Expert Elicitation Summary: Chough Feasability

Background

Once widespread throughout the UK, in Scotland red-billed choughs (Pyrrhocorax pyrrhocorax) have recently become extinct in much of their historical breeding area and are now restricted to Islay and Colonsay. This population is declining, and it is estimated that the breeding population in Scotland is now <50 breeding pairs.

Detailed scientific research shows that the population decline is mainly due to poor survival in the pre-breeding period (years one and two post fledging), primarily driven by habitat change, resulting in food shortages at critical times of year. Parasite burdens, and reduced genetic diversity resulting from small population size, are now also additional contributory factors. Without long term intervention, it is estimated that, if current trends continue, the red-billed choughs could be extinct in Scotland within 50 years.

The Scottish Chough Forum is now trying to decide whether to reinforce the existing, red-billed chough population on Islay and/or Colonsay to improve genetic diversity and achieve population recovery over the next 50 years. Although the drivers of chough decline are thought to be primarily ecological and well-understood, whether favourable conditions for choughs can be established and maintained in the future is uncertain. As such, the Scottish Chough Forum is deciding whether to do translocations or not in the face of irreducible uncertainty over future land management.

Following a questionnaire, as well as several discussions and workshops both online and in-person with a variety of stakeholders, we have built nine potential (not necessarily exhaustive) translocation strategies to assess (Table 1). The first of these strategies is ‘Do nothing’, i.e. not doing any translocations. The remaining eight strategies are differentiated by the release demographics (eggs, sub-adults, breeding adults), whether the birds would be released immediately or held in temporary aviaries and undergo a staged release, whether the birds would be habituated to humans or not during the aviary stage, and where the birds would be sourced from (captivity or the wild). We go into more detail about the specifics of each of these below.

Table 1. Nine translocation strategies to be assessed and their constituent parts made up of the demographic to be released, where these birds would be released, what time of year the birds would be released, whether they’d be released immediately or first held in aviaries and undergo a staged release, whether the birds would be habituated to humans or not during a stage release, and where the birds would be sourced from. For further details on each aspect of the release strategies, please refer to the document you received along with this link.

Strategy name	Demographic	Release site	Release timing	Release type	Habituation	Source
Do nothing	–	–	–	–	–	–
Eggs	Eggs	Northwest Rinns, Islay	April–May	Immediate into nests	–	Captive or wild
Sub-adults (C-St-H)	Sub-adults	Northwest Rinns, Islay	Late winter (Dec – Feb)	Staged from aviaries	Yes	Captive
Sub-adults (C-St-NH)	Sub-adults	Northwest Rinns, Islay	Late winter (Dec – Feb)	Staged from aviaries	No	Captive
Sub-adults (W-St-H)	Sub-adults	Northwest Rinns, Islay	Late winter (Dec – Feb)	Staged from aviaries	Yes	Wild
Sub-adults (W-St-NH)	Sub-adults	Northwest Rinns, Islay	Late winter (Dec – Feb)	Staged from aviaries	No	Wild
Adults (C-St-H)	Breeding adults	Ballygrant valley, Islay	Late winter (Dec – Feb)	Staged from aviaries	Yes	Captive
Adults (C-St-NH)	Breeding adults	Ballygrant valley, Islay	Late winter (Dec – Feb)	Staged from aviaries	No	Captive
Adults (W-Im)	Breeding adults	Ballygrant valley, Islay	Late winter (Dec – Feb)	Immediate	–	Wild

To support this decision-making process, we are now seeking your expert judgement on a number of parameters related to chough demography under the different translocation strategies described. Your input will form part of an online expert elicitation aimed at assessing the feasibility of reinforcing the red-billed chough population on Islay.

Terminology

This questionnaire uses specific terminology regarding different age classes and life history processes. The following terms are defined for clarity:

• “First-year” individuals – Post-fledging individuals in the first year of their life.
  
• “Sub-adult” individuals – Individuals in the second year of their life.
  
• “Adult” individuals – Individuals in their third year or older, capable of pairing, nesting, and reproducing.
  
• Nesting success probability – The probability that a breeding pair will produce at least one fledgling in a given year.
  
• Brood size – The total number of fledglings that emerge from a clutch.
  
• Conditional brood size – The number of fledglings produced from a clutch, given that at least one fledgling is produced (i.e., conditional on the nest being successful).
  
• Immediate release – The release of individuals directly into the wild (e.g., Islay) without prior containment in an on-site aviary.
  
• Staged release – A release strategy where individuals are initially housed in an aviary at the release site and are allowed to exit gradually at their own pace, encouraging acclimation before full release.
  
• Habituation – The process by which released individuals become accustomed to human presence, through exposure in an aviary prior to and during release.

For further details on each aspect of the release strategies, please refer to the document you received along with the questionnaire.

Four-point elicitation

This method is believed to improve the quality of expert judgements. It requires you to provide four pieces of information for each question.

Values 1-3: estimates. We ask for the lowest plausible value and highest plausible value that you think the answer could be and your best guess (i.e. what you believe is the most likely value).
NOTE: the best guess is not necessarily the midpoint between these values – you could be more confident on one side of this distribution. For example, a low probability event could have a lowest plausible value of zero, a best guess of 0.1 but a highest plausible value that could be much higher such as 0.6. We use these numbers to fit a probability distribution; this puts the emphasis on your best guess but accounts for the full range of uncertainty.

Value 4: confidence. We ask how confident you are that the true value lies between your lowest and highest plausible values. We use your confidence to rescale the low and high values such that you would be 100% confident the truth lies in that range. This helps us compare between experts using the same scale.
NOTE: the options for confidence start at 50% because a value lower than that means you are more confident the true value would lie outside the range you gave. If this is truly the case, it is more sensible to simply specify a broader range.

Play with the values and confidence and see how they change. Ensure you are happy with the final values as displayed on the graphs – do the transformed values describe what you believe? If not, then please adjust.

