Parental care strategies, reproductive success and environmental stress in eiders

 

 
  • Care for the young alone or in a kindergarten?
  • Why are some daredevils and others fearful? Does it really matter?
  • Whom to cooperate with?
  • How to divide parental care and reproduction in groups?
  • Does parenting ability or the environment steer reproductive success?
  • How does climate, food and predation affect reproductive success?
  • Why are Baltic eiders declining?

 

 

Markus Öst, Kim Jaatinen & Martin Seltmann

 

These are questions that we aim to answer. We mainly work with eiders in which females team up and share the work of rearing ducklings (‘kindergartens'), but also with Barrow's goldeneyes, which are notorious for their reluctance to cooperate, but sometimes stealing each others' young. Our eider study population breeds close to Tvärminne Zoological Station. The goldeneye work has been done at Riske Creek in B.C., Canada.

Birds are marked to aid individual identification.

 

Individual variability and reproductive decisions

 

Imagine what you can do with just a pile of eider droppings or a drop of blood! Corticosterone, the prime avian stress hormone, gives us

a measure of stress experienced by the eider female. Stress levels in blood reveal instantaneous stress, while stress levels in droppings summarize the stress from a longer time period. This information, together with data on dominance and boldness, define personality. Just like humans, some animals are shy and softy, and others bold and fearless. However, not much is known about how personality affects the tendency to cooperate, and how well different personalities co-operate in groups. These open questions are currently the subject of intense study in an exciting project that started up in 2009, and which resulted in the PhD thesis of Martin Seltmann at Åbo Akademi University on 17 January 2014, entitled “Of Milquetoasts and Daredevils – Personalities in Female Eiders”.

For more information, contact Martin Seltmann or Markus Öst



Division of parental effort and reproductive skew in relation to individual quality and relatedness

 


Birds are marked to aid individual identification. Eider females are
adorned with wing flags with an
individual colour combination.

Individual quality, measured by female body condition and breeding experience, affects eider parental care. Body condition is important because females use stored energy reserves for breeding (capital breeding), and they fast for nearly a month before the ducklings hatch - no wonder many females are emaciated when that finally happens! Female age in turn affects social dominance and attractiveness as a partner in a brood-rearing coalition. Both a female's body condition and her age affect whether she cares for her ducklings alone, in a group, or abandons them. We also study how females divide the guarding of the young and their share of offspring in the group. Both condition, age and status in the female dominance hierarchy are important. Females forming brood-rearing coalitions are usually not related to each other. However, in some years females do preferentially associate with kin, for reasons that we still do not fully understand. We explore why kin sometimes group together, and whether the division of parental effort and reproduction among co-operating females could be conditional on relatedness.

For more information, contact Markus Öst or Kim Jaatinen



Spatial structure of broods

 

An eider data factory. Kristina takes a blood smear to check for the presence of parasites, Kimi equips the female with colour rings and Markus mainly enjoys the sunshine.

 

Eider ducklings are not randomly distributed in mixed broods: offspring stay closest to their mother. According to selfish herd theory, animals use conspecifics as a shield from predation, so that central locations are the most sought-after. Eider females show a dominance hierarchy and aggressions are common - it is thus possible that the survival prospects of ducklings depend on their mother's social status, which in turn determines her spatial position in the brood. We investigate the factors determining who will seize a central position, and how a female's spatial position affects her behaviour and behavioural coordination with other group members.

For more information, contact Markus Öst

 

 

 

Partner choice among co-tending eider females


Body condition also affects partner choice. Two good-condition females are seldom found in the same brood – why?. A good-condition female is able to successfully rear her brood on her own, so in order to co-operate, she will be require a central position for her offspring to increase their survival, which her prospective partners may unwillingly accept. By contrast, poor-condition females may be less choosy, since they are unable to cope with the strain of solo brood care. Currently, we are investigating why some females get on well together, while others do not. The key may be that similar-sized broods are more likely to merge, because both sub-groups will then gain a similar benefit of predator dilution. This is because the sub-group in minority would enjoy more safety than the subgroup in majority, should such families mix.

For more information, contact Markus Öst or Kim Jaatinen



Alternative reproductive strategies in Barrow's goldeneyes

 


This project was the domain of Ph.D. student Kim Jaatinen finishing his thesis in 2009. It is common for Barrow's goldeneye females to "parasitize" each other by laying eggs in each others' nests, and females also adopt each others' ducklings by force. Kimi's thesis dealt with the consequences of parasitic eggs for the host's breeding success, whether this behaviour should be regarded as real parasitism or a special case of co-operation between relatives, and whether hosts recognize parasitic eggs.

For more information, contact Kim Jaatinen

 



Baltic eiders in the face of changing climate, food conditions and predation risk

 

Between the devil and the deep blue sea.
Open islands are favoured hunting grounds for white-tailed
sea eagles, while incubating females on forested islands are
threatened by mammals.

We have investigated how female parental care strategies and individual quality affect duckling survival. One interesting finding was that groups with two or three tenders have the highest duckling survival, and such groups are also most common in our population. As a part of the Ph.D. project by Aleksi Lehikoinen (defended in 2009), we predicted how the future reproductive success of eiders will respond to a warming climate (more information here). It is paradoxical that while a warmer climate is predicted to boost reproductive success, the population is actually decreasing. This suggests that factors such as deteriorating food conditions, elevated predation risk, and an increasingly male-biased sex ratio overbalance any positive climatic effects. We are currently examining the relative role of environmental, social and maternal factors for offspring survival in more detail. The combined stress in terms of predation and potential food shortage faced by nesting eiders in Tvärminne is also reflected in their stress hormone profiles.

For more information, contact Markus Öst