Question

Tinbergen observed that after gull nestlings hatch, the parents remove the eggshells from the nest. To understand why (ultimate causation), he painted chicken eggs to resemble gull eggs, which had camouflage coloration to allow them to be inconspicuous against the natural background. He distributed them throughout the area in which the gulls were nesting, placing broken eggshells with their prominent white interiors next to some of the eggs. As a control, he left other camouflaged eggs alone without eggshells. He then noted which eggs were found more easily by crows. Because the crows could use the white interior of a broken eggshell as a cue, they ate more of the camouflaged eggs that were near eggshells. Tinbergen concluded that eggshell removal behavior is adaptive: it reduces predation and thus increases the offspring's chances of survival.

Rank these experiments from worst to best to study why gulls remove broken eggshells from their nests.

O Place broken eggshells near real gull eggs, and record predation by crows.
O Place broken eggshells near brown chicken eggs painted with dark brown spots, and record predation by undergraduate students acting as "predators".
O Place broken eggshells near brown chicken eggs, and record predation by undergraduate students acting as "predators".
O Place broken eggshells near brown chicken eggs painted with dark brown spots, and record predation by crows.
O Place broken eggshells near white chicken eggs, and record predation by undergraduate

Answer 1

Tinbergen's experiments with gull nestlings revealed that removing eggshell fragments from the nest provides camouflage and reduces predation by predators like crows, hence increasing offspring survival. Experiments to study this behavior are best when they replicate natural conditions and involve natural predators.

Step-by-step explanation:

Tinbergen's experiment on gull nestlings aimed to understand the ultimate causation behind the behavior of gull parents removing eggshells from nests. He discovered that the removal of eggshells, which contrast with the camouflage coloration of the eggs, reduces the chances of predation by making the eggs less conspicuous to predators such as crows.

Therefore, this behavior is adaptive as it heightens the offspring's likelihood of survival. For an experiment to accurately study why gulls remove broken eggshells from their nests, it should ideally involve the natural predators of the eggs, such as crows, and replicated environmental conditions mirroring the gulls' natural nesting habitat.

To rank the mentioned experiments from worst to best, the following order could be considered:

1. Place broken eggshells near brown chicken eggs, and record predation by undergraduate students acting as 'predators'.
2. Place broken eggshells near white chicken eggs, and record predation by undergraduate students acting as 'predators'.
3. Place broken eggshells near brown chicken eggs painted with dark brown spots, and record predation by undergraduate students acting as 'predators'.
4. Place broken eggshells near real gull eggs, and record predation by crows.
5. Place broken eggshells near brown chicken eggs painted with dark brown spots, and record predation by crows.

This ranking is based on increasing similarity to the natural conditions under which the behavior occurs, with the best experiment using the actual bird species and their natural predator.