Questionnaire 1: Foraging improvement

Question 1

What is the probability that management changes will be implemented on Islay that lead to favourable foraging conditions for chough?

Participant	Minimum Plausible	Most Likely	Maximum Plausible	Confidence
FR	50	75	90	95
KB	20	40	70	80
NR	50	80	100	50
QN	5	50	70	60
RG	0	15	30	70
SQ	5	25	50	60
TQ	40	55	65	81
VK	35	55	70	90
XQ	50	65	100	70

Summary of discussion

There was high uncertainty among participants due to the many factors likely to influence outcomes. Responses were provided on the assumption that conditions would shift enough to drive population-level changes for choughs. Some participants were more pessimistic about the feasibility of landscape-scale change across Islay and therefore gave low probabilities. Others, more optimistic, saw potential for improvement if targeted action were taken in the north of the island. Some questioned whether the agri-environment scheme was the best way to achieve these changes. While the potential for improvement has long existed, two cycles of the agri-environment scheme have so far failed to deliver meaningful results. An optimistic view is that the species is well studied and its needs are understood, meaning effective action can be taken. It was noted that, although there have been small shifts in policy, large-scale changes currently seem unlikely.

Comments

Probability of improved conditions

• TQ: You have to be an optimist to work in conservation. That said, I believe if the decision was made to move away from the general Agri- Env support system to a more refined and targeted management agreement system for chough it would be easier to make progress where it is required.
• NR: I do not know the commitment government to support Chough friendly management or the likelihood of suitable financial packages, nor the individual plans of land managers so my confidence in my responses is <50%
• SQ: High possibility of small beneficial changes occurring dependent on funding and agri-env schemes, but difficult to see landscape scale change across Islay with ageing farming demographic, push for reduction in livestock numbers from government, etc.
• VK: This is very hard to predict because so many factors influence probability: economics, land-manager motivations, climate change - all very hard, or impossible, for conservationists to influence. E.g., Macroeconomics, coupled with the practical difficulties (and extra costs) of island life, make it hard to counter the long-term trend in cattle destocking. Ensuring invertebrates populations respond to management changes is not guaranteed. The impacts of long-term use of vetmeds may be hard to counter, both in terms of getting farmers to stop relying on them as heavily (some use will always be necessary) and allowing invert populations to recover.

• XQ: My answers take into account following;

  Maintenance of area of grassland grazed by livestock = Assumption that most of Islay will still be grazed grassland. However, recent increase in area of grassland converted to barley production to meet distillery demands will impact on availability of inbye/silage field grassland. But barley aftermath will still be available to chough and likely in rotation with short term grass leys. = RELATIVELY NEUTRAL IMPACT ON FAVOURABLE FORAGING CONDITIONS

  Maintenance of number of livestock (particularly cattle) on Islay = Potential for continued steady decline as farming population ages and fewer new starts in the industry, store cattle market margins not favourable, and uncertaintaties over future public support for farming. On the contrary downstream beef markets are strong, Islay always had a reputation as a cattle breeding hotspot. Always likely to be reasonable numbers of cows on the island - perhaps just not in the less productive parts of the island co-inciding where the current chough population is concentrated. = SLIGHTLY NEGATIVE IMPACT ON FAVOURABLE FORAGING CONDITIONS

  Shift in grassland management practices = i.e. farmers encouraged to shift to regenerative grazing practices through adaptation to climage change, input price increases, and public policy and funding. Once regen grazing system established less silage needed as forage all year round, fields grazed rotationally i.e. daily such that swards get longer rest periods and never grazed below 10-20 cm (-ve?). Means, until corresponding soil health improves, chough may have less access to short sward soils before they can adapt to longer sward soils potentially richer in soil invertebrates (+ve). NEUTRAL IMPACT ON FAVOURABLE FORAGING CONDITIONS

  Farmers rely less on using anthelmintic drugs in regenerative grazing systems? = rotaional grazing could mean livestock spending much less time in same field, more breaks in parasitic worm lifecycles = less worm burden = healther cows needing less drug treatment. Also shift to herbal leys introduces sward species with natural anthelmintic properties. = SLIGHTLY POSITIVE IMPACT ON FAVOURABLE FORAGING CONDITIONS

  Climate change impacts on seasonal weather patterns = warmer wetter winters, cooler wetter summers. Leading to increased propensity for cattle to poach grassland particularly in winter. Farmers less likely to keep cattle outdoors all year round leading to less dung/invertebrate availability for chough (-ve). However, regen grazing can increase soil drainage and rely more on rotational grazing that lessens poaching in any one location (+ve). Regen grazing will be fairly fundamental to the future sustainability of cattle farming on Islay hence = NEUTRAL IMPACT ON FAVOURABLE FORAGING CONDITIONS.

  Likely level of public support for cattle farming on Islay that leads to favouable foraging conditions. Scottish Government committed to maintaining guaranteed base payment support for farming in Scotland (contrasting with rest of UK). Started to increase conditionality for recieving base support around nature, climate and sustainability measures that favours regenerative grazing practices (+ve). Most land on Islay either in payment region 1 or 2 which attracts highest payment rates (+ve). Islay always faired strongly in competitive agri-environment focussed schemes because of presence of protected sites and species (+ve). However, overall agriculture budgets not keeping up with inflation and rising costs (-ve). Meanwhile, increasing options for private finance for formely public supported goods e.g. distilleries paying for peatland restoration. = POSITIVE IMPACT ON FAVOURABLE FORAGING CONDITIONS

Question 2

If such changes occur, by what year do you estimate chough foraging conditions are going to be favourable?

