, no nests and no nestlings were parasitized in southwestern Ohio. Reproductive rate (young fledged/nest) did not differ between southwestern Ohio and Hocking Hills (2.4 ± 0.1 young/nest at southwestern Ohio vs. 2.7 ± 0.2 at Hocking Hills; P = 0.214). Parasitized nests at Hocking Hills were no more likely to have been used in the previous breeding season than non-parasitized nests (χ2 = 0.903, P = 0.342, n = 22). Simil...

Effects of Parasitism by Brown-headed Cowbirds May Persist Into Post-fledging

Brood parasitism by Brown-headed Cowbirds (Molothrus ater) typically decreases the number of host juveniles that fledge: however, little information exists regarding the effect of cowbird parasitism during the post-fledging period. We monitored 115 Ovenbird (Seiurus aurocapilla) nests in 2006–2008 in northcentral Minnesota, six of which were parasitized. We used radiotelemetry to monitor movements of 36 Ovenbird fledglings (nine additional fledglings depredated <24 hrs after fledging were excluded from the movement analysis) from non-parasitized nests and one fledgling from a parasitized nest. Clutch sizes and productivity were lower in parasitized Ovenbird nests than non-parasitized nests, similar to populations at other locations. The fledgling we tracked from a parasitized nest (in 2008) died after 26 days. It was the only fledgling in our study that died (n = 20) with no sign of predation and an empty stomach. That fledgling took 12 days to travel >50 m from its nest and 25 days to travel >100 m from its nest. Fledglings from non-parasitized broods tracked for ≥25 days during 2008 (n = 16) took 4.1 ± 0.71 and 9.5 ± 1.14 days to travel the same distances. Our observations suggest that negative effects of brood parasitism may persist into the post-fledging period, possibly confirming observations of cowbird-only survival compiled from the literature.