Banding Effort

Figure 1 summarises the pre-season banding effort in Canada and the USA (note: I’ve removed all unknown age and sex birds from the data summaries ). Banding effort in Canada has always been higher than in the USA, and has remained fairly stable up to ~2010, afterwhich the numbers of birds banded in Canada have been declining. The number of pre-season black ducks banded in the USA was higher in the 1960s and 1970s, but dropped significantly in the early 1980s.

Figure 1. Summary of pre-season banding effort on Canada and the USA

Figure 1. Summary of pre-season banding effort on Canada and the USA

Winter Bandings

Figure 2 summarizes the number black ducks banded in the winter. Hstorically the USA has banded many black ducks and much fewer were banded in Canada. Numbers of black duck ducks banded in winter has been higher to try and estimate winter survival of black ducks.

Figure 1. Winter banding effort in Canada and USA.

Figure 1. Winter banding effort in Canada and USA.

Direct Recovery (Harvest) Rates

Figure 3 summarises the harvest rates by age, sex and country for black ducks banded pre-season in Canada. Note: I’ve corrected the direct recovery rate for reporting rates, however I did not have the most recent estimate of reporting rates. Recent estimates of the reporting rate suggest the rate is higher in the USA than in Canada, hence recent estimates of harvest are likely biased a bit high in the USA for the last years with web-only addresses.

The banding data suggest the USA generally has a higher harvest rate of adult males than in Canada, and Canada harvests juveniles at a higher rate. This makes intuative sense as most all these bandings occured in Canada, most of which occurs on the natal marshs and these marshes are hunted recieve significant hunting pressure on the opening of the season in Canada. Since AHM kicked in the harvest rates for juveniles in Canada and the USA are simialar.

Figure 3. Country speific harvest rates for black ducks banded in the pre-season in Canada.

Figure 3. Country speific harvest rates for black ducks banded in the pre-season in Canada.

Notes

  • The main effect of the Parity Function appears to have reduced the Canadian harvest rate on juveniles to a similar level to the USA.
  • US harvest rates on adults, especially males, appear to be uneffected by the parity function.

Harvest rate ignoring age and sex

Figure 4 summarizes the overall harvest rate in Canada and the USA for black ducks banded in Canada. This rate was estimated from the direct recoveries from all Canadian bandings. The banding data suggest the harvest rates in Canada and the USA were never similar until 2005.

In Figure 5, I’ve divided the Canadian harvest rate by to overall harvest rate. The using harvest rate estimated from the banding data suggest Canada took the majority of the harvest until around 2005. About the time the black duck AHM attempted to force parity in harvest between Canada and the USA.

  • I suspect Canada does not take the majority of the harvest, but the Canadian harvest rate estimated from the banding data is biased.
    • Most of the banding in Canada occurs on natal marshes.
    • The majority of birds banded are juveniles and many are banded just prior to the season opening.
    • The majority of harvest in Canada occurs on the natal marshes in week the season opens.
  • NOTE The overall harvest rate I’ve calculated does not take into account the effects of age and sex. We need to figure out how to estimate the combined harvest rate from the age/sex cohorts.
Figure 4. Overall harvest rate in Canada and USA.

Figure 4. Overall harvest rate in Canada and USA.

Figure 5. Proportion of harvest occuring in Canada estimated from the banding data.

Figure 5. Proportion of harvest occuring in Canada estimated from the banding data.

Harvest rates for black ducks banded on staging areas

Here I restricted the analyses to black ducks the were banded in Labrador and on fall staging sites in the Codroy Valley, NL and Bathurst, NB. These are fall staging areas or are distant from primary hunting areas in Canada.

Age/sex specific harvest rates are summarized in Figure 6, unlike Figure 3 that suggests tnat Canada has much higher harvest rates on juveniles, harvest rates estimated from the staging areas are very similar between Canada and the USA. Figure 7 is a rerun Figure 4 with the Canadian banded data restricted to non-natal marsh bandings. The patterns in the harvest rates are similar suggesting this data has less bias.

Figure 6. Proportion of harvest occuring in Canada estimated from the banding data.

Figure 6. Proportion of harvest occuring in Canada estimated from the banding data.

Figure 7. Proportion of harvest occuring in Canada estimated from the banding data set resticted to bandings in Labrador and fall staging sites.

Figure 7. Proportion of harvest occuring in Canada estimated from the banding data set resticted to bandings in Labrador and fall staging sites.

Harvest Surveys

The portion of harvest avilable to each country was set using the harvest survey data. Country specifc harvest estimates are summarized in Figure 8. (Note: When I requested the US data I thougth back to 1980 would be fine, but it apears I should have went back to 1974 as it appears more harvest occured in the USA at that time. I will update the data soon.

Since 1980, black duck harvest has declined from ~650-750,000 birds to about ~150,000 anually. I’m not sure what timeframe was used to establish the relative levels of harvest in each country. I would expect the late-70s though to the mid-80s (before US harvest restrictions on Black Ducks were implimented) would be the appropiate time period. At least in the early-80s Canada took most of the Black Duck harvest (Fig. 9) and I’m not quite sure why we settled on parity. Maybe we were nice guys or maybe it was reversed in the 70s and it averaged out to 50%. Regardless, the harvest survey data suggests parity in the harvest distribution between Canada and the USA has been rare. Althougth the distributin of harvest measured from the banding data suggests the harvest has been at parity, or maybe favouring Canada (Fig. 5).

