TABLE 3

Factors influencing the occurrence and abundance of tick infestation on birds sampled during spring migrationa

EffectBinomial modelCount model
Estimateχ2PEstimateχ2P
Intercept−2.62 ± 0.29−9.24 ± 99.60
Intercontinental migrantsb−0.16 ± 0.260.370.546−1.01 ± 0.650.520.104
Understoryc−0.88 ± 0.2714.200.0010.40 ± 0.621.440.486
Canopy and subcanopyc−0.71 ± 0.2214.200.001−0.41 ± 0.601.440.486
Fatd−0.37 ± 0.137.890.005−0.20 ± 0.340.370.543
  • a The binomial model tests for relationships in the presence or absence of ticks, and the count model tests for relationships within positive samples (n = 3,839 samples; df = 11).

  • b Compared to birds that overwintered locally.

  • c Compared to ground-foraging birds.

  • d Fat score increased from completely depleted fuel (score 0) to low fuel (score 1) to moderate and considerable fuel (scores 2 to 4).