The blue eggs found in ground nests are often the eggs of killdeer, a type of plover bird. Killdeer are medium-sized shorebirds with brown backs, white undersides, and distinctive black bands around their necks and across their chests. They lay clutches of 4 eggs that have a speckled, olive or buff appearance with dark splotches. However, some killdeer eggs can appear blue-green or turquoise in color. This unique coloration helps camouflage the eggs when the adult killdeer nests on the ground in open fields, gravel lots, or on the shores of lakes and rivers. The blue-green hue of the eggs allows them to blend in with the surroundings. In this article, we’ll explore why killdeer eggs can look blue, where killdeer build their nests, and how to identify killdeer eggs if you find some in a ground nest while out exploring nature.
Why Do Killdeer Eggs Look Blue?
Killdeer eggs can take on a blue-green cast due to pigments called biliverdins that are deposited in the eggshell as the egg develops. Biliverdins are created from the breakdown of red blood cells and contribute a blue-green hue to tissues, secretions, and eggshells in some bird species. The biliverdins act as a sunblock and may help protect the developing chick embryo from harmful UV radiation. The blue-green biliverdin pigments combine with the base tan or brown speckled color of killdeer eggs to create the turquoise masked appearance. The biliverdin concentration can vary from egg to egg which results in some eggs looking more brightly colored than others within the same clutch. The vivid blue eggs likely stand out less against the backdrop of blue water, open sky, or gravel lots where killdeer frequently nest. So the blue-green eggs act as camouflage to help conceal the eggs when the adults aren’t incubating them.
Where Do Killdeer Build Their Nests?
Killdeer construct very minimal ground nests made up of a shallow scrape or depression dug into gravel, sand, dirt, or pebbles. They add bits of grass, sticks, shells or rocks around the rim of the nesting site. Killdeer nest in open fields, pastures, golf courses, gravel roads, parking lots, rooftops, shorelines, and other landscapes with short vegetation and sparse tree coverage. Since they don’t build elevated nests, their ground nests blend into the surroundings very well. Their speckled, blue-green eggs are incredibly difficult to spot when the adult leaves the nest to search for food. The exposed nests are adaptations to the killdeer’s environment and life history. Ground nesting decreases competition with other bird species that place their nests up in trees and shrubs. It also enables quick and easy access for the precocial baby killdeer that leave the nest within hours after hatching. However, ground nests have their risks. The eggs and young are more vulnerable to predators and accidental destruction by vehicles, machinery, or foot traffic. The blue-green egg coloration provides vital camouflage that helps offset some of those risks.
Identifying Killdeer Eggs
If you come across some suspicious bright blue eggs in a ground nest, there are a few key features that can help confirm if they belong to killdeer:
- Size and shape: Killdeer eggs are ovate or pyriform in shape. They are intermediate in size, averaging about 1.5 inches long by 1.1 inches wide.
- Color: Ranges from tan, olive or brown base color with darker spotting to various shades of blue-green caused by biliverdin pigment deposition.
- Markings: Surface has brown, black or purplish-gray spots, speckles, scrawls concentrated around the wider end.
- Clutch size: Killdeer lay clutches of 3-6 eggs, usually 4. Though clutch sizes from 6-10 eggs have been reported on rare occasions.
- Nest site: Eggs are directly on ground in shallow scrape nests in open habitat like gravel, fields, roofs, shorelines etc. No elaborate nest construction.
- Egg texture: Smooth, slightly glossy surface sometimes with fine pitting.
Observing these egg characteristics along with clues like adult killdeer acting agitated or performing distraction displays around the nest site can help confirm that the blue eggs belong to killdeer.
Being able to identify the eggs hidden in ground nests takes some sleuthing skills. But it opens up insights into the incredible diversity of egg colors and shapes that have evolved in birds to aid survival. While brightly colored eggs might seem foolishly conspicuous, blue-green killdeer eggs demonstrate how even flashy eggs can be concealed when paired with the right nesting strategy and habitat. Those vivid turquoise gems practically disappear in ground nests built right out in the open!
Killdeer Egg Color Variation
Though some killdeer eggs take on a blue-green hue, there is lots of variation in color and patterning across killdeer clutches:
Egg Color | Description |
---|---|
Brown or tan | Base background color ranging from rich brown to light tan. |
Buff | Pale yellowish-brown base color. |
Pinkish | Base has a pinkish or rosy tint. |
Creamy | Eggs have a cream colored background. |
Greenish blue | Biliverdin pigments give the eggs a greenish-blue cast. |
Turquoise | More intense biliverdin staining leads to turquoise eggs. |
This range of background colors and intensities of blue-green overlay allows killdeer eggs to blend into a variety of environments from sandy beaches to grasses to gravel and dirt. Theegg color diversity within a clutch may maximize camouflage coverage.
Killdeer Egg Markings
In addition to diverse background colors, killdeer eggs also display an array of spotting and marking patterns:
Marking Type | Description |
---|---|
Spots | Covered with scattered round or oval spots. |
Speckles | Tiny speckles densely distributed across egg surface. |
Scrawls | Linear scribbles, wavy lines or scrawled patterns. |
Splotches | Large blotchy spotting concentrated around wider end. |
Sparse | Very light spotting overall. |
Heavy | Heavily marked with very dark spotting. |
This diverse palette of speckling and mottling further helps the eggs blend into ground nest environments. It also makes each egg unique for individual identification!
