Helpers at the nest may allow mother birds to lay smaller eggs

November 23, 2017

Cooperatively breeding birds and fish may have evolved the adaptive ability to reduce the size of their eggs when helpers are available to lighten the parental load, a new study suggests. The findings indicate that in some species, the social environment may influence female reproductive decisions even prior to the birth of offspring.

According to the research from the University of Cambridge, females in species such as the sociable weaver, superb fairy-wren and daffodil cichlid fish, tend to produce smaller eggs when help with rearing offspring is at hand compared to when parents are on their own.

The authors of the paper, which was published today in the journal PeerJ, looked at data from 12 studies on 10 species of cooperatively breeding vertebrates in order to analyse the relationship between the number of helpers present and egg size. The reduction in egg size in relation to helper availability was stronger in species where mothers also reduce the energy they put into post-natal care when other members of the social group are available to help protect, incubate and feed offspring after laying.

The findings suggest that breeding females, by laying smaller, less energy-consuming eggs and providing less food to offspring at the nest, may conserve energy to increase their own chances of survival to the next year or to have the next set of offspring sooner. If helpers compensate for the reduced investment into the current offspring, this could lead to females producing more offspring in total over the course of their lifetimes.

Read more at: 

Blood ties fuel cooperation among species, not survival instinct

February 22, 2017

Over 4,000 different bird species, including White Fronted Bee Eaters, were observed in the study, which found that survival instinct did not influence species cooperative breeding decisions. Instead, it shows communal living and helping …more

Cooperative breeding, when adults in a group team up to care for offspring, is not a survival strategy for animals living in extreme environments. It is instead a natural result of monogamous relationships reinforcing stronger genetic bonds in family groups. Siblings with full biological ties are more likely than others to stay with their family and help day to day, a new Oxford University study has found.

Previous research showed that animals that breed in this way are more likely to live in harsher climates, such as deserts, than those who go it alone. Without any evidence for why this happens, scientists drew the intuitive conclusion that team thinking was at play, and larger family structures were formed as a survival strategy.

However, the new findings from Oxford's Department of Zoology have turned these previous conclusions on their head, proving that communal family dynamics are often built before animals enter difficult climates, and that the two are actually not related.

From observing 4,707 bird species, the team collated and analysed data to test competing explanations for how much environmental conditions influence and drive species' decision to live communally. These potential explanations included: entering harsh environments in a large family group offers stronger chances of survival than as an individual; there is in fact no relationship between the two at all; and that a third variable may be at play, such as female polyandry, when the mother has multiple partners.

The study found that parental relationships - specifically whether they were polyandrous or monogamous plays a key role in whether animal families stay together as a group or not.

Cooperative breeding is a social behavior that occurs in many animal and bird species, including Arabian Babblers. Credit: Yitzchak Ben Mocha

A cooperative living structure was more likely to be favoured when both parental genes were shared by siblings, a trait known as "kin selection." Bolstered by this dynamic the groups are then able to enter difficult climates, and set up home in new territories, that they may not have been able to survive in alone.

The research was conducted in partnership with the University of Lund, Sweden, Columbia University, USA and Washington University, St Louis, USA. The full study features in the journal Nature Ecology & Evolution.

Professor Ashleigh Griffin, Research Fellow in the Department of Zoology and co-author of the study said: "For decades, biologists have noted that animals living in harsh desert environments often live in cooperative groups. This seems to make intuitive sense - when times are hard, it may take teamwork to survive. We tested this hypothesis in an analysis of over 2,000 species of birds, looking at whether species were cooperative and where they lived. Surprisingly, we found no evidence to support the widely held assumption that species in the desert were more likely to become cooperative. Instead, cooperation evolves as a result of close genetic bonds in family groups. These cooperative family groups are then better able to invade new territory, where the climate is too harsh for uncooperative, solitary species to survive."


Read more at:

Overcrowding forces pheasants to cooperate in Hawaii

Date: September 7, 2016

Source: Central Ornithology Publication Office

"Survival of the fittest" usually means that animals put their own needs first, but occasionally it pays to work together. A new study in The Auk: Ornithological Advances describes an unusual example of cooperative breeding in an introduced pheasant population in Hawaii, where young males help care for chicks and defend against intruders rather than striking out on their own.

Cooperative breeding, where members of a social group provide care to young that are not their own offspring, is rare in "precocial" bird species like pheasants -- those where chicks are already well-developed when they hatch and don't require intense parental effort. However, Lijin Zeng of the University of California-Riverside and her colleagues have discovered that cooperative breeding is the norm among Kalij Pheasants in Hawaii's Volcanoes National Park. While females incubate their eggs alone, all group members, including up to six males as well as the breeding female, feed the chicks after they hatch and defend the group against intruders. Dominant males father the most chicks, but almost a third are fathered by subordinate males within the same group or males from other groups.

This is only the third time cooperative breeding has been observed in the pheasant family, and Kalij Pheasants, introduced in Hawaii in the 1960s, are not known to breed cooperatively in their native range in Asia. Possibly due to a lack of predation and disease, their population density in Volcanoes National Park has grown very high, and overcrowding may prevent young males from being able to establish their own territories. Instead, their best hope to pass on their genes is to stay with the group and wait to move up in the dominance hierarchy, fathering a few chicks in the meantime.

Continued 

Some Birds Become 'Maiden Aunts' to Defend Relatives' Chicks against Cuckoos

Birds know that there is safety in numbers, which is why some choose against laying eggs and instead become 'maiden aunts' to protect their relatives' chicks against cuckoos, a new study from Australia reported.

The study, conducted by biologists at the Australian National University and their colleagues at the University of Melbourne, found that birds have evolved co-operative breeding to protect their chicks against parasite birds such as cuckoos.

In about nine percent of bird species, some choose to take care of relatives' chicks instead of producing their own brood, according to Dr Naomi Langmore of the ANU Research School of Biology. Biologists often found it hard to explain such behavior.

Continued