Arxiu d'etiquetes: brood parasitism

Parent love? Costs of parental care in birds

Parental care is an evolutionary adaptation, widespread in a large number of species, in which parents try to increase the chances of success of their children. However, there are decisions that parents must make and they will directly affect the survival not only of their descendants, but of themselves and their own species. We will see what happens in the case of birds.


According to the Theory of parental investment (Trivers, 1972), the animals that reproduce sexually must assess the cost to them to invest in their children.

Reproduction is costly, and individuals are limited to what they can devote time and resources to raising and growing their offspring, and such an effort can be determinant in their survival and future reproductive activities. According to the Principle of Allocation, the energy that an individual obtains must be distributed among the requirements derived from its maintenance, growth and reproduction. Extra energy being channeled to any of these activities will result in less energy available to the remaining ones.

Principle of assignment. Source: Introduction to the science of animal behavior. Carranza.

Caring for the offspring consists of a series of activities carried out by the parents and an increase in the probabilities of survival of offspring, effects that will be considered as benefits. At the same time, these activities will have negative consequences on the parents, affecting their survival and the probability of producing new offspring in the future, since they involve an expense of time and energy or costs. Each individual must consider both, costs and benefits, to make the most beneficial choice.

Breeding of broad-snouted caiman (Caiman latirostris) in the mouth of his mother. Photo: Mark MacEwen


Parental investment must be considered from the beginning of reproduction, and not only from the birth of offspring.

We can distinguish different stages in the parental investment of birds:

Investment prior to fertilization: birds need to establish nesting and feeding grounds with conditions conducive to raising their offspring, such as the availability of food. In addition, once the territory is selected, they will have to choose a safe place for predators to set up their nest. In some cases they will also dedicate energy to the construction of the same, adding costs to the parental investment. The production of gametes is another process that supposes an energetic expense for the individual.

Placement and incubation: The laying of the eggs implies a great investment for the female, who is the one who does it. In relation to egg production, the energy investment of the female will vary depending on the development of the chicken at birth. In precocial birds or nidifugous (that present a state of advanced development at birth and can leave the nest, being able to move and Regulate its own temperature), the percentage of yolk will be greater and therefore, the greater the energy demand in its production. On the other hand, in altricial birds (born in premature developmental state, with eyes and ears not developed, body without feathers and without capacity to move), the percentage of yolk has been seen that is smaller and with this also the energy investment of the female. However, this initial differential investment may be later compensated for in the parental care necessary after hatching, which will be higher in altricial birds.

Percentage of yolk in eggs of different species of altricial and precocial birds. 1. Bohemian waxwing (Bombycilla garrulus), 2. Ruddy duck (Oxyura jamaicensis), 3. Malleefowl (Leipoa ocellata), and 4. North Island brown kiwi (Apteryx mantelli). Source: Sotherland & Rahn, 1987

Once the female makes the egg laying, a very delicate stage begins in which the correct development of the embryo will be determined by the incubation conditions: temperature, humidity, ventilation and egg turnover.

Care after birth. After the hatching of the eggs, the offspring will need food, temperature regulation, and protection, by the parents. But this care will vary depending on their development at birth, being smaller in the precocial than in the altricial.

Difference between chickens of altricial (left) and precocial (right) birds at birth. Photo: Bloomsbury Publishing

Precocial and superprecocial birds are characterized by patterns of simple parental care, with minimal assistance in the nest. As an example are galliformes and anseriformes, who seek their own food since they are born, but will depend on their parents to protect themselves. At the other extreme, altricial species are characterized by sophisticated parental care, with a high level of offspring assistance. These features associated with altricial development are also related to an increase in the variety of flight styles, flight speed, and ecological habits (Dial, 2003).

Relationship between parental investment and mobility / ecological habits. Source: Dial, 2003.

Finally, we can find different models of parental care according to the individuals involved in the care of the young. In breeding parasitism, individuals try to reduce the costs of parental care by involving other individuals in caring for their offspring. (Lying birds: Brood parasitism in birds, the continual struggle for survival). Another possibility is that only one member of the pair, male or female, cares for the offspring; Or that both engage in that task (male and female). Finally, cooperative breeding is a system in which adult individuals (assistants) provide parental care, such as feeding, thermoregulation, grooming and advocacy, to juveniles who are not their direct descendants. If only a pair is reproduced, it will be cooperative breeding, if they reproduce more, it is called communal breeding.

In emperor penguin (Aptenodytes forsteri), all individuals in the group create a circle around the young to keep warm. Source:


The conflict of interests between males and females begins in the production of gametes. The male gametes, smaller and simpler, need less investment on the part of the individual. In contrast, as we have seen, female gametes need more investment of female resources.

From the point of view of the male, the most advantageous would be to fertilize as many females as possible and let them be the ones who would care for the young, while he is engaged in seeking and fertilizing more females. On the contrary, the most advantageous for a female would be for the males she mates to take care of the pups so that she could devote her time, energy and resources to mating again and producing more pups.

However, the choice of one or another strategy will be determined mainly by several factors: physiological limitations, types of life cycles and ecological factors. According to the balance of costs and benefits for males and females in each ecological context, each sex will try to maximize its reproductive success, even at the expense of the reproductive interests of the other sex.

Distribution of parental care between females and males. From left to right: greater painted-snipe (Rostratula benghalensis), wattled jacana (Jacana jacana), eurasian stone-curlew (Burhinus oedicnemus), Eurasian oystercatcher (Haematopus ostralegus), white-rumped sandpiper  (Calidris fuscicollis), and ruff (Philomachus pugnax). Source: Szekely et al. (2006)

The conflict between the sexes in parental care can be explained through the classic Maynard-Smith model (1978), represented by the Matrix of Game Theory, which will determine the parents’ decisions about whether or not to care for their offspring as a function of Success or benefit they obtain. Success will depend on the number of offspring produced (W), their chances of survival when they receive more or less parental care (P), and the male’s chances of mating again if he deserts (p).

Matrix of game theory that represents the conflict between both parents on whether or not to care for offspring. Source: Maynard-Smith, 1977

The selection will favor the desertion of one of the progenitors when the progenitor has a high probability of re-pairing, when the desertion has a small effect on the survival of the offspring and when the contribution of this progenitor is small (Lazarus, 1989). Even when both parents care for the offspring, there are conflicts of interest with respect to the level of investment that males and females provide, so that what each sex is willing to invest will depend in part on their partner’s level of investment.


  • Birkhead, T.(2016) The art of hatching and egg.
  • Carranza, J. (1994). Ethology. Introduction to the Science of Behaviour.
  • Gill, Frank B (2007). Ornithology. New York: W. H. Freeman & Company. 758p
  • Kenneth P. Dial (2003). Evolution of avian locomotion: correlates of flight style, locomotor modules, nesting biology, body size, development, and the origin of flapping flight The Auk, 120 (4)
  • Sotherland, P., & Rahn, H. (1987). On the Composition of Bird Eggs The Condor, 89 (1)

Sara de la Rosa Ruiz

Lying birds: Brood parasitism in birds, the continual struggle for survival

Some birds have development an interesting reproductive strategy to deceive other birds and put the eggs in their nests, so foster parents are forced to feed other chicks. But what is behind this strange behaviour?


The brood parasitism is a type of biological interaction between two organisms, in which one of them (the parasite) obtains resources from the other one (the host). In birds, the parasite obtains some benefits of parental cares from the host, developing a breeding strategy cold brood parasitism. The brood parasitism, although has been studied mostly in birds, also happens in other groups of vertebrates: for example in fish (Sato 1986, Baba et al. 1990) and some insects such as Himenoptera, Coleoptera and Heteropterous.

Brood parasitism –

According the characteristics of each relation, there are different types of brood parasitism:

  • Optional brood parasitism: the parasite species is capable of breeding a part of its own offspring and also, to parasite other individuals. A example in birds is in genus Coccyzus (Cuculidae).
  • Forced brood parasitism: hosts breed all the offspring of the parasite bird, as happens in common cucko (Cuculus canorus).
  • Intraspecific brood parasitism: host and parasite are of the same species. This is a common strategy in colonial species and in other species with nidifugous chicks.
  • Interspecific brood parasitism: host and parasite are the different species.

In addition parasites are classified, by their specialisation on one or several host species, in general parasites (parasite large number of species) or specialist (only parasite one or a few species).


Everything suggests that the main focus of this behavior was decreased the parental investment (less cost) increasing the chance of success (major benefits), although this is not always the case.