Participant	Minimum Plausible	Most Likely	Maximum Plausible	Confidence
FR	2027	2028	2030	90
KB	2026	2030	2035	60
QN	2026	2029	2040	58
RG	2030	2032	2045	70
SQ	2028	2035	2040	60
TQ	2030	2032	2035	80
VK	2027	2032	2036	85
XQ	2028	2032	2035	75

Summary of discussion

There is a central tendency for improved foraging conditions to emerge around 2032. However, estimates have long tails, with upper bounds potentially extending far into the future. Even if action is taken immediately, a time lag must still be overcome before invertebrate availability reaches the levels required to support chough.

Comments

Improved conditions

• TQ: If action for chough is targeted at key areas and funded sufficiently - 5 years is a reasonable timescale.
• SQ: Dependent on many external factors, so impossible to predict.

• XQ: My answer based on following assumptions;

  This is the timescales by which Scottish Government have set out the roadmap to changing the way agriculture support is delivered in Scotland. Starting this year 2025. But not all changes anticipated until at least 2030.

  But changes happening incrementally and arguably not fast enough, or clearly enough, for farmers to make positive changes to their grazing systems to bring about favourable foraging conditions sought for chough. Only early adopters likely to take up changes before they become mandatory. Mandatory likely only kick in from late 2020s/2030.

  Likely that conventional farming inorganic inputs (particularly NPK) going to become ever more expensive due to world wars, trade disruptions, cost of production (high emission systems etc). Therefore encouraging farmers to adopt regen systems to reduce costs before compelled to do so in order to receive future ag support.

  Some key farmers already started to make the change or participating in agri-environment contracts to achieve right foraging conditions for chough. Next 5 years critical for whether they can be maintained and attractive enough for the next generation to succeed the current encumbents who are likely to retire within this period. Signs are new generations more willing to adopt changed grazing practices.

• NR: See comments on Q1 - it is impossible to answer this question from the knowledge I have

  if details of a funding package were available then it might be possible to estimate this, but not currently….
• VK: Broad scale habitat improvement will depend heavily on the new AES and whether it offers the right options to farmers, and whether those options are attractive enough to ensure widespread uptake. Experience suggests this may not be the case, at least in the first tranche (around 2027 I think). There is also an assumption (I think) that the new AES, and other policy instruments, may push agriculture towards a more climate-resilient model. No idea what that will look like, but it may not be good for choughs which like heavily grazed swards and cattle dung. It may be possible to carry out bespoke, localized interventions on some key sites meanwhile, but again this is dependent upon lots of interwoven factors (farmer motivation, economics, farming systems…).

Questionnaire 2: Demography

Demography under different scenarios

General notes

There was some confusion about how supplementary feeding was defined, that is, whether it referred to supplementary feeding in general or specifically to the practices currently in place on Islay. For all questions, “supplementary feeding” refers to the current level of activity occurring on the island. One question specifically explores the effect of additional supplementary feeding, and is explicitly worded to convey that distinction.

Survival

Question 1

What do you believe is the average annual survival of 1st year red-billed choughs under the following different scenarios:
- Conditions are the same as now, without supplementary feeding or any type of management.
- Supplementary feeding of individuals with mealworms.
- Conditions in Islay change so that the foraging conditions are optimal for chough.
- Conditions in Islay change so that the foraging conditions are optimal for chough, and supplementary feeding continues.

Participant	Foraging condition	Minimum Plausible	Most Likely	Maximum Plausible	Confidence
FR	No management	20	20	60	100
	Supplementary feeding	40	65	80	97
	Restored foraging	40	65	75	100
	Restored foraging + supplementary feeding	40	75	80	93
JG	No management	1	16	91	100
	Supplementary feeding	1	60	91	100
	Restored foraging	1	60	91	100
	Restored foraging + supplementary feeding	1	65	91	100
KB	No management	0	15	50	100
	Supplementary feeding	0	20	60	100
	Restored foraging	10	40	70	70
	Restored foraging + supplementary feeding	10	50	80	70
NR	No management	5	15	50	75
	Supplementary feeding	15	40	80	75
	Restored foraging	20	40	80	75
	Restored foraging + supplementary feeding	25	45	90	75
QN	No management	5	17	31	85
	Supplementary feeding	14	25	45	85
	Restored foraging	15	41	50	86
	Restored foraging + supplementary feeding	16	42	55	85
RG	No management	5	15	25	90
	Supplementary feeding	15	22	35	85
	Restored foraging	25	35	45	90
	Restored foraging + supplementary feeding	25	37	45	89
SQ	No management	0	10	60	70
	Supplementary feeding	0	20	60	75
	Restored foraging	0	25	60	75
	Restored foraging + supplementary feeding	0	30	60	75

Summary of discussion

There was general agreement that supplementary feeding and improved foraging conditions have a strong effect on this parameter. Estimates from the 2007–2009 cohorts (when survival rates crashed and before supplementary feeding was introduced) were around 12%. Prior to that crash, mean survival was 42.5%, with substantial variation between years. There is no evidence from any population that mean survival across years exceeds 50%, so this was used as a reasonable upper bound.

Analysis of current levels of supplementary feeding on Islay indicates that it has been sufficient to prevent population decline, but not enough to restore survival rates to pre-2007 levels.

In Jersey, first-year survival with supplementary feeding is approximately 70%. However, the feeding regime differs significantly: supplementary feeding on Islay accounts for about 10% of the birds’ expected dietary requirements, whereas in Jersey it is closer to 50%, and in Kent it approaches the full dietary requirement.

Comments

No management

• RG: Note that we know that there is quite a lot of among-year variation, so the average might not be fully informative.

Restored foraging

• RG: Again, among-year variation and associated cohort effects.

Restored foraging + supplementary feeding

• XQ: Current chick survival poor with supplementary feeding. So likely very poor without. Restored forage may be enough to match equivalent of supplementary feeding but both restored forage and supplementary feeding likely needed in medium term whilst population re-builds
• JG: Increasing food availability is going to increase survival chances, whether its through supplementation or habitat improvement. Combining the two might boost it further but its still going to be limited by other factors not related to food.

