The Avian Brood Parasites: Deception at the Nest

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Screen music and the question of originality - Miguel Mera — London, Islington. Edition: Available editions United Kingdom. Female cuckoo finch and female southern red bishop. But which is which? Claire Spottiswoode , Author provided. William Feeney , University of Cambridge. The art of deception Brood parasites never build their own nests or raise their own offspring. Adam Wykes. Prinia egg rejection filmed by Jolyon Troscianko.

Brood parasitism in fish

This outraged tawny-flanked prinia has just seen a cuckoo finch near its nest. A model cuckoo finch. William Feeney Surprisingly, we found that the prinias were extremely aggressive to both the harmful female cuckoo finches and harmless southern red bishops — treating both as threats. The outside circle shows eggs laid by tawny-flanked prinia females, and the inside circle shows eggs laid by different cuckoo finch females. Claire Spottiswoode Just as expected, we found that the prinias were much more likely to reject the foreign egg after seeing one of the two female species than when they saw a male bird.

You might also like Zebra finches may have the potential to become brood parasites. Keith Gerstung.

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A juvenile black-eared cuckoo being fed by an adult speckled warbler. David Cook. Little bronze-cuckoo: my eggs are the best. Of these hypotheses the nest-site selection and habitat selection have been most supported by experimental analysis. Among specialist avian brood parasites, mimetic eggs are a nearly universal adaptation. The generalist brown-headed cowbird may have evolved an egg coloration mimicking a number of their hosts.

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

The eggshells of brood parasites are often thicker than those of the hosts. For example, the eggs of cuckoos are about One hypothesis, the puncture resistance hypothesis, states that the thicker eggshells serve to prevent hosts from breaking the eggshell, thus killing the embryo inside. This is supported by a study in which marsh warblers damaged their eggs more often when attempting to break cuckoo eggs, but incurred less damage when trying to puncture great reed warbler eggs put in the nest by researchers.

Another hypothesis is the laying damage hypothesis, which postulates that the eggshells are adapted to damage the eggs of the host when the former is being laid, and prevent the parasite's eggs from being damaged when the host lays its eggs. Most avian brood parasites have very short egg incubation periods and rapid nestling growth. In many brood parasites, such as cuckoos and honeyguides, this short egg incubation period is due to internal incubation periods up to 24 hours longer in cuckoos than hosts.

Some non-parasitic cuckoos also have longer internal incubation periods, suggesting that this longer internal incubation period was not an adaptation following brood parasitism, but predisposed birds to become brood parasites. Being larger than the hosts at growth is a further adaptation to being a brood parasite.

There is a question as to why the majority of the hosts of brood parasites care for the nestlings of their parasites. Not only do these brood parasites usually differ significantly in size and appearance, but it is also highly probable that they reduce the reproductive success of their hosts. The "mafia hypothesis" evolved through studies in an attempt to answer this question. This hypothesis revolves around host manipulations induced by behaviors of the brood parasite. Upon the detection and rejection of a brood parasite's egg, the host's nest is destroyed and nestlings injured or killed.

This threatening response indirectly enhances selective pressures favoring aggressive parasite behavior that may result in positive feedback between mafia-like parasites and compliant host behaviors. There are two avian species that have been speculated to portray this mafia -like behavior: the brown-headed cowbird of North America, Molothrus ater , and the great spotted cuckoo of Europe, Clamator glandarius. The great spotted cuckoo lays the majority of its eggs in the nests of the European magpie , Pica pica.

It repeatedly visits the nests that it has parasitised, a precondition for the mafia hypothesis. They observed the effects of the removal of cuckoo eggs on the reproductive success of the magpie and measured the magpie's reaction; the egg was considered accepted if it remained in the nest, ejected if gone in between visits, or abandoned if eggs were present but cold.


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If any nest contents were gone between consecutive visits, the nests were considered to have been depredated. The magpie's reproductive success was measured by number of nestlings that survived to their last visit, which was just before the nestling had been predicted to fledge from the nest. The results from these experiments show that after the removal of the parasitic eggs from the great spotted cuckoo, these nests are predated at much higher rates than those where the eggs were not removed. Through the use of plasticine eggs that model those of the magpie, it was confirmed that the nest destruction was caused by the great spotted cuckoo.

