Readers’ wildlife photos (and videos)

Professor Bruce Lyon continues to regale us with stories, pictures, and his own videos about his group’s research on the fascinating American Coot (Fulica americana). There’s a lot of good science in these, so don’t skip the text! I especially like the “tousling” behavior described below. One lesson is that if you watch an animal very carefully (and quantitatively), you discover complexities that are both fascinating and overlooked by the casual observer.

Bruce’s words are indented, and he’ll be looking at the comments in case there are questions.

Coot Soap Opera, Part III

This is my third post on the soap opera that is family life in American coots (here, here). Work with my former student, Dai Shizuka, now a professor at the University of Nebraska, revealed that coot family life is somewhat more nuanced than the death-and-destruction picture I previously painted. What I described was the first phase in the life of a coot family, but there is a very different second phase that warms the heart (well at least for some of the chicks). In first ten days after hatch, the chicks seem to control who gets fed—without any clear parental interference—but this free-for all ends when the parents suddenly begin to exert control and determine which chicks are fed.

Below: The first ten days after hatch comprise a ‘first-come-first-served stage’: the chicks follow the parents around the territory and when a parent finds food, it typically offers the food to the nearest chick. Or, if there is a group of chicks, the parent holds the food out and one of the chicks grabs the food.

Most of the chick mortality occurs during the first ten days when parents do not exert control. We believe that size gives the older chicks an advantage—being larger, they can swim faster and are more likely to be able to get to a proffered prey item. We have never seen evidence for direct aggression among chicks: unlike some birds like raptors and egrets, the bigger chick never beat up their smaller chicks. Instead, if food is limiting, the younger, smaller chicks simply do not get fed enough and eventually get too weak to follow the family and perish.

Below. The video clip shows how chick size affects which chicks are fed. A parent offers a food item to three chicks that are following it and the largest chick, which is farther away than the others, rushes in and grabs the food.

Around day ten (roughly), things change dramatically. Parents take control and start to show aggression towards chicks. Parents ‘tousle’ the chicks by grabbing them by the back of the neck and shaking them. This behavior is common and screams of chicks getting spanked often ring through the wetlands. We are not the first to study this tousling behavior: it has been previously studied in two other rails: moorhens (Gallinula chloropus) and Eurasian coots (Fulica atra). However, the family life in these other two species differs a bit from that of the American coot.

Below: This parent is not eating its chick, it is tousling it (AKA spanking).

Below: Another photo of a parent tousling one of its chicks that nicely shows the shaking motion.

Below: Still photos do not do justice to the parental aggression so here is a video of a parent tousling one of its chicks. Although the chicks scream blue murder during the tousling they are not seriously hurt by their spankings. They do, however, give the parent a wide berth for a while after getting spanked.

We initially thought that tousling might be used to cull the brood during brood reduction, as has been suggested for European coots, but our observations do not support this idea—most of the chick mortality occurs early in the free-for-all stage, before parents use aggression to take control of food allocation.

Why, then, do coots beat up their kids? It turns out that they are intervening to help the smallest remaining chicks in the brood survive. Parents use aggression to make sure the smallest chicks get enough food. Larger chicks are tousled more than small chicks and, as a result, they spend less time near the parents and are fed less. Given the extreme hatching asynchrony, we suspect that without parental intervention and control of food allocation, brood reduction would continue until only one or two very fat chicks remained.

Below: Sometimes larger chicks dash in and take food that is clearly intended for a smaller chick. These thefts are often punished by a spanking, as shown in the video below. Note the sequence of events: the parent offers the food to the smaller chick, a larger chick rushes in and grabs the food but is then chased and tousled. Kind of like watching human families at the supermarket! And hard not to chuckle sometimes.

There is an additional layer of complexity to the parental control—the parents divide the brood so that mom has her chicks that only she feeds, and dad has his chicks. Once this ‘brood division’ occurs, each parent continues to feed the same subset of chicks until the chicks are independent. Interestingly, both parents often forage in the same general area so brood division is not the result of the parents dividing up the territory spatially and keeping the two subsets of the brood separate. It seems clear that the parents recognize the individual chicks in their brood.

Below: Video showing brood division, where the male is foraging while ‘his’ chicks follow him around, and the female is attended by ‘her’ chicks. The yapping adult is the male—it is easy to tell the sexes apart by their calls. The larger male has a higher pitched call, which is a reversal from animals generally where larger animals have deeper vocalizations.

The brood is not divided randomly by the two parents, nor is the pattern of feeding by each parent. Each parent typically takes one of the two youngest remaining chicks in the brood, which then becomes its favored chick. These chicks are fed more than the other chicks, often dramatically so, and they are tousled far less. Even though these chicks start out smaller than their sibs, they are so pampered and stuffed with food that they catch up and even surpass their older sibs in size. We believe that parent coots use this parental favoritism to level the playing field and undo the negative effects of hatching asynchrony.

Sometimes it is hard not to think of these little favorites as spoiled brats. They show a behavior called ‘pestering’, first documented in Eurasian coots by John Horsfall, who coincidentally did the work while at the Edward Grey Institute of Ornithology, David Lack’s old stomping grounds. It is mainly the favorites that pester their parents: this involves making a rapid twittering noise and clambering around the neck and lower back of the parent. This pestering is annoying and therefore causes the parent to lash out and tousle a chick. Surprisingly it is not the pestering chick that receives the parent’s wrath, but rather the victim is a sibling that has come too close and threatens the dear little precious small chick’s monopoly on food. It sure looks to us like the favorites use pestering to cause the parents to chase off the favorite chick’s competition. This is a bizarre form of indirect dominance—the pesterers use a parental enforcer to exert dominance over their larger sibs. The non-favored chicks even learn their station in life and begin to defer to the pesterer by moving away as soon as the pestering starts. The closest similar behavior I can think of is inherited dominance in primates: based on inherited rank, a small baby of a dominant female can be socially dominant over other adults that could beat the crap out of the baby.

Below: A photo showing pestering in action. The chick riding the parents back is the pesterer. Note that the parent is not spanking the annoying pesterer but a second chick that is nearby. “Mommy, Bobby threatened to steal my food!”

Below: Video of pestering. The video starts with a pesterer bugging its parent (note the twittering calls), the parent takes a couple of swipes at a second chick, who hightails it for safety to avoid getting tousled.

That’s it for the coot soap opera for now. In a few weeks I will prepare a couple of posts on the bizarre chick coloration and the brood parasitism, where female coots lay eggs in each others’ nests.