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Original title of C.F.M. Swynnerton's 1918 paper, published in Ibis, in which his experimental results confirmed egg ejection by several species of potential cuckoo hosts in southern Africa.
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... to study reactions of birds to cuckoo eggs. In a remarkable series of experiments followed by insightful interpretations and new ideas, Swynnerton (1916,1918) recorded responses of adult birds at more than 60 manipulated nests of nearly as many species of passerines, all potential cuckoo hosts, to eggs of other species placed into their nests (Fig. 1). The results were not replicated but they provided the most extensive in- formation on ejection by hosts of foreign eggs available at the time and, thus, implicitly, of cuckoo eggs. Swynnerton (1916:557) summarized his first experiment un- der the heading "The selective factors in the matter of Cuckoos' ...
Similar publications
Hosts of avian brood parasites are under intense selective pressure to prevent or reduce the cost of parasitism. Many have evolved refined egg discrimination abilities, which can select for eggshell mimicry in their parasite. A classic assumption underlying these coevolutionary dynamics is that host egg recognition depends on the perceivable differ...
Citations
... At the hosts' nest, parasitic cuckoos usually hatch first and then evict their hosts' entire clutch, resulting in a complete loss of fitness [1,2]. In response to the costs of parasitism, many cuckoo hosts have evolved effective defence mechanisms [3,4]. Rejection of parasitic eggs stands out as one the most commonly evolved defence mechanisms, and it often depends on visually perceived differences in features such as eggshell colour [1,5,6]. ...
Avian brood parasitism is a model system for understanding coevolutionary arms races, and the great reed warbler (Acrocephalus arundinaceus, hereafter 'warbler') and its parasite the common cuckoo (Cuculus canorus, hereafter 'cuckoo') are prime examples of this coevolutionary struggle. Here, warblers select for egg colour mimicry by rejecting poorly matched cuckoo eggs. Contrary to long-held assumptions, recent work showed that warblers tend to reject lighter and browner eggs but tended to accept darker and bluer eggs rather than basing rejection decisions solely on perceived colour differences (i.e. the degree of mimicry). This counterintuitive, colour-biased rejection behaviour would select for bluer and darker cuckoo eggs, but would only be adaptive if cuckoos were consistently lighter and browner than warbler eggs. Therefore, we tested whether warbler eggs were consistently bluer and darker than cuckoo eggs. To do so, we re-analysed eggshell reflectance spectra of warblers and the cuckoos that parasitized them in the Czech Republic. As expected, we found that warbler eggs were significantly bluer and darker than the cuckoo eggs at the population level. Thus, we demonstrate imperfect mimicry in a long-coevolved cuckoo host-race and provide insights for exploring the coevolutionary interactions among hosts and their brood parasites.
... The pressure exerted by such high costs forces the host to evolve abilities to recognize and reject parasitic eggs or to take defensive actions such as guarding against and attacking parasites (Davies and Brooke 1989;Soler et al. 1999;Røskaft et al. 2002;Avilés et al. 2004;Moskát 2005). Recognizing and rejecting parasitic eggs, compared to other defensive strategies, is an effective anti-parasitic strategy when parasitism happens because it is time-and effort-saving, and avoids direct confrontation with parasitic birds (Davies and Brooke 1989;Moksnes et al. 1991Moksnes et al. , 2013Sealy and Underwood 2012). ...
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.
... To combat host defenses, some lineages of brood parasites have evolved sophisticated eggshell mimicry to fool the hosts, which in turn, have evolved fine-tuned abilities to discriminate and reject the foreign egg. This suite of antiparasite defense behaviors has attracted considerable observational, comparative, and experimental research attention in the last decades (e.g., Grim, 2007;Medina and Langmore, 2015), albeit the first such experiments had been performed by naturalists already more than a century ago (reviewed in Sealy and Underwood, 2012). Experiments usually involve adding to or exchanging one or more foreign eggs in the host nest and observing the host's reaction. ...
The capability of hosts to reject the odd egg from their nest is one of the key defenses against avian brood parasitism. Considerable research effort has been devoted to exploring which phenotypic traits of eggshells facilitate to cue the recognition of the parasitic egg. Here we have reviewed studies addressing salient egg traits involved in the rejection of foreign eggs and used a formal meta-analysis to quantify their relative importance. Hosts appear to rely to a large extent on eggshell color traits, followed by maculation patterns. Hosts respond with similar rates of egg rejection to natural vs. model eggs and when breeding in both closed and open nests. Analyses of experiments on hosts of Cuculus and Molothrus parasites, the two best studied brood parasitic lineages with different co-evolutionary histories, yield similar conclusions. We also identify several poorly studied potential egg recognition cues, such as odor or weight, and recommend exploring even the visual traits in more detail, including chromatic and achromatic contrasts or experimentally manipulated egg maculation characteristics. Recent technological and sensory ecological advances open many new research avenues to experimentally examine the role of diverse egg characteristics in antiparasite defenses.
... An adaptive parasite has to choose the right time to quickly lay its eggs and then escape the crime scene, avoiding an attack from the host or reducing the suspicion and detection of the eggs by the host [6][7][8]. In addition to laying eggs in such a limited time (3-10 s) [7,8], the parasite usually removes one or two eggs from the host's nest [9][10][11]. ...
Avian obligate brood parasites gain an advantage by removing
the eggs of the cuckoos who have already visited the nest,
which can increase the chances of survival for their offspring.
Conversely, to prevent their eggs from being picked up by
the next parasitic cuckoo, they need to take some
precautions. Egg mimicry and egg crypsis are two alternative
strategies to prevent the parasitized egg from being picked
up by another parasitic cuckoo. Here, we tested whether the
egg crypsis hypothesis has a preventative effect when
common cuckoos (Cuculus canorus) parasitize their Oriental
reed warbler (Acrocephalus orientalis) hosts. We designed two
experimental groups with different crypsis effects to induce
common cuckoos to lay eggs and observed whether the
cuckoos selectively picked up the experimental eggs with
low crypsis levels in the process of parasitism. Our results
supported the egg crypsis hypothesis; the observed cuckoos
significantly preferred to select the more obvious white
model eggs. This shows that even in an open nest, eggs that
are adequately hidden can also be protected from being
picked up by cuckoo females during parasitism so as to
increase the survival chance of their own parasitic eggs.
... Which sensory cues hosts use to discriminate own vs. other eggs has been the subject of a vast experimental literature (reviewed in Moskát et al. 2008, Sealy & Underwood 2012, Manna et al. 2017, and points to the use of visual (e.g. Stoddard & Hauber 2017) and tactile (Tosi-German et al. 2020), but not olfactory (Soler et al. 2014), shell traits to recognize parasitic eggs. ...
Hosts of obligate avian brood parasites can reduce the costs of raising parasitic offspring by rejecting foreign eggs from their nests. Rejecter hosts use various visual and tactile cues to discriminate between own and foreign eggs. The blunt pole hypothesis specifically states that avian-perceivable visual information at and around the broader pole of the eggshell contains more salient recognition cues than does the sharp pole of the same egg. The directional prediction is, therefore, that eggs painted non-mimetically on their blunt pole should more likely be rejected relative to those similarly painted on their sharp pole. This hypothesis had been experimentally tested and its predictions supported solely in mimetic avian host-parasite systems, with hosts producing denser and more variable eggshell maculation patterns at the blunt pole, and in one species with immaculate eggs but still with distinctly discernible blunt-pole specific colouration. Here we aimed to expand upon these previous works and assessed whether the blunt pole of model eggs contains more salient egg rejection cues, relative to the sharp pole, for the American robin (Turdus migratorius), a robust rejecter of non-mimetic brown-headed cowbird (Molothrus ater) eggs. In this system host eggs are uniformly immaculate whereas the brood parasitic shell is maculated. We painted model cowbird-sized eggs on either the blunt or the sharp half to mimic the immaculate robin egg colours and the other half to resemble non-mimetic egg colours and patterns. There was no statistical support for the predicted outcomes of the blunt pole hypothesis in our trials as rejection rates were similar regardless of whether eggs were painted with non-mimetic colours on the blunt or sharp poles. Future work should test the role of asymmetrical signalling content for anti-parasitic rejection of eggs in additional host species, especially those with both immaculate own and mimetic parasitic eggs.