I looked at this another way. I calculated the preportion of the harvest that occurred in Canada as measured by the banding and harvest surveys. We would expect the relationship between these to be 1:1, but it is not (Figure 10). The banding estimates of harvest rate are above the 1:1 line. The intercept is 14.8% (p = 0.02) suggested the harvest estimates from the banding data are biased about ~15% higher than from the harvest survey data.

Figure 8. Black duck harvest in Canada and the USA.

Figure 8. Black duck harvest in Canada and the USA.

Figure 9. Proportion of the Black duck harvest that occurs in Canada estimated from the banding data and harvest survey

Figure 9. Proportion of the Black duck harvest that occurs in Canada estimated from the banding data and harvest survey

Figure 10. Relationship between the proportion of Black duck harvest that occurs in Canada estimated from the banding vs. the same estimated from the harvest surveys.

Figure 10. Relationship between the proportion of Black duck harvest that occurs in Canada estimated from the banding vs. the same estimated from the harvest surveys.

Possible Explainations for lack of recovery

There have been a few potenial issues identified that may caused the decline and prevented the recovery of black ducks. They the main factots have been:

So far there is little support that these factors are the limiting the recovery of black ducks. Productivity has been depressed for a long period and they are now speculating that there has been some reduction in carring capacity in the northern parts of thier breeding range. As a result the BDJV is funding a large tracking study of black ducks to try and determine that breeding habitats used by black ducks. My feeling is this study will produce lots of interesting information on black ducks breeding in the boreal, but I do not think that any of these guys have actually been in the north. I’ve been surveying these areas for almost 30 years and we’ve never seen better conditions.

My feeling is the loss of productivity results from the loss of black ducks breeding in the southern portion of their breeding range. I’m not familar with the US breeding areas, but in Canada we’ve lost them from southern Ontario, the St. Lawrence Lowlands, and since my return to Sackville, NB in 2012, we’ve seen the species composition from our banding programs flip from black duck dominated to mallards. Figure 1 shows steep reductions on the number of juvenile black ducks caught in Canada at about 2010. The productiviy of these southern breeding areas are mmuch higher than in the northern Boreal.

When looking at Fig. 1, I was quite struck with the reductions of banding in the USA. They were banding ±4,000 birds annually in the 1960s and 1970s. The currently band a few hunderd. The reduction in bandings maybe explained by reductions in banding effort, but I suspect this is not the case and the reductions in effort result from the loss of birds.

Figure 11 summarises the country specific harvest rates for black duck banded in the pre-season in the USA. Canada harvests very few of these birds. This has some implicaitons for parity as I’m certain that US bandings are not used in the parity calculations. The US harvest rate on this segment of the population was reduced during the harvest restrictions imposed in the 1980s and 1990s. The current harvest rate is very high on this segment of the population. Granted the current number of bandings in the USA are low and there maybe sampling errors. However, if the rates are close to true there, is little wonder what there has been no recovery… they are being shot.

I suspect this is a result of how the AHM model was structured. As I mention above, we Canadians argued for use of the harvest data to aportion avilable harvest between Canada and the USA. However, the US modellers instead used the harvest rates estimated from the banding data which we expect biases the Canadian harvest high and favours the USA. We Canadians also srongly opposed a single population approach to management of black ducks and favored a model with geographic structure… it made no sense to impose the same restrictive regulaitons in the Atlantic and Mississippi Flyways, or from our perspective, the same restrictions in Ontario as Newfoundland (K. Dickson, D. Bordage, K. Ross pers. comm.) . However, the AHM models were complicated and failed. Canada agreed as an interm solution that the AHM model be collapsed into a single model with the understanding that it was only a step to a model with geographic components (E. Reed pers. comm.). Well its been about 15 years of AHM and we now have multi-species model, but no geographic component. We still are under the same regulatory packages in eastern Newfoundland as sothern Ontairo.

My thought is another consequence of single black duck population model is very high harvest rates on some segments of the population which may at minimun impede recovery, and worst, drive those segements of the populaitons into a very low state.

Figure 11. Harvest rates for black ducks banded pre-season in the USA.

Figure 11. Harvest rates for black ducks banded pre-season in the USA.

Mississippi Flyway

Here I restricted the analyses to black ducks the were banded in the Mississippi Flyway (USA and Ontatio). Figure 12 summarises the pre-season banding effort in the Mississippi Flyway. The number of black ducks banded in the Mississippi Flyway declined rapidily from the 1960s to the mid-80’s, than increased when restrictive regulations were imposed in the mid-80s. However, they peaked in the early 90s and have been declining ever sense.

Figure 13 summarises the Age/sex specific harvest rates in the Mississippi Flyway. The Harvest rate black ducks banded in the Mississippi (Canada and the USA) has been high (Fig. 13), and except for the intial period of restrictive regulations in the mid-80s, harvest has exceeded 20% for all age sex cohorts. (note the number of bandings in recent years has been very low and the harvets rates are now very precise).

Figure 12. Summary of pre-season banding effort in Ontario and Mississippi Flyway

Figure 12. Summary of pre-season banding effort in Ontario and Mississippi Flyway

Figure 13. Harvest rates for black ducks banded in the pre-season in Mississippi Flyway

Figure 13. Harvest rates for black ducks banded in the pre-season in Mississippi Flyway