Consequences of the size structure of fish populations for their effects on a generalist avian predator

Size-structured interspecific interactions can shift between predation and competition, depending on ontogenetic changes in size relationships. I examined the effects of common carp (Cyprinus carpio), an omnivorous fish, on the reproductive success of the red-necked grebe (Podiceps grisegena), an avian gape-limited predator, along a fish size gradient created by stocking distinct age-cohorts in seminatural ponds. Young-of-the-year (0+) carp were an essential food source for young grebes. Only adult birds were able to consume 1-year-old (1+) fish, while 2-year-old (2+) fish attained a size refuge from grebes. Amphibian larvae were the principal alternative prey to fish, followed by macroinvertebrates, but the abundance of both dramatically decreased along the carp size gradient. Fledging success was 2.8 times greater in ponds with 0+ versus 1+ carp; in ponds with 1+ carp, chicks received on average 2.6–3 times less prey biomass from their parents, and over 1/3 of broods suffered total failure. Breeding birds avoided settling on 2+ ponds. These results show that changes in prey fish size structure can account for shifts from positive trophic effects on the avian predator to a negative impact on the predator’s alternative resources. However, competition did not fully explain the decrease in grebe food resources in the presence of large fish, as carp and grebes overlapped little in diet. In experimental cages, 1+ carp totally eliminated young larvae of amphibians palatable to fish. In field conditions, breeding adults of palatable taxa avoided ponds with 1+ and older carp. Non-trophic interactions such as habitat selection by amphibians or macroinvertebrates to avoid large fish may provide an indirect mechanism strengthening the adverse bottom-up effects of fish on birds.     

Food Provisioning in Red-Necked Grebes (Podiceps Grisegena) at Common Carp (Cyprinus Carpio) Ponds

Parental feeding patterns were studied in red-necked grebe (Podiceps grisegena) broods throughout the entire period of parental care in a common carp (Cyprinus carpio) fish-pond area in SE Poland in 1993–2002. Fish formed a substantial part of prey provided to the flightless young from their second week of life. Although the numbers of large invertebrates and tadpoles, the alternative prey to fish, did not decrease during the chick rearing period, grebe parents gradually shifted from delivering predominately invertebrates to delivering fish, and the average size of fish fed to chicks increased with brood age. Broods with relatively high fledging success (at least two chicks fledged) had a larger proportion of fish in their diet than broods seriously reduced because of undernourishment. The dive duration of foraging grebe parents did not differ between carp, wild fish and non-fish prey, but carp prey required significantly more time for handling. The percentage of prey rejected by chicks increased over the prefledging period from 2 to 24%. Of the prey rejected, 82% were fish apparently too large for the young to swallow. Fish prevalence in the diet of red-necked grebe chicks at carp ponds contradicts the results of other studies on the feeding habits of the nominative subspecies during breeding season. However, the red-necked grebe is a gape-limited predator and the piscivory of the chicks is limited to small-bodied fish.     

Fish stocking creates an ecological trap for an avian predator via effects on prey availability

In anthropogenic landscapes animals may be lured into low‐quality habitats where they survive or reproduce poorly (‘ecological traps’). I investigated breeding habitat selection in relation to intra‐seasonal changes in food availability and reproductive output in red‐necked grebes Podiceps grisegena, a size‐limited predator, of common carp Cyprinus carpio ponds. Carp farms constitute highly heterogeneous habitat mosaics due to separate stocking of different age/size fish. Pond features significant for grebe settling decisions, i.e. hydroperiod and emergent vegetation cover, had no obvious effects on prey abundance for chicks and on fledging success. Breeding grebes avoided ponds containing fish too large for them to ingest but exhibited little preference between ponds with medium‐sized one‐year‐old carp that could be exploited by pre‐laying birds, and ponds designated for young‐of‐the‐year carp, where only invertebrates and amphibians were available as prey in early spring. Red‐necked grebes settling on ponds with medium‐sized fish failed to predict future shifts in interactions with carp stocks; carp exceeded the prey‐size threshold of chicks and adversely affected their non‐fish prey levels. The resulting food shortage led to severe egg‐to‐fledging mortality rates compared to fishless ponds or those containing young‐of‐the‐year fish. This study shows that waterbirds vulnerable to competition from fish can risk maladaptive habitat selection due to unrecognised spatial and temporal variation in food resources caused by fish stocking practices. Ecological traps created by perturbations to trophic interactions may be common but difficult to detect because altered dynamics of trophic resources can affect wildlife indirectly. As with other types of ecological traps, manipulation of habitat features identified as attractive cues for settling animals, but not related to critical food resources, may help to reduce perceptual pitfalls. For example, wetland management to mitigate trap effects driven by commercially stocked fish should preserve abundant emergent vegetation in habitats with weak fish impact and extend their hydroperiod.     