This destruction benefits the cuckoo, for the possibility of re-nesting by the magpie allows another chance for the cuckoo egg to be accepted. A similar experiment was done in — by Hoover et al. In their experiment, researchers manipulated the cowbird egg removal and cowbird access to the warbler's predator—proof nests.

In this hypothesis, female cuckoos select a group of host species with similar nest sites and egg characteristics to her own.

Brood parasite

This population of potential hosts is monitored and a nest is chosen from within this group. Research of nest collections has illustrated a significant level of similarity between cuckoo eggs and typical eggs of the host species. A low percentage of parasitized nests were shown to contain cuckoo eggs not corresponding to the specific host egg morph. In these mismatched nests a high percent of the cuckoo eggs were shown to correlate to the egg morph of another host species with similar nesting sites.

This has been pointed to as evidence for nest- site selection. A criticism of the hypothesis is that it provides no mechanism by which nests are chosen, or which cues might be used to recognize such a site. Parental-care parasitism emphasizes the relationship between the host and the parasite in brood parasitism.

Parental-care parasitism occurs when individuals raise offspring of other unrelated individuals. The host are the parents of offspring and the parasites are individuals who take advantage of either the nest or eggs within the family construct. Such dynamics occur when the parasites attempt to reduce their parental investment so they can invest the extra energy into other endeavors. Given the harm that avian brood parasites can do to their hosts' reproductive success , hosts have come up with various defenses against this unique threat.

Given that the cost of egg removal concurrent with parasitism is unrecoverable, the best strategy for hosts is to avoid parasitism in the first place. This can take several forms, including selecting nest sites which are difficult to parasitize, starting incubation early so they are sitting on the nests when parasites visit them early in the morning, and aggressively defending their territory. The host may be the one that ultimately ends up raising offspring after they return from foraging.

Once parasitism has occurred, the next most optimal defense is to eject the parasitic egg.

Medina: Evolution of tolerance in hosts of avian brood parasites? An integrative approach

According to parental investment theory, the host can possibly adopt some defense to protect their own eggs if they distinguish which eggs are not theirs. Recognition of parasitic eggs is based on identifying pattern differences or changes in the number of eggs.

Ejection behaviour has some costs however, especially when host species have to deal with mimetic eggs. Hosts may mistake one of their own eggs for a parasite's on occasion and eject it, and may damage their own eggs while trying to eject a parasite's egg. Among hosts not exhibiting parasitic egg ejection, some abandon parasitized nests and start over again. NET The black-headed duck relies entirely on other birds to incubate its eggs. Dale James, Ph. Did You Know? Brood parasitism is believed to be common among cavity nesters in part because the birds suffer from a shortage of suitable nesting sites, which can result in several females laying eggs in the same nest.

However, studied populations of common goldeneyes and black-bellied whistling ducks indicate that more than 50 percent of nest boxes remain unused in some locales, so additional explanations likely exist for this behavior. Placing nest boxes in conspicuous locations, such as on the edge of a pond, or in groups can increase the incidence of brood parasitism among wood ducks and other cavity-nesting waterfowl.

This occurs because parasitic hens can easily observe host birds coming and going from these man-made nest sites. Thus, nest boxes should be placed in less visible locations—such as in wooded areas—near suitable wetland habitats.

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In south Texas, researchers discovered that due to dump nesting one black-bellied whistling duck nest contained eggs laid by multiple females. Amazingly, a single hen incubated and hatched 38 of those eggs. Hooded mergansers, which are well-known brood parasites, have eggs that closely resemble billiard balls in size and thickness. Initially, waterfowl biologists believed that the eggs' hard shells offered protection from host females, who could try to break them if they were discovered in their nest.

However, most cavity-nesting waterfowl have relatively thick-shelled eggs, presumably because they are laid in confined spaces where they are more likely to be jostled during incubation.

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Researchers have found that rates of nest parasitism are lower among smaller ducks that nest in cavities, such as buffleheads. This is likely because smaller nest cavities are more numerous in the environment, giving these species more potential nesting opportunities, especially in secluded habitats. Brood Parasitism or Bust Some bird species, known as obligate brood parasites, forgo nesting altogether and rely entirely on other species to incubate their eggs. Related du magazine research science understanding waterfowl. Recently Added.



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