Image copyright Carin Bondar 'The Nature of Human Nature'
My neighbor and I had our daughters at approximately the same time. We spent a lot of time together during the first few months, had lots of play dates and tea time. We enjoyed the comraderie and our daughters benefited from sharing each others’ company. Then something terrible happened: my neighbor had to go back to work. Suddenly her tiny little child was without both of her parents for many long days per week. I didn’t see my neighbor for months as she and her husband began their new schedule of long work days, dealing with out of home daycare and caring for their daughter when they were not at work…frankly I don’t think they saw much of each other either. However, this is reality. Times are tough, and in order to provide adequate resources for your family the necessary steps must be taken. If this means leaving your newly reared youngster with an alloparent while you go off to gather resources, then so be it. During times of adversity parents must find ways to provide the necessary resources for their offspring and for themselves, whether you are a human being or not.
Colonially breeding seabird parents must periodically leave their offspring unattended. Up to 98% of these organisms breed within densely populated nesting territories where food resources are not available1. Sustenance is therefore collected from the ocean or elsewhere and brought back to the nesting area for consumption by parents and offspring. When chicks are left unattended by both parents (not common when food is easy to find) a form of alloparenting takes place. In common murre (Uria aalge) populations, non-breeders or failed breeders in the colony have been found to provide sufficient care to chicks that have been left alone to enable them to survive to fledging2. Some biologists speculate that the payoff for such alloparental care is a form of allopreening, grooming of the adult daycare providers3, not entirely unlike the fees we pay to those that mind our own children during the day. It seems as though this kind of allparental care is a viable option for seabirds when conditions are favorable and parents don’t spend too much time away from the nest simultaneously. However; when environmental conditions are adverse and food is scarce, the costs of leaving the offspring behind can escalate beyond the food benefits obtained by both parents foraging…
In a series of behavioral observations taken during a time of severe food shortage on the Isle of May in the UK, it was found that both parents of common murre offspring spent the majority of their time foraging away from the nest and offspring3. More than 50% of the young in the breeding colony were frequently left unattended. Did the alloparenting/allopreening tradeoff save the day for these unattended chicks? In a word: no. Instead of providing alloparental care, neighboring conspecifics attacked unattended chicks. They did so in such aggressive and repeated fashion that it accounted for 69% of chick mortality during the season. It is thought that the abusive adults wanted to safeguard against adopting or mistakenly feeding the unattended chicks when their own offspring were also on the verge of starvation. The message is clear: when times are tough, take care of your own progeny first, not the poor little orphans who stumble into your territory.
Over 20 years of behavioral data for another colonial nesting seabird, Nazca boobies (Sula granti) in the Galapagos Islands showed that up to 80% of non-parental adults in a breeding colony engage in a ‘mixture’ of behaviors with unattended chicks4, and these non-parental adult visits (NAVs) could take the form of aggressive or sexually abusive attacks. The chicks involved were generally at an age where their food demands were high enough to result in both parents foraging for some periods of the day, but young enough so as not to be able to repel the unsolicited visits. Although aggressive attacks by NAVs on unattended chicks did not usually result in the direct death of the chick (as it did with the murres discussed above), lacerations left on the chicks’ bodies left them vulnerable to death by blood-feeding ectoparasitc land birds (species that drink their blood). It is suggested that this abusive behavior might result from the NAV attempting to eliminate future competition for mates (in same sex attacks) or resources (in attacks on both sexes), although the fact that sexual behavior towards the chicks was observed in 14.3% of male NAV visits, and 6.8% of female NAV visits is as yet unexplained. Kind of makes you want to stretch your coupon savings a little further doesn’t it?
Parents of many species are faced with a daunting tradeoff when it comes to providing for our young. When times are tough and dual foraging becomes a necessity, there is an unavoidable risk to the offspring. Not only in terms of the loss of emotional bonding opportunity between parent and offspring (which is likely of low importance to colonial seabirds but not to humans), but in terms of sub-optimal treatment of young when both parents are absent. Humans are far from being alone in the animal kingdom when it comes to making this difficult choice.
1Perrins, C. M. & Birkhead, T. R. 1983 Avian ecology. Glasgow, UK: Blackie.
2Birkhead, T. R. & Nettleship, D. N. 1984 Alloparental care in the common murre (Uria aalge). Can. J. Zool. 62, 2121–2124.
3Ashbrook, K., Wanless, S., Harris, M.P. and Hamer, K.C. 2008. Hitting the buffers: conspecific aggression undermines benefits of colonial breeding under adverse conditions. Biology letters 4: 630-633.
4Anderson, D. J., Porter, E. T. & Ferree, E. D. 2004 Nonbreeding Nazca boobies (Sula granti) show social and sexual interest in chicks: behavioural and ecological aspects. Behaviour 141, 959–977.