Originally published on Thursday, June 7, 2012
What is crop milk?
What is crop milk?Shortly after a baby dove hatches, parents start feeding the naked, blind, basically helpless chick crop milk. The milk is derived from sloughed-off, liquid-filled cells lining the crop of both parents. It's rich in fats and proteins to meet the baby's nutritional needs. The baby eats by sticking its head inside the parent's open mouth. That action causes the parent to produce the crop milk. The crop is part of the bird's digestive system, a sack where food can be stored for a while.
We've seen fewer Inca doves in our habitat this year. Could competition from white-winged doves be the reason? We've heard it can be. It's time to search for answers. Here's some of what we found.
White-winged doves' expanding range
Management of white-winged dove populations (relating to hunting the doves) uses information such as where the white-winged doves are, how many there are, and changes in these. Marked expansion of the white-winged doves' range in Texas has occurred since 1980. In contrast, Arizona's white-winged doves range and numbers have substantially decreased.
Most of Texas' expansion has been into urban areas. Historically, they were migratory. Currently, white-winged doves breed in more than 200 Texas counties; excluding most of East Texas. In 1980, only 10 Texas counties, all in the Rio Grande Valley, had regular breeding populations.
Inca doves' expanding range
Inca dove populations have expanded north from Mexico and the Rio Grande Valley as people settled the areas, and brought agriculture with them. Inca doves also inhabit urban backyards. And Inca doves (considered "friendly") even nest in patio flower boxes.
Crop milk for hatchlings
Both white-winged doves and Inca doves feed crop milk to their young the first 5-10 days after they hatch.
When courting, doves may vocalize (coo), strut, even perform aerial displays. Because many dove species have rather lengthy breeding seasons, their coo-ing may be heard much of the year.
Incas can even be heard on the hottest summer afternoons, because almost all other birds are silent at that time. Many listeners report their call sounds sad and monotonous ("no hope," "no hope") or resigned ("too hot"). Some also make one-syllable sounds resembling a desperate growl.
White-winged doves are a species having an aerial courting display. Dove species' display flights involve exaggerated flapping and clapping of wings. In one white-winged dove display flight, the male uses stiff wings to circle the female he's courting.
Incas heating up
Incas frequently flock together in cold weather. To preserve heat, a dozen or more of them perch on each others' backs to form a pyramid two to four tiers tall. After a few minutes, the birds on the bottom tier move to the top tier. And the Inca doves may maintain the pyramid for an hour or so.
Doves and pigeons are the only North American birds that can suction water into their esophagus. That means they can drink without having to raise their head. Other birds must dip their bill into water, then let the water drain into their throat by raising their head.
That's a very useful ability for doves. Lab studies have shown that some dove species drink as much as 15-25 percent of their body weight in water daily. Some may also depend on cactus fruit's water. Some that regularly eat fleshy fruit and berries may get much of their water from the food.
In dry areas, doves' water needs can require long flights to reach it, maybe even 25 miles. People seeking water have followed doves to a source because doves can remember where there's water and return to it. Early settlers in arid areas learned what a help the birds could be.
Sources: Sibley, "The Sibley Guide to Bird Life & Behavior"; Rylander, "The Behavior of Texas Birds"; Tveten, "The Birds of Texas"
Paul and Mary Meredith are master naturalists. Contact them at firstname.lastname@example.org.