Nests and nesting behavior of Crow

Crows, particularly the House Crow (Corvus splendens) and the Large-billed Crow (Corvus macrorhynchos), are recognized as some of the most intelligent avian builders. Crows construct substantial, well-engineered structures that reflect their high cognitive abilities and adaptability.

 

The House Crow is a typical tree‑nester, placing its nests high in tall trees close to human habitation. Nests are usually located 8–12 m above ground on strong horizontal branches or at branch forks, which provide mechanical support and partial concealment. In highly urbanised areas, when suitable trees are scarce, crows may also nest on artificial structures such as electric poles or communication towers.

Nest structure and materials

• The nest of the House Crow is a large, deep, cup‑shaped structure with a firm outer framework and a softer inner lining. 
• The outer part is built of interwoven twigs and small branches, tightly locked to form a rigid platform that can bear the weight of adults and chicks and withstand wind. 
• In agricultural and urban habitats, crows frequently incorporate anthropogenic materials such as metal wires, plastic strings, ropes, cloth pieces and polythene, which further bind and strengthen the framework.

• The inner cup is neatly lined with softer materials including dry grasses, rootlets, leaves, fibres, feathers, cotton and rags.
•  In many Indian populations, fresh Eucalyptus leaves are  added to the lining, and these are believed to play a role in insect‑repellence and nest sanitation. 

        Nest‑building behaviour

• Nest construction generally begins in early April in North Indian plains and can extend into June, with maximum activity in May. 
• Both sexes participate in nest building: the pair first establishes and defends a nesting territory around a suitable tree, then repeatedly brings material to the chosen branch. Adults break twigs directly from trees or collect them from the ground and transport them singly to the nest site, where they are woven and compacted into place. 

• Construction of a fresh nest usually requires about 1–2 weeks before egg‑laying, although some pairs continue to add material during incubation. House Crows may repair and reuse old nests in subsequent breeding seasons, or partially dismantle old structures to obtain material for new nests, especially in colony sites where nest material is in high demand. The use of wires and plastic in urban areas reflects strong behavioural plasticity and adaptation to human‑modified environments.

 
        Nesting cycle and parental behaviour

• In India, the main breeding season of the House Crow extends from about March/April to July/August, though some populations may also breed in a secondary period later in the year. The typical clutch consists of 3–5 pale blue‑green eggs speckled or streaked with brown. Incubation is shared by both sexes, with the female usually undertaking a larger proportion of sitting, while the male provides food and helps guard the nest.

• Incubation lasts roughly 15–20 days, and the nestlings remain in the nest for about 3–4 weeks before fledging, depending on locality. 
• Both parents feed the chicks with a wide range of food items (insects, grains, kitchen refuse, small vertebrates), and parental care continues for some time after fledging as young birds accompany adults to foraging sites. 

• House Crows are highly protective and aggressive at the nest: they produce loud alarm calls and may mob potential predators or human intruders, a behaviour that, together with colonial nesting in some sites, enhances nest defence.

Feature	House Crow Nesting Summary
Nest Type	Deep, robust cup-shaped platform.
Building Materials	Twigs, metal wire, Eucalyptus leaves (sanitation), soft fibers.
Site Preference	High branch forks (8–12m); proximity to human refuse.
Parental Roles	Biparental; shared incubation and feeding; communal defense.
Major Threat	Brood parasitism by the Asian Koel.

Nests and Nesting behavior of Pigeon

Species:  Rock Pigeon / Feral Pigeon (Columba livia).

The nesting behavior of Columba livia is characterized by evolutionary conservatism. Despite their successful colonization of urban environments, their nesting remains tethered to their ancestral origins as cliff-dwellers. Their approach is often described as "minimalist," prioritizing site security and metabolic efficiency over structural complexity.

Natural sites: cliffs, caves, rock ledges, crevices.

Urban/man‑made sites: Ultimate urban opportunists, building ledges, balconies, under eaves, inside abandoned rooms, stairwells, bridges, gutters, AC ledges.

 Microhabitat preference:

·        Sheltered from direct rain and strong wind.

·        Overhead cover and side walls for concealment.

·        Safe, stable support such as a corner, niche, or flat ledge.