Ecological constraints on breeding system evolution: the influence of habitat on brood desertion in Kentish plover

1. One of the fundamental insights of behavioural ecology is that resources influence breeding systems. For instance, when food resources are plenty, one parent is able to care for the young on its own, so that the other parent can desert and became polygamous. We investigated this hypothesis in the context of classical polyandry when females may have several mates within a single breeding season, and parental duties are carried out largely by the male. 2. We studied a precocial wader, the Kentish plover Charadrius alexandrinus, that exhibits variable brood care such that the chicks may be raised by both parents, only by the female or, more often, only by the male. The timing of female desertion varies: some females desert their brood at hatching of the eggs and lay a clutch for a new mate, whereas other females stay with their brood until the chicks fledge. Kentish plovers are excellent organisms with which to study breeding system evolution, as some of their close relatives exhibit classical polyandry (Eurasian dotterel Eudromias morinellus, mountain plover Charadrius montanus), whereas others are polygynous (northern lapwing Vanellus vanellus). 3. Kentish plovers raised their broods in two habitats in our study site in southern Turkey: saltmarsh and lakeshore. Food intake was higher on the lakeshore than in the saltmarsh as judged from feeding behaviour of chicks and adults. As the season proceeded and the saltmarsh dried out, the broods moved toward the lakeshore. 4. As the density of plovers increased on lakeshore, the parents spent more time defending their young, and female parents stayed with their brood longer on the lakeshore. 5. We conclude that the influence of food abundance on breeding systems is more complex than currently anticipated. Abundant food resources appear to have profound implications on spatial distribution of broods, and the social interactions between broods constrain female desertion and polyandry.     

Horned grebe habitat use of constructed wetlands in Alberta,Canada

Wetland degradation has resulted in declines in populations of aquatic birds throughout North America. Horned grebe (Podiceps auritus), a migratory diving bird experiencing population decline, may benefit from wetland construction. We examined horned grebe use of borrow pits (ponds created during highway construction) in Alberta, Canada. Our goals were to document patterns of occurrence and breeding success of grebes on borrow pits and to determine if occupied and unoccupied sites differed in local habitat or landscape characteristics. In May 2003 and 2007, 330 constructed ponds were surveyed for horned grebes. We chose 100 occupied and 100 unoccupied ponds for additional surveys in 2007 and 2008, and collected habitat and landscape data for these sites. We used generalized linear mixed model and generalized linear model regression, coupled with Akaike's Information Criterion, to determine which environmental variables were most effective in explaining occurrence of horned grebes. The best model included all measured local and landscape habitat features. Horned grebes occurred on 36% of ponds in May 2003 and 2007, and chicks were produced on 74.5–81.3% of occupied ponds in 2007 and 2008. Grebes occupied larger ponds with more emergent and riparian vegetation and avoided ponds that supported beavers, contained human structures, and were primarily surrounded by forest within 1 km. On ponds with grebe pairs, chicks were produced more often on sites surrounded by more riparian vegetation. We conclude that the construction of small wetlands offers a promising means of increasing breeding habitat for horned grebes and present specific recommendations for breeding pond construction. © 2012 The Wildlife Society.     

Adoption Behaviour in Little and Common Terns (Aves; Sternidae): Chick Benefits and Parents' Fitness Costs