Supplementary feeding

• RG: Also some among-year variation in efficacy of supplementary feeding

Question 2

What do you believe is the average annual survival of sub-adult red-billed choughs under the following different scenarios:
- Conditions are the same as now, without supplementary feeding or any type of management.
- Supplementary feeding of individuals with mealworms.
- Conditions in Islay change so that the foraging conditions are optimal for chough.
- Conditions in Islay change so that the foraging conditions are optimal for chough, and supplementary feeding continues.

Participant	Foraging condition	Minimum Plausible	Most Likely	Maximum Plausible	Confidence
JG	No management	39	68	95	100
	Supplementary feeding	39	80	95	100
	Restored foraging	39	80	95	100
	Restored foraging + supplementary feeding	39	85	95	100
KB	No management	20	50	70	90
	Supplementary feeding	30	55	80	90
	Restored foraging	40	60	80	80
	Restored foraging + supplementary feeding	40	65	90	80
NR	No management	30	60	75	75
	Supplementary feeding	45	70	80	75
	Restored foraging	45	65	80	75
	Restored foraging + supplementary feeding	50	70	90	75
QN	No management	10	57	68	76
	Supplementary feeding	61	68	75	85
	Restored foraging	65	68	76	76
	Restored foraging + supplementary feeding	65	69	77	76
RG	No management	25	55	70	95
	Supplementary feeding	35	59	70	95
	Restored foraging	50	63	70	95
	Restored foraging + supplementary feeding	55	65	75	95
SQ	No management	20	75	90	60
	Supplementary feeding	25	70	95	60
	Restored foraging	30	75	95	60
	Restored foraging + supplementary feeding	40	80	95	60

Summary of discussion

The same general pattern was observed, with supplementary feeding and improved foraging conditions having a similar, positive, though smaller, effect on survival. One point raised was that participants’ estimates suggest these actions influence the minimum and maximum plausible values, which was considered a reasonable interpretation.

Comments

Restored foraging + supplementary feeding

• JG: As with the previous question, ensuring a food source will increase their chances. As sub-adults, they’ve already overcome the threat of genetic blindness. Still face threats of predation, disease transmission, etc.

Question 3

What do you believe is the average annual survival of adult red-billed choughs under the following different scenarios:
- Conditions are the same as now, without supplementary feeding or any type of management.
- Supplementary feeding of individuals with mealworms.
- Conditions in Islay change so that the foraging conditions are optimal for chough.
- Conditions in Islay change so that the foraging conditions are optimal for chough, and supplementary feeding continues.

Participant	Foraging condition	Minimum Plausible	Most Likely	Maximum Plausible	Confidence
FR	No management	60	70	80	100
	Supplementary feeding	69	87	95	100
	Restored foraging	69	87	95	100
	Restored foraging + supplementary feeding	69	87	95	100
JG	No management	69	87	95	100
	Supplementary feeding	69	87	95	100
	Restored foraging	69	87	95	100
	Restored foraging + supplementary feeding	69	90	95	100
KB	No management	50	75	85	90
	Supplementary feeding	50	80	85	90
	Restored foraging	50	80	90	90
	Restored foraging + supplementary feeding	50	85	90	90
NR	No management	55	85	90	75
	Supplementary feeding	65	90	95	75
	Restored foraging	65	85	95	75
	Restored foraging + supplementary feeding	75	90	95	75
QN	No management	69	75	85	75
	Supplementary feeding	80	85	90	75
	Restored foraging	80	85	90	75
	Restored foraging + supplementary feeding	81	86	91	75
RG	No management	75	80	85	95
	Supplementary feeding	75	82	85	95
	Restored foraging	78	83	86	95
	Restored foraging + supplementary feeding	79	83	86	95
SQ	No management	70	85	95	75
	Supplementary feeding	70	87	95	75
	Restored foraging	70	87	95	75
	Restored foraging + supplementary feeding	70	90	95	75

Summary of discussion

Some participants suggested that supplementary feeding would not improve adult survival, as adult birds do not appear to make use of the supplementary feed. However, a close inspection of the monitoring data shows a slight increase in adult survival. Given the small size of this effect, it is possible that supplementary feeding may not act synergistically with improved foraging conditions to further enhance survival.

Comments

No management

• JG: I’m confused as to why your current distribution (unmanaged) is higher than the default setting of no management. Should they not be the same?

Restored foraging + supplementary feeding

• JG: The background info states adult survival isn’t affected at the moment by the supplemental feed, despite them eating it. So I don’t think supplementation or optimal habitat will change the numbers. Maybe combined, they make a difference to the variety and quality of inverts available increasing chances. Other threats remain.

Fecundity

Question 4

What do you believe is the expected probability of nesting success of adult red-billed choughs under the following different scenarios:
- Conditions are the same as now, without supplementary feeding or any type of management.
- Supplementary feeding of individuals with mealworms.
- Conditions in Islay change so that the foraging conditions are optimal for chough.
- Conditions in Islay change so that the foraging conditions are optimal for chough, and supplementary feeding continues.