Structural Morphology and Composition

Pigeon nests are structurally primitive compared to the intricate weaving seen in passerines (e.g., weaver birds).

• General Architecture: A shallow, flimsy platform nest. It is a loosely arranged, slightly concave disc designed primarily to prevent eggs from rolling off a flat surface.

• Primary Materials: The foundation consists of fine twigs, stems, and dry grasses.

• Anthropogenic Adaptation: In urban ecosystems, pigeons exhibit high plasticity in material selection, incorporating wire, plastic zip-ties, string, and paper debris.

• The Biological "Cement": A unique feature of pigeon nests is the role of guano (feces). Unlike many bird species that practice nest sanitation, pigeons do not remove droppings. Over successive broods, the accumulation of feces, eggshells, and organic matter desiccates and hardens, transforming a flimsy twig platform into a reinforced, "pot-like" mound.

Site Selection and Philopatry

Pigeons are obligate ledge and cavity nesters. Their selection criteria are driven by two main factors:

1. Topographical Mimicry: They select high, flat surfaces (window ledges, bridge girders, rafters) that replicate the verticality and security of Mediterranean sea caves and rocky cliffs.

2. Philopatry (Site Fidelity): Pigeons are highly site-faithful. They tend to return to the same nesting site for multiple years. This reuse leads to a massive accumulation of nesting material and hardened waste, providing increased thermal mass for future broods.

3. Predation Buffer: They prioritize sites with an "overhang" or shelter, protecting the brood from aerial predators and adverse weather.

 Division of Labor

Nest building is a highly coordinated, dimorphic cooperative activity.

A. Role of the Male (The Collector)

• Site Scouting: The male identifies and defends the territory. He utilizes acoustic (cooing) and visual (strutting) displays to signal site suitability to the female.

• Material Acquisition: The male is responsible for the majority of the physical labor. He retrieves materials one item at a time, delivering them to the female.

B. Role of the Female (The Architect)

• Structural Arrangement: The female remains stationary at the chosen site. As the male delivers materials, she tucks them around her body, using her own breast to shape the internal concavity of the nest.

Nesting Behavior:

The pigeon’s nesting strategy is "low-cost, high-frequency." By using minimal materials and a shared workload, they can focus energy on rapid reproduction and year-round brood rearing, making them one of the most successful avian species on the planet.

Pigeons are opportunistic breeders, often producing 5–6 broods per year if food is abundant.

• Clutch Size: Almost invariably two white eggs.
• Shared Incubation: Both parents share the metabolic cost of incubation. The male typically takes the "day shift" (approx. 10:00 AM to 4:00 PM), while the female incubates during the night and early morning.

Crop Milk:

• Both parents produce this protein- and fat-rich secretion in their crop lining, regulated by the hormone prolactin.
• For the first few days, the "squabs" (chicks) are fed exclusively on this milk, allowing for an incredibly rapid growth rate that is independent of the external availability of insects or seasonal food sources.

Feature	Urban Population	Wild Rock Dove (C. livia)
Substrate	Concrete, metal, AC units	Limestone crevices, sea caves
Nesting Material	Twigs, wire, synthetic debris	Seaweed, roots, sticks
Sanitation	Low (Fecal accumulation)	Low (Fecal accumulation)
Primary Predators	Feral cats, Peregrine Falcons	Snakes, gulls, rodents.

Study of Phototaxis behavior in insect larvae

Phototaxis is the innate behavioral response of an organism to a light stimulus, resulting in directed movement toward (positive) or away from (negative) a light source. In insect larvae, this behavior is a critical survival mechanism, primarily driven by the need to balance foraging with protection.

 Biological Drivers

• Sensory Anatomy: Lacking complex compound eyes, larvae rely on Bolwig’s organs—simple clusters of photoreceptors located at the head.

• Navigation Strategy: Larvae use klinotaxis, a method of orientation where they swing their heads side-to-side to compare light intensities, choosing the direction that minimizes or maximizes exposure.

• Evolutionary Advantage: For most species, negative phototaxis is dominant. By moving into the dark, larvae remain concealed from predators, avoid lethal UV radiation, and stay within moist, nutrient-rich substrates (like soil or decaying fruit) to prevent dehydration.