There are several hyphotesis to explain the origin of the brood parasitism in birds:

  1. Firstly, it is probably that parasites were displaced individuals that did not have any territory or lost their laying, and they try to lay their eggs in other nests to achieve greater breeding success (Sorenson 1998, Sandell y Diemer 1999).
  2. Other hypothesis suggests that this parasitism could be a stable strategy for evolution of the population, which has similar benefits to breed its own offspring (Eadie y Fryxell 1992).
  3. Finally, the third hyphotesis considers this parasitism like an additional strategy to the parent care and some individuals could be used it to reduce the sibling competition in their nest, or to reduce the number of chicks to feed without decreasing the breeding success (Moller 1987, Jackson 1993).



Hosts have learned to protect their offspring about the threat posed by brood parasitism.

Common cuckoo (Cuculus canorus) and rufous bush robin (Cercotrichas galactotes) have this relation, the first one lay a egg in the rufuos bush robin nest that it will be born before other chicks and kill them, capturing all the parental care.

One of the main host defences against brood parasites is the recognition and rejection of parasitic eggs. Because obligated brood parasites need appropriated individuals hosts for reproduction, such host defence-mechanisms simultaneously select for counter-defences in brood parasites, causing a coevolutionary arms race between hosts and parasites.

Rejection of parasitic eggs –



There is a particular case, the strategy of the great spotted cuckoo (Clamator glandarius) when is a parasite of the common magpie (Pica pica). The great spotted cuckoo lays an egg in the nest of common magpie and this chick possess adaptations to exploit the host parental care, it does not kill directly their siblings but has advantages in relation to begging behaviour and in the order of birth (cuckoo chick is born four or six days before magpie chicks.

Common magpie (Pica pica) –

Magpies have development a selective advantage to recognize and ejection of parasitic egg. However, it has been observed that cuckoos react to this behaviour returning to the parasitized nest and destroying it. This situation conditions the behaviour of the magpies in the future and they are forced to accept the parasite egg.

Eggs of cuckoo in magpie nest –
Cuckoo chicks are born some days before magpie chicks –
Development of cuckoo chicks in the nest –

The result of this evolutionary fight is the mafia-type behaviour of cuckoo that leads to a co-evolutionary arms race between species to avoid parasitism, in one hand, and maintain it, in the other one.

Great Spotted Cuckoo (Clamator glandarius) – Fveronesi1. Flickr, Creative Commons


  • Parasitism and nest predation in parasitic cuckoo (American Naturalist, 1995)
  • Mafia Behaviour and the Evolution of Facultative Virulence (Journal of Theoretical Biology, 1995.)
  • Magpie Host Manipulation by Great Spotted Cuckoos: Evidence for an Avian Mafia? (Evolution, 1997.)
  • Retaliatory mafia behavior by a parasitic cowbird favors host acceptance of parasitic eggs (PNAS, 2006)
  • Cover photo: Cuckoo chick in parasitic nest reciving food of host –



Symbiosis: relationships between living beings

Predation, parasitism, competition… all living beings, besides interacting with the environment, we relate to other living beings. What types of relationships in addition to those you know? Do you feel like to know them?


The group of all living beings in an ecosystem is called biocenosis or community. The biocenosis is formed in turn by different populations, which would be the set of individuals of the same species occupying an area. For survival, it is imperative that relations between them are established, sometimes beneficial and sometimes harmful.


They are those that occur between individuals of different species. This interaction it is called symbiosis. Symbiotic relationships can be beneficial to a species, both, or harmful to one of the two.

Detrimental to all the species involved:

Competition: occurs when one or more resources are limiting (food, land, light, soil …). This relationship is very important in evolution, as it allows natural selection acts by promoting the survival and reproduction of the most successful species according to their physiology, behavior …

Las selvas son un claro ejemplo de competencia de los vegetales en busca de la luz. Selva de Kuranda, Australia. Foto de Mireia Querol
Rainforests are a clear example of competition between vegetals in the search for light. Kuranda rainforest, Australia. Photo by Mireia Querol
One species has benefits and the other is detrimented:
  • Predation: occurs when one species (predator) feeds on another (prey). This is the case of cats, wolves, sharks
foca, león marino,
Great white shark (Carcharodon carcharias) jumping to depretade a marine mamal, maybe a sea lion. Photo taken from HQ images.
  • Parasitism: one species (parasite) lives at the expense of other (host) and causes it injury. Fleas, ticks, pathogenic bacteria are the best known, but there are also vertebrate parasites, like the cuckoo that lay their eggs in the nests of other birds, which will raise their chicks (brood parasitism). Especially interesting are the “zombie parasites”, which modify the behavior of the host. Read this post to learn more!
    Carricero (Acrocephalus scirpaceus) alimentando una cría de cuco (Cuculus canorus). Foto de Harald Olsen
    Reed warbler (Acrocephalus scirpaceus) feeding a cuckoo’s chick (Cuculus canorus). Photo by Harald Olsen

    Parasites that live inside the host’s body are called endoparasites (such as tapeworms), and those who live outside ectoparasites (lice). Parasitism is considered a special type of predation, where predator is smaller than prey, although in most cases does not cause the death of the host. When a parasite causes illness or death of the host, it is called pathogen.

