Many species of birds call at dawn in temperate regions. The phenomenon is referred to as "Dawn Chorus". Several explanations have been proposed for this. Which one of the options is NOT a correct explanation for the occurrence of "Dawn Chorus"?
The syrinx muscles are unable to move freely after early morning, resulting in poorer control over song production at later times of the day.
Dawn Chorus Explanation
The phenomenon where many bird species sing intensely at dawn, particularly in temperate regions, is known as the "Dawn Chorus". Scientists have proposed several reasons why birds engage in this behaviour.
Let's look at some of the common explanations for the Dawn Chorus:
- Acoustic Transmission: Sound travels better in the cooler, still air typical of dawn. This allows bird songs, which are often used for territorial defense and attracting mates, to travel further and more clearly.
- Honest Signalling: Singing is energetically demanding. Birds may be low on energy reserves after a night without feeding. Singing vigorously at dawn demonstrates their fitness and quality to potential mates and rivals, acting as an "honest signal" because only fit individuals can afford this energy expenditure at this time.
- Time Allocation: Dawn might be a good time to sing because it doesn't conflict with peak feeding times. Birds can dedicate the early morning hours to singing before they need to spend more time foraging later in the day.
The question asks which option is NOT a correct explanation for the occurrence of "Dawn Chorus". Based on the typical scientific understanding of bird behaviour and physiology, the explanation that suggests syrinx muscles become unable to move freely after early morning, resulting in poorer control over song production later in the day, is not considered a valid or widely accepted reason for the Dawn Chorus. Bird syrinx muscles are generally capable of complex movements throughout the day, and there is no biological basis for them becoming significantly restricted or losing control specifically after early morning hours in a way that would explain the peak in singing activity at dawn and reduced singing control later.
Therefore, the statement that the syrinx muscles are unable to move freely after early morning, resulting in poorer control over song production at later times of the day, is NOT a correct explanation for the Dawn Chorus.
Important Questions from Evolution and Behavior
Reduction in the frequency of heterozygous genotype with a concomitant increase in the frequency of homozygous genotype, in context of random mating is due to
A founder population has an Aa heterozygous genotype with a frequency of 1, and no individual with either AA or aa genotypes. With repeated self-fertilization, the frequency of AA, Aa and aa after three generations will be:
- Column X lists evolutionary ideas and scientists who proposed them, and Column Y lists the description of these ideas.
Column X
Column Y
A.
Modern synthesis by Julian Huxley
I.
A stochastic process where lineages show random geneological relationships when traced back in time.
B.
Phyletic gradualism by Charles Darwin
II.
Evolutionary change appears instantaneous between geological sedimentary layers.
C.
Punctuated equilibrium by Stephen Jay Gould and Niles Eldredge
III.
Synthesis between Mendelian genetics, population genetics, and selection theory.
D.
Coalescent model (inspired by) Wright- Fisher model
IV.
New species arise by the gradual transformation of ancestral species.
Which one of the following options represents all correct matches between Column X and Column Y? Which one of the following statements about the molecular clock hypothesis as proposed by Zuckerkandl and Pauling 1962 is CORRECT?
Consider alleles ‘A’ and ‘a’ in a population. The frequency of heterozygotes will be highest when:
