If you’ve found a bird’s egg and are wondering if it contains a living embryo or is unfertilized, there are a few ways you can check without disturbing the delicate life inside. Being able to determine if an egg is alive is important for conservation efforts and satisfying curiosity.

If you’re short on time, here’s a quick answer to your question: Look for veins or movement inside the egg when candling it with a bright flashlight in a dark room. If you see the network of veins or the embryo moving, the egg is fertile and developing.

In this comprehensive guide, you’ll learn foolproof techniques used by experts to check for signs of life non-invasively. We’ll cover candling, floating, appearance, weighing, listening, timing from the lay date, and more.

With the right knowledge, you can easily and accurately assess if a bird egg contains a living embryo.

Candling the Egg

What is candling

Candling is a process of shining a bright light through an egg to observe the growth and development of the embryo inside. It allows you to visually inspect the egg without breaking it open. Candling takes its name from the original practice of using a candle as the light source.

Candling is commonly done by poultry farmers, bird breeders, and pet bird owners to check the fertility and progress of incubated eggs. It’s a useful way to identify clear, rotten, or dead eggs early on so they can be removed from the incubator.

Candling can also help determine how far along the embryo growth is and estimate the best hatching time.

How to candle an egg

Candling an egg is a simple process that involves using a bright focused light to illuminate the interior of the egg.

Here are the basic steps:

  • Obtain a bright flashlight or special “egg candler” designed for the purpose.
  • Place the large end of the egg directly against the light source in a dark room.
  • Hold the egg gently between your thumb and forefinger.
  • Shine the light through the egg while rotating it to get a full view of the interior.
  • Look for signs of fertility, embryo development, or problems.
  • Candle eggs after 5 to 7 days of incubation and again just before hatching.

For best results, choose a powerful flashlight that can pass light through the egg clearly. An egg candler with a bright bulb or LED light works great. The room should be completely dark to see inside the egg.

What to look for when candling

Here is what you may observe when shining a light through an incubated egg:

  • Clear egg – Indicates the egg is infertile and does not contain an embryo. The yolk and white will look clear without any veins or opaque spots.
  • Fertile egg – A network of veins radiating from the yolk indicates a developing embryo. You may see a dark spot or pulsating area where the embryo’s heart is beating.
  • Large air cell – As the embryo grows, an air pocket forms inside the large end of the egg. The air cell getting larger shows development is progressing.
  • Cracked egg – Cracks or punctures allow bacteria inside, so cracked eggs should be discarded.
  • Blood spots – Small blood vessels rupturing can leave small blood spots inside a fertile egg. It does not indicate a problem unless extensive.
  • Rotten egg – A rotten or dead egg will have a dark, murky interior with an unpleasant odor when opened.

Candling is a useful tool for monitoring incubated eggs. With some experience, you can determine the fertilization status, embryo growth stage, and expected hatching time. Knowing when a chick is ready to hatch helps ensure a successful entry into the world.

Floating the Egg

How to float an egg

Floating an egg is a simple but effective way to determine if it is still viable or not. Here are the steps to follow:

  1. Fill a bowl or cup with cold water. Make sure the container is deep enough for the egg to be fully submerged.
  2. Gently place the egg in the water. Be careful not to crack the shell when putting it in.
  3. Observe what happens. If the egg sinks to the bottom and lays flat on its side, it is very fresh. If it sinks but stands on its pointed end, it is a bit older but still good. If it floats, it is old and should be discarded.

The reason an egg floats when it gets older is that air builds up inside the egg as it ages, increasing its buoyancy. As an embryo develops, air pockets form that make the egg lighter. This difference in density makes a bad egg float.

What sinking or floating means

Here is a quick summary of what it means if an egg sinks or floats in water:

  • Sinks and lays flat on its side – Very fresh, just laid
  • Sinks but stands on its pointed end – Good, still edible but not as fresh
  • Floats – Old, discard it

As a general rule, if the egg sinks nicely to the bottom and lays flat, it is still good to eat or incubate. Floating means air has built up and bacteria may be growing, so it should not be used.

