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A chart showing an acceptance threshold for foreign eggs.
Relative trait distribution at A) one-egg and B) many egg stages of laying in the reed warbler. As more eggs are laid, the variation among eggs also increases. The birds increase their acceptance threshold to reduce costs of misrecognition if it is more likely that foreign eggs will resemble their own, which results in decreased rejection rates of parasitic eggs that once fell outside of their range of acceptable traits.
Redrawn from Moskat and Hauber 2007.

The importance of intraclutch variation in affecting the costs of mistaken recognition explains the success of another type of host bird. One species that shows great success against cuckoo eggs is the blackcap ( Sylvia atricapilla ). Within clutches, the birds’ own eggs show very little variation, so rejection decisions are based on the degree of mimicry of cuckoo eggs when compared to own eggs. In this case, there is very little cost to learning to distinguish own eggs and foreign eggs, so learning to recognize and reject is adaptive (Honza et al. 2004).

The effect of parasitism probability on egg rejection

The likelihood that a host will be parasitized will result in differences in frequency of egg rejection. If the threshold for accepting eggs is too low, then many of the host’s own eggs will be rejected along with the parasitic eggs. However, if the threshold is set too high, then the host will accept many of the parasitic eggs, but retain its own eggs. Among reed warblers, this threshold is set depends on the stage of egg laying as described above as well as their perceived probability that the nest has been parasitized. Birds that recognized a cuckoo at their nest usually rejected an egg afterward because the probability of benefitting from rejection was much greater than if no cuckoo had been observed at the nest (Davies et al. 1993) (See also [link] ). On the other hand, the rejection behavior of reed warblers that did not observe a parasite at the nest was best explained by the parasitism level in the area. As parasitism level decreases overall, the benefit of rejecting eggs diminishes since it is more likely that a bird will mistakenly reject its own eggs. Therefore, lower parasitism levels results in increased acceptor behavior.

How to recognize a cowbird

While species such as reed warblers will reject eggs based on whether they see a parasite at the nest, it is unclear how host birds learn to recognize parasites. One study performed on yellow warblers ( Dendroica petechia ), a species that suffers heavily from brown-headed cowbird parasitism, found several cues that elicited defensive responses such as sitting in the nest. Female yellow warblers responded strongly to stuffed cowbirds, which had shorter bills than models that had been modified with a longer bill. The authors suggest that recognition of shape confers an advantage since parasitism usually occurs in low light conditions.

Additionally, yellow warblers respond differently to male and female cowbirds even though their physical appearances are quite similar. When female cowbird chatter and male cowbird songs were played, female yellow warblers responded much more intensely to the female vocalizations, suggesting that difference in sexes is recognized by sound.

Questions & Answers

find the 15th term of the geometric sequince whose first is 18 and last term of 387
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The answer is neither. The function, 2 = 0 cannot exist. Hence, the function is undefined.
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Differences Between Laspeyres and Paasche Indices
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At high concentrations (>0.01 M), the relation between absorptivity coefficient and absorbance is no longer linear. This is due to the electrostatic interactions between the quantum dots in close proximity. If the concentration of the solution is high, another effect that is seen is the scattering of light from the large number of quantum dots. This assumption only works at low concentrations of the analyte. Presence of stray light.
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Source:  OpenStax, Mockingbird tales: readings in animal behavior. OpenStax CNX. Jan 12, 2011 Download for free at http://cnx.org/content/col11211/1.5
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