Participant	Foraging condition	Minimum Plausible	Most Likely	Maximum Plausible	Confidence
FR	No management	30	60	80	95
	Supplementary feeding	40	70	80	100
	Restored foraging	36	65	86	100
	Restored foraging + supplementary feeding	36	65	86	100
JG	No management	36	65	86	100
	Supplementary feeding	36	75	86	100
	Restored foraging	36	75	86	100
	Restored foraging + supplementary feeding	36	80	86	100
KB	No management	50	60	80	80
	Supplementary feeding	50	65	80	80
	Restored foraging	50	70	90	90
	Restored foraging + supplementary feeding	50	75	90	90
NR	No management	35	65	85	75
	Supplementary feeding	35	65	85	75
	Restored foraging	70	85	95	75
	Restored foraging + supplementary feeding	70	85	95	75
QN	No management	53	73	88	82
	Supplementary feeding	53	80	90	80
	Restored foraging	70	87	98	83
	Restored foraging + supplementary feeding	73	90	98	81
RG	No management	60	70	80	90
	Supplementary feeding	65	72	82	90
	Restored foraging	70	75	85	90
	Restored foraging + supplementary feeding	70	75	85	90
SQ	No management	50	75	90	75
	Supplementary feeding	50	75	90	75
	Restored foraging	50	80	90	75
	Restored foraging + supplementary feeding	50	80	90	75

Summary of discussion

This is one of the more uncertain parameters, as it is the least investigated. Unpublished data suggest considerable variation (ranging from 60% to 80%) but show no clear trend. It was therefore suggested that while supplementary feeding may have a positive effect, the overall impact is likely to be small. Observations from the Jersey and Kent translocations indicate that easier access to food for parents may lead to a slight increase in nesting success.

Comments

No management

• FR: much will depend on how the climate, sand dune management and grazing levels change
• QN: Fenn et al. 2020 paper suggests there may be some differences between male and female nest success, so I have suggested an average across males and females in my answers.

Restored foraging + supplementary feeding

• NR: I have estimated the percentages of nests which are successful - not the number of eggs which lead to fledglings
• JG: Supplemental feeding of nesting pairs can save the birds a lot of energy, depending on location, and guarantee them a consistent source of food = increased survival. Still have genetic blindness risk, disease issues, predation etc.

Supplementary feeding

• RG: Note that there is (or was) quite substantial spatial variation in some demographic parameters within Islay, including nesting success

Question 5

What do you believe is the expected number of individuals fledgling from successful nesting attempts of adult red-billed choughs under the following different scenarios:
- Conditions are the same as now, without supplementary feeding or any type of management.
- Supplementary feeding of individuals with mealworms.
- Conditions in Islay change so that the foraging conditions are optimal for chough.
- Conditions in Islay change so that the foraging conditions are optimal for chough, and supplementary feeding continues.

Participant	Foraging condition	Minimum Plausible	Most Likely	Maximum Plausible	Confidence
FR	No management	0.0	2.75	4.00	93
	Supplementary feeding	1.0	2.75	4.00	100
	Restored foraging	2.2	2.75	3.40	100
	Restored foraging + supplementary feeding	2.2	2.75	3.40	100
JG	No management	2.2	2.75	3.40	100
	Supplementary feeding	2.8	3.40	3.60	100
	Restored foraging	2.8	3.20	3.60	100
	Restored foraging + supplementary feeding	2.8	3.40	3.60	89
KB	No management	1.0	2.50	5.00	100
	Supplementary feeding	1.0	2.50	5.00	100
	Restored foraging	1.0	3.00	5.00	100
	Restored foraging + supplementary feeding	1.0	3.50	5.00	100
NR	No management	1.5	2.50	3.30	90
	Supplementary feeding	1.5	2.50	3.30	90
	Restored foraging	2.0	3.00	3.75	90
	Restored foraging + supplementary feeding	2.0	3.00	3.75	90
QN	No management	2.2	2.70	3.50	79
	Supplementary feeding	2.6	3.00	3.50	81
	Restored foraging	2.7	3.00	3.50	80
	Restored foraging + supplementary feeding	2.7	3.00	3.70	80
RG	No management	2.2	2.70	3.10	85
	Supplementary feeding	2.4	2.70	3.10	85
	Restored foraging	2.4	2.80	3.20	90
	Restored foraging + supplementary feeding	2.4	2.80	3.20	90
SQ	No management	1.0	2.50	5.00	95
	Supplementary feeding	1.0	2.50	5.00	95
	Restored foraging	1.0	2.75	5.00	95
	Restored foraging + supplementary feeding	1.0	2.75	5.00	95

Summary of discussion

Responses were in general similar, with differences mainly in the reported confidence levels and upper and lower bounds. Overall, participants appeared to be in general agreement.

Comments

Restored foraging + supplementary feeding

• QN: As for nesting success, there may be differences between adult male and females in average fledglings produced, so I have given an average across these.
• FR: Breeding success has generally been good - more weather dependent. It is post-fleging that is problematic
• NR: Need to know the age class structure of the population
• RG: Note that this varies a lot among years
• JG: Improving nutrition can lead to improved female fitness and over time we could see an increase in clutch size, egg quality, hatching rates, and ultimately fledging rates. In the short term, supplementation can boost chicks survival. Genetic blindness is still limiting numbers, so I’ve kept it below 4.0. I’m not confident with the numbers on this one. Maybe in the long term, improved food sources lead to clutch sizes of 5 being the norm. Fledging rates will still be impacted by genetics, nest conditions etc

Releases

Question 6

After releasing a sub-adult individual, how long do you expect it to take for the animal to acclimate and exhibit demographic rates comparable to those of resident individuals?
Note: answer this question for captive-reared individuals and wild-caught ones. Assume all released sub-adults go through a staged release, either with or without human habituation. See below for an index of release strategies:

Wild-St-NH: Wild-caught individuals, staged release in aviaries, habituated to humans pre release
Wild-St-NH: Wild-caught individuals, staged release in aviaries, not habituated to humans pre release
Captive-St-H: Captive-reared individuals, staged release in aviaries, habituated to humans pre release
Captive-St-NH: Captive-reared individuals, staged release in aviaries, not habituated to humans pre release

Participant	Release Strategy	Minimum Plausible	Most Likely	Maximum Plausible	Confidence
FR	Wild-St-H	3	3	12	100
	Wild-St-NH	3	6	12	100
	Captive-St-H	2	2	6	100
	Captive-St-NH	2	6	12	100
KB	Wild-St-H	12	12	24	70
	Wild-St-NH	12	12	24	70
	Captive-St-H	12	24	36	70
	Captive-St-NH	12	24	36	70
QN	Wild-St-H	1	3	12	60
	Wild-St-NH	1	3	12	60
	Captive-St-H	1	4	12	60
	Captive-St-NH	1	4	12	61
RG	Wild-St-H	0	3	7	80
	Wild-St-NH	0	3	7	80
	Captive-St-H	0	4	8	81
	Captive-St-NH	0	4	8	79
SQ	Wild-St-H	3	18	36	50
	Wild-St-NH	3	12	24	50
	Captive-St-H	6	18	36	50
	Captive-St-NH	6	18	36	50

Comments

Wild-St-H

• QN: captive-reared individuals may find/ use the supplementary feeding quicker than wild-caught birds, but captive-reared birds may be slower at finding/ using natural food sources and may be less good at avoiding predation and finding good roosting/ breeding sites.

