Reanalysis Of Link Between Osprey Reproduction and Menhaden Abundance

​A recent academic exchange has brought to light differing perspectives on the statistical analysis of the relationship between osprey reproductive rates and menhaden abundance in the Chesapeake Bay. In 2024, researchers Latour, Gartland, and Ralph critiqued the statistical methods employed in a prior study by Watts et al., suggesting that the original analysis may have inadequately addressed uncertainties and potentially violated key statistical assumptions.

In response, Watts and colleagues defended their methodology, asserting that their use of Poisson regression was appropriate and that their findings remain robust. They emphasized that their conclusions about the positive relationship between osprey reproduction and menhaden abundance are supported by significant statistical evidence.

Latour et al. (2024) raised concerns over the statistical methods used to analyze the relationship between osprey reproductive rates and the menhaden index, questioning the use of mean values, assumptions of normality in linear regression, and the lack of uncertainty measures. They proposed a lognormal error model and conducted simulations using data extracted from graphs to assess model robustness. Their results suggested only a marginally significant relationship, casting doubt on previous conclusions.

However, researchers behind the original study say Latour’s conclusions are flawed due to the use of recreated datasets rather than the actual data, which had been publicly available. Reanalysis using Poisson regression on the original dataset—following Latour’s own suggested approach—revealed a highly significant relationship (p = 1.1 x 10⁻¹⁵) between osprey productivity and menhaden abundance. Simulations using 1,000 random subsets of the actual data confirmed the finding, with every result showing statistical significance.

Regression models incorporating two- and four-year lags in menhaden abundance also remained statistically significant, reinforcing the conclusion that menhaden availability is a key driver of osprey reproductive success.

The original authors also refuted assumptions made by Latour et al. about the rationale for including correlations among various menhaden indices. These correlations, they explain, were meant to illustrate covariance structures, not justify index selection. Regressions using different indices—including the Maryland juvenile index, coast-wide juvenile index, and mid-Atlantic adult index—all showed significant results, further validating the findings.

Beyond the statistical analysis, field data revealed that osprey breeding declines in Mobjack Bay were closely tied to reduced menhaden provisioning, increased food stress, and lower nest energy intake. Experimental supplementation with menhaden increased reproductive output, confirming the species’ critical role in osprey diet.

While the researchers acknowledge that local menhaden abundance data would improve understanding, they maintain that the coast-wide index remains a useful proxy. They urge future studies to pursue finer-scale monitoring to explore local dynamics within the broader context of coast-wide management strategies.