    Cymothoa exigua es un parásito que acaba sustituyendo la lengua de los peces por su propio cuerpo. Foto de Marcello Di Francesco.
    Cymothoa exigua is a parasite that replaces the tongue of fish with their own body. Picture by Marcello Di Francesco.

Kleptoparasitism is stealing food that other species has caught, harvested or prepared. This is the case of some raptors, whose name literally means “thief.” See in this video a case of kleptoparasitism on an owl:

Kleptoparasitism can also occur between individuals of the same species.

One species has benefits and the other is not affected:
  • Commensalism: one species (commensal) uses the remains of food from another species, which does not benefit or harm. This is the case of bearded vultures. It is also commensalism the use as transportation from one species over another (phoresy), as barnacles attached to the body of whales. The inquilinism is a type of commensalism in which a species lives in or on another. This would apply to the woodpeckers and squirrels that nest in trees or barnacles living above mussels. Finally, metabiosis is the use of the remains of a species for protection (like hermit crabs) or to use them as tools.
    El pinzón carpintero (Camarhynchus pallidus) utiliza espinas de cactus o pequeñas ramas para extraer invertebrados de los árboles. Foto de
    The woodpecker finch (Camarhynchus pallidus) uses cactus spines or small branches to remove invertebrates from the trees. Picture by Dusan Brinkhuizen.
    Both species have benefits:
  • Mutualism: the two species cooperate or are benefited. This is the case of pollinating insects, which get nectar from the flower and the plant is pollinated. Clownfish and anemones would be another typical example, where clown fish gets protection and food scraps while keeps predators away and clean parasites of the sea anemonae. Mutualism can be optional (a species do not need each other to survive) or forced (the species can not live separately). This is the case of mycorrhizae, an association of fungi and roots of certain plants, lichens (mutualism of fungus and algae), leafcutter ants

    Las hormigas Atta y Acromyrmex (hormigas cortadoras de hogas) establecen mutualismo con un hongo (Leucocoprinus gongylophorus), en las que recolectan hojas para proporcionarle nutrientes, y ellas se alimentan de él. Se trata de un mutualismo obligado. Foto tomada de Ants kalytta.
    Atta and Acromyrmex ants (leafcutter ants) establish mutualism with a fungus (Leucocoprinus gongylophorus), in which they gather leaves to provide nutrients to the fungus, and they feed on it. It is an obligate mutualism. Photo taken from Ants kalytta.


They are those that occur between individuals of the same species. They are most beneficial or collaborative:

  • Familiars: grouped individuals have some sort of relationship. Some examples of species we have discussed in the blog are elephants, some primates, many birds, cetaceans In such relationships there are different types of families.
  • Gregariousness: groups are usually of many unrelated individuals over a permanent period or seasonal time. The most typical examples would be the flocks of migratory birds, migration of the monarch butterfly, herds of large herbivores like wildebeest, shoal of fish

    El gregarismo de estas cebras, junto con su pelaje, les permite confundir a los depredadores. Foto tomada de Telegraph
    Gregariousness of these zebras, along with their fur, allow them to confuse predators. Photo taken from Telegraph
  • Colonies: groups of individuals that have been reproduced asexually and share common structures. The best known case is coral, which is sometimes referred to as the world’s largest living being (Australian Great Barrier Reef), but is actually a colony of polyps (and its calcareous skeletons), not single individual.
  • Society: they are individuals who live together in an organized and hierarchical manner, where there is a division of tasks and they are usually physically different from each other according to their function in society. Typical examples are social insects such as ants, bees, termites

Intraspecific relations of competition are:

  • Territorialityconfrontation or competition for access to the territory, light, females, food can cause direct clashes, as in the case of deer, and/or develop other strategies, such as marking odor (cats, bears), vocalization

    Tigres peleando por el territorio. Captura de vídeo de John Varty
    Tiger figthing for territory. Video caption by John Varty
  • Cannibalism: predation of one individual over another of the same species.

And you, as a human, have you ever thought how do you relate with individuals of your species and other species?