Summary of discussion

There was a high level of uncertainty among participants regarding acclimation periods under different release strategies, with estimates ranging from just a few months to over a year.

It was noted that acclimation would likely be influenced by the time of year and the specific details of the release. However, since the options in these questions relate specifically to winter releases, this context was taken into account. One participant suggested that the acclimation period would need to be at least a year to allow birds to become familiar with the environment across all seasons.

A key point raised was that suitable habitat can be created for chough without the birds discovering it, highlighting the importance of social cues in foraging. This social dynamic makes acclimation around resident birds particularly important.

In both Kent and Jersey, most losses occur within the first few weeks after release. With staged releases and supplementary feeding, birds tend to stay near the release site for the first few months, followed by an exploratory phase—typically around October, or approximately three months post-release. This pattern was observed again in March this year.

Choughs’ sociable nature and tendency for social learning may enable faster acclimation if they are integrated into an existing flock. Additionally, the provision of supplementary feed can encourage exploratory behaviour, increasing the chances of individuals locating high-quality habitat.

One participant cautioned that winter releases may hinder acclimation, as harsher weather conditions add further challenges, especially for captive-bred birds. However, on Islay, summer is the season of greatest food scarcity, with lower survival rates. For this reason, late winter was considered the preferred release period.

Question 7

Imagine sub-adult birds are released into Islay. While they acclimate, what are the relative odds that those individuals are going to die during the acclimation period, compared to the odds of native individuals dying during the same period?
Note 1: For example, relative odds of 1 would mean the chance of a translocated individual dying over the acclimation period would be the same of a resident one. Relative odds of 2 would mean the translocated individual has twice the chance of dying as residents, while 0.5 would mean they would be half as likely to die.
Note 2: answer this question for captive-reared individuals and wild-caught ones. Assume all released sub-adults go through a staged release, either with or without human habituation. See below for an index of release strategies:

Wild-St-NH: Wild-caught individuals, staged release in aviaries, habituated to humans pre release
Wild-St-NH: Wild-caught individuals, staged release in aviaries, not habituated to humans pre release
Captive-St-H: Captive-reared individuals, staged release in aviaries, habituated to humans pre release
Captive-St-NH: Captive-reared individuals, staged release in aviaries, not habituated to humans pre release

Participant	Alternative	Minimum Plausible	Most Likely	Maximum Plausible	Confidence
FR	Wild-St-H	0.5	0.70	1.0	100
	Wild-St-NH	0.5	1.00	2.0	100
	Captive-St-H	0.5	1.00	2.0	100
	Captive-St-NH	0.5	1.00	2.0	100
JG	Wild-St-H	0.5	2.00	2.0	100
	Wild-St-NH	0.5	2.00	2.0	100
	Captive-St-H	0.5	1.00	2.0	100
	Captive-St-NH	0.5	1.75	2.0	100
KB	Wild-St-H	0.5	1.50	2.0	70
	Wild-St-NH	0.5	1.50	2.0	70
	Captive-St-H	0.5	2.00	3.0	70
	Captive-St-NH	0.5	2.00	3.0	70
NR	Wild-St-H	0.9	1.00	1.1	50
	Wild-St-NH	0.8	1.10	1.2	50
	Captive-St-H	0.9	1.20	1.5	50
	Captive-St-NH	0.8	1.10	1.3	50
QN	Wild-St-H	1.0	1.40	2.0	55
	Wild-St-NH	1.0	1.50	2.0	100
	Captive-St-H	1.0	1.50	2.0	100
	Captive-St-NH	1.0	1.50	2.0	56
RG	Wild-St-H	0.8	1.00	1.1	75
	Wild-St-NH	0.8	1.00	1.1	75
	Captive-St-H	0.9	1.00	1.1	75
	Captive-St-NH	0.9	1.00	1.1	75
SQ	Wild-St-H	1.0	2.00	10.0	50
	Wild-St-NH	1.0	2.50	10.0	50
	Captive-St-H	1.0	3.00	10.0	50
	Captive-St-NH	1.0	3.50	10.0	50

Summary of discussion

The non-linear nature of this question (and questions 9 and 11) made it challenging for many participants, as it asks about relative odds rather than absolute probabilities. Participants are encouraged to revisit these questions now that a graphical interface is available to illustrate the outcomes of different relative odds based on a baseline probability.

One source of uncertainty is the assumption that, despite undergoing an acclimation period, released individuals are likely to be fitter than the resident birds on Islay, and therefore may have a higher baseline survival rate.

To improve the survival of released birds, enhancing supplementary feeding should be a key consideration.

Comments

Captive-St-H

• JG: This group is more likely to survive the first few weeks of release and establish themselves than any of the other three scenarios.

Captive-St-NH

• SQ: So many variable here, i have no confidence in my answers.
• JG: This group will react similarly to the wild-caught birds. I’m treating this group as the equivalent to parent-reared sub-adults in the Jersey and Kent releases.