... In response to the often severe costs of brood parasitism (Davies 2000), many avian hosts reject foreign eggs from the nest (Sealy & Underwood 2012). An extensive experimental literature has explored how the size (e.g., Rothstein 1982), weight (Ruiz-Raya et al. 2015), shape (Guigueno & Sealy 2009), color ), maculation (Moskat et al. 2008, and/or surface texture (Kemal & Rothstein 1988) of natural or model eggs causes egg rejection within the same or across diverse host species. ...
Hosts of obligate avian brood parasites can diminish or eliminate the costs of parasitism by rejecting foreign eggs from the nests. A vast literature demonstrates that visual and/or tactile cues can be used to recognize and reject natural or model eggs from the nests of diverse host species. However, data on olfaction-based potential egg recognition cues are both sparse and equivocal: experimentally-applied, naturally-relevant (heterospecific, including parasitic) scents do not appear to increase egg rejection rates in two host species, whereas unnatural scents (human and tobacco scents) do so in one host species. Here I assessed the predictions that (i) human handling of mimetically-painted model eggs would increase rejection rates, and (ii) applying unnatural or natural scents to mimetically or non-mimetically painted model eggs alters these eggs’ respective rejection rates relative to controls. I studied wild American Robins (Turdus migratorius), a robust rejecter species of the eggs of obligate brood parasitic Brown-headed Cowbirds (Molothrus ater). There was no statistical evidence to support either prediction, whereas poorer color-mimicry was still a predicted cause of greater egg rejection in this data set. Nonetheless, future studies could focus on this and other host species and using these and different methods to apply and maintain the scenting of model eggs to more directly test hosts’ use of potential olfactory cues in the foreign-egg rejection process.
... Parasitism can have severe and negative impacts on host fitness, forcing hosts to evolve corresponding counter-adaptations against parasites (Davies 2000(Davies , 2011Soler 2014;Feeney et al. 2014). Among the various anti-parasite strategies, one such adaptation is the ability to recognize and reject foreign eggs (Davies and deL Brooke 1989a, b;Sealy and Underwood 2012). ...
Characteristics of egg surfaces serve as recognition cues that allow avian hosts to detect and reject foreign eggs in brood parasitism.
The blunt egg pole hypothesis suggests that the blunt egg pole is an essential signal in parasitic egg recognition. In the
present study, eggs of Yellow-bellied Prinia (Prinia flaviventris) were painted with black spots at either the blunt or sharp egg
pole to determine and compare the responses of different populations exposed to brood parasitism (parasitized population)
or not (non-parasitized population). These results supported the above hypothesis and showed that the parasitized population
displayed a higher rate of rejection of eggs with blunt pole-painted spots than with sharp pole-painted spots. In contrast, the
non-parasitized population accepted all experimental eggs, which may be related to decreased egg recognition resulting from
low exposure to brood parasitism.
... Egg recognition experiments are the most efficient tool used in the study of the relationships between brood parasites and their hosts. Pioneer naturalists began to study egg discrimination by hosts by introducing alien eggs into their nests as early as the beginning of the nineteenth century [13]. In the 1970s the first properly designed experiments (Rothstein 1970, in [13]) provided the foundation for future studies [7,8,10,[14][15][16][17][18]. ...
... Pioneer naturalists began to study egg discrimination by hosts by introducing alien eggs into their nests as early as the beginning of the nineteenth century [13]. In the 1970s the first properly designed experiments (Rothstein 1970, in [13]) provided the foundation for future studies [7,8,10,[14][15][16][17][18]. Numerous studies involving egg recognition experiments have been performed since then (see Appendix in [2]). ...
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.
... Such antiparasite adaptation may trigger cuckoos to evolve counteradaptations leading to an arms race, which provides a model system for studying co-evolution (Feeney et al. 2014, Soler 2014. Among several defenses of cuckoo hosts against parasitism, egg recognition and rejection behavior are among the most important (Moksnes et al. 1991, Davies 2000, Sealy and Underwood 2012. To reduce the costs of being parasitized, avian hosts have evolved the ability to recognize and remove foreign eggs (Brooke and Davies 1988, Davies and Brooke 1989a, b, Moksnes et al. 1991, Underwood and Sealy 2006b, De M á rsico et al. 2013. ...
Avian hosts of brood parasites can evolve anti-parasitic defenses to recognize and reject foreign eggs from their nests. Theory predicts that higher inter-clutch and lower intra-clutch variation in egg appearance facilitates hosts to detect parasitic eggs as egg-rejection mainly depends on the appearance of the egg. Therefore, we predict that egg patterns and rejection rates will differ when hosts face different intensity of cuckoo parasitism. We tested this prediction in two populations of the plain prinia Prinia inornata: Guangxi in mainland China with high diversity and density of cuckoo species, and Taiwan where there is only one breeding cuckoo species, the oriental cuckoo Cuculus optatus. As expected, egg patterns were similar within clutches but different among clutches (polymorphic eggs) in the mainland population, while the island population produced more uniform egg morphs. Furthermore, the mainland population showed a high rate of egg rejection, while the island population exhibited dramatically reduced egg grasp-rejection ability in the absence of parasitism by the common cuckoo Cuculus canorus. Our study suggests that prinias show lower intra-clutch consistency in egg colour and lose egg-rejecting ability under relaxed selection pressure from brood parasitism.
... Thus, by blocking the UV reflectance of the host eggs, the difference in the UV range between normal and UV-blocked host eggs is opposite to the difference between normal cowbird and host eggs. This supports evidence from previous studies indicating that rejecter species will reject any egg that differs sufficiently from their own, and that they do not necessarily recognize cowbird eggs as parasitic (Sealy & Underwood, 2012). ...
... We also found that the timing of laying affected egg rejection. Hosts were more likely to reject eggs later in the season than during mid-season, possibly indicating that hosts learn the appearance of their own eggs after their first breeding attempt (Lang, Bollinger, & Peer, 2014;Sealy & Underwood, 2012), as all hosts in our study usually attempt at least two broods per season (Cavitt & Haas, 2014;Smith, Hatch, Cimprich, & Moore, 2011;Vanderhoff, Sallabanks, & James, 2014). Lahti (2015) critiqued the use of UV-block in UV reflectance studies. ...
One of the most effective adaptations to counter avian brood parasitism is rejection of the parasitic egg, yet relatively few hosts reject eggs of the brown-headed cowbird, Molothrus ater. Studies have demonstrated that ultraviolet (UV; 300-400. nm) reflectance of eggs plays a role in egg rejection by hosts of parasitic cuckoos Cuculus spp. Only two studies have experimentally tested whether a cowbird host utilizes UV light when making egg rejection decisions, and those studies found no evidence that UV light was a significant factor. We experimentally blocked the UV reflectance of one host egg in the clutches of three rejecter species: brown thrasher, Toxostoma rufum, American robin, Turdus migratorius, and grey catbird, Dumetella carolinensis, to determine whether they utilize UV reflectance when rejecting eggs. We also measured the UV reflectance of each species' eggs. All host species rejected more of their own UV-blocked eggs than they did control eggs, but brown thrashers were significantly more likely to reject their own UV-blocked eggs than were American robins and grey catbirds. Brown thrasher eggs also reflected significantly more UV light than both American robin and grey catbird eggs. Our results coupled with those from similar studies suggest that hosts with brighter UV-reflecting eggs should be more likely to reject UV-blocked eggs than hosts with duller UV-reflecting eggs. This is the first study to demonstrate that UV reflectance is a parameter used by hosts of the brown-headed cowbird when rejecting eggs and further increases our understanding of the mechanisms of egg recognition in brood-parasitic hosts.