Adoption seeking by semi-precocial chicks of some bird species can be adaptive since it provides an alternative tactic to permit poorly cared-for young to survive despite their neglectful parents' behaviour. Moreover, own-nest desertion may enhance inclusive fitness of fugitive chicks by increasing survival prospects of siblings. On the other hand, adoption by breeding adults can be detrimental to foster parents' fitness if they invest resources in promoting survival of others' offspring at the expense of their own. In this study we report on the proximate causes and survival consequences of adoption seeking by chicks, and on the presumed costs of adoption sustained by foster parents in two colonial, ground-nesting tern species: the little tern (Sterna albifrons) and the common tern (Sterna hirundo). Adoptions were frequent in little tern and, notably, in common tern colonies. Chicks that deserted their original brood were poorly fed compared with resident chicks, but crowding in the brood and age rank relative to nest companions did not influence the chances of desertion. Deserting their original brood was risky for little tern chicks since stray chicks experienced higher mortality than resident ones. Common tern chicks deserted their original nest significantly more often than little tern chicks. Adoptees of both species benefited by the same survival prospects as resident chicks. A negative correlation existed between the proportion of food given to strange chicks and seasonal fitness or chick survival rate of breeding pairs. This was not predictable because: (1) foster parents could have increased their parental efforts, thus ensuring the same survival prospects to their own chicks, and (2) chicks of foster parents could have been, in turn, adopted thus obliterating the negative fitness effects of adoption. The sexes were identical with respect to their proneness to provide food to strange chicks. We suggest that adoption seeking by little and common tern chicks has evolved as an alternative tactic that is pursued to counter the effects of poor parental care. Adoption behaviour seems maladaptive since it is accompanied by a reduction in seasonal fitness in both species. Possible alternative explanations for nest desertion and adoption behaviour are also discussed.     

The function of habitat change during brood-rearing in the precocial Kentish plover <Emphasis Type="Italic">Charadrius alexandrinus</Emphasis>

Food availability is often variable during the breeding season. Parents with nonmobile, altricial young have no choice but to accept changes in local food availability, whereas in precocial animals, the parents may lead their young away from poor sites to areas that have rich resources and/or are safe from predators. We investigated the latter hypotheses in the Kentish plover Charadrius alexandrinus, a precocial shorebird that raises its young in two habitats: on lakeshore and in saltmarsh. Parents move with their broods from saltmarsh to lakeshore, especially late in the breeding season, and we hypothesized that lakeshores provide more food than the saltmarsh. Consistent with our hypotheses, plover chicks grew faster on the shore, and the difference in growth rates between the two habitats was amplified later in the breeding season. In addition, brood survival was higher on lakeshore than in saltmarsh and decreased with hatching date. Taken together, our results suggest that Kentish plover parents increase their reproductive success by switching brood-rearing habitats strategically.     

Fish reduce habitat coupling by a waterbird: evidence from combined stable isotope and conventional dietary approaches

Aquatic consumers can function as habitat couplers by using allochthonous subsidies of prey that migrate across ecosystem boundaries. We examined the relative use of allochthonous (invertebrates—terrestrial or living on littoral vegetation; immigrating amphibians) versus autochthonous (aquatic invertebrates, fish) resources by the red-necked grebe Podiceps grisegena, a generalist predator, on fishless ponds versus ponds stocked with common carp Cyprinus carpio. We combined conventional methods of diet estimation with stable carbon and nitrogen analyses of egg yolks and putative prey of grebes. Prelaying grebes were observed to take mainly adult amphibians on fishless ponds and fish on stocked ponds. Alimentary tract analyses gave more weight to invertebrate prey, especially leaf beetles Donaciinae, apparently picked off water or emergent plants. Bayesian isotopic mixing models did not reveal predominance of a single food source but indicated that in the presence of fish grebes received relatively less energy for egg formation from amphibians and leaf beetles. Overall, our results show that grebes relied more on allochthonous resources (range of means 50–97 % of the biomass contribution estimated by different assessment methods) in the absence than in the presence of fish (8–23 %). We suggest that habitat coupling by waterbirds may be controlled by fish, which can suppress external prey subsidies, apart from being an attractive food for piscivorous birds.     

Brood reduction in the Red-necked Grebe Podiceps grisegena

Brood reduction in Red-necked Grebes Podiceps grisegena breeding on fish ponds in south-eastern Poland occurred either through the desertion of the last-laid eggs after partial hatching of the clutch and/or the selective starvation of the smallest chicks. Abandonment of unhatched eggs was not influenced by the number of young already hatched or by the breeding date, but it was more likely in larger clutches and in families suffering chick starvation. Chicks from the largest broods had a higher probability of survival until fledging than those from single-chick broods. Larger chicks obtained food more successfully through better positioning during food delivery. In families that did not suffer brood reduction, chicks were better provisioned with food than in reduced broods. Although allocation of food among chicks in reduced broods was more skewed to the disadvantage of the younger siblings, dominant chicks obtained less food prior to brood reduction than dominant siblings in unreduced broods. Sibling aggression did not differ between unreduced and reduced broods before death of the weakest chicks. Post-laying adjustment of the number of offspring to prevailing feeding conditions occurred at two stages: by parental manipulation of the number of hatched eggs at the time when parents and chicks leave the nest and by competition between chicks. It is suggested that late egg desertion may be an adaptive mechanism of brood-size adjustment, when elimination of the weakest chicks through sibling competition is not very efficient.     