Wild-St-H

• SQ: Struggling with how the numbers work on this, so hope it makes sense
• FR: will depend on time of year and weather

• JG: Wild-caught sub-adults are not going to be habituated to humans so I’m not sure how to answer that one. Release success of wild-caught sub-adults is likely to be lower than captive-reared habituated individuals as they are more prone to panic/becoming overwhelmed and immediately leaving the release site into sub-optimal habitat, possibly unreachable with supplemental food to support them through the learning phase. I don’t think all individuals will do this. A percentage of the cohort will fail within the first few weeks of release.

  All my answers to this question related to the first cohort released. Chances of proceeding cohorts could increase gradually, assuming there are some survivors of the first flock to anchor to.

• NR: for the wild caught individuals it may depend on the food sources used in their capture area

  my confidence in these responses is <50%

Question 8

After releasing an adult individual, how long do you expect it to take for the animal to acclimate and exhibit demographic rates comparable to those of resident individuals?Note: answer this question for each release strategy, described below:

Wild-Im-NH: Wild-caught individuals, immediate release, not habituated to humans pre release
Captive-St-H: Captive-reared individuals, staged release in aviaries, habituated to humans pre release
Captive-St-NH: Captive-reared individuals, staged release in aviaries, not habituated to humans pre release

Participant	Release Strategy	Minimum Plausible	Most Likely	Maximum Plausible	Confidence
FR	Wild-Im	3	6	12	100
	Captive-St-H	4	4	5	100
KB	Wild-Im	0	12	24	70
	Captive-St-H	0	18	24	70
	Captive-St-NH	0	18	24	70
NR	Wild-Im	0	24	48	50
	Captive-St-H	0	12	24	50
	Captive-St-NH	0	12	36	50
QN	Wild-Im	1	5	12	57
	Captive-St-H	1	5	12	57
	Captive-St-NH	1	5	12	57
RG	Wild-Im	0	12	36	95
	Captive-St-H	0	12	36	80
	Captive-St-NH	0	12	36	80
SQ	Wild-Im	0	6	12	50
	Captive-St-H	3	12	24	50
	Captive-St-NH	3	9	24	50

Summary of discussion

There were similar levels of uncertainty regarding the acclimation period for adult birds. One participant noted that wild birds released via immediate release are at a greater disadvantage than others. Participants highlighted that releasing adult birds tends to be particularly stressful, as these individuals are already established in their place of origin and may attempt to return, expending significant energy in the process.

Additionally, adult birds may take longer to establish a new territory, and, because they are not part of existing flocks, they miss out on the social learning opportunities that flocks provide. While young birds are generally more exploratory, adult birds are less predictable in this regard, contributing to greater uncertainty.

Overall, participants appeared to agree that the release of adult birds is likely to face significant challenges and may have a lower chance of success.

Comments

Wild-Im

• QN: Is this assuming the released individuals all survive? If they die within a few weeks of release they will never acclimate/ exhibit comparable demographic rates.

Question 9

Imagine adult birds are released into Islay. While they acclimate, what are the odds those individuals are going to die during the acclimation period, relative to the odds of native individuals dying during the same period?
Note 1: For example, relative odds of 1 would mean the chance of a translocated individual dying over the acclimation period would be the same of a resident one. Relative odds of 2 would mean the translocated individual has twice the chance of dying as residents, while 0.5 would mean they would be half as likely to die.
Note 2: answer this question for each release strategy, described below:

Wild-Im-NH: Wild-caught individuals, immediate release, not habituated to humans pre release
Captive-St-H: Captive-reared individuals, staged release in aviaries, habituated to humans pre release
Captive-St-NH: Captive-reared individuals, staged release in aviaries, not habituated to humans pre release

Participant	Alternative	Minimum Plausible	Most Likely	Maximum Plausible	Confidence
FR	Wild-Im	0.50	0.70	1.0	100
	Captive-St-NH	0.50	1.00	2.0	100
JG	Wild-Im	1.00	2.00	2.0	100
	Captive-St-H	0.50	1.00	2.0	100
	Captive-St-NH	0.50	1.75	2.0	100
KB	Wild-Im	0.50	1.50	3.0	70
	Captive-St-H	0.50	2.00	3.0	70
	Captive-St-NH	0.50	2.00	3.0	70
NR	Wild-Im	0.50	0.80	1.0	50
	Captive-St-H	0.80	1.00	1.3	50
	Captive-St-NH	0.70	0.90	1.1	50
QN	Wild-Im	1.00	1.60	2.0	55
	Captive-St-H	1.00	1.40	2.0	55
	Captive-St-NH	1.00	1.50	2.0	55
RG	Wild-Im	0.90	1.00	2.0	75
	Captive-St-H	0.95	1.00	2.0	75
	Captive-St-NH	0.95	1.00	2.0	75
SQ	Wild-Im	1.00	4.00	10.0	50
	Captive-St-H	1.00	3.00	10.0	50
	Captive-St-NH	1.00	3.00	10.0	50

Summary of discussion

The non-linear nature of this question (and questions 7 and 11) made it challenging for many participants, as it asks about relative odds rather than absolute probabilities. Participants are encouraged to revisit these questions now that a graphical interface is available to illustrate the outcomes of different relative odds based on a baseline probability.

As pointed in the previous questions, releasing adults, specially from captivity, seems to be have a high cost on mortality.

Comments

Captive-St-H

• NR: will depend on whether captive reared birds integrate with local population during staged release…

  confidence in response is <50%

Wild-Im

• SQ: Too many variables for me to have any confidence in my answers here.

• NR: Will depend on the food sources used by the wild-caught adults in their source area before capture

  my confidence in these figures is <50%

Question 10

Imagine all eggs in an established chough nest on Islay have been replaced with eggs from elsewhere. What is the probability that the nest in question will be abandoned by its parents?