This simple float test takes just a minute and gives you an easy way to check the freshness of eggs. Before incubating or eating an egg, make sure to float it in water first. Sinking is good, floating is bad. Following this quick tip will ensure your eggs are viable and safe to use.

Inspecting Egg Appearance

Color, texture, and markings

When inspecting a bird egg, one of the first things to look for is the color, texture, and any markings or spots on the shell. The color can provide clues as to whether an egg is fertilized or not. For example, robin eggs are usually a bright blue color which indicates the egg is likely fertile.

On the other hand, if the egg appears whitish or pale, that could be a sign that the egg is infertile. The texture of the shell also offers hints – a hard, smooth shell is a positive indicator, while a thin or cracked shell may mean the egg is not viable.

In addition to the base color, look for speckles, spots, or streaks on the egg. These markings are often reddish-brown in color. Their presence suggests the egg has been fertilized since the markings are a result of pigments deposited as the egg develops in the mother’s oviduct.

An absence of markings can indicate an unfertilized egg. That said, some species naturally lay immaculate eggs without markings, so it depends on the type of bird. When in doubt, compare to other known fertile eggs from the same species.

Signs of fertility

When candling an egg – shining a bright light through the shell to see the interior – a few key signs can indicate if the egg is fertile and developing. A fertile egg will have a discernible air cell where the air pocket forms at the broad end of the egg.

As the embryo develops, blood vessels will become visible radiating out from the air cell. You may also see a dark spot which is the developing embryo. An infertile egg will lack blood vessels and the dark spot when candled.

During incubation, a fertile egg will grow increasingly opaque as the air cell enlarges and the egg solidifies. The developing embryo may cause the egg to rock back and forth slightly. Infertile eggs will remain translucent and still.

Always candle eggs at least twice, a few days apart, to allow time for development. Candling is the most reliable way to identify early signs of fertility.

Other tips for determining egg viability:

  • – Fertile eggs feel heavier when weighed in hand due to higher water content
  • – Hold egg up to ear – chirping or movement sounds can indicate a live embryo
  • – Carefully examine shell for hairline cracks – cracks suggest the egg is nonviable

Remember, never rotate or shake an egg after embryotic development begins – this can kill the growing embryo. Handle all eggs with care during inspection. When in doubt, let incubation continue and confirm signs of fertility.

Patience and careful observation will reveal whether bird eggs are progressing healthily.

Weighing the Egg

Getting an accurate weight

Getting an accurate weight of an egg during incubation is crucial to determine if the embryo inside is developing properly. Here are some tips for weighing eggs accurately:

  • Use a digital kitchen scale that measures in grams and can register small weight changes. Scales that only show whole ounces are not sensitive enough.
  • Make sure the scale is on a flat, level surface and the platform is clean.
  • Place the egg directly on the weighing platform, not in a bowl or cup which can affect the weight.
  • Weigh the egg in the same place each time under the same conditions.
  • Handle the egg carefully and minimize moisture loss by quickly moving it from the incubator to the scale and back.
  • Calibrate the scale periodically to ensure accuracy.

Record the weight of each egg on day 1 of incubation. Be consistent and weigh at the same time of day each time. Even small weight gains or losses can signal problems.

Weight changes over incubation

During incubation, an egg will usually experience the following characteristic weight changes if the embryo is developing normally:

  • Gradual weight loss during the first half of incubation as moisture evaporates through the shell and the embryo grows. About 10-15% loss is expected.
  • At around 10-12 days into incubation, the weight will reach its lowest point and start to climb.
  • Steady weight gain after “the dip” as the embryo rapidly develops and absorbs fluids.
  • Many experts recommend a total gain of at least 4-8% of the egg’s initial weight by pipping to indicate likely hatching success.

Weighing eggs periodically thus serves as a useful benchmark to determine if the chick is progressing properly inside the egg. Sudden gains or losses in weight can signify problems like incorrect incubation temperatures, improper humidity, or embryo death.

Paying close attention to egg weights during incubation is one of the best ways to monitor the hatching process.

Listening for Sounds

What to listen for inside the egg

When determining if a bird egg is alive, one of the key things to listen for is movement sounds coming from inside the egg. As the embryo develops inside the egg, its movements will make small tapping or scratching noises that can indicate the egg is still viable.

Here are some tips for listening to eggs:

  • Get close to the egg and listen carefully – any faint tapping or scratching sounds are positive signs of life inside the egg.
  • Tap lightly on the egg yourself and listen for a response – the embryo may tap back if it is alive and developed enough to move.
  • Compare to other eggs – if most eggs in a clutch are making noise but one is silent, it may not be developing.
  • Listen over several days – sounds will get louder and more frequent as the embryo grows. Lack of increasing sound may indicate the embryo is no longer thriving.

Subtle pipping sounds may also be audible in the last days before hatching as the chick starts to break through its shell with its egg tooth. However, be cautious about disturbing the egg at this point since the hatching process is delicate.

When to start listening

For most bird species, it’s best to start listening for sounds inside the egg after at least two-thirds of the incubation period has passed. Here are some guidelines:

  • Finches: Start listening after 6 days if the normal incubation period is 13-14 days.
  • Parrots: Start listening after 18 days if incubation takes 24-28 days.
  • Chickens: Start listening after 10 days for a 21 day incubation period.
  • Ducks: Listen from day 20-23 during a 28 day incubation.

Listening too early may give false results since the embryo has not developed enough to make audible noises. However, in the final third of incubation, tapping sounds are a great way to determine if the chick is actively moving and alive inside its egg.

Be sure to sanitize your listening tools and wash hands thoroughly before handling eggs to avoid transferring bacteria. With some careful listening at the right times, you can gain valuable insight into the progress of the embryo without disturbing its delicate development.

Estimating Lay Date

Why lay date matters

Knowing the approximate lay date, or date when a bird egg was laid, provides useful information for monitoring the status of wild bird populations. The lay date helps determine the age of nestlings and gives clues about whether a breeding pair is experiencing issues.

For example, early and late seasonal lay dates may indicate problems. Birds that lay eggs much earlier or later than normal could have difficulty finding food, establishing territory, or securing a viable mate.

Understanding lay dates over time provides data on how climate change and other factors influence breeding cycles.

On an individual nest basis, an accurate lay date assists with estimating the hatch date and fledging date. This helps wildlife rehabilitators determine if orphaned chicks are premature or delayed. It also aids researchers in scheduling important developmental assessments of chicks at standard ages.

How to estimate lay date in the wild

Since wild birds rarely lay eggs when observers are present, lay dates must be estimated. The main methods include:

  • Observing parental behavior – Guarding and incubating behaviors signal the parents are tending eggs. Back-calculating from the hatch or fledge date based on species incubation and nestling periods provides an estimated lay date range.
  • Egg floatation – Gently floating fresh eggs in water can help determine their age based on float levels. This suggests a lay date range. However, the egg must remain unwashed and technique accuracy varies.
  • Brood patch condition – Developed brood patches on adult birds indicate they are maintaining eggs. Noting patch size and vasculature can yield clues to lay timing.
  • While these methods provide good lay date approximations, the most accurate approach involves locating nests early in the breeding season and directly observing egg laying. However dedicated monitoring is often impractical.

    By combining less intrusive estimation techniques, reliable lay date ranges can be obtained. These are instrumental for properly assessing and tracking wild bird populations over time.


    Determining if a bird egg is alive takes some knowledge of egg development, but is fortunately something anyone can learn. Using techniques like candling, floating, inspecting, weighing, and listening non-invasively allows you to assess fertility without disturbing the embryo.

    With the right tools and these techniques, you can satisfy your curiosity about found eggs and contribute valuable data to conservation efforts. Understanding how to identify signs of life empowers both experts and casual observers to protect bird species for future generations.

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