Prolactin stress response does not predict brood desertion in a polyandrous shorebird

One of the fundamental principles of the life-history theory is that parents need to balance their resources between current and future offspring. Deserting the dependent young is a radical life-history decision that saves resources for future reproduction but that may cause the current brood to fail. Despite the importance of desertion for reproductive success, and thus fitness, the neuroendocrine mechanisms of brood desertion are largely unknown. We investigated two candidate hormones that may influence brood desertion in the Kentish plover Charadrius alexandrinus: prolactin ('parental hormone') and corticosterone ('stress hormone'). Kentish plovers exhibit an unusually diverse mating and parental care system: brood desertion occurs naturally since either parent (the male or the female) may desert the brood after the chicks hatch and mate with a new partner shortly after. We measured the hormone levels of parents at hatching using the standard capture and restraint protocol. We subsequently followed the broods to determine whether a parent deserted the chicks. We found no evidence that either baseline or stress-induced prolactin levels of male or female parents predicted brood desertion. Although stress-induced corticosterone levels were generally higher in females compared with males, individual corticosterone levels did not explain the probability of brood desertion. We suggest that, in this species, low prolactin levels do not trigger brood desertion. In general, we propose that the prolactin stress response does not reflect overall parental investment in a species where different parts of the breeding cycle are characterized by contrasting individual investment strategies.     

Begging behaviour of nestlings and food delivery by parents: the importance of breeding strategy

Studies of begging behaviour and food provisioning have produced contradictory results. Here, I present a new idea that may explain these apparent contradictions based on the fact that in species with brood reduction (brood reducers) some chicks starve, but in species that adjust clutch size (clutch adjusters) all chicks typically survive to fledge. This suggests that parents adopting these different strategies may follow different provisioning rules. In clutch adjusters, parents tend to distribute food equitably among their chicks, preferentially feeding young that are in poorer condition, but in brood reducers parents selectively feed larger chicks independently of begging intensity. Received in revised form: 27 March 2001 Electronic Publication     

Influence of fish on the breeding of the red-necked grebe Podiceps grisegena (Boddaert, 1783)

I determined whether selection of breeding sites by thered-neckedgrebe Podiceps grisegena (Boddaert, 1783) was affectedbycompetition for food with fish. During 1987–89, ten ponds inScania, southern Sweden were investigated, five with(breedingsites) and five without breeding red-necked grebe(non-breedingsites). I quantified the biomass of fish and macrozoans(here:larger invertebrates and small vertebrates) and measured thephysical and chemical conditions of the ponds.Breeding sites had significantly lower relative fish abundancethannon-breeding sites. They were either devoid of fish or hadonly nine-spined sticklebackPungitius pungitius. The biomass (dry weight) ofmacrozoans,many of which represent a food resource for grebes, was 16timesgreater at breeding than at non-breeding sites. The physicalandchemical conditions of the ponds did not differsignificantly.These results are consistent with the hypothesis thatcompetitionfor macrozoans occurs between red-necked grebe and fish andthat adense population of many fish species caused red-necked grebestoavoid otherwise acceptable breeding sites.     

Impact of Great Crested Grebes (Podiceps cristatus L.) on fish ponds

Because Great Crested Grebes (Podiceps cristatus L.) mainly feed on fish, fish-farmers sometimes claim that economic losses are caused by grebes (EIFAC, 1988). Such claims were not based on scientific research.Therefore, a study was carried out to measure the impact of Great Crested Grebes on a fish-farm, managed by the Organization for the Improvement of Inland Fisheries (O.V.B.) in Valkenswaard (The Netherlands) during the period 1986–1988. The O.V.B. provided fish data for each pond including fish density and fresh fish weight for each fish species. The number of grebes was counted at least once a week. Activity patterns, including nocturnal activity, were determined both for the period with and without young. No nocturnal foraging activity was observed. Furthermore, fish biomass consumed per 1000 s foraging time by adult birds and chicks was calculated.In some fish-ponds grebes ate coarse fish, and chicks especially were fed these fish. The average daily fish consumption was 222 g for adults and 108 g for juveniles.Based on available fish data, it can be concluded that grebes consumed fewer fish than the number expected to die, and only marginally influenced the fish populations in the aquaculture ponds studied.     