Participant	Minimum Plausible	Most Likely	Maximum Plausible	Confidence
JG	0	60	100	90
KB	0	50	100	100
QN	20	50	90	57
RG	5	10	30	75
SQ	0	5	50	75

Summary of discussion

There was a high level of uncertainty among participants, likely due to the under-specification of the techniques involved in egg swapping. It was noted that egg swapping is a feasible technique with a high likelihood of success, but this depends on having skilled personnel on site and detailed knowledge of the nesting pairs. The question was rephrased to highlight that best practice guidelines are followed when carrying out egg swaps.

Comments

Nest abandonment

• FR: Really depends on how this is done. Could cause desertion
• JG: The timing of when you swap the eggs is crucial for the survival of the embryo and to limit the risk of abandonment. I have successfully swapped eggs in captive chough nests; therefore, it might be possible in wild nests. However, wild birds are likely to be less tolerant to human presence at the incubating stage. I’m not confident, but think you’ve got an ok chance of not being abandoned.
• QN: I don’t know if chough have any egg recognition abilities, but they can be sensitive to nest disturbance.
• NR: Don’t know

Question 11

Imagine all eggs in an established chough nest on Islay have been replaced with eggs from elsewhere. What are the relative odds that those eggs are going to survive until fledging, compared to the odds of native eggs during the same period?
Note: For example, relative odds of 1 would mean the chance of a translocated egg surviving until fledgling would be the same of a resident one. Relative odds of 2 would mean the translocated eggs have twice the chance of surviving as residents, while 0.5 would mean they would be half as likely to survive.

Participant	Minimum Plausible	Most Likely	Maximum Plausible	Confidence
JG	0.5	1.0	1.50	89
KB	0.5	1.0	2.00	100
NR	1.0	1.1	1.33	50
QN	0.4	0.7	1.00	58
RG	0.8	1.1	1.30	85
SQ	1.0	1.0	10.00	75

Summary of discussion

The non-linear nature of this question (and questions 7 and 9) made it challenging for many participants, as it asks about relative odds rather than absolute probabilities. Participants are encouraged to revisit these questions now that a graphical interface is available to illustrate the outcomes of different relative odds based on a baseline probability.

Participants in general seemed to express similar fledging probability from translocated and resident eggs, with one expert believing the would perform better, where another believed they would perform worse.

Similarly to the previous question, it was raised that if the egg swapping is done correctly, the probabilities of fledgling would be similar.

A source of uncertainty, similar to previous questions, is that translocated birds would have a genetic advantage and therefore can perform better than resident ones, despite the cost of release.

Genetic blindness was raised as an issue that would make resident birds less likely to fledge than translocated one, but it seems to have become a rare occurence in Islay and happens often in broods with more birds. So it might not be a driving factor of fledging differences.

Comments

Implanted eggs fledging odds

• RG: It depends a bit on the source and methods
• QN: transporting eggs may decrease hatching success rate

• JG: If the nest isn’t abandoned, and the foster pair is an established pair, the eggs should have the same chance of survival to fledge as the pair’s own clutch would. If you are taking from a pair that don’t tend to do well and giving to a proven breeding pair, then the eggs stand a better chance of success - assuming reasons for previous failures are not related to the female’s fitness and therefore, in turn, egg/embryo fitness.

  This is all assuming that you are taking the eggs at the optimal stage and transferring correctly to prevent damage to the embryo.
• SQ: Struggling to make the graph make sense, was still putting in %, but changed now, so hopefully makes sense. Trying to say they should have the same chance to get to fledging.
• NR: Will depend on whether there are blind double recessives in the clutch……then 33% better chance of survival to/at fledging
• FR: Very much depends on how this is done. I don’t think complete clutch swaps will work -

Extra questions

Question 12

Imagine 1st-year birds are released into Islay. They are released using the same strategy as the one deployed in the Kent and Jersey releases: Individuals are released in summer, following a staged released protocol with human habituation. What do you believe is the probability a given released individual will survive until the following summer?
Note 1: Answer this question for captive-reared individuals and wild-caught ones
Note 2: Assume a 12 month period between the summer release and the following summer

Participant	Alternative	Minimum Plausible	Most Likely	Maximum Plausible	Confidence
KB	Wild	20	35	70	70
	Captive	20	35	70	70
QN	Wild	5	21	45	57
	Captive	5	20	45	57
RG	Wild	10	25	45	90
	Captive	43	86	99	100
SQ	Wild	5	25	60	60
	Captive	5	30	80	60

Summary of discussion

Even though in other translocations summer is deemed to be the best season to release 1st year individuals, it is known that the highest mortality of that age class happens on that period, therefore this is why most strategies include a late winter release, where the weather is not at its worst, but the individuals are past the critical food shortage phase in the island, and the day length is starting to get longer.

It has been raise that a complement to that strategy would be to do an improved version of supplementary feeding for the released birds. This has been incorporated into to the question by changing the wording.

Comments

Wild

• RG: Depends on whether there’s supplementary feeding!

Question 13

Imagine 1st-year birds are released into Islay. Individuals are released in winter, following a staged released protocol with human habituation. What do you believe is the probability a given released individual will survive until the following summer?
Note 1: Answer this question for captive-reared individuals and wild-caught ones
Note 2: Assume a 6 month period between the winter release and the following summer

Participant	Alternative	Minimum Plausible	Most Likely	Maximum Plausible	Confidence
KB	Wild	20	30	70	70
	Captive	20	30	70	70
QN	Wild	5	24	45	56
	Captive	5	21	45	56
RG	Wild	60	80	90	90
	Captive	65	93	99	100
SQ	Wild	5	30	80	60
	Captive	5	40	80	100

Comments

Captive

• SQ: This is assuming they would be fed throughout this period and be trained to return for feed etc.

Summary of discussion

The discussion of this question was bundled wih the above questions, with the same points standing about the differences between summer and winter releases and the implication for food shortage but also for the learning period of released birds.