Objective

To determine whether insect larvae exhibit positive phototaxis (moving toward light) or negative phototaxis (moving away from light), and to quantify the strength of that response.

Materials & Equipment

• Subjects: 20–30 third-instar Drosophila larvae (or similar slow-moving larvae).

• Testing Arena: A large Petri dish or a flat plastic tray lined with 1% agar (provides a moist, crawlable surface).

• Light Source: A directional LED lamp or a focused flashlight.

• Dark Room: Or a blacked-out box to eliminate ambient light interference.

• Contrast Background: A black sheet of paper placed under the agar dish to make the white larvae visible.

• Tools: Fine paintbrush (for transferring larvae), stopwatch, and a ruler.

Experiment

1. Preparation of the Arena

A thin layer of 1% non-nutrient agar is prepared in a Petri dish. This ensures the larvae don't dehydrate and can move easily.
Divide the bottom of the dish into three zones using a marker on the outside: Light Zone, Neutral (Middle) Zone, and Dark Zone.

2. Control Setup

Before testing light, place 10 larvae in the center of the dish under dim, uniform lighting. Observe them for 5 minutes. If they distribute randomly, your arena is unbiased.

3. The Phototaxis Test

Dark Adaptation: Keep the larvae in a dim environment for 10 minutes prior to the test to standardize their sensory state.

Positioning: Place a single larva (or a small group) exactly in the Neutral Zone using a moistened paintbrush.

Light Application: Position the light source at one end of the dish so that the "Light Zone" is brightly illuminated while the "Dark Zone" remains shaded (use a piece of cardboard as a foil if necessary).

Observation: Start the stopwatch. Record the position of the larvae every 30 seconds for a total of 5 minutes.

4. Quantifying Movement & Data Collection

   Response index (RI)= (N_light-N_{dark ) /} N_total

N_{light: Number of larvae in the light zone.}

N_{dark: Number of larvae in the dark zone.}

N_{total: Total number of larvae tested.}

  

RI Value	Interpretation
+1.0	Perfect Positive Phototaxis (all moved to light)
0.0	Neutral/Random movement
-1.0	Perfect Negative Phototaxis (all moved to dark)

5. Comment: The movement of Drosophila larvae is a precise interplay between physical constraints and developmental programming.

• Locomotory Barriers: Initial inactivity is often due to surface tension; the larvae must generate enough force to overcome the adhesive properties of the moisture film on the agar.

• The Behavioral Switch:

  • Young Larvae (Positive Phototaxis): Driven by the need to forage, young larvae move toward light and moisture to locate food sources.

  • Older Larvae (Negative Phototaxis): Pre-pupal larvae transition to light-avoidance behavior to find dark, protected environments for pupation.

• Experimental Rigor: Given this 180-degree shift in behavior, consistency in larval age is the most critical factor for obtaining reproducible data.

Study of geotaxis behavior in earthworm

 

Investigating geotaxis, the movement of an organism in response to gravity is a classic behavioral biology experiment. Earthworms (Lumbricus terrestris) are subterranean organisms that have evolved complex sensory mechanisms to navigate their environment without the aid of sight. Understanding their geotactic response is crucial for comprehending how they maintain their biological niche. By sensing the pull of gravity, earthworms can effectively burrow deeper into the soil to reach optimal moisture levels, avoid surface-level predators, and escape the lethal effects of UV radiation.

Earthworms typically exhibit positive geotaxis (moving toward gravity) as an adaptation to stay underground, maintain moisture, and avoid predators.

1. Objective

To determine whether earthworms exhibit positive, negative, or neutral geotaxis when placed on an inclined plane.

2. Materials Required

• Organisms: 5–10 healthy earthworms (e.g., Lumbricus terrestris).
• Apparatus: A flat wooden or plastic board (approx. 30cm x 50cm), a protractor, and a stopwatch.
• Environment: Paper towels, dechlorinated water, and a dim light source (earthworms are photonegative).
• Safety: Gloves and a soft brush for handling.

3. Experimental Procedure

Setup

1. Preparation: Cover the board with a damp (not soaking) paper towel. This provides traction and prevents the worm from desiccation.
2. Angle Selection: Use a stack of books or a laboratory stand to tilt the board at a specific angle (e.g., 45°).