Relationships between brood size and parental provisioning performance in chinstrap penguins during the chick guard phase

 Chinstrap penguins (Pygoscelis antarctica) normally lay two eggs, but brood size is often reduced by mortality during incubation or after hatching. We hypothesized that this variation in brood size would affect the parents’ foraging behavior and their chick provisioning performance. We studied patterns of adult foraging trip duration and frequency, food load delivery, and chick growth rates in relation to brood size during the guard phase in four breeding seasons (1991–1994) on Seal Island, Antarctica. Within a given year, parents with two chicks made more frequent foraging trips to sea and may have transported larger food loads to the nest; however, the duration of foraging trips was unrelated to brood size. Overall, parents with two chicks spent ∼15% more time at sea than parents with only one chick. Both the frequency and duration of foraging trips varied between years. Foraging trip duration may partly reflect the birds’ foraging radius, which probably varies with time in response to shifts in krill distribution. Chick growth rate varied betwen years, but was related to brood size only in 1992, when chicks from two-chick broods grew significantly more slowly than chicks from one-chick broods. Food loads transported to chicks, as well as chick growth rates, were highest in 1994, when concurrent hydroacoustic studies indicated that regional krill biomass was severely depressed. This apparent anomaly suggests that the spatial scale of the krill survey may have been too coarse to detect some high-density krill aggregations within the penguins’ foraging range. Received: 26 September 1995 / Accepted: 12 May 1996     

Food competition and niche separation between fish and the Red-necked Grebe Podiceps grisegena (Boddaert, 1783)

During the breeding season, the aquatic bird Red-necked Grebe Podiceps grisegena feeds on small aquatic animals, which are also an important food source for many fish species. Because grebes have to provide substantial amounts of invertebrates to their brood, competitive interactions with fish may be expected during the breeding season of grebes. Based on this hypothesis, the distribution of Red-necked Grebes, the abundances of macroinvertebrates, fish, and vegetation, as well as the water depth were determined in a shallow lake during two consecutive breeding seasons. The Red-necked Grebes only utilised the reed bed as breeding site, whereas the adjacent Lagoon, although potentially suitable as breeding site, was not used. Macroinvertebrate biomass was 5–10 times higher in the reed beds than in the Lagoon. The abundance of fish was low in the reed bed but considerably higher in the Lagoon. The results indicate habitat separation between breeding Red-necked Grebe and fish in Lake Tåkern, and that the separation is related to distribution of food resources birds and fish have in common.     

Brood parasitic European starlings do not lay high-quality eggs

Chicks of obligate brood parasites employ a variety of morphologicaland behavioral strategies to outcompete nest mates. Elevatedcompetitiveness is favored by natural selection because parasiticchicks are not related to their host parents or nest mates.When chicks of conspecific brood parasites (CBPs) are unrelatedto their hosts, they and their parents would also benefit fromtraits that enhance competitiveness. However, these traits mustbe inducible tactics in CBPs, since conspecific brood parasitism(CBP) is facultative. Such tactics could be induced by resourcespassed to offspring through the egg. Thus, females engagingin CBP should allocate to their eggs resources that will enhanceoffspring competitiveness. We tested this prediction in a populationof European starlings (Sturnus vulgaris) breeding in southernSweden. Previous research showed that almost all CBPs in thispopulation are floater females that have yet to breed in thecurrent season. We identified putative brood parasitic eggsthrough monitoring egg laying and verified parasitism usingprotein fingerprinting. We then determined whether parasiticeggs were larger, larger-yolked, or had higher concentrationsof yolk testosterone or androstenedione than control eggs. The14 brood parasitic eggs laid in active nests (those with clutchesof at least two eggs that were eventually incubated) did notdiffer from controls in any of these characteristics. Ten dumpedeggs, laid in nonactive nest-boxes or on the ground, were smallerand smaller-yolked than control eggs but did not differ in yolkandrogen concentrations. The failure of our prediction couldbe the result of high costs of investing in eggs, lack of competition-basedbenefits for chicks, or physiological constraints on egg manipulation.     

