A Closer Look at Chicks
April 14, 2017 ~ This is my fifth year to visit the Smith Oaks Rookery and watch the birds court, nest and raise their young. The first time I was totally overwhelmed by all the activity, but I have found my most successful trips are when I focus on a particular species or behavior. One year I concentrated on the Great Egret's nest building activities and wrote Here is a Stick for You. Watching them closely you can often notice unusual behavior such as extra-pair coupling I told you about in Twigs and Trickery. And last year I wrote about the Great Egret chicks and how the youngest chick is seldom successful in getting enough food to thrive in Return to the Rookery.
On my last trip I wanted to look at what the Great Egret parents were feeding their offspring. And by concentrating on the chicks I noticed a lot more than I bargained for.
Let's start with a quick overview of the Great Egrets life cycle. We are lucky to have them year round here on the Texas Coast. They are solitary birds most of the year, but congregate in large single species or mixed-species colonies to court and raise their young. The male may start a nest to attract a female; the pair will then finish the nest. She generally lays 3-4 eggs and begins to incubate with the first laid egg. She will lay an egg each day or even two days apart which means the chicks hatch over a period of days or asynchronously. The first hatched chick has a head start and the last hatched is severely disadvantaged in comparison to his older nest mates.
This is not what you see with your backyard Bluebirds and Wrens; they wait until the egg laying is finished and then incubate all the eggs together - which ensures they all hatch within hours of each other.
Here is our parent taking a break from sitting on the multiple eggs. Incubation duties are shared. They may stand and shade the nest if the temperatures are too high to avoid overheating the eggs. You can see the adults rising and resettling, even rearranging the eggs with their bill.
And here we have the doting and protective parent with three loving chicks. Two are alert and upright and one is nestled down in the nest a bit. Go ahead, click on the photo for a larger view. You knew you can do that with all the photos I post, right?
Feeding time is not very pretty. All the literature says "the chicks are fed regurgitated food" so my goal for the day was to see exactly what regurgitated food looked like. Because we all are familiar with baby food; and these are babies, right? The expectation is for something with pablum consistency.
Not a whole frog.
At least this fish is small and bit sized. I think the adult had several fish in its gullet as I saw the chicks pecking frantically at the bottom of the nest. Some must have escaped as the adult released the food.
And this one looks to be more... ah... processed than the previous. The chicks latch on the the adult's bill as soon as it can be reached. It may take a while for the food to become available as I have seen adults stand at the nest for 5 minutes or more before submitting to the grab fest below. The strongest chick latches on and monopolizes all of the offered food. The adult makes no effort to parcel out the food equitably. She may offer food more than once, but the recipient is whoever is the strongest and most tenacious.
With this kind of aggression, the last born and/or weaker chicks do not get enough food to survive. This late in the season most of the remaining chicks are active and strong with the weaker ones dead and pushed out of the nest.
This photo is from last year. The smaller chick in the front had struggled to get part of the food; you can see some liquid on his bill, and his larger nest mate has attacked him for his success. Not only does the runt lose out on being fed, he is mercilessly picked on by the stronger chicks.
Great Egrets, many raptor and other large birds practice siblicide or killing of a brother or sister either by violence or starvation. Originally thought to be a strategy for brood reduction in times of scarce resources in that the senior chicks would get most of the food and survive. Parents did not have to distribute resources equally; the chicks resolved the issue. In times of plenty, perhaps all the chicks survived. See Douglas Mock, 1986
Later literature seems to imply it is a bit more complicated. Aggression in Great Egrets chicks diminishes when there are only two chicks; as there is less competition for food and an avoidance of unnecessary conflict and injury might be present. Parents have been observed to abandon nests with only one chick so maybe killing all your nest mates is not a good chick strategy. See H.C.J. Gadfray, 1986
Great Egrets offer food in ways that seem to provoke aggression; the chicks must latch on to the bill thus monopolizing the food source. Great Blue Herons are also large long-legged waders but they drop the regurgitated food into the nest which offers all the chicks a more equal chance to feed. And, the Great Blue Heron chicks are not as aggressive toward their nest mates. What happens if you swap the chicks? Researchers have done that and the Great Blue Heron chicks raised by Great Egrets become more aggressive when the food presentation manner is changed. And when the Great Egret chicks are offered food by Great Blue Heron foster parents that cannot be monopolized? They are aggressive no matter who raises them. See a summary of the literature by Dina Catallo
Further analysis of Cattle Egrets show the first laid eggs have more than twice the level of testosterone and other androgens in their egg yolk than later laid eggs. Egret chicks are "programed" from the beginning to be aggressive in the nest. NY Times article by Carol Kaesuk Yoon, 1996
When I first started watching this nest, the parent that had been standing guard started preening when the other parent arrived with food. There were two chicks in the nest and one at the edge. I am thinking "oh my, the poor little thing is going to fall out!"
One of the chicks mobbed the adult to provoke feeding and the other... started pecking and pushing the other chick away from the nest. He was stabbing him with his little bill and the victim retreated further from the nest.
This nest is just below the nest shown in the photo above. I am almost certain this is the dislodged chick from the nest above; I cant be sure but I think it is. There is so much action at the rookery, it is hard to piece together the timeline. I was watching the first nest, and then got distracted by Spoonbill mating behavior. The chick on the limb I had been watching wasn't there any longer. So, I think they pushed him out and he landed in the greenery below near a different nest. The bare branch curves above this chick match the ones of the nest above.
But, these three chicks in this nest are not happy about the situation.
He was repeatedly stabbed by the other chick, but I think he was too far gone to react. Note there are two chicks still in this nest but one is hunched over and not active.
And less than a minute later... there is only the poor chick from the nest above, the tormentor at the edge of the nest and a chick standing alone in the nest... where there had been two before. Some other photographers on the deck above us said they saw a chick fall, but the ground in this location was hidden by reeds, so I don't know what happened to him. Except he is missing.
We also saw some Spoonbills work for over half an hour to dislodge a dead baby Egret from the edge of their nest. The photos are just to dark and confusing to tell much of what was going on, but eventually the dead baby egret hit the ground. The Spoonbill nest was low in a tree that had numerous Great Egret nests above.
So, I did learn a bit more about food supplied for the chicks, but I saw clear evidence of the aggression among nest mates. There is no room in the nest for weak offspring; the parents will not waste time or energy on any chick but the strongest. We did see an adult warn off a Spoonbill that got too close to a nest, but that is the only protective behavior by the adults that I observed. And, that was for the group, not for an individual chick.
Have you made the trip to Smith Oaks Rookery yet? Do raw nature facts bother you or do you prefer the Disney version? Do you think the Roseate Spoonbill chicks will be aggressive or laid-back and complaisant? Let me know what you think about all this chick behavior in the comments below: