Table 3. Flock biomechanics.

Wingbeat frequency predictors	Estimate	S.E.	T	d.f.	P
Intercept (dowitchers)	8.82	0.132	66.5	2817	<0.00001
Godwit	−2.19	0.035	−63.5	2817	<0.00001
Avocet	−1.91	0.040	−47.5	2817	<0.00001
Airspeed (m s−1)	−0.05	0.013	−4.3	2817	0.00002
Flock position	0.13	0.032	4.0	2817	0.00006
Nearest neighbor distance (wingspans)	−0.03	0.010	−3.2	2817	0.00153
Nearest neighbor species	−0.45	0.038	11.9	2817	<0.00001
Z-speed (m s−1)	0.29	0.019	15.1	2817	<0.00001
Airspeed predictors	Estimate	S.E.	T	d.f.	P
Intercept (dowitchers)	10.69	0.225	47.5	2832	<0.00001
Godwit	−0.25	0.067	−3.7	2832	0.00022
Avocet	−1.51	0.067	−22.6	2832	<0.00001
n.n. distance (wingspans)	−0.08	0.015	−5.2	2832	<0.00001
Edge distance (wingspans)	−0.03	0.003	−10.3	2832	<0.00001
Wingbeat frequency (H z)	−0.12	0.025	−5.0	2832	<0.00001
Flock position	−0.24	0.045	−5.4	2832	<0.00001
Aerodynamic neighbor	0.23	0.040	5.7	2832	<0.00001

Results from linear mixed-effects models relating wingbeat frequency and airspeed to other measured variables. Nearest neighbor only defined when this bird is leading the focal bird. Godwit and avocet are dummy variables coding species differences relative to dowitchers. Nearest neighbor species is coded −1 for a smaller neighbor, 0 for same the species, and 1 for a larger neighbor. Flock position is continuously scaled from 0.0 (front) to 1.0 (back). Aerodynamic neighbor was coded 1 for birds flying within 0.7–1.5 wingspans lateral distance and within two wingspans distance from their nearest leading neighbor, 0 otherwise. Models were selected using Bayesian information criteria. The data used to generate this table are available in Table 3—source data 1. d.f., degrees of freedom.