Parental allocation of food to nestling tree swallows: the influence of nestling behaviour, sex and paternity

Parents are expected to invest more in young that provide the greatest fitness returns. The cues that parents use to allocate resources between their offspring have received much recent attention. In birds, parents may use begging intensity, position in the nest or nestling size as cues to provision the most competitive young or those most likely to survive. It may also benefit parents to invest in young differentially by sex or relatedness if the fitness returns of sons and daughters differ or broods are sired by multiple males. We examined the allocation of food to tree swallow, Tachycineta bicolor, nestlings in relation to their begging behaviour, size, sex and paternity. Provisioning by parents was not related to nestling size, sex or paternity. The begging behaviour of nestlings did not differ with respect to sex or paternity. Both parents were more likely to feed nestlings that begged first or were closer to the nest entrance, suggesting that parents allocate food resources in response to cues that nestlings control. As a consequence, brood reduction was facilitated by biased provisioning within the brood in addition to the nestling size hierarchies created by hatching asynchrony. Copyright 2003 Published by Elsevier Science Ltd on behalf of The Association for the Study of Animal Behaviour.      

Physiological costs and carry-over effects of avian interspecific brood parasitism influence reproductive tradeoffs

Although models of co-evolution between brood parasites and their hosts primarily focus upon the cost to hosts in the current reproductive bout, the impact of brood parasitism may carry over to future reproductive attempts by altering resource allocation. Glucocorticoid stress hormones help mediate resource allocation to reproduction, yet they have rarely been examined in brood parasitic systems. Here we determined if shifts in parental care and corticosterone had carry-over effects on future reproductive effort in the rufous-and-white wren (Thryophilus rufalbus), a host of the Central American striped cuckoo (Tapera naevia). We found that parasitized parents had significantly higher stress-induced, but not baseline, corticosterone than natural parents during the fledgling stage, which was associated with changes in parental care. The high investment in current reproduction while parasitized may be due to the value of fledged chicks in tropical systems. This maladaptive response by parasitized parents was associated with delayed re-nesting and a reduced likelihood of nesting in the subsequent breeding season. Although a reduction in future reproductive effort can result from a combination of factors, this work suggests that fitness costs of brood parasitism are mediated by changes in corticosterone and parental care behavior that carry over into subsequent breeding seasons.     

Brood division in robins

Broods of fledgling robins Erithacus rubecula are sometimes divided between their parents so that each parent feeds only some of the chicks. These associations between a parent and certain of its young (‘family units’) are shown to be stable over periods of days. Brood division is most frequent in broods that are not followed by another nesting attempt. Experimental manipulation of the food supply suggests that brood division is relaxed when food is readily available. An analysis of the interactions between parents and chicks demonstrates that both adults and fledglings play a role in brood division. The possible functions of brood division are discussed with reference to ‘other types of care’, ‘parental efficiency’, ‘cheat countermeasure’ and ‘two types of chick’ hypotheses. Male parents feed chicks with shorter winglengths than do females: since females tend to have shorter winglengths than males, this suggests that chicks are cared for by parents of the opposite sex. Possible causes and consequences of this observation are discussed.     

Low survival of parasite chicks may result from their imperfect adaptation to hosts rather than expression of defenses against parasitism

Host parents exhibit a variety of behaviors toward avian brood parasites, but not all of their actions have necessarily evolved in response to costs imposed by parasites. To investigate whether common waxbills (Estrilda astrild) have evolved defenses specifically against parasitic pin-tailed whydahs (Vidua macroura), I studied the specificity and flexibility of host behaviors toward nestlings at two sites that differed significantly in parasitism rates and intensities. I focused on documenting nestling survival because V. macroura young match the elaborate gape morphology of E. astrild nestlings, a pattern that suggests hosts may possess unique defenses against parasite chicks. Parasite young survived significantly worse than host young in mixed broods. However, this apparent discrimination was not associated with parasitism risk as would be expected if defenses had evolved specifically to counter parasitism. Parasite young may have survived poorly compared to host young because individual chicks were less able to stimulate sufficient care from foster parents or because they were more susceptible to nestling competition, disease, or reduced provisioning by hosts. Mortality may have also been exacerbated by poor timing of parasite egg laying. In nonparasitized and parasitized nests, rates of nestling survival were similar, further suggesting that parenting behaviors that result in chick mortality did not evolve solely in response to parasite young. In addition, orange-breasted waxbills (Amandava subflava) and zebra finches (Taeniopygia guttata), rarely parasitized and nonparasitized relatives of E. astrild, experience similar levels of nestling mortality presumably as a result of phylogenetically widespread parenting strategies. Despite the similarity of parasitic V. macroura nestlings and E. astrild nestlings, I found no evidence that E. astrild parents possess defenses that allow for specific discrimination against parasite chicks during the nestling period. Rather than being subject to host defenses evolved in an arms race, Vidua chicks may simply be imperfectly adapted to life in the nests of their hosts.