Figure S1 exhibits an increasing trend in elephant poaching in the years prior to transference. In the absence of transference to AP management, elephant poaching may have continued to increase. In this scenario, our ATT of -0.153 would underestimate the true reduction in elephant poaching due to AP management. We use the R package HonestDiD to implement the approach described in Section 2.4.3 of Ref. [98] in order to quantitatively assess this bias. Under the scenario that the pre-trends would have continued in the absence of transference to AP management, this approach considers how the average trend in the pre-period coefficients would extrapolate across the post-period and change the treatment coefficients and confidence intervals. The resulting confidence interval accounts for both estimation error in the treatment coefficients and in the pre-trend. The 95% confidence interval is (-0.728, -0.286), indicative of a larger reduction in elephant poaching than our ATT. Thus, the pre-trends in Figure S1 do not invalidate our inference that AP management reduces elephant poaching.

## **A.1.1 Spillovers**

A separate concern relates to spillovers to control protected areas. Since AP seems to increase monitoring and enforcement, PIKE could increase in control protected areas if elephant poachers reallocate their effort away from protected areas managed by AP. This increase in poaching in control areas because of AP management would cause us to overestimate the reduction in poaching that is due to AP. We test for this possibility by identifying “spillover” protected areas.

For each area transferred to AP, we identify the geographically nearest control area, and we assign the control area the same transference year as the protected area that was actually transferred to AP. We repeat our primary specification with these spillover protected areas as the treatment group, excluding the areas managed by AP from the regression. The control group in this regression therefore contains areas that are less likely to be affected by AP’s activities because they are geographically farther from areas managed by AP. The spillovers appear to operate in the opposite direction from that described above. Instead of increasing following transference of a nearby area to AP management, PIKE decreases in nearby spillover areas, though the coefficient is not statistically significant (ATT = -0.099 with a standard error of 0.096). It is therefore unlikely that spillovers cause us to overestimate the reduction in PIKE due to AP management; if anything, we may be underestimating the reduction.

As an additional assessment of the influence of spillovers on our main result in Table S3, we repeat our primary specification excluding spillover protected areas from the control group. The treatment group is areas transferred to AP management, and the control group is areas geographically farther from AP-managed areas. We obtain a similar estimate as our main result (ATT = -0.146 with a standard error of 0.082, compared to our main result of ATT = -0.153 with a standard error of 0.069).

# **A.2 Bird Abundances (Figures S2 to S7 and Tables S4 and S7)**

eBird, a citizen science platform for birding enthusiasts, captures species-specific observations from birding trips across the globe [58]. During each birding trip, observers 3