Clutch Sizes
A typical killdeer clutch contains 4 eggs, though clutch sizes can range from 3-10:
Clutch Size | Frequency |
---|---|
3 eggs | Uncommon |
4 eggs | Most common clutch size |
5 eggs | Common |
6 eggs | Fairly common |
7-10 eggs | Rare |
Why do killdeer lay so many eggs? With risky ground nesting, some eggs may get destroyed. Laying multiple eggs ensures a better chance at hatching at least a few chicks. The eggs are laid at intervals of 1-2 days so if the clutch is lost, the adult can re-nest and lay a new clutch. Large clutches maximize offspring productivity.
Incubation Period
Once the entire clutch is laid, incubation starts:
– Incubation period: 24-26 days
– Only the adult female incubates the eggs
– Adult may feign a broken wing to lure predators away
– Eggs left unattended are very well-camouflaged
– Eggshells very resistant to water loss
– Both parents feed newly hatched chicks
The excellent camouflage of the eggs allows the parents to occasionally leave the nest to search for food during incubation. The adaptations of the killdeer allow them to successfully hatch eggs despite minimal nest construction and lots of time off the nest.
Development of Killdeer Embryos
The embryos develop as follows inside the turquoise-colored eggs:
Day 1 | Fertilized egg with embryo just beginning development. |
---|---|
Day 3 | Heart starts to beat and nervous system forming. |
Day 4 | Beak starts to form. |
Day 6 | Face details like eyes visible. Egg tooth develops. |
Day 10 | Legs, wings, and tail feathers visible under thin skin. |
Day 16 | Scales, claws, and egg tooth hardened. Chick in final position for hatching. |
Day 19 | Yolk sac drawn into body in preparation for hatching. |
Day 24-26 | Chick hatches after pecking air cell, pipping egg, and pecking off cap. May use egg tooth to slice larger opening. |
The hidden transformation from embryo to hatchling takes place slowly within the confines of the egg. The bright blue eggs camouflage the baby birds as they grow.
Newly Hatched Killdeer Chicks
Killdeer chicks are precocial meaning they leave the nest shortly after hatching:
– Hatch with eyes open and downy feathers
– Able to walk and feed right away
– Follow parents who brood them at night or during cold weather
– May use distraction displays like injured wing act
– Fledge at 25-30 days old
– Resemble miniatures of the adults
The early mobility of killdeer chicks allows them to escape predators and quickly move to optimal feeding sites. Their ground nesting and early development are key adaptations to their open habitat niche.
Threats to Killdeer Eggs
Though well-camouflaged, killdeer eggs face substantial threats:
- Predators – Skunks, raccoons, crows, ravens, foxes, owls, hawks, snakes, rodents, and shrikes may raid nests.
- Weather – Flooding, hail, extremes of heat and cold can destroy eggs.
- Nest destruction – Farming, mowing, vehicle traffic, development, trampling by livestock, and gravel extraction can crush nests.
- Infertility – About 13% of killdeer eggs fail to hatch, some due to infertility.
- Human collection – People raiding nests for egg collections.
Yet despite all these hazards, killdeer continue to thrive due to their resiliency and repeatedly attempting to re-nest when needed. Their high egg output helps compensate for regular egg losses.
Killdeer Habitat and Range
Killdeer inhabit open ground over much of North America:
– Habitat: Open fields, pastures, meadows, shorelines, gravel lots, athletic fields, roofs, etc. Prefers minimal vegetation with good visibility.
– Range: Widespread across lower 48 United States and southern Canada.
– Migration: Northern populations migrate south for the winter. Southern populations may remain year-round.
– Nesting sites: Choose open ground with small stones, gravel, or low growing plants. Sparse human disturbance preferred.
– Feeds on insects, worms, snails and other small invertebrates.
– Forages mainly on ground but sometimes probes in shallow water.
Killdeer are adaptable birds able to thrive around human habitation. Their noisy calls and distraction displays announce their presence. Keep an eye out for their wonderfully camouflaged eggs in surprising settings!
Conservation Status
The killdeer has an extensive range and large total population. The species is considered to be of Least Concern by the IUCN. However, localized declines have occurred due to:
– Habitat loss from development and agriculture
– Increased predation from cats, foxes and ravens
– Vehicle collisions
– Human disturbance of nest sites
Maintenance of suitable shoreline, gravel lot, and open field breeding habitat will be important for long-term killdeer health. Reducing vehicle speed near nesting areas and keeping pets away from nests can also help bolster productivity. Protecting the killdeer helps maintain biodiversity and provides opportunities to observe these fascinating shorebirds up close!
Conclusion
The bright blue eggs peeking out from ground nests have a bird tale to tell! Their unique color likely evolved to help camouflage killdeer eggs in their open habitat by blending into the surroundings. But the blue hue also signals attentive parents, intricate embryonic development, and the incredible resilience of a bird that refuses to construct a proper nest! Next time you encounter a clutch of aqua eggs while out and about, remember they represent the continuation of the killdeer line. Take a moment to appreciate the wonder hidden in those colorful shells.