Execution

1. Orientation: Place an earthworm in the center of the board, oriented horizontally (perpendicular to the pull of gravity).

[ Starting them horizontally ensures they must actively choose to turn upward or downward.]

2. Observation: Allow the worm to acclimate for 30 seconds.
3. Recording: Once the worm begins moving, track its head direction for 2 to 3 minutes.
4. Repetition: Repeat the trial at least 5 times with different worms to ensure statistical significance.
5. Variable Change: Adjust the incline to different angles (30⁰, 60⁰&  90⁰) to see if the intensity of the response changes with the gravitational gradient.

4. Data Collection Table

Trial	Incline Angle	Initial Direction	Final Direction (Up/Down)	Time Taken (s)
1	450	Horizontal	Downward	45
2	450	Horizontal	Downward	38
3	450	Horizontal	Downward	40

5. Analysis and Interpretation

To quantify the behavior, one can calculate the Mean Response Ratio:

R = n_down - n_up  /  N

Where:

• n_down = Number of worms moving downward.

• n_up = Number of worms moving upward.

• N = Total number of trials.

Result: In most conditions,  the earthworm will turn its prostomium (head) downward and move toward the base of the board. This confirms positive geotaxis.

Fig: Design of experiment to study geotaxis behavior in earthworm

6. Critical Success Factors

• Moisture Control: If the board is too dry, the worm may exhibit "escape behavior," moving randomly and rapidly regardless of gravity.

• Light Interference: Ensure the light source is directly above the board. If light comes from one side, the worm may move away from the light (negative phototaxis), which could be mistaken for a geotactic response.

• Vibrations: Earthworms are sensitive to vibrations; keep the lab environment quiet to avoid startling the specimens.

Study of Circadian functions in humans (daily eating, sleep and temperature patterns).

 Study of Circadian functions in humans (daily eating, sleep and temperature patterns).

 

The study of circadian rhythms examines the endogenous (internal) biological clocks that coordinate physiological processes over a 24-hour cycle. In humans, these rhythms are primarily governed by the Suprachiasmatic Nucleus (SCN) in the hypothalamus.

Understanding the interplay between core body temperature (CBT), sleep-wake cycles, and nutritional intake is vital, as chronic disruption (circadian misalignment) is linked to metabolic disorders, cardiovascular disease, and cognitive decline. This study aims to map these three variables over 30 days to observe their phase relationships and stability.

Procedure

The study follows a longitudinal observational design over 30 consecutive days. Participants are required to maintain their "free-living" conditions while adhering to strict data logging protocols.

1. Temperature Monitoring

• Device: Use a continuous wearable thermometer or a tympanic thermometer for manual checks.

• Frequency: Measurements are taken every 2 hours during wakefulness and once immediately upon waking and before sleep.

• Goal: To identify the nadir (lowest point) and peak of the body's thermal rhythm.

2. Sleep Tracking

• Method: A combination of actigraphy (wrist-worn motion sensors) and a daily sleep diary.

• Metrics: Record "Lights Out" time, "Sleep Onset" latency, total sleep duration, and subjective sleep quality on a scale of 1–10.

3. Dietary Mapping

• Method: Real-time logging of all caloric intake using a mobile application.

• Metrics: Record the exact timestamp of the first and last meal (the feeding window).

• Restriction: Participants are asked to note any caffeine or alcohol consumption, as these act as chemical "zeitgebers" that can shift the internal clock.

4. Data Correlation

• Analysis: At the end of 30 days, the data is plotted to see if the temperature nadir consistently occurs ~2 hours before waking and how meal timing influences the onset of evening sleepiness.

Data Sheet:

https://drive.google.com/file/d/1S07rrWUzTnAGmkGZTLdSsnoxMXFST-wj/view?usp=drive_link

Conclusion:

• Average Body Temperature: 37.0 +/- 0.5 degree C
• Sleep/Wake Cycle: Regular 8-hour sleep windows from 11:00 PM to 7:00 AM.
• Metabolic Cues: Three distinct eating events per day at 8:00 AM, 1:00 PM, and 7:00 PM.

·     The 30-day data reveals a highly synchronized circadian system. The core body temperature follows a robust sinusoidal pattern, peaking in the late afternoon and reaching its nadir at approximately 4:00 AM. This thermal dip aligns perfectly with the mid-sleep phase, facilitating deep restorative rest.

·    The feeding window (08:30–19:30) acts as a stable metabolic anchor. By concluding meals three hours before sleep, the subject avoids digestive thermogenesis, allowing the body temperature to drop efficiently for sleep onset. Overall, the minimal phase drift suggests strong entrainment to light and lifestyle cues, indicating optimal physiological health and rhythmic stability.

Model questions : Mitochondria

 

     Section 1: Structure and Organization

• Describe the structure of mitochondria.

• Name the enzymes present in mitochondria.

• Define mitoplast.

• Describe the structural differences between the inner mitochondrial membrane (IMM) and the outer mitochondrial membrane (OMM). How does the protein-to-lipid ratio reflect their functions?

• What is the role of cardiolipin in the inner membrane, and how does its unique structure support the function of the respiratory chain complexes?
• Explain the significance of mitochondrial cristae junctions. How does the shape of the cristae affect the local pH gradient?

• How is the intermembrane space (IMS) chemically different from the cytosol, considering the presence of porins in the OMM?

• Define mt DNA.
• What is Cristae mitchondralis?
• Define Subunits of Person & Subunits of Fernandez Moran.
• Briefly describe Mitochondrial membrane.
• What are the function of mitochondris.
• 
  

• Section 2: The Mitochondrial Respiratory Chain (ETC)

• Describe the Q-cycle in Complex III. Why is it necessary for a two-electron carrier (Ubiquinol) to transfer electrons to a one-electron carrier (Cytochrome c)?
• What are the specific prosthetic groups involved in Complex IV (Cytochrome c Oxidase) that allow for the reduction of oxygen to water without releasing reactive oxygen species (ROS)?
• Explain the inhibitory mechanism of Rotenone, Antimycin A, and Cyanide on specific complexes of the ETC.
• Compare and contrast the entry points of electrons from NADH and FADH₂. Why does NADH oxidation result in more ATP than FADH₂?
• Complex II (Succinate Dehydrogenase) is unique in the ETC. Explain its dual role in the TCA cycle and the respiratory chain.

Section 3: Chemiosmotic Hypothesis

• Define the Proton Motive Force ( Δp) and explain its two components: the electrical potential (ΔΨ) and the chemical gradient ( Δ pH).
• How did Peter Mitchell’s Chemiosmotic Hypothesis challenge the previous "chemical intermediate" theory of ATP synthesis?
• What is the effect of uncoupling proteins (UCP1/Thermogenin) on the proton gradient, and what is the physiological outcome in brown adipose tissue?
• If the IMM were to become permeable to protons, how would this affect the rate of oxygen consumption versus the rate of ATP synthesis?

Section 4: ATP Synthase and Oxidative Phosphorylation

• Describe the structural symmetry of the F1 and Fo subunits of ATP Synthase. Which part acts as the "stator" and which as the "rotor"?
• Explain Paul Boyer’s Binding Change Mechanism. Distinguish between the three conformational states of the β subunits: Open (O), Loose (L), and Tight (T).
• How does the flow of protons through the c-ring generate rotational torque? Mention the role of the aspartate (or glutamate) residue in the c-subunit.
• Calculate the theoretical P/O ratio for NADH. Why is the actual observed ratio in vivo often lower than the theoretical maximum?
• Describe the role of the Adenine Nucleotide Translocase (ANT) and the Phosphate Translocase in maintaining a steady supply of substrates for ATP synthesis.
• How does the Glycerol-3-Phosphate shuttle differ from the Malate-Aspartate shuttle in terms of the number of ATP molecules produced per cytosolic NADH?
• Explain the phenomenon of Respiratory Control. How does the concentration of ADP in the matrix regulate the rate of oxygen consumption?
• Write notes on: Q cycle, ATP synthase, uncouplers, Hydrogen ion concentration.
• Name  the inhibitors acts on Complex I,II,III & IV
• Describe the flow of electrons from NADH⁺+H⁺  produced in TCA Cycle to ATP synthesis.
• Give a brief account of the structure of ATP synthase. Discuss the mechanism